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Two parasite types may worsen malaria in humans
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Two genetically distinct Plasmodium knowlesi parasite subpopulations associated with different monkey host species in Malaysia are causing malaria in humans, raising the possibility that hybridization could lead to the creation of a more virulent strain with enhanced transmission, according to research published in PLoS Pathogens.
“We were very surprised to find that knowlesi malaria is really two separate zoonoses going on at the same time,” David J. Conway, PhD, professor of biology at the London School of Hygiene & Tropical Medicine, said in a press release. “There is a lot of genetic diversity within each of the parasite types, but the high level of divergence between them indicates they are probably different subspecies being transmitted separately within the same areas. If zoonotic transmission continues to be common, it becomes more likely that the two types may hybridize genetically, leading to new possibilities for parasite adaptation to humans or additional mosquito vectors.”
Conway and colleagues developed species-specific genotyping methods to analyze 552 humans and 47 macaques — both long-tailed and pig-tailed — with P. knowlesi infections from 10 high-volume sites in Malaysia.
The researchers identified two highly divergent populations of P. knowlesi in human cases associated with different species of reservoir host. The first type, predominant in long-tailed macaques, was responsible for about two-thirds of human malaria overall and at most sites, while the P. knowlesi type associated with pig-tailed macaques accounted for the remainder.
Results also indicated that the majority of human malaria infections belonged to a single genotype, while macaques commonly develop malaria infection of mixed genotypes, which supports higher transmission rates in monkeys.
According to study researcher Paul C.S. Divis, MSc, a research degree student at the London School of Hygiene & Tropical Medicine, the hybridization of two species or subspecies, which has been observed in other parasites, is associated with greater pathogenicity.
“Therefore, the transmission of two types of P. knowlesi in humans might increase the opportunity for evolution of virulence or enhanced transmission,” he said in the release.
The researchers wrote that additional analysis of whole genome sequences and expanding research into other areas of Southeast Asia could provide greater clarity on the divergence of parasite subpopulations and its impact on human health. – by David Jwanier
Disclosure: The researchers report no relevant financial disclosures.
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