Researchers discover that populations of Plasmodium vivax on the continent are as genetically diverse as in Southeast Asia, where malaria transmission is more frequent. Vivax's greater genetic diversity in the Americas in comparison with Falciparum species might be explained by a wider range of migratory routes.
As P. falciparum, the predominant species of malaria parasite displays low genetic diversity in the Americas compared with other regions, scientists believed the same was true for P. vivax. This belief is mistaken, according to a study by researchers at the University Of Sao Paulo (USP) et al. The results were published in PLOS Neglected Tropical Diseases. "The discovery that populations of P. vivax in the Americas are more diverse than populations of P. falciparum was surprising."
"If we accept the hypothesis that both P. falciparum and P. vivax came to the Americas after European colonization, we would expect to find similar levels of genetic diversity in both species, as they would have undergone an intense population squeeze during their 'migration' to the New World. However, this is simply not the case," said, the Brazilian scientist.
The study of P. vivax's genetic diversity in the Americas seeks clues to the origin of the many lineages or populations found on the continent.Upon arriving in the Americas, P. vivax appears to have retained much more of its existing diversity, as in Africa for example, than P. falciparum.
"A possible explanation is that the populations of P. vivax that came to the Americas originated in a wider geographical area, including Africa, Europe and perhaps Asia, than the populations of P. falciparum that came here, as these were predominantly African, but this has yet to be demonstrated," Urbano Ferreira said.
"The diversity of P. vivax in Brazil is substantial, given more than 300 years of slave trading, one of the ways the parasite migrated. However, it entered Brazil in many ways at different times, not least in the nineteenth century with the first wave of immigrants," said Thaís Crippa de Oliveira, first author of the article published in PLOS Neglected Tropical Diseases.
Blood samples were collected from patients in Northwest Brazil. Brazil accounts for 37% of all malaria cases reported in the Americas. All nine patients were found to be infected with P. vivax.
The parasites in the samples were separated, and their nuclear DNA was isolated and subjected to whole-genome sequencing. To place these sequences in a regional context, the researchers performed whole genome sequencing of 75 other clinical isolates of P. vivax from Brazil (2), Peru (23), Colombia (31) and Mexico (19) obtained via international gene banks. The study showed that the genetic diversity found in Brazil's P. vivax population is similar to that found in other countries of the Americas.
Urbano Ferreira said. "Mitochondrial genomes are very useful in these studies, but we certainly need complete nuclear genomes to make more definitive inferences."The researchers are now working on a new sample collected by Urbano Oliveira from a single community during 12 months of study.
Whole-genome sequencing of these parasites will enable them to evaluate the levels of genetic variation in populations of P. vivax over time and infer some of the mechanisms that contribute to such variation, including migration and recombination.