Principal mode of spread of malaria is by the bites of female
anopheles mosquito.
(Want to know more about
the mosquito? Click on it.)
The female
anopheles mosquito is the vector for human malaria. Some 60 species of this mosquito have
been identified as vectors for malaria, and their distribution varies from country to
country. When a mosquito bites an infected individual, it sucks the gametocytes, the
sexual forms of the parasite, along with blood. These gametocytes continue the sexual
phase of the cycle and the sporozoites fill the salivary glands of the infested mosquito.
When this female mosquito bites the man for a blood meal, which it needs to nourish its
eggs, it inoculates the sporozoites into human blood stream, thus spreading the infection.
The female anopheles mosquito bites man
between 5 PM and 7 AM, with maximum intensity at midnight.
Other modes of transmission: Rarely
malaria can spread by the inoculation of blood from an infected person to a healthy
person. In this type of malaria, asexual forms are directly inoculated into the blood and
pre-erythrocytic development of the parasite in the liver does not occur. Therefore, this
type of malaria has a shorter incubation period and relapses do not occur.
1. Blood transfusion (Transfusion
malaria): This is fairly common in endemic areas.
Following an attack of malaria, the donor
may remain infective for years (1-3 years in P. falciparum, 3-4 years in
P. vivax, and
15-50 years in P. malariae.)
Most infections occur in cases of
transfusion of blood stored for less than 5 days and it is rare in transfusions of blood
stored for more than 2 weeks. Frozen plasma is not known to transmit malaria.
The clinical features of transfusion
malaria occur earlier and any patient who has received a transfusion three months prior to
the febrile illness should be suspected to have malaria.
Donor blood can be tested with indirect
fluorescent antibody test or ELISA, and direct examination of the blood for the parasite
may not be helpful.
In endemic areas, it is safe to
administer full course of chloroquine to all recipients of blood transfusion.
In transfusion malaria, pre-erythrocytic
schizogony does not occur and hence relapses due to dormant hepatic forms also does not
occur. Therefore, treatment with primaquine for 5 (or14) days is not indicated.
2. Mother to the growing fetus (Congenital malaria): Intrauterine transmission of infection
from mother to child is well documented. Placenta becomes heavily infested with the
parasites. Congenital malaria is more common in first pregnancy, among non - immune
populations.
3. Needle stick injury: Accidental
transmission can occur among drug addicts who share syringes and needles. (Therapeutic
inoculation of malarial parasites, so as to induce fever, was a mode of treatment for neurosyphilis!)
|
