Why we need to rethink the way fight parasites on a warming planet

Researchers studying rabbits in Scotland say that as climate changes we may need new strategies to respond to parasite infections—in wildlife and people.

“Our research shows that how we target treatment for parasite infections—not only in wildlife like the rabbits we studied, but also in humans and livestock—will depend on how the climate changes and whether or not the host can mount an effective immune response,” says Isabella Cattadori, associate professor of biology at Penn State.

Cattadori and colleagues assessed the infection dynamics of two species of soil-transmitted parasites in a population of rabbits in Scotland every month for 23 years. Previous work in Cattadori’s laboratory had shown that infections from one of the parasite species monitored in the study are controlled by an immune response in the rabbits, but infections from the other parasite species are not controlled, even though the rabbit does have an immune response to the parasite.

“Over the course of 23 years, we saw clear evidence of climate warming at our study site in Scotland. The warmer climate leads to increases in the number of soil-transmitted parasites in the pastures where the rabbits live because the parasites can survive longer in the soil,” says Cattadori.

“With more parasites, there is an increased risk of infection, but how this increased risk affects the severity of the infection in the long term depends on the ability of the host to mount an immune response.”

For the parasite that is not controlled by the rabbit’s immune response, the researchers observed an increase in the intensity of infections in adult rabbits with climate warming.

“Because they can’t clear the infection with an immune response, the rabbits accumulate more and more parasites as they age, so that older individuals carry most of the infection in the population,” says Cattadori.

For the parasite that is controlled by the rabbit’s immune response, the researchers saw no longterm increase with climate warming in the intensity of infections in the rabbit population overall. However, the severity of infection did increase in young rabbits that had not yet developed a very strong immune response.

“Our research shows that as climates continue to change, we will need to tailor our treatment of parasite infections based on whether or not the host can mount an effective immune response,” says Cattadori. “When a host’s immune response cannot control the infection, treatment should be targeted at older individuals because they carry the most severe infections. When a host’s immune response can control the infection, treatment should be targeted at younger individuals because they are at the greatest risk.”

The National Science Foundation funded the study, which will appear in the Proceedings of the National Academy of Sciences.