ama1 Genes of Sympatric Plasmodium vivax and P. falciparum from Venezuela Differ Significantly in Genetic Diversity and Recombination Frequency

BACKGROUND: We present the first population genetic analysis of homologous loci from two sympatric human malaria parasite populations sharing the same human hosts, using full-length sequences of ama1 genes from Plasmodium vivax and P. falciparum collected in the Venezuelan Amazon. METHODOLOGY/PRINCIPAL FINDINGS: Significant differences between the two species were found in genetic diversity at the ama1 locus, with 18 distinct haplotypes identified among the 73 Pvama1 sequences obtained, compared to 6 unique haplotypes from 30 Pfama1 sequences, giving overall diversity estimates of h = 0.9091, and h = 0.538 respectively. Levels of recombination were also found to differ between the species, with P. falciparum exhibiting very little recombination across the 1.77 kb sequence. In contrast, analysis of patterns of nucleotide substitutions provided evidence that polymorphisms in the ama1 gene of both species are maintained by balancing selection, particularly in domain I. The two distinct population structures observed are unlikely to result from different selective forces acting upon the two species, which share both human and mosquito hosts in this setting. Rather, the highly structured P. falciparum population appears to be the result of a population bottleneck, while the much less structured P. vivax population is likely to be derived from an ancient pool of diversity, as reflected in a larger estimate of effective population size for this species. Greatly reduced mosquito transmission in 1997, due to low rainfall prior to the second survey, was associated with far fewer P. falciparum infections, but an increase in P. vivax infections, probably due to hypnozoite activation. CONCLUSIONS/SIGNIFICANCE: The relevance of these findings to putative competitive interactions between these two important human pathogen species is discussed. These results highlight the need for future control interventions to employ strategies targeting each of the parasite species present in endemic areas

Clonal diversity of the glutamate dehydrogenase gene in Giardia duodenalis from Thai Isolates: evidence of genetic exchange or Mixed Infections?

Background: The glutamate dehydrogenase gene (gdh) is one of the most popular and useful genetic markers for the genotypic analysis of Giardia duodenalis (syn. G. lamblia, G. intestinalis), the protozoan that widely causes enteric disease in humans. To determine the distribution of genotypes of G. duodenalis in Thai populations and to investigate the extent of sequence variation at this locus, 42 fecal samples were collected from 3 regions of Thailand i.e., Central, Northern, and Eastern regions. All specimens were analyzed using PCR-based genotyping and recombinant subcloning methods. Results: The results showed that the prevalence of assemblages A and B among these populations was approximately equal, 20 (47.6%) and 22 (52.4%), respectively. Sequence analysis revealed that the nucleotide diversity of assemblage B was significantly greater than that in assemblage A. Among all assemblage B positive specimens, the allelic sequence divergence within isolates was detected. Nine isolates showed mixed alleles, ranged from three to nine distinct alleles per isolate. Statistical analysis demonstrated the occurrence of genetic recombination within subassemblages BIII and BIV was likely. Conclusion: This study supports increasing evidence that G. duodenalis has the potential for genetic exchange

Determination of discriminatory power of genetic markers used for genotyping Giardia duodenalis

Small subunit ribosomal DNA (SSU-rDNA), glutamate dehydrogenase (gdh), beta-giardin, triosephosphate isomerase (tpi), and elongation factor 1-alpha (ef1-alpha) genes are useful genetic markers for genotypic analysis of the intestinal protozoan, Giardia duodenalis (syn. G. lamblia, G. intestinalis), the cause of enteric disease in humans. To quantitatively compare the discriminatory power of these loci, 43 fecal samples were collected from central, northern and eastern Thailand and G. duodenalis specimens were analyzed using PCR-based genotyping and subcloning methods. Approximately equal prevalence of assemblage A (21) and B (22) were present among these populations. Analysis of Simpson's index and Wallace coefficient values from assemblage B isolates together with the data obtained from Gen Bank showed that the combination of two loci provides a higher discrimination power for subgenotyping G. duodenalis than using any single locus