Evidence for clonal propagation in natural isolates of Plasmodium falciparum from Venezuela

Abstract

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.

New Insights into Clonality and Panmixia in Plasmodium and Toxoplasma

“…The inference followed that "uniparental and biparental lineages may coexist within this species, for which a sexual cycle has been a classical notion" (Tibayrenc et al, 1990). Although this inference was corroborated by further studies (Ben Abderrazak et al, 1999;Urdaneta et al, 2001), it resulted in a vehement outcry (Dye et al, 1990;Walliker, 1991;Walliker et al, 1990). Our proposal was widely rejected.…”

“Clonal” population structure of the malaria agent Plasmodium falciparum in high-infection regions

“…Anderson et al (5) observed significant linkage disequilibrium among 12 microsatellite loci in all localities with low infectivity and in two of five populations from regions with high transmission frequencies. Other results have been interpreted as indicating that P. falciparum reproduction may be genetically clonal in low-infectivity regions but predominantly panmictic in high-infectivity regions (13,14). Nevertheless, Durand et al (30) found significant linkage disequilibrium in two African populations from the Republic of the Congo, where infectivity is high.…”

“…The incidence of clonality or inbreeding versus outbreeding or panmixia is estimated indirectly by measuring genetic diversity, linkage disequilibrium, and the like (2,6,(8)(9)(10)(11)(12)(13)(14)(15)(16). Hence the conflicting evidence favoring different levels of clonality or panmixia, although it is often accepted that P. falciparum displays different population structures in different places, ranging from clonality to panmixia in approximate correlation with the increasing intensity of transmission (2,5,6,(8)(9)(10)(11)(12)(13)(14)(15)(16).…”

Population genetic structure of Plasmodium falciparum in the two main African vectors, Anopheles gambiae and Anopheles funestus

“…The extent of cross-fertilization and panmixia relative to clonal reproduction in P. falciparum has indeed been the subject of considerable debate during the last decade (13,19,(26)(27)(28)(29)(30). The current consensus is that this parasite species displays a range of population structures associated with the levels of transmission intensity (13).…”