Infectious Disease

The researchers identify the “hidden” life cycle of malaria parasites in the human spleen

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Researchers said they had identified a new “hidden” life cycle of malaria parasites in the human spleen – a finding that could have implications for malaria elimination programs, one of them said.

Results from a study of 15 largely untreated and asymptomatic adults in a malaria-endemic region of Indonesia were published today in the New England Journal of Medicine. Laboratory tests confirmed that nine of the participants were infected with Plasmodium falciparum and six with Plasmodium vivax.

Malaria parasite infographic

Source: Kho S. et al. N Engl J Med. 2021; doi: 10.1056 / NEJMc2023884.

For the study, the researchers collected spleen tissue and peripheral blood from each participant. All participants had a splenectomy.

The researchers discovered a large biomass of parasites in the asexual stage in the spleen of patients with non-phagocytosed red blood cells, the parasite density of which was hundreds to a thousand times higher than that observed in the circulating blood (P = 0.02 for P. falciparum; P =). 03 for P. vivax).

Of the total identified parasites in the asexual stage of P. vivax, 98.7% (95% CI, 89.4-99.8) were found in the spleen, they reported. In addition, they estimated that the splenic biomass of P. falciparum in the asexual stage was “at least twice as large as that in the circulatory system”.

Nicholas Anstey

“From a public health perspective, some people with large numbers of viable parasites hiding in the spleen had no parasites detectable in the blood even by PCR. This hidden reservoir of infection is likely another factor limiting the success of malaria elimination programs, which rely on mass testing of blood and only treat those with detectable infection. ” Nicholas Anstey, MBBS, FRACP, PhD, An infectious disease doctor at the Menzies School of Health Research in Darwin, Australia told Healio.

“Chronic asymptomatic malaria should be viewed primarily as an infection of the spleen, with only a small fraction of the parasites circulating in the peripheral blood,” Anstey said.

He said they were surprised to find much higher densities of P. vivax parasites in the spleen than in the peripheral blood.

“Our study was conducted in chronically asymptomatically infected residents of a malaria-endemic area and not in patients with acute symptomatic malaria, as trauma-induced splenectomy is rare in acute untreated malaria,” said Anstey. “We believe that in patients with acute symptomatic malaria there will also be a hidden life cycle of malaria parasites in the spleen, but in patients with acute malaria we do not yet know in what proportion of the total body biomass of malaria parasites the spleen is hiding and what proportion circulates in the blood. “

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