Genetic restriction of Plasmodium falciparum in an area of stable transmission: an example of island evolution?

To date, a high degree of polymorphism has been demonstrated at both the MS P1 and MSP2 loci in parasites from areas of stable malaria transmission. As a consequence, in such areas it is rare to find parasites of the same 2-lo cus genotype in more than 1 subject. We have studied MSP1 and MSP2 diversit y in parasites collected from subjects with both symptomatic (n = 86) and a symptomatic (34) malaria living on the island of Santo, Vanuatu, an area of stable malaria transmission. Polymorphism at the MSP1 and MSP2 loci was co nsiderably less than previously reported: only 5 MSP1 and 5 MSP2 alleles we re detected and these showed no size variation within alleles. Santo is uni que amongst the areas studied so far in that it is a small island at the li mit of the malaria belt in the South Pacific. Thus, the evolution of the pa rasite population may have been affected by the small size and isolation of this island population. Moreover, limited parasite diversity may explain t he unusually mild nature of Plasmodium falciparum disease on Santo. Islands have fascinated biologists for centuries and fuelled the advancement of ev olutionary theory, since they are natural laboratories for the study of evo lution. The simplicity of the Vanuatu P. falciparum population may facilita te the use and interpretation of sequence level analyses to address the mec hanisms by which genetic diversity is generated and maintained in natural p opulations.