Increased human exposure to the macaque malaria parasite Plasmodium knowlesi may result in its increased ability to invade older blood cells. As the parasites’ current preference is for younger blood cells, the work, published in Nature Communications, suggests that P. knowlesi virulence in humans and its transmissibility may increase in the future.

Caeul Limand colleagues report that P. knowlesi’s poor growth in human blood is due to its preference for invading a young subpopulation of cells. The authors demonstrate that continuous exposure to human blood leads to evolution of the parasite and its increased ability to infect a wider range of blood cells. These results may explain the high parasite loads and severity of disease already occurring in some human infections.

The authors suggest that future work is required to decipher the mechanisms leading to adaptation as this information could be used to prevent further expansion of this parasite into the human population.