Clinically silent relapsing malaria may still pose a threat

Nonhuman primates with clinically undetectable Plasmodium relapse infections still harbor parasitic gametocytes that may be infectious to mosquitoes, according to a study published in the open-access journal PLOS Pathogens recently. The study has important epidemiological implications relevant to malaria elimination strategies.

The protozoal parasite Plasmodium vivax is a major cause of malaria – a life-threatening mosquito-borne disease responsible for hundreds of thousands of deaths globally each year.

They found that relapses were clinically silent compared to initial infections, and they were associated with a robust memory B cell response. This response resulted in the production of antibodies that were able to mediate clearance of relapsing, asexual parasites.

Despite this rapid immune protection, the sexual-stage gametocytes, which may be infectious to mosquitoes, continued to circulate.

According to the authors, the number of clinically silent relapse infections, and their infectiousness to mosquitoes, remains largely unknown and should be evaluated carefully in the future.

As a next step on the path to eliminating P. vivax and other relapsing malaria parasites, studies should identify the factors that influence relapse pathogenesis, immunity, and infectiousness to mosquitoes.