Sunday, July 24, 2011

The origin of malaria

Plasmodium infected red blood cell
If you have taken an introductory Anthropology course you have probably heard about malaria. It is a devastating killer disease in the tropics caused by an infection of the Plasmodium falciparum parasite which infects human blood cells.  We talk about it in intro anthro courses because of the relationship between malaria and another devastating disease, sickle cell anemia.  Sickle cell anemia is a genetic disorder caused by having two copies of the recessive gene which causes it. However, individuals which are merely carriers for the disease (having only one copy of the bad gene) don't get the anemia, and actually have increased resistance to malaria.  Its a classic case of a balanced polymorphism, and it explains why sickle cell anemia is prevalent in parts of the world where malaria is endemic.

In this article in PNAS, Prugnolle et al. discuss the possible origins of malaria, based a survey of the diversity of malarial parasites in several different monkey species in Central Africa.  They detected P. falciparum (the human killer) for the first time in monkeys.  This strain appears to be specific to non-human primates.  This opens up the possibility for a monkey source for human malaria, instead of the gorilla source which had been suggested by other workers.  This study is part of a fascinating recent revolution in primatology, involving the study of parasites from a genetic perspective.  I will take up that topic in a future post. 

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