Parasites must develop to a certain stage in their life cycle before they can infect another animal. Whether the parasites develop in host animals, such as slugs or snails, or out on their own, temperature plays a big role in this part of their life cycle. Her work on musk oxen helped to demonstrate how much temperature controls the rate of development of parasites. For example, at 10 degrees Celsius lungworm will take more than 80 days to develop in slugs to the stage where they can infect other musk ox. But if the temperature doubles to 20 degrees, the parasites develop so rapidly that they can infect an animal in just 12 days.
Parasites can cause lung disease, anemia and lesions in the animals that they infect.
Host animals also suffer reduced appetite and weight loss. During warm years, parasites may develop faster and may infect animals earlier in the season. Parasites more common now in the south could also start to expand their range to the North. There are signs that this may be happening already, as in the NWT ticks are already being reported more frequently. Kutz says that warmer temperatures could mean not only more types of parasites in the North, it could also mean increased numbers of them.