Wednesday, April 13, 2005

News: Malaria P. vivax diffused from Southeast Asia?

The following abstract of a recent scientific article is of interest because malaria tends to diffuse due to human/mosquito migration.

Mosquitos alone are quite territorial and tend to return again and again to the same host. Occasionally they seek new hosts in the same area, thus spreading the disease.

Since malaria types are linked to specific mosquitos, infected humans traveling alone are not enough to spread the disease from one area to another. It is thought that the main mode of diffusion is humans accidentally transporting infected mosquitos.

While malaria can spread to some extent through trade and other contact, studies have shown that population movement is the most important method of spreading the disease especially over long distances and certain geographical barriers.

The new study shows that P. vivax the parasite that spreads one type of malaria, originated in Southeast Asian macaques. If it can be shown the spread of P. vivax into places like Africa is linked with modern human migration, it would suggest extensive and possibly very ancient links between Southeast Asia and Africa.

Paul Kekai Manansala

Proc Natl Acad Sci U S A. 2005 Feb 8;102(6):1980-5. Epub 2005 Jan 31.

A monkey's tale: The origin of Plasmodium vivax as a human malaria parasite.

Escalante AA, Cornejo OE, Freeland DE, Poe AC, Durrego E, Collins WE, Lal AA.

Division of Parasitic Diseases, Centers for Disease Control and Prevention, Chamblee, GA 30341.

The high prevalence of Duffy negativity (lack of the Duffy blood group antigen) among human populations in sub-Saharan Africa has been used to argue that Plasmodium vivax originated on that continent. Here, we investigate the phylogenetic relationships among 10 species of Plasmodium that infect primates by using three genes, two nuclear (beta-tubulin and cell division cycle 2) and a gene from the plastid genome (the elongation factor Tu). We find compelling evidence that P. vivax is derived from a species that inhabited macaques in Southeast Asia. Specifically, those phylogenies that include P. vivax as an ancient lineage from which all of the macaque parasites could originate are significantly less likely to explain the data. We estimate the time to the most recent common ancestor at four neutral gene loci from Asian and South American isolates (a minimum sample of seven isolates per locus). Our analysis estimates that the extant populations of P. vivax originated between 4! 5,680 and 81,607 years ago. The phylogeny and the estimated time frame for the origination of current P. vivax populations are consistent with an "out of Asia" origin for P. vivax as hominoid parasite. The current debate regarding how the Duffy negative trait became fixed in Africa needs to be revisited, taking into account not only human genetic data but also the genetic diversity observed in the extant P. vivax populations and the phylogeny of the genus Plasmodium.