Climate change to increase risk and transmission of parasitic infections

Climate change is expected to cause a rise in the number of parasites being transmitted from human to human. However, research shows that as the temperature increases, the defining factor in handling these parasites will be the body's immune system.

Research published in the journal Proceedings of the National Academy of Sciences shows that host immunity will have the final say in the battle against parasites, as climate change worsens. The study showed that infections from various parasites will differ, dependent on the age of the human.

The study used two different scenarios to explain their findings. On one hand, parasites could either be controlled by the immune system – which means the younger generation will be at higher risk because their immune system is not as strong. Conversely, if the parasite is not covered by the human immune system, the older generation would be more at risk.

"If there is no immune response to a parasite, then we should probably target [vaccines at] the older individuals, because those are the ones that carry a lot of parasites and they are higher risk," said researcher Isabella Cattadori, from Pennsylvania State University.

"If there is an immune response, and immunity plays a role in controlling these infections, the younger individuals can't defend themselves, and we should definitely try to target those individuals."

The scientists conducted a 20-year long investigation on rabbits to discover the results. They sampled the rabbits monthly, assessing the prevalence of parasitic worms within them.

They combined these results with temperature data from the James Hutton Institute, to see how the worms changed depending on climate, which warmed by 1 degree Celsius over the course of the investigation.

The rabbits exhibited two different reactions to two different parasitic worm species– or helminths. For Graphidum strigosum, the rabbit's immune system does not have a responsive action, and therefore the older rabbits ultimately paid the price. Likewise, the rabbits could defend themselves against Trichostrongylus retortaeformis, and so the younger, weaker rabbits died.

"If you think about climate change, especially in the temperate climates – in the latitudes that we live in – the weather is getting warmer, and because of that, these parasites can live longer in the soil," said Cattadori.

"We need to start thinking about the impact of climate on the distribution of these parasites, and the risk of infection for humans, livestock and wildlife."