New research shows malaria parasites gather and accumulate inside the human spleen within a week of catching the infection.

The discovery of the dormant malaria parasites in the spleen is an important breakthrough in research on recurring malaria. In 2020, the world saw around 230 million malaria cases, according to the World Health Organization. 10 countries from tropical regions carry the burden of 70% of the world’s malaria cases and 71% of the world’s estimated deaths from malaria. India, which is among the ten countries, has the fifth-highest number of malaria cases around the world. Early detection and preventative measures are necessary to eradicate malaria altogether.

Malaria is caused by a plasmodium parasite — in turn transmitted by mosquitoes. Different types of malaria parasites include Plasmodium vivax (or P. vivax), Plasmodium ovale (or P. ovale), Plasmodium malariae (or P. malariae). and Plasmodium falciparum (or P. falciparum). Published inPLOS Medicine, the small study involved seven volunteers who were infected with malaria for the first time.

Three of the volunteers were infected with plasmodium vivax and four with plasmodium falciparum — two types of malarial parasite. While P.vivax is more widespread globally, P.falciparum is believed to be more fatal. Via MRI and PET scans, researchers discerned that P.vivax had a predilection for the spleen. They concluded these parasites were often found lurking in large amounts within the spleens of individuals who have relapses in malaria infections.

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Mature Plasmodium parasites that cause malaria usually infect the red blood cells in the human body, causing malaria symptoms. The human spleen is a reservoir for immature blood cells, which the P.vivax targets while invading the body; researchers found biomass of the parasites present within the spleen. The parasite remains dormant in the spleen till it matures within 5-21 days (or up to 2 years in rare cases), which explains why some malaria relapses don’t show up on blood tests. Usually, relapses can occur in short bursts after the first attack in tropical climates — due to dormant parasites within the liver, which is where the parasites move first after entering the body.

This discovery also highlights the importance of full-body scans with respect to diagnosing malaria cases early. Previously, researchers relied on blood and tissue samples recovered during surgery or after death to continue studying parasite behavior. However, these scans are expensive, and may not be available in regions where malaria is endemic — especially tropical and subtropical rural regions. Even if they are available, these machines are concentrated in urban public hospitals, which rural individuals take several days to reach, making it harder to detect early malaria infections.

“Malaria parasites outside of the circulation contribute to disease but are very difficult to study. By performing this novel imaging study in participants undergoing experimental malaria infection, we have been able to look at what is happening inside specific organs during the earliest stages of blood-stage infection,” Dr. John Woodford, the study lead author from the University of Queensland, said in a statement.

Early detection of malaria is thus important in order to ensure rapid disease management and to prevent the disease from reaching its critical stage.