Asymptomatic malaria carriers can be detected thanks to mass collection and testing of blood samples. Image Credit: Antoine Claessens (CC BY 4.0)
Malaria is a life-threatening, mosquito-borne illness caused by the parasite Plasmodium falciparum. In 2023 alone, over 200 million people were diagnosed with the disease, and hundreds of thousands died from it. Yet the true scale of the problem is likely underestimated.
Indeed, most infected individuals do not experience symptoms and therefore do not seek treatment. However, they can still pass the parasite to any mosquito that bites them, thereby contributing to the disease silently persisting within the population.
These asymptomatic infections therefore complicate malaria eradication efforts, in part because they pose a challenge to studying Plasmodium genetics. Controlling the disease often requires a detailed understanding of how different strains of the parasite wax and wane in a population across regions and seasons; without considering asymptomatic individuals, this knowledge remains incomplete.
To address this issue, Guery et al. studied Plasmodium infections in four nearby villages in The Gambia for over two years. In this region, a long dry period during which malaria spreads slowly is followed by a short, wet season marked by high transmission levels. The team analysed samples from 425 asymptomatic participants, generating unique genetic ‘barcodes’ for each strain of the parasite they detected. These data were then used to construct Plasmodium ‘family trees’ and determine transmission dynamics.
The analyses revealed a high degree of genetic diversity in Plasmodium from this region, which increased during the wet season. This typically indicates high levels of transmission within the population, with frequent mosquito bites increasing the chance of Plasmodium strains recombining their genetic make-up. In contrast, Plasmodium parasites found in members of the same household were much more likely to be genetically related. This suggests that individuals living together were infected at the same time by one mosquito, or that the insects spread the disease between people living in close quarters. Finally, parasites could persist for over a year for certain asymptomatic individuals.
These results shed new light on the factors affecting Plasmodium spread and genetic diversity, highlighting the role of asymptomatic carriers and household-level transmission. Guery et al. hope their findings will pave the way to more effective malaria control strategies. Mass testing could be important to identify asymptomatic carriers, for example, as well as treating those living with infected individuals.
