Résumé
We have analyzed 75 isolates of Plasmodium
falciparum, collected in Venezuela during both the dry
(November) and rainy (May–July) seasons, with a range of genetic
markers including antigen genes and 14 random amplified polymorphic DNA
(RAPD) primers. Thirteen P. falciparum stocks from Kenya
and four other Plasmodium species are included in the
analysis for comparison. Cross-hybridization shows that the 14 RAPD
primers reveal 14 separate regions of the parasite's genome. The
P. falciparum isolates are a monophyletic clade,
significantly different from the other Plasmodium
species. We identify three RAPD characters that could be useful as
“tags” for rapid species identification. The Venezuelan genotypes
fall into two discrete genetic subdivisions associated with either the
dry or the rainy season; the isolates collected in the rainy season
exhibit greater genetic diversity. There is significant linkage
disequilibrium in each seasonal subsample and in the full sample. In
contrast, no linkage disequilibrium is detected in the African sample.
These results support the hypothesis that the population structure of
P. falciparum in Venezuela, but not in Africa, is
predominantly clonal. However, the impact of genetic recombination on
Venezuelan P. falciparum seems higher than in parasitic
species with long-term clonal evolution like Trypanosoma
cruzi, the agent of Chagas' disease. The genetic structure of
the Venezuelan samples is similar to that of Escherichia
coli, a bacterium that propagates clonally, with occasional
genetic recombination.