Malaria is caused by the parasites called Plasmodia.
Phylum: Protozoa Subphylum:
Apicomplexa
Class: Sporozoa Subclass:
Coccidia
Order: Coccidiida Suborder:
Haemosporina
Family:
Plasmodiidae
Genus: Plasmodia
Subgenera:
Plasmodium, Laverania
Species (affecting
man)
Quartan group: P.
(Plasmodium) malariae, P. (P.) brasilianum
Benign tertian group: P.
(P.) vivax, P. (P.) cynomolgi, P. (P.) cynomolgi bastianellii
Malignant tertian group: P.
(Laverania) falciparum
Ovale group: P. (P.)
ovale, P. (P.) simium
Knowlesi group: P. (P.)
knowlesi
P. malariae, P. vivax, P. falciparum
and P. ovale are the most important types affecting man. The other species are
primarily parasites of monkeys or apes, affecting man only rarely and not seriously.
While the benign malaria parasites (P.
vivax, P. malariae, P. ovale) seem to have evolved from primate malaria, the
malignant malaria (P. falciparum) appears to have evolved only 10000 years ago
from avian malaria species.
3 subtypes of P. vivax have been
reported: Two variants of the circumsporozoite protein of P. vivax (VK210 and
VK247) have been identified and recently, a putative third CS variant of P. vivax,
referred to as causing P. vivax-like malaria has been reported. The CS protein of
this P. vivax-like malaria parasite is identical to that of P. simiovale, a
monkey parasite. (Lancet. 1993 Mar 27;341:780-3). This P. vivax-like malaria
parasite has been reported from diverse geographical areas. It remains to be clarified
whether it is a fifth species of human malaria or a member of the P. vivax species
complex [http://www.pngimr.org.pg/]
P. vivax is the commonest cause
of human malaria in Central America, North Africa, southern and western Asia. P.
falciparum is the predominant species in Africa, New Guinea and Haiti. Both
P. vivax and
P. falciparum are found in South America, other parts of Asia and Oceania. P. falciparum
is the cause for all mortality and most of the morbidity due to malaria.
P. ovale is
restricted to western Africa. P. malariae is probably more wide spread than as
made out to be in only a few pockets here and there.
Comparison of
malarial parasites
| |
P. falciparum |
P. vivax |
P. ovale |
P. malariae |
Tissue schizogony |
8 - 25 days |
8 - 27 days |
9 - 17 days |
15 - 30 days |
Erythrocytic phase |
48 hours |
48 hours |
48 hours |
72 hours |
Red cells affected |
All |
Reticulocytes |
Reticulocytes |
Mature RBC's |
Merozoites per schizont |
8 - 32 |
12 - 24 |
4 - 16 |
6 - 12 |
Relapse from persistent liver forms |
No |
Yes |
Yes |
No, but blood forms can persist up to 30 years |
Drug resistance |
Yes |
Yes |
No |
No |
|
