How the parasites that cause leishmaniasis adapt to their vector hosts

Leishmaniasis is a parasitic disease that affects several mammal species including humans. Leishmania, the parasites responsible, have a life cycle that involves them successively infecting both mammals and "vector" insects – phlebotomine sandflies – in turn. But Leishmania can be highly genetically diverse, and this can alter the symptoms they cause and make them more or less susceptible to drugs.

To characterize how the environment encountered in the digestive tract of sandflies affects this genetic variability, scientists from the Institut Pasteur and Charles University in Prague used secure protocols to infect sandflies with Leishmania donovani, one of the species that causes disease. They also mapped the genome of the parasites before and after infection to compare the two.

A hostile environment that drives selection

The scientists observed that the genome of Leishmania was modified when they infected sandflies – but in a very specific way. "Our analyses revealed signature mutations of oxidative DNA damage, suggesting that Leishmania suffer from oxidative stress inside the sandflies' digestive tract," confirms Gerald Spaeth, Head of the Institut Pasteur's Molecular Parasitology and Signaling Unit and co-author of the study. In this unfavorable environment, the parasite comes under the pressure of natural selection, and the individuals that specifically develop these mutations have an evolutionary advantage that facilitates their survival.