Climate warming may increase the risk and transmission of parasite infections caused by worms called helminths, according to a 20-year study of rabbits. And that effect is influenced by variations in host immunity. The findings are published in Proceedings of the National Academy of Sciences this week.
To better understand the impact of climate change on the interactions of hosts with their parasites, researchers need to know how different sorts of immune responses among hosts impact the severity of disease driven by climate warming. So, Penn State’s Isabella Cattadori and colleagues studied the dynamics of two soil-transmitted gut parasites of rabbits: Trichostrongylus retortaeformis and Graphidum strigosum. The researchers sampled these helminth species, which live in the small intestine and stomach of rabbits, in Scotland every month from 1977 to 2002.
The findings show that interactions between climate change and host immunity can affect parasite infections. The availability of infective parasites of both species increased with higher temperature and rising humidity, the team found, but the actual parasite accumulation in the rabbits depended on the hosts’ immune response to the worms.
G. strigosum infections aren’t controlled by the rabbit immune response, so their intensity increases with warming – leading to a major accumulation of G. strigosum in the rabbit population, especially in adults. T. retortaeformis infections, on the other hand, are controlled by the immune system of rabbit hosts, and this offsets the effects of climate; this results in a relatively constant intensity of infection in the rabbit population over time.
However, climate warming also shifted the seasonal peak of T. retortaeformis infection toward young (more susceptible) rabbit hosts that haven’t developed a strong immune response. So while immunity can reduce the severity of infection in a population, it can also exacerbate parasite intensity in the younger individuals in the summer during warmer years.