M
alaria has always been the subject of research for medical
practitioners from time immemorial. Many ancient texts,
especially medical literature, mention of various aspects of
malaria and even of its possible link with mosquitoes and
insects.
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Charaka |
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Susruta |
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Hippocrates |
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Terentius Varro
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Celsus |
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Galen |
Early man, confronting the manifestations of
malaria, attributed the fevers to supernatural influences: evil
spirits, angered deities, or the black magic of sorcerers. The
ancient Chinese believed the frightening symptoms and signs to
be the work of three demons, one with a hammer, one with a pail
of cold water, and a third with a stove. The ancient Romans
worshiped a fever goddess, three demons rolled into one.
The connection between malaria and swamps was known even in
antiquity and the evil spirits or malaria gods were believed to
live within the marshes.
One of the oldest scripts, written several thousand years ago in cuneiform script on clay
tablets, attributes malaria to Nergal, the Babylonian god of destruction and
pestilence, pictured as a double-winged, mosquito-like insect.
In 800 B.C. the Indian sage Dhanvantari wrote that bites of mosquitoes could causes
diseases, fever, shivering etc. The Charaka Samhita
written in approximately 300 BC, classified the fevers into five different
categories, namely continuous fevers, remittent fevers, quotidian fevers,
tertian fevers and quartan fevers. Susruta Samhita, written about 100 BC,
associated fevers with the bites of the insects.
Hippocrates was probably the
the first malariologist. By 400BC, he described the various malaria fevers of man.
Hippocratic corpus distinguished the intermittent malarial fever
from the continuous fever of other infectious diseases, and also
noted the daily, every-other-day, and every-third-day
temperature rise. The Hippocratic corpus was the first document
to mention about splenic change in malaria and also it
attributed malaria to ingestion of stagnant water: "Those who drink [stagnant
water] have always large, stiff spleens and hard, thin, hot stomachs, while
their shoulders, collarbones, and faces are emaciated; the fact is that their
flesh dissolves to feed the spleen..." Hippocrates also related the fever to the time of
the year and to where the patients lived.
The recurrence of malaria is a phenomenon that was known to the ancients and first recorded by
Roman Poet Horace (December 8, 65 BC - November 27, 8 BC) in his third satire.
Noting the phenomenon of shaking chills recurring consistently, the ancient Romans named the disease
by measuring the elapsed time from the beginning of the first episode to the
end of the second. Thus, fever recurring on Tuesday and Thursday was called
a tertian or "every third day" fever, although only forty-eight hours
separated the two attacks. A fever appearing on Tuesday and Friday was be
called quartan. A number of Roman writers attributed malarial diseases to the
swamps. In ancient Rome, human habitation in mosquito-infested
districts were routinely prohibited and shepherds returning from
a summer in the Apennines furnished their small cabins with a
few sheep to satisfy the mosquitoes so as to protect themselves
from malaria. In first century B.C., a Roman agriculturist Collumella
wrote thus: "A marsh always throws up noxious and poisonous
steams during the heats and breeds animals armed with
mischievous stings which fly upon us in exceeding thick
swarms... whereby hidden diseases are often contracted, the
cause of which even the physicians themselves cannot thoroughly
understand." In the first century A.D., Roman scholar
Marcus Terentius Varro
(116-27 BC) suggested
that swamps breed
"certain animalcula which cannot be seen with the eyes and which we
breathe through the nose and mouth into the body, where they
cause grave maladies." By about 30 A.D., Celsus described two types of tertian fevers
and agreed with the views expressed by Varro. However, all these excellent observations were subverted for
centuries
by Galen's dogmatic, widely accepted medical theories that attributed malaria
to internal causes.
Claudius Galenus of Pergamum (131-201 AD), more popularly
known as Galen, was an ancient Greek physician who worked in
Rome from 162 AD, where he attained a brilliant reputation as a
practitioner and a public demonstrator of anatomy. His influence
held sway for more than 1500 years. He recognized the appearance
of fevers with the summer season and a jaundice in infected
people. But he believed that malaria was due to a disorder in the four humors of the
body. According to him, tertian fever was the result of an imbalance of yellow bile; quartan was caused by too much black bile, and quotidian by an excess of phlegm
and a blood abnormality was the cause of continuous fever. Galen
suggested that the normal humoral balance should be restored by
bleeding, purging, or both. Vomiting accompanying malaria was believed to be the body's attempt to expel
poisons. The bleeding supposedly rid the body of "corrupt humors."
These tenets were accepted without question for the next fifteen
hundred years.
In 1696 Morton presented the first detailed description of the clinical picture
of malaria and its treatment with cinchona. Morton also suggested that the disease
is produced by some poison which enters the body from without. Fransesco Torti,
professor of medicine at Modena, accurately described the intricate course of
the disease that was curable by the cinchona in 1712.
By early seventeenth century, Italian physician
Giovanni Maria Lancisi made some astounding observations on malaria. In 1716, he first
described a characteristic black pigmentation of the brain and
spleen in the victims of malaria. Lancisi linked malaria with poisonous
vapours of swamps or stagnant water on the ground. In 1717, in his monograph
titled Noxious Emanations of
Swamps and Their Cure, he echoed the old theories of
Varro and Celsus by speculating that malaria was due to minute
"bugs" or "worms" which entered the blood and revived the old
idea that mosquitoes might play a role.
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Giovanni Maria Lancisi (1654-1720) |
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Lancisi
was born in Rome in 1654 and studied theology before turning to natural science.
After mastering anatomy, chemistry, and botany at the Collegio de Sapienza,
he was awarded his doctorate at age eighteen. By age thirty he had been appointed
professor of anatomy at his alma mater, and at age forty-three he was named
professor of the theory and practice of medicine, a position he held until his
death in 1720.
Lancisi's extraordinary powers of observation soon attracted
the attention of Pope Innocent XI, who appointed him a papal physician in 1688. Innocent
XII and his successor, Clement XI, renewed the appointment. When Clement commissioned Lancisi to investigate the cause of sudden death in Rome, the resulting study
became a classic in the history of cardiology. A voluminous writer, Lancisi
composed three other major treatises, including the important Aneurysms of the
Heart and Blood Vessels, a work that lucidly describes the vascular changes
in syphilis. But today he is best known for his two-volume monograph Noxious
Emanations of Swamps and Their Cure.
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Lancisi postulated two ways in which malaria might be spread by mosquitoes.
In one, the insects deposit microscopic organisms in uncovered food and drink,
and the human consumption of this contaminated material produces the disease. Lancisi's second postulated mechanism was the correct one for malaria. Mosquitoes,
he writes, "always inject their salivary juices into the small wounds which
are opened by the insects on the surface of the body." Because "all
their viscera are filled with deleterious liquids...no controversy can arise
among professional men concerning the harmful effect which the insects of the
swamps, by mixing their injurious juices with the saliva...inflict upon us." But, lacking proof, Lancisi conceded that there might still be some validity
in the old bad-air theory. Lancisi also proposed the draining of marshes to
eradicate malaria.
For considerable time it was believed that the vapours were
given off by marsh vegetation and some held that microscopic animals
elaborated them. One American physician, James K. Mitchell, wrote that malaria
was due to certain spores present in marshy regions. In 1796, John Crawford,
physician living in America, wrote a series of essays contradicting the bad-air
theory. He asserted that malaria was "occasioned by eggs insinuated, without our
knowledge, into our bodies." These eggs, laid during a mosquito bite, hatched in
the wound and migrated through the host's body, producing the manifestations of
malaria. But these notions were considered as absurd by contemporaries and
the local medical journals summarily rejected all of Crawford's articles. Soon
he was being disparaged so loudly that his medical practice began to suffer.
Fearing ruin, he carried his ideas no further.
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Rasori |
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Nott |
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But the swamp theory finally started to crumble.
In 1816, Giovanni Rasori
(1766-1837) of Parma, while suffering from
malarial fever in prison, doubted the "bad air" theory and
suggested that a microorganism is responsible for the disease.
"For many years," he wrote, "I have held the opinion that the intermittent
fevers are produced by parasites which renew the paroxysm by the act of their
reproduction which recurs more or less rapidly according to the nature of the
species." Two other Americans, Josiah Clark Nott and Lewis Daniel Beauperthy, echoed Crawford’s
ideas. Nott in his essay "Yellow Fever Contrasted with Bilious Fever,"
published in 1850, dismissed the miasma theory as worthless, arguing that
microscopic “insects” somehow transmitted by mosquitoes caused both
malaria and yellow fever. In 1854, Beauperthy, a “traveling naturalist”,
wrote that malaria and yellow fever "are produced by venomous fluid injected
under the skin by mosquitoes like poison injected by snakes." Marshes and
swamps, he added, were not made treacherous by their miasmic vapors but by the
mosquitoes that proliferated within them.
The black pigment, first noted by Lancisi 1716, was again identified by many workers in mid nineteenth
century. In 1847, a German physician, Heinrich Meckel, identified round, ovoid, or spindle-shaped
structures containing black pigment granules in protoplasmic masses in the blood of a
patient with fever and in the spleen during
an autopsy of an insane person. Thus Meckel probably saw the malaria parasites
for the first time, but could not recognize the true importance of his finding.
In 1848 Schutz specifically associated these pigments with malaria when he
observed it in the internal organs of patients who had died of malaria. In 1849,
Virchow demonstrated pigmented bodies in the blood of a patient who had died
from chronic malaria. In 1850, Hischl confirmed the presence of pigment with
intermittent fevers.
In 1878, a Mississippi jury convicted a person for murder on the basis of finding
malaria pigment in the blood stains. But even with all this, the black
granular bodies were somehow never suspected to be the cause of malaria until
1879, when Afanasiev proposed that these bodies might be the agents of the
disease.
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Klebs |
By 1878-79, malaria research took a wrong turn. It was announced that a a
malaria bacillus had been found. Under the spell of the germ theory of disease
when all epidemic diseases were sought
to be blamed on bacteria, this announcement was greeted with much excitement and very little skepticism. Edwin Klebs, the German
pathologist who had isolated the diphtheria bacillus, and Corrado Tommasi-Crudeli,
an Italian bacteriologist, isolated a microbe from the soil, a short rod that
they named Bacillus malariae, in Roman Campagna. This organism, they
wrote, could be found in damp soil and low-lying air in malarious regions, and
would grow on fish gelatin. Soil infested with the bacteria, when injected into
rabbits, was said to produce a malarial fever and enlargement of the spleen;
soil from malaria-free regions caused a different sort of fever and splenic
change. The two authors even asserted that humans receiving an injection of
pure Bacillus malariae cultures would develop the symptoms of malaria.
Probably no scientific article ever written has contained more wishful thinking
than this one. In an 1879 editorial, one prestigious British medical journal
even declared that the malaria problem had been solved.
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Laveran |
Finally, it was Charles Louis Alphonse Laveran, a French physician
working in Algeria and a student of Pasteur, who identified the malaria parasite in 1888.
After his medical school and war time duties, Laveran was transferred to the
military hospital at Constantine, Algeria in 1878. In Constantine, Laveran was confronted with hospitals full of
malaria. The calm, reserved, unemotional but exceptionally astute Laveran
sweated under the burning Algerian sun for two years as he pored over tissue
specimens from malaria victims. The autopsies of victims showed the graphite
pigmentation of the brain and spleen and black granular microscopic bodies in
the blood that were long ago described by others. When all his efforts revealed
nothing more he decided to confine his search to the fresh blood of malaria patients
and began taking blood specimens
from pinpricks in the fingers of sick soldiers. After spreading a droplet into
a thin film on a glass slide, he would peer at it for hours through a small,
crude microscope. On November 6, 1880, while
examining a fresh blood specimen taken from a new hospital arrival, a moving
object on the slide caught Laveran’s eye. Under high power, this proved
to be a tiny malarial body wriggling vigorously. Laveran watched amazed as the
little crescent-shaped object lashed about so energetically that an entire red
blood cell jiggled. Even the pigment granules appeared to be in frenzied motion.
This important observation could never be made before, probably because no previous investigator
had used wet blood films. Laveran immediately
knew that he had found a living organism that caused malaria and named the parasite
Oscillaria malariae. He identified it within the blood of 148 other patients
out of a total of 192 examined. Laveran believed that the tertian, quartan,
and quotidian malaria occurred during different stages in the parasite's
development.
On December 24, 1880 in Italy, Laveran communicated the identification of pigmented
erythrocytic cells in 26 malaria patients. His descriptions included crescents
(gametocytes), pigmented trophozoites, and the process of exflagellation.
Laveran wrote a letter to the Academy of Medicine in Paris, communicating his
discovery. The observations were quickly confirmed. Laveran reported them to
a friend, Dr. E. Richard, stationed at Philippeville, a French Mediterranean
military base fifty miles from Constantine. After finding the fully developed,
wriggling parasite, Richard identified an even younger form than Laveran had
seen, merely a tiny, colorless spot in the red cell. Laveran believed that the
organism lived on the surface of the cell, but Richard correctly
observed that it developed within the cell, growing larger and
larger until it finally burst out.
But under the sway of bacteriology, the scientific community remained unconvinced
about Laveran's discovery. The arguments presented by Klebs and Tommasi-Crudeli
for their Bacillus malariae had been accepted almost without question,
and an Italian pathologist, Ettore Marchiafava, even claimed to have found the
bacillus in several dead malaria patients. Laveran traveled to Rome in 1882
to demonstrate the parasites to Marchiafava and Agnello Celli, but these two
could not be convinced.
The US Army sent Major George Sternberg, a bacteriologist of
considerable standing, to study malaria in New Orleans, where the incidence
was particularly high. He made bacterial cultures from the air, from mud, and
from nearby marshes and no organism he found was capable of producing malaria
in an animal. By 1881 he had shown positively that the Bacillus malariae
of Klebs and Tommasi-Crudeli was not responsible for malaria.
Meanwhile, in 1884, Russian physiologist, Basil Danielewsky was able to observe
parasites of malaria in the blood of wild birds. The same year, Louis Pasteur became convinced of the soundness of Laveran's observations.
In 1884, Marchiafava and Celli,
while studying wet blood smears from malarious patients with the new oil-immersion
lens, looked at unstained blood and saw a active amoeboid ring (trophozoite)
in the red blood cells. They published this finding and named it Plasmodium,
but did not refer to Laveran since they thought it was something different
from what he showed them. The name chosen for the parasite by them turned out to
be an incorrect one, since the organism is not actually a plasmodium. But the
name stuck despite years of haggling.
In 1884, at the Bayview hospital
in Baltimore, Maryland, Dr. William T. Councilman performed autopsies on two
fatal cases of malaria. He described the brain as a dull chocolate color, lungs
inflated and contained much pigment, the liver large, soft and of a dark slatey
color. Pigment was the consistent pathologic link of severe fatal disease to
malaria.
Dr. William Osler, an authority
on blood microscopy, was also skeptical of Laveran's theory. In 1886 he stated
that the malarial bodies were nothing more than incidental findings. When his
colleague, Dr. William T. Councilman, persuaded him to reconsider, Osler spent
many hours looking at wet-blood films and
confirmed Laveran's findings with his own description of blood film examinations
from 70 patients. He also detailed excellent drawings of the parasites and related
forms seen with different types of malaria fever. Osler also instituted
routine blood smear analyses to diagnose malaria in the work-up of febrile
patients at Johns Hopkins Hospital. Yet in the first edition of his textbook, The Principles and Practice of Medicine,
in 1892, Osler continued to maintain a peculiar ambivalence toward the cause
of malaria.
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Camillo Golgi
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Camillo Golgi was a rare scientist
to develop both a new instrument and new ideas. He
was the inventor of a
revolutionary staining technique for nerve tissue. The "reazione nera,"
or black reaction, which he discovered in 1873 after systematic
experiments, consisted of immersing specimens in silver nitrate
after fixation with potassium dichromate. He also formulated a theory that nerve-cell processes formed a giant anastomotic network. His name is also linked with the
discovery of several microscopic cellular structures (tendon organ,
muscle spindle) and subcellular structures (the Golgi apparatus). He
is also known for his contributions to general medicine with regard to intestinal-worm infections,
Bright's disease of the kidney, and especially malaria. |
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In 1885 Camillo Golgi, an Italian
neurophysiologist, established that there were at least two forms of
the disease, one with tertian periodicity (fever every other day) and one with quartan periodicity (fever every third day). In 1886 he was the first to observe
that the tertian and quartan forms produced differing numbers of segmentations
on maturity, implying that the two diseases were caused by two distinct parasites.
He also demonstrated that the fever coincided with the rupture and release of
merozoites into the blood stream and that the severity of symptoms correlated
with the number of parasites in the blood. (He was awarded a Nobel Prize in
Medicine for his discoveries in neurophysiology in 1906). Camillo Golgi was
also the first to photograph the pigmented quartan malaria parasite in 1890. Many scientists accepted Golgi's findings, but others, including Laveran, did
not. The dissenters were apparently not ready to accept the fact that there
existed many varieties of malaria parasite that caused the same disease in birds,
monkeys and man (as was known by then from studies of Danielewsky and others).
In 1891, Romanowsky described staining methods for identifying malarial parasites
and with the better blood-staining methods available, Golgi was shown to be
correct. It became clear that many parasite varieties did indeed exist,
developing in the blood at different rates and that in each species there was a
segmented form that reproduced by division and an ovoid form that never
segmented. In
1893, presaging
discovery of tissue stages of human malarial parasites
by over 50 years, Golgi
suggested that parasites of human malaria may have
an undiscovered tissue phase
in endothelial cells not affected by antimalarial drugs and that the protected
parasites could be the source of relapses.
However,
the first to publish a theory regarding the existence of a tissue stage of the parasite was
Pel in 1886. Pel's explanation of long-term malarial latency was as follows. "During the
latent period the germ is fixed somewhere or not able to reproduce, until by some
cause its conditions for life become more favorable. Then the germs can multiply or
shift to another more active stage of development, reach the
blood and cause particular
disease symptoms."
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Stephens
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The nomenclature
of malaria parasites has been a matter of intense debate and acrimonious confusion.
Laveran had seen different forms of the malaria parasite in 1880 and firmly
believed that all of the parasites belonged to one species, and he called them
Oscillaria malariae. In 1884 Marchiafava and Celli called the same forms
as Plasmodium. Sakharov in 1889 and Marchiafava and Celli in 1890 identified
the parasites that caused malignant tertian fever separately from the ones causing
tertian and quartan fevers. The Italian investigators Giovanni Batista Grassi
and Raimondo Filetti first differentiated and introduced the names Haemamoeba
vivax and H. malariae for two of the malaria parasites in 1890. In
1892, Grassi and Feletti, as an honor to Laveran, proposed the genus name
Laverania which was zoologically correct. In 1897, an American, William
H. Welch, proposed the name Haematozoon falciparum for the parasite with
the crescent-shaped gametocytes and causes malignant tertian malaria.
A generic name Haemomonas was also proposed. Confusion continued well
into the 20th century over whether all of the parasites belonged to one species
or to several. The genus name Plasmodium of Marchiafava and Celli was
maintained for all species. The species name of the parasite suggested by Laveran
as malariae, by Grassi and Feletti as vivax and by Welch as falciparum
continued. What parasites Laveran saw and described thus came to be known later
as P. malariae and gametocytes of P. falciparum. A change back to the name given by Laveran was not possible as the use of these
terms had already become extensive in the literature. The fourth human parasite,
P. ovale was identified by John William Watson Stephens in 1922.
Meanwhile in 1895, Thayer and Barker compiled 616 well documented
malaria cases complete with fever curves and species-specific blood film microscopy,
plus four autopsies of three P. falciparum cases and one P. vivax
case. In 1897 Thayer published a series
of lectures with several references to relapse in vivax malaria. In his speculations
to explain latency, which must obtain preceding a relapse, he postulated that
there must be an undiscovered form of the parasite. He wrote "the organism
may remain perhaps within the cell body of certain phagocytes for long periods
of time, only to be set free again as a result of some insult, the nature of
which is not as yet appreciable to us."
The true nature of the ovoid
forms seen by Laveran and others was unclear. Many scientists, noting that this
phenomenon took place only in blood removed from the body, believed with Laveran
that they were witnessing nothing more than a "death spasm." Such
a notion fit in with the old Hippocratic idea that malaria might come from ingesting
stagnant water, and it also conformed to a newer theory that the organism was
transmitted by contaminated water, as was cholera.
In 1897, Dr. William G. McCallum
and Opie of the Johns Hopkins Hospital demonstrated the sexual process of the
malaria parasite. By using the pigmented Halteridian species, Haemoproteus
columbae MacCallum observed under a glass slide the penetration of a vermicule
from a male gametocyte into a rounded female gametocyte. Later, they confirmed
their findings in the case of P. falciparum. More study suggested that
only plasmodia outside the body behaved in this fashion.
Meanwhile, on February 10, 1882,
Albert Freeman Africanus King, a gynecologist at George Washington University
and author of an obstetrics textbook, presented his ideas on malaria to the
Philosophical Society of Washington, and in September 1883 this lecture was
published in Popular Science Monthly. The characteristics of malaria,
King said, "may be explicable by the supposition that the mosquito is the
real source of the disease rather than the inhalation or cutaneous absorption
of a marsh vapor." After listing nineteen sound reasons for implicating
the mosquito as the vector, he added, "While the data to be presented cannot
be held to prove the theory, they may go so far as to initiate and encourage
experiment and observation by which the truth or fallacy of the views held may
be demonstrated.. which either way, will be a step in the line of progress...."
He went on to suggest a grandiose and impractical plan for malaria control in
Washington DC. He claimed that Washington could be ridded of malaria by surrounding
the entire city with an enormous screen of fine mosquito netting as high as
the Washington Monument. This was greeted with an enormous guffaw and even today
no one is certain whether King was serious or attempting a joke. But this certainly
discouraged anyone reading his paper from testing the highly sensible mosquito
hypothesis.
Many others thought of mosquitoes as a possible cause for transmission of malaria.
Laveran expressed such an idea briefly in 1884, evidently independently of King.
Seven years later he mooted the same idea again very briefly and without giving
many reasons. Robert Koch during his first visit to India in the winter of 1883-1884
for research on cholera came in contact with malaria and thought of a possibility
of mosquitoes spreading the disease. R. Pfeiffer talked about the same idea
in 1892.
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Sir Patrick Manson |
Patrick Manson then working
in China was also speculating about the nature of malaria. He sought to draw
a comparison between malaria and filariasis, for which the mode of transmission
by mosquitoes was discovered by him. In 1878 Manson had begun to study the blood
of malaria patients looking for a blood borne agent as its cause, but abandoned
the effort when he could not find any. In 1881, when he learned of the supposed
discovery of the "Bacillus malariae" by Klebs and Tommasi-Crudeli
he tried again but was never able to isolate the bacillus from the blood of
a malaria victim. Having moved rom Amoy to Hong Kong in December 1883, he learned
of Laveran's discovery in 1884 and immediately set out to identify the parasite
for himself, but failed yet again. After returning to Scot land in 1889, he
joined the Seamen's Hospital Society in London in 1890 where he could get the
the blood specimens of sailors from all parts of the world. He could finally
see Laveran's malarial parasite and he studied the observations of Golgi, Laveran,
and others. He then confirmed to his own satisfaction that there were indeed
several species of parasite that could infect a human being, each having its
own appearance and producing its own symptoms and signs. Especially intriguing
to Manson was "exflagellation," the formation by the ovoid form of
the tiny, whip-like appendages first reported by Laveran. Manson did not agree
with the death spasm theory. To him, the exflagellation represented another
phase in the parasite's development. "Since the flagella appear only when
malarial blood gets outside the body," he reasoned, "their purpose
must be to continue the life of the parasite in the outer world." This
logic had stimulated him to seek an extracorporeal form of the filaria of elephantiasis
and had led directly to his discovery of the mosquito as the vector. In addition,
an American doctor, Theobald Smith, and an epidemiologist, F. L. Kilborne had
proved in 1893 that Texas cattle fever was produced by a parasite that went
through a developmental phase within cattle ticks that transmitted the disease
and in 1894, David Bruce, a British medical officer, identified the trypanosome
as the causative organism and tsetse fly as the vector of an African animal
infection, called nagana. Reasoning by analogy with the findings of Smith, Kilborne,
and Bruce, Manson postulated a mechanism for the transmission of malaria. According
to his schema, when a mosquito fed on the blood of a human with malaria, the
flagellated form of the plasmodium ended up in the insect's stomach. From there
it migrated into the tissues, where it grew into a form capable of infecting
another human. But Manson tripped up when postulating how the parasite passed
from the mosquito back to man because entomologists at the time believed that
the insect died after depositing its eggs in water. The parasites, Manson theorized,
escaped from the dead mosquito's body and were carried to the next victim by
contaminated water. Thus he had neatly fitted in another piece of the puzzle,
yet was still forced to fall back on the old Hippocratic notion that attributed
malaria to the ingestion of stagnant water. This new theory of malarial transmission
was quickly published. To allow it to gain acceptance, Manson eagerly accepted
invitations to lecture on it and discuss it. The scientific establishment considered
the theory wildly speculative, and Manson was not able to get hold of the malaria-carrying
mosquitoes that would enable him to clinch his argument. He applied for a scientific
grant so that he might travel to a malarious area abroad and collect the evidence
he needed, but no money was forthcoming. Manson, however, was an indefatigable
teacher and demonstrator, whose reputation as a tropical medicine expert continued
to grow. Invariably younger men returning from the far comers of the Empire
solicited his medical advice. And one of these men was Surgeon Major Ronald
Ross of the Indian Medical Service.
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Ronald Ross |
Ronald Ross was a reluctant physician
who had hoped to revolutionize mathematics and write poetry, music, plays, and
novels that he did not mind publishing at his own expense, but was stimulated
into research by Manson that finally brought him the Nobel prize! Ross apparently
set out on his scientific experiments without much expert reading on the literature
that existed at the time, he came to know most of the things on his own! The
mosquitoes that he encountered soon after landing in India were to occupy him
for the rest of his life. During his work in many hospitals in India, Ross studied
these insects in great detail and noticed many facts about their habits and
habitats besides finding in them the vector for malaria. This single minded
work paved the way for malaria control efforts later on.
Ross joined the Indian Medical
Service in 1881 and during his initial years, was forced to tackle the mosquitoes.
Outside his bungalow quarters he saw mosquitoes breeding in a barrel, swarming
in to attack him through an open window. Ross solved the problem by simply tipping
over the barrel. "When I told the adjutant of this miracle," Ross
wrote, "and pointed out that the mess house could be rid of mosquitoes
in the same way (they were breeding in the garden tubs, in the tins under the
dining table and even in the flower vases) much to my surprise he was very scornful
and refused to allow men to deal with them.." He made such observations
at many places and this later helped him to explain that malaria did not emanate
from the marshes as was believed, but from pots and tubs thrown everywhere!
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Time Line For Scientific Discoveries |
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Ancient Times |
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Early man attributed the fevers to evil spirits, angered
deities, demons, or the black magic of sorcerers |
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Severel
thousand years ago |
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Babylonian cuneiform script attributes malaria to a god,
pictured as a mosquito-like insect |
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800 BC |
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Indian sage Dhanvantari wrote that bites of mosquitoes could causes
diseases, fever, shivering etc. |
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400 BC |
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Hippocrates described the various malaria fevers of man; distinguished the intermittent malarial fever
from the other continuous fevers;
noted the daily, every-other-day, and every-third-day
temperature rise; mentioned about splenic change in malaria; attributed malaria to ingestion of stagnant water; also related the fever to the time of
the year and to where the patients lived. |
| |
300 BC |
| |
Charaka Samhita
in India classifies the fevers into five different
categories, namely continuous, remittent, quotidian,
tertian and quartan fevers.
|
| |
100 BC |
| |
Susruta Samhita
in India associates fevers with the bites of the insects |
| |
First
Century BC |
| |
Roman
agriculturist Collumella suggested
that the diseases are caused by animals
that breed in the marshes |
| |
First
Century AD |
| |
Roman
scholar Marcus Terentius Varro suggested
that the grave maladies are caused by inhalation of certain animalcula
that breed in the swamps |
| |
30 AD |
| |
Celsus described two types of tertian fevers |
| |
160-200 AD |
| |
Galen suggested that malaria was due to a disorder in the
four humors of the body and suggested bleeding and/or
purging as treatment; this view stayed for 1500 years |
| |
1696 AD |
| |
Morton presented the first detailed description of the
clinical picture of malaria and its treatment with cinchona. |
| |
1712 AD |
| |
Fransesco Torti
accurately described the intricate course of the disease
that was curable by the cinchona |
| |
1716-1717 AD |
| |
Lancisi first described a characteristic black pigmentation
of the brain and spleen in the victims of malaria. He linked malaria with poisonous
vapours of swamps or stagnant water on the ground. In 1717, in his monograph
titled Noxious Emanations of
Swamps and Their Cure, he echoed the view that malaria was due to minute
"bugs" or "worms" which entered the blood and revived the old
idea that mosquitoes might play a role. |
| |
1796 AD |
| |
John Crawford, American physician contradicted the bad-air
theory and suggested that the eggs, laid during a mosquito
bite, hatched in the wound and migrated through the host's
body, producing the manifestations of malaria |
| |
1816 AD |
| |
Giovanni Rasori doubted the "bad air" theory and
suggested that a microorganism is responsible for the disease |
| |
1847 AD |
| |
German physician, Heinrich Meckel, identified round, ovoid, or spindle-shaped
structures containing black pigment granules in protoplasmic masses in the blood
and in the spleen; he probably saw the malaria parasites for
the first time, but could not recognize the true importance
of his finding |
| |
1848-1850 AD |
| |
Schutz, Virchow and Hischl confirmed the presence of pigment
with intermittent fevers. |
| |
1850 AD |
| |
American Josiah Clark Nott dismissed the miasma theory and
suggested that microscopic “insects” transmitted by
mosquitoes caused both malaria and yellow fever |
| |
1854 AD |
| |
Beauperthy,
American naturalist, wrote that malaria and yellow fever
"are produced by venomous fluid injected under the skin by
mosquitoes |
| |
1878-79 AD |
| |
Edwin Klebs and Corrado Tommasi-Crudeli announced the
"discovery" of Bacillus malariae, a bacteria that
supposedly caused malaria |
| |
November 6, 1880 |
| |
Charles Louis Alphonse Laveran, a French physician working
in Algeria , found a moving object while examining a fresh
blood film from a patient of malaria. He called this parasite Oscillaria malariae. |
| |
1881 |
| |
George Sternberg, American bacteriologist proved that the Bacillus malariae was not responsible for malaria |
| |
1882 |
| |
Albert Freeman Africanus King, a
gynecologist at George Washington University, suggested that
the mosquito is the real source of malaria |
| |
1884 |
| |
Russian physiologist, Basil Danielewsky identified malaria
parasites of in the blood of wild birds |
| |
1884 |
| |
Marchiafava and Celli
demonstrated active amoeboid ring in unstained blood and named it Plasmodium, |
| |
1886 |
| |
Louis Pasteur, William Osler and Camillo Golgi confirm
Laveran's finding |
| |
1886 |
| |
Pel suggested the existence of a tissue stage of the parasite |
| |
1886 |
| |
Golgi
observe
that the tertian and quartan forms produced differing numbers of segmentations
on maturity; also demonstrated that the fever coincided with the rupture and release of merozoites
into the blood stream |
| |
1891 |
| |
Romanowsky
described better staining methods for identifying malarial
parasites |
| |
1893 |
| |
Golgi
suggested that malaria parasites may have
an undiscovered tissue phase
in endothelial cells not affected by antimalarial drugs and could be the source of relapses. |
| |
1897 |
| |
William G. McCallum
and Opie demonstrated the sexual process of the malaria parasite.On August 20,
1897, a tired, discouraged Ronald Ross |
| |
August 20, 1897 |
| |
Ronald Ross demonstrated oocysts in the gut of anopheline
mosquito at Secunderabad, India, proving that mosquito was
the vector for malaria |
| |
July, 1898 |
| |
Ronald Ross demonstrated the sporozoites in the salivary
glands of the mosquito and then transmitted malaria to birds
through infected mosquitoes. |
| |
September, 1898 |
| |
Giovanni Battista Grassi transmitted vivax malaria to a
human volunteer |
| |
1900 |
| |
Patrick
Manson transmitted malaria to volunteers in London from
infected mosquitoes brought from Italy. |
| |
1911 |
| |
Brown suggested the hematin
origin of the 'black pigment' and suggested the
action of a proteolytic enzyme on hemoglobin to be the most probable mode of
elaboration of the malaria pigment |
| |
1948 |
| |
Shortt & Garnham
demonstrated the tissue form of P. vivax malaria |
| |
1975 |
| |
William Trager cultured P. faliciparum inside red
blood cells |
| |
1977 |
| |
Lysenko
et al. suggested latent forms of P. vivax malaria that cause
relapses |
| |
1987 |
| |
Dr. Manuel Elkin Patarroyo, a Colombian biochemist, developed
the first synthetic Spf66 vaccine against P. falciparum |
| |
2002 |
| |
The genome of Anopheles gambiae and Plasmodium falciparum sequenced |
|
|
|
|
In 1892 Ross learned of Laveran's
discovery but was unable to see the parasites even after spending hours peering
through his microscope at blood smears. Thoroughly exasperated, he strongly
questioned the soundness of Laveran's observations and even wondered if the
Frenchman might have falsified his data. When he took his second furlough to
England in 1894, he told his colleagues about his failure to see what Laveran
had described. They sent him to Dr. Patrick Manson. Ross spent many hours following
Manson on ward rounds at the Seamen's Hospital and in Manson's private laboratory.
There, for the first time, Ross was able to locate the tiny malarial parasites
under the microscope. Manson, impressed with this eager, capable student, expounded
upon his ideas to Ross one November afternoon in 1894: "Do you know,"
he remarked to Ross while the two were on the way to the hospital, "I have
formed a theory that mosquitoes carry malaria just as they carry filaria."
This meeting with Manson was to change his life forever. Manson guided Ross
throughout his research, suggested new approaches, encouraged Ross when he became
depressed and came to his aid whenever superiors thwarted him. There was a continuous
exchange of ideas between the two men, first directly and then by letter.
Manson suggested that the filaments
in the crescents were actually living bodies and the mosquito sucked the filamented
crescents into its stomach while feeding on the blood of a malaria patient.
The filaments proceeded to travel through the stomach into the insect's tissues.
After the mosquito died laying its eggs, the "flagellated spores"
emerged into the water, ready to infect anyone who came to drink.
These theories, which had earned
for Manson the titles "pathological Jules Verne" and "Mosquito
Manson," sent the young Ross into raptures of ecstasy. Suddenly the fame
that had eluded him despite years writing poems, music, plays, novels, and equations
seemed within his grasp. He had but to prove what Manson had presented to sound
like gospel truth. He went about it with an almost manic enthusiasm.
Following Manson's instructions,
Ross captured the ubiquitous mosquitoes and tried to induce them to bite malaria
patients. But they obdurately refused to bite any one, even Ross. The mosquitoes
caught were probably too frightened to bite, Ross reasoned. So he raised new
mosquitoes from grubs. Still no luck. He baked the patients in the hot sun "to
bring their flavor out." Nothing happened. On May 13, 1895, Ross' birthday,
a heavy rain soaked the bed and netting of a malaria patient. Made ravenous
by the moisture, the mosquitoes attacked the patient with alacrity. Ross grabbed
four of them, expressed their ingested blood on a glass slide, and peered at
it with his microscope. Just as Manson had prophesied, there were the parasites.
To be certain of the results, Ross tried the same experiment with six more mosquitoes
the next day. "Every point that you predicted seems to come true,"
he wrote to Manson. "Certainly there is nothing contrary to the theory.
The parasites are present in the blood of the mosquito, and what is even more,
they appear to be there in greater numbers than in blood from the finger. Also,
the development of the crescents, and the formation of the flagella, seem to
be favored by conditions in the mosquito's stomach. Yes, the crescent-sphere-flagella
metamorphosis does go on inside the mosquito to a much greater degree than in
control specimens of finger blood."
Manson immediately wrote back
with more instructions. "Let mosquitoes bite people sick with malaria,"
he advised, "then put those mosquitoes in a bottle of water and let them
lay eggs and hatch out grubs. Then give that mosquito-water to people to drink."
So Ross allowed four mosquitoes
to feed on a patient named Abdul Kadir. These insects were then kept in a bottle
full of water until they died. After the promise of a suitable emolument, Lutchman,
Ross's native servant, was persuaded to swallow the liquid in the bottle. Ross
waited anxiously for ten days for Lutchman to develop fever. On day eleven,
Lutchman complained of a headache and was found to have a slight temperature
elevation. Now thoroughly excited, Ross admitted his experimental subject to
the hospital and impatiently sat by him, measuring his temperature every thirty
minutes. Not a parasite was to be seen in his blood. Lutchman probably only
had the flu and recovered completely a few days later. Ross repeated the experiment
with other volunteers, and these men were totally unaffected by the mosquito
water.
Meanwhile in 1896, Amico Bignami,
an Italian scientist, attempted to prove Manson's mosquito theory in man. Bignami
captured mosquitoes from regions with a high incidence of malaria and allowed
them to bite healthy human beings. But he failed and this threw the mosquito
theory into some disrepute.
The repeated failures to introduce
malaria by 'mosquito water' had prompted Ross to question Manson's theory. So
he began to formulate his own theories. "She always injects a small quantity
of fluid with her bite," Ross noticed. "What if the parasites get
into the system in this manner?" To test this, Ross allowed mosquitoes
that had fed on a malaria patient to bite a healthy man. Nothing happened. The
experiment was repeated again and again. No fever developed. Still enthusiastic,
he communicated his new notion to Manson.
Manson, however, had quite an
imperfect understanding of mosquito behavior. Believing that the insect bit
only once during its life, he was convinced that Ross could not be correct.
"Follow the flagella," he wrote back, and forget this crazy idea.
In February 1897 Ross was able
to observe the true fate of the flagella. Within a blood smear he saw two parasites
near each other. The first was giving off flagella, while the second, which
was spherical and unsegmented, had a single flagellum wiggling slowly inside.
Had Ross begun a moment earlier, he might have watched the flagellum emitted
by the first parasite penetrate the second and so perceive the true nature of
the process. But from his vantage point, he surmised that the single wiggling
flagellum was trying to escape the sphere rather than fertilize it. When McCallum
in Baltimore correctly interpreted the process a few weeks later, Ross was deeply
humiliated, and "always felt disgraced as a man of science" for incorrectly
interpreting his own observation.
When his experiments did not
yield the desired results, Ross found inspiration while re-reading Manson's
original article on filariasis, being reminded of the fact that only one species
of mosquito was capable of carrying filariasis. Manson had also suggested that
each form of the malarial plasmodia might require a particular mosquito species.
Ross suddenly realized he had used the wrong species of mosquito. Most of his
cases had been falciparum malaria, and he had consistently employed the common
house mosquito. After a little searching, Ross was able to come up with another
species of mosquito. This "dappled winged mosquito," as he called
it, had no breathing tube and floated parallel to the water surface in its larval
form. The adult sat with its tail pointed upward.
A malaria patient named Hussein
Khan was the first experimental subject. Ross let loose a dozen of these mosquitoes
under the mosquito netting of Hussein Khan's bed, and trapped each one, after
it had fed, in a separate bottle. Two mosquitoes were then examined immediately.
Two days later others were dissected. More of the insects died during the night
and quickly decomposed. In all of them Ross found nothing. On August 20, 1897,
a tired, discouraged Ronald Ross dissected one of the two remaining mosquitoes.
Just as he was about to give up, he noted a queer structure within the cells
lining the insect's stomach: an almost perfectly circular cell containing a
group of black pigment granules very similar to those seen in the malarial parasites
found in blood smears. Nearby were identical circular cells. Ecstatic with joy,
Ross wrote, "Those circles in the wall of the stomach of the mosquito--those
circles with their dots of black pigment, they can't be anything else than the
malarial parasite, growing there...." On August 21 he dissected and examined
the last mosquito, and again saw the pigment-filled circles. With this he had
proved that the malaria parasite developed in the mosquito's gut. His report,
"On Some Peculiar Pigmented Cells Found in Two Mosquitoes Fed on Malarial
Blood," was published in the December 18, 1897 issue of the British
Medical Journal.
Soon after, he was transferred
Kherwara in the deserts of Rajasthan, a place that had hardly any cases of malaria.
Yet the resourceful Ross did not quite languish. He knew of Danielewsky's studies
of bird malaria, and verified for himself that some types of pigeons carried
the disease. At the time, many biologists believed that mosquitoes did not attack
birds. After studies of pigeons, sparrows, and crows, Ross verified that birds
were indeed bitten by mosquitoes, as well as by other insects.
He was transferred again to Calcutta
in February 1898, but he could not get human volunteers to continue his work.
So Ross turned to the study of bird malaria again. He got an able assistant
called Mohammed Bux who brought in many live sparrows, larks, and crows. Into
the cages covered with mosquito netting went the mosquitoes. In almost no time
Ross could demonstrate that the plasmodium passed from bird to mosquito, just
as it did in humans. Moreover, the same pigmented, circular cells would form
in the wall of the insect's stomach. Only one difference was noted. The common
gray mosquito was the carrier of bird malaria. The brown, dapple-winged vector
of human malaria could not be infected by the bird parasite.
But how did the parasite pass
from the mosquitoes to the birds? According to Manson's theory, the parasites
were ingested with water in which the mosquitoes had died while laying eggs.
Ross easily tested this theory by feeding infected mosquitoes to healthy sparrows.
The result: The birds remained free of malaria.
The true answer finally emerged
as Ross continued to study infected mosquitoes. As the circular cells within
the mosquito's stomach enlarged, the pigmented granules grew into little rod-shaped
bodies. Soon, Ross discovered that the circular cells in the stomachs of the
mosquitoes ruptured and the rods migrated to the insect's thorax. On July 4,
1898, Ross discovered their final destination. Examining the insect's head,
he noted the salivary gland to be so loaded with rods that it quivered. Here
then was the answer. Malaria was passed back to the birds in the mosquito's
saliva during the act of biting. This remarkable finding, Ross later wrote,
"brought him up standing." As a final verification, he sent Mohammed
Bux to capture a group of healthy sparrows. Mosquitoes that had fed on infected
birds were allowed to bite these healthy ones. Within a few days the blood of
the new birds was loaded with malarial parasites.
Manson received the news at a
meeting of the new Tropical Diseases Section of the British Medical Association.
When he read Ross's report to the assembled delegates, it generated intense
excitement. "I am sure you will agree with me," Manson said, "that
the medical world, I might even say humanity, is extremely indebted to Surgeon
Major Ross for what he has already done, and I am sure you will agree with me
that every encouragement and assistance should be given to so hard-working,
so intelligent, and so successful an investigator to continue his work."
But that was not to be. Ross
did not receive any such support and disgusted, he decided to abandon any further
work on his malaria research and returned to England.
But things were different in Italy, where malaria was rampant in the Roman
Campagna. By the mid-nineteenth century, any scientist wishing to study the
disease could be assured of financial support from Italian industrialists and
agriculturists.
 |
|
|
Robert Koch |
|
Robert Koch, who had developed interest in malaria and the role of the mosquito
during his visit to India in 1883, rekindled his interest in the topic and in
1898 went to Italy to try and demonstrate that human malaria was caused by a
mosquito bite. But he too did not succeed in his efforts, like Bignami, as he
did not believe that a particular species of mosquito was necessary to transmit
human malaria. Koch also thought that the infant mosquito inherited the parasite
from its mother, probably based on the observations of Theobald Smith with regard
to the transmission in the ticks of Texas cattle fever.
In September 1898, Italian physician
Giovanni Battista Grassi was able to report that this insect, Anopheles claviger,
was the carrier of human malaria. The proof was obtained by means of a human
experiment. The subject, a Mr. Abele Sola, had been for six years a patient
in the Hospital of the Holy Spirit, atop one of the hills of Rome. Malaria had
never been seen in this vicinity and neither had the anopheles mosquito. With
Mr. Sola's permission, Grassi, Amico Bignami and Dr. Giuseppe Bastianelli, a
hospital physician, shut Mr. Sola in a room with anopheles mosquitoes every
night for ten nights. On the eleventh day, the patient developed a malarial
chill. Examination of his blood revealed large numbers of plasmodia: "The
rest of the history of Sola's case has no interest for us," Grassi wrote,
"but it is now certain that mosquitoes can carry malaria, to a place where
there are no mosquitoes in nature, to a place where no case of malaria has ever
occurred, to a man who has never had malaria--Mr. Sola!".
|
 |
|
GB Grassi |
Grassi's successful repetition
of the experiment on other patients somehow leaked out. The newspapers were
incensed and implied that Grassi was ruthlessly endangering the lives of his
human guinea pigs. He ignored them and continued with his work.
To refute Robert Koch's assertion
that the infant anopheles inherited the malarial infection from its mother,
Grassi raised anopheles mosquitoes from eggs, as was done by Ross in all his
experiments earlier. Then he allowed the mosquitoes to bite him and six other
volunteers. All remained free of malaria.
The complete cycle of P. falciparum
was observed by Grassi, Bignami, and Bastianelli in 1899 and in the same
year, Bastianelli and Bignami accomplished the same feat with P. vivax.
The Italian studies on the sporogonic cycle of malaria were summarized in what
was to become a classical monograph by Grassi in 1900.
In the course of his experiments,
Grassi came to read Ronald Ross's articles on bird malaria. But when he published,
he failed to give Ross credit. Ross was furious. Thoroughly convinced that Grassi
was trying to steal his discovery from him, Ross sent angry letters to the journals
that had published Grassi's papers, asserting that Grassi was a mountebank,
a cheap crook, a parasite who survived on the ideas of others. Grassi replied
in equally acrimonious terms. So vicious did the correspondence become that
journal editors, fearful of libel, hesitated to publish the letters.
But Ross and Grassi did not stop
feuding. Both enlisted the aid of the authorities on tropical medicine. Ross
was able to obtain letters from Dr. T. Edmundston Charles, an English observer
of the Italian work in Rome. Using this evidence, Ross asserted that Grassi
had been aware of the studies on bird malaria, though Grassi later denied such
awareness. When Ross could not find a publisher for a book containing his case
against his Italian adversary, he paid for the printing himself, carrying the
work through two editions. This bitter conflict lasted for more than two decades.
But the Nobel Prize Committee had no trouble deciding who deserved the recognition
and Grassi was ignored or dismissed as the author of an important footnote to
Ross's discovery.
Meanwhile, Patrick Manson repeated
Grassi’s experiment on select human volunteers. In 1900, Manson arranged
for three people from the London School of Tropical Medicine to spend the summer
near Ostia in the Roman Campagna. Their days were spent in various excursions
in the vicinity, but each night was passed in special mosquito-proof tents where
they stayed until an hour after sunrise. The three did not come down with the
disease, although transmission of malaria continued at its usual high rate in
the vicinity and many around them contracted malaria. This outcome was dramatized
by the fate of a police detachment sent from Rome to capture a criminal in the
Campagna while the Englishmen were there. Though they remained in the Campagna
for only a day, all the policemen developed malaria shortly after returning
to Rome. The second part of Manson's experiment was most chilling, though it
ended happily. Manson managed to obtain live, malarious Italian mosquitoes,
which he made to bite his own healthy son, P.
Thurburn Manson. In fourteen days, the young medical student
was ill with typical vivax malaria. Manson's laboratory assistant, George Warren,
then allowed a few more of the infected mosquitoes to bite him, remarking that
it would have been "a great pity to waste them." He too quickly contracted
malaria. Both young men survived after treatment with quinine. After these results
had been reported in newspapers and magazines throughout the world, the last
resistance to the mosquito theory finally crumbled. This
experiment also proved to be the first experimentalevidence ofr relapse in P. vivax malaria. Following treatment,
young Manson continued in good health until
9 months later when he had a typical relapse which he himself reported in detail
in 1901. Another volunteer in the same time period, Major C. F. Fearnside who
had a similar experience of relapse
which he reported in 1903.
In 1900 Battista Grassi, having observed morphological differences between the nuclei
of the sporozoite and of the youngest red cell trophozoite, hypothesized that
an intermediate stage would occur between the two forms and that the
sporozoite did not develop directly into blood parasites. In
1900, Bignami and Bastianelli found
that they could not infect an individual with blood containing
only gametocytes.
Three years later in 1903, in a memorable paper on P. vivax,
Fritz Schaudinn described in detail the penetration of the red cell by the sporozoite.
In that paper, which for three decades stood as a classic work in malariology,
he considered Grassi’s hypothesis to be improbable. Fritz Schaudinn in
1902 claimed that the Plasmodium vivax sporozoite penetrated the erythrocyte.
Schaudinn’s accompanying drawings even showed the entry of a malaria sporozoite
into a red blood cell. The first doubts of Schaudinn’s theory came from the
malariatherapy centres treating patients with neurosyphilis (General Paresis).
For such treatment, mostly P. vivax was induced either by direct inoculation
of infected blood or by inoculating sporozoites by mosquito bites. It was demonstrated
by Yorke and Macfie in 1924 and Yorke in 1925 that there
was a difference in the response to therapy in blood-induced and sporozoite
induced infections. The blood-inoculated patients were radically
cured with quinine but the sporozoite-induced infections relapsed after the
same therapy. In 1931, James suggested that sporozoites, after being injected by the mosquito,
are carried to the internal organs where they enter reticulo-endothelial cells
and go through a cycle of development with the eventual production of merozoites
which parasitize red blood cells. This proposal was based primarily on the fact
that therapeutic regimens known to be effective against malaria could not cure
an infection when administered during the incubation period. It was reasoned,
that if sporozoites entered directly into the red blood cells and became trophozoites
and schizonts, they would have been destroyed by the drugs and no active infection
could have resulted. In 1935, Huff and Bloom clearly demonstrated exoerythrocytic stages to be a fundamental
part of the life cycle of bird malaria parasite, P. elongatum. As data
about fixed tissue parasites from birds accumulated, mainly the work of James
and Tate (1937) and the brilliantly executed studies of Huff and his co-workers
(1943 to 1948), it became abundantly clear that such a cycle must also occur
in primate malarias. In 1946, Sapero presented presumptive evidence for the link between fixed tissue
stages and relapse. Sir Neil Hamilton Fairley in Australia in 1947 showed that the blood
of volunteers injected with large numbers of P. vivax sporozoites was
infectious to other volunteers for only 30 minutes. The blood then became "sterile"
until 7 days later when it once again became infectious to volunteers. In
1948,Coatney and Cooper reported that 8-aminoquinolines and certain biguanides were active against the presumed
exoerythrocytic forms of human and simian malarias.
In 1947 Garnham discovered the exoerythrocytic schizogony
of the related parasite Hepatocystis kochi.
| |
HE Shortt and PCC Garnham |
| |
Both Shortt and Garnham
were physician-naturalists and devoted protozoologists known for many seminal contributions to medical protozoology.
Henry Edward Shortt (CIE,FRS,MD, DTM&H; 15
Apr. 1887-9 Nov. 1987) worked for the Indian Medical Service in his
initial years. He had varied interests - from single-celled parasites, tigers, trout
to houseflies. —was a retiring man and yet generous and caring to his associates
and students. SR Christophers and Shortt
carried out the first scientific malaria survey of war during 1914-1918, modelled on Christophers'
earlier malaria surveys in India. Shortt later
worked with Indian Medical Service as Director, King Institute
of Preventive Medicine, Madras from 1935-1939; Inspector-General of Civil Hospitals
and Prisons in Assam during World War II and later as Professor of Parasitology
at London School of Hygiene and Tropical Medicine from 1945-1951.
Shortt was very generous and caring to his associates and
students.At the time of his famous work on malaria, he
was nearing retirement.
Percy Cyril Claude Garnham (CMG, MD, DSc, FRCP, Hon. FRCP(E),
FRS; 15 January 1901-25 December 1994)
belonged to East African Medical Service. He was an aesthete who skied and played the cello.
He was as comfortable in discussing the theatre, opera and literature as he
was in eruditely explaining the lives and times of the Haemosporidia. In
1947 he returned to London to the London School of Tropical Medicine and
Hygiene where he subsequently became Head of the Department of Parasitology
and Professor of Medical Protozoology at the University of London.
Shortt and
Garnham were awarded the Darling Foundation Prize of WHO in 1951. In
1970, Garnham was honoured with the unusual and highly regarded appointment as a
Pontifical Academician, Academy of Science, to the Vatican. |
| |
|
Soon thereafter in 1948, Shortt & Garnham (at the Ross Institute of the London School of Hygiene
and Tropical Medicine, England) and Malamos published their milestone finding of the cyst-like body,
filled with thousands of merozoites, in the liver of a rhesus monkey that had
been inoculated 102 days before with
from 500 mosquitoes. In a laboratory near St. Albans, Hertfordshire, the
rhesus monkey was put into a cage with 500 mosquitoes carrying Plasmodium cynomolgi sporozoites
(previous experiments had used 20 to 100). A solution of killed the mosquitoes
was also injected into the monkey's muscles and chest. With their bold experiment they solved a centuries-old
mystery — the source of malaria’s parasitaemic relapses. P.G. Shute and Sir
Gordon Covell, placed the discovery of the exoerythrocytic (EE) hepatic phase
of mammalian malaria parasites in the following historical context: "Just as
the name of Ross will forever be associated with the discovery that mosquitoes
transmit malaria, so too, will the names of Shortt and Garnham be remembered
in connection with the primary tissue phase of the parasite."
To test this in humans, a patient with general paresis who was to be treated
with inoculation of P. vivax malaria was used. The patient and his wife
agreed that doctors could perform a liver biopsy, seven days after he had
been bitten by infected mosquitoes. At 5 o'clock one morning Dr. Shortt got the
sliver of liver, rushed to his laboratory and worked until 11 that night. The
tissue stage of
P. vivax was thus demonstrated by Shortt, Garnham, Covell and Shute
in 1948. Later, similar preerythrocytic forms were demonstrated for P. falciparum (Shortt et
al, 1949; Jeffery et al, 1952). Tissue
stages of P. ovale (Garnham et al., 1954), and P. malariae (Bray,
1959) were also identified later on.
The demonstration of the exoerythrocytic stages of avian and primate malarias opened new proposals
to explain the phenomenon of relapse in malaria. Although relapses were known
since antiquity and Pel in 1886 and Golgi in 1893, and Thayer in 1897 (See above) had made some
suggestions in this regard, the hiding place
of the parasite, during long periods when the patients were clinically and parasitologically
negative, had been debated for many years. In 1926, even before the full life cycle of malaria parasites was disclosed,
Marchoux outlined three possible mechanisms to account for relapse: (i) parthenogenesis of
macrogametocytes; (ii) persistence of schizonts in small numbers
in the blood where their multiplication is inhibited by
immunity and this immunity disappears; and (iii) reactivation of an encysted body in the blood.
The theory of parthenogenesis of gametocytes was put to rest with
Bignami and Bastianelli in 1900 and again Gainham in 1930 not being able to
infect individuals with blood containing only gametocytes. The second theory, a persistent blood
stage infection, had been proposed by Ross and Thompson in 1910 and also by
Corradetti and held true for P. malariae, which can remain in the blood at undetectable
levels for many years. In 1946, Shute, who was infecting large numbers of mosquitoes with vivax malaria
for malariotherapy of neurosyphilis, noticed that, even though heavily infected
mosquitoes fed on a patient, an immediate malarial infection did not always result, although
symptoms would be exhibited several months later. He speculated that this was due to a "resting parasite."
Sapero proposed in 1947 that perhaps a link existed between a tissue stage not yet discovered in patients
with malaria and the phenomenon of relapse. The discovery of the exoerythrocytic
stages of primate malarias seemed to have revealed their hiding place. With
the report of an exoerythrocytic schizont in the liver of a monkey 3˝ months
after sporozoite inoculation by Shortt and Garnham in 1948, it was thought that
a direct relationship existed between these fixed tissue stages and true relapses.
Various workers, involved in experimental therapy of malaria, had predicted
that an exoerythrocytic stage of the parasite was responsible for long term
relapses in P. vivax. Shannon and Earle in 1945 and Fairley et al
in 1947 proposed that a persistent tissue phase was absent in P.
falciparum and these workers as well as Huff in 1947 supported the view that persistent tissue phase was the source of
the parasites in typical P. vivax relapses. When the work of Coatney and Cooper in 1948,
showing that massive blood transfusions
during latency, following treatment of the initial attack, failed to produce
infections in recipients, although the donors' infections relapsed later, was
combined with the demonstration of an exoerythrocytic schizont of P. cynomolgi
3˝ months after sporozoite inoculation, most workers considered the relapse story to be complete.
The specific mechanism
proposed was that merozoites from mature exoerythrocytic schizonts enter red blood cells, producing the familiar clinical and parasitological
features of malaria. It was thought that merozoites erupting from mature schizonts would reinvade
hepatic parenchymal cells in a more or less continuous cycle until waning immunity allowed
them to invade erythrocytes and initiate another blood cycle. This concept of Shortt and Garnham was widely
accepted as the most likely explanation for the production of relapses in certain species
of both human and simian malaria but it did not account for several subsequent observations. Lysenko et al.
in 1977 suggested a series of postulates to explain the phenomena of long incubation periods and relapses. They theorized
that the duration of the preerythrocytic development of P. vivax is a polymorphic characteristic controlled by several gene loci and that sporozoites
are divided into two complex groups of phenotypes, i.e., the slow-developing and fast-developing types advocated by Ungureanu et
al in 1976. A latent tissue stage was found by Krotoski and coworkers in the liver of a monkey
heavily infected with P. cynomolgi in 1980. In 1981, Krotoski et al. described the
48-h preerythrocytic form of P. cynomolgi by using the indirect fluorescent-antibody method (IFA).
Routine use of this technique to examine heavily infected monkey liver eventually led to the
discovery of a uninucleate stage of the parasite seen initially at
7 days postinfection in animals infected with P. cynomolgi in 1982. These uninucleate forms, found by
immunofluorescence and restained with Giemsa-colophonium stain, were thought to
be the long-sought dormant stage of the parasite. Experiments were undertaken to establish the true nature of this form,
and it was subsequently found by Bray et al in 1985 to be present from 3 to 229 days after sporozoite inoculation
and to remain virtually unchanged during that period. This finding served to underscore the latent nature
of this stage, named the hypnozoite (sleeping animalcule) stage by Garnham in 1977. In
1985 it was demonstrated by Krotoski, Garnham, Bray and others that hypnozoites were in fact present
in two strains of P. vivax, the first such demonstration in a human malaria species. To
determine whether hypnozoites were present in a nonrelapsing type of malaria, Krotoski
and Collins examined liver biopsy samples from monkeys infected with P. knowlesi with IFA
and no hypnozoites were seen. Thus, hypnozoites were demonstrated species of Plasmodium causing relapsing malaria
and had not been found in a Plasmodium species causing a nonrelapsing malaria. These stages had been
shown to be dormant, present in 229 days after sporozoite inoculation and undoubtedly malarial in nature.
In keeping with the history of malaria research, however, the theory had its detractors.
In 1981, Shortt, one of the original discoverers of malaria tissue stages, took issue with
the preliminary report of the discovery of hypnozoites. He questioned their malarial
nature, speculating that they might be contaminants from the mosquito (microsporidia
etc.) or even merozoites from early schizonts that had reinvaded liver cells.
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His objections were answered systematically by Garnham in a published reply.
In 1985, Bray et al. recorded a hypnozoite of P. cynomolgi having two nuclei at 49 days after sporozoite inoculation
suggestive of a dividing form. In 1989, Atkinson et al. published what
may be the first electron micrograph of a hypnozoite. (See) The first to observe hypnozoites in culture were Hollingdale et al. in 1985.
They observed persistent non-dividing P. vivax parasites in cultured hepatoma cells.
In 1975 William Trager cultured P. faliciparum inside red blood cells.
In 1911, Brown distinguished melanin from malarial pigment by deducing the hematin
origin of the latter and stated that the black malarial pigment could
hardly be pure hematin, but should contain impurities. He astutely suggested the
action of a proteolytic enzyme on hemoglobin to be the most probable mode of
elaboration of the malaria pigment. Controversy on the biochemical composition of hemozoin
continued for more than 80 years until the 1990s, when several workers showed
hemozoin to be composed solely of heme arranged in a crystal structure. Only then
was hemozoin formation proved to be the target of widely used antimalarial drugs such
as chloroquine and quinine.
In 1973 human protection from malaria by vaccination was first reported. However, the vaccination consisted of the bites of
about a thousand mosquitoes infected with malaria parasites that had been X
irradiated. For about 20 years, progress occurred mainly in experimental models
rather than in human vaccine trials. In 1987, Dr. Manuel Elkin Patarroyo, a Colombian biochemist, developed
the first synthetic Spf66 vaccine against P. falciparum parasite. But
phase III trials showed that lacked efficacy. During the past 5 years,
many candidate vaccine approaches have been tested in clinical trials.
In 2002, the genome of Anopheles gambiae and Plasmodium falciparum were sequenced
Newer diagnostic tests have been developed for malaria. Becton
and Dickenson developed a fluorescene staining technique using a capillary tube
called as Quantitative Buffy Coat test in 1991-92. Many
non-microscopic, rapid dip stick test shav ebeen developed based on the
detection of various antigens of malaria parasites. P. falciparum Histidine Rich
Protein II (Rock et al, 1987), parasite aldolase (Meier
et al 1992) and parasite Lactate dehydrogenase (Makler et al 1998) are the target antigens used for such tests.
Sources:
Also See
History of
Origin of Malaria
Parasite And Its Spread
History of Malaria During
Wars and Upheavals
History of Malaria And Its
Famous Victims
Malaria In
Ancient
Literature
History of
Anti
Malaria treatment
History of Malaria
Control
History of Malaria
And Its Control In India
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