Impact of climate change on parasite infections depends on host immunity

We wanted to know how climate warming affects the number and distribution of two gut parasites in a population of rabbits. Climate change is a big environmental component and host immunity something that is happening within the host so how to link those two. I think it's an important question if the host has immunity that the scenario is probably different from a host that have no immune response. If you think about climate change especially in temperate areas in our latitudes where we live, the weather is getting warmer and because of that these parasites can survive for a longer time in the soil. And so the risk to get infected with these parasites increases with climate warming. We've been very lucky to be able to monitor this rabbit population in Scotland every month for twenty years so we had very detailed data on the rabbit and on the parasites and we also found that in this area there's been clear evidence of climate warming and this is the data set we used to develop these models to understand the role of climate change and immunity.

So the parasites that is regulated by immunity there is no increasing in parasites abundance in the rabbit population over the years because of climate change. But if we look at the abundance of parasites by host's age we see that the distribution of parasites is very uneven so rabbits that are young they don't have been very strong immune response and so they get infected very quickly and the parasites remain in the host because the host is not able to get rid of those. But the adults have a very strong immune response and even if they get infected they're able to clear the infection. So for the parasite that is not regulated by immunity when we look a this across the entire population of rabbits we see that with climate warming these rabbits get more and more infected. When we look at the dynamics of this amount of parasite by host age, older individuals are the ones that carry most of the infection. So what do we learn from this work? If you just move away from the rabbits, and you just think about human infections but also livestock infections and you think about how should we treat individuals based on what we found; the suggestion is if there is no immune response to a parasite then probably we should target the older individuals because those are the ones that carry a lot of parasites and they are higher risk.

If there is an immune response and immunity plays a role in controlling these infections; because the younger individuals can't defend themselves we should definitely try to target those individuals. And nowadays, yes, children are the ones they are usually treated against these soil-transmitted infections, but with climate changes we should expect, well we will expect, these individuals to become even more infected. Then we should probably start thinking about the impact of climate on the distribution of these parasites and the risk of infection for humans, animals, livestock and wildlife..