researchPublished 2006
Parasites and climate change
Amid increasing evidence for anthropogenic climate change, Peter Hudson, Isabella Cattadori and collaborators have considered how rising and increasingly volatile environmental temperatures might affect host-parasite interactions.
Many parasitic worms have free-living stages outside their definitive or intermediate hosts. Under harsh conditions, parasites inside the host can enter an arrested stage until conditions improve. Therefore, increased average temperatures — and in some cases, increased fluctuations in temperature — can mean:
- Free-living stages develop faster
- Arrested stages are shorter
- Hosts reproduce more often, so increasing the number of young, susceptible individuals in the population
Thus, warmer temperatures might be expected to lead to higher parasite prevalence and/or intensities. Hudson et al. argue that this does indeed occur, but only when hosts don't acquire immunity to the parasites. When hosts can develop strong immunity, the parasite population size is regulated by host immunity: while peak abundance may be larger and occur in younger individuals, levels in adults later in the season may actually fall.
The researchers support their argument with empirical data from a long-term study of gastro-intestinal worms in rabbits. They also present a simple model predicting that when hosts don't acquire strong immunity, host-parasite dynamics can become increasingly unstable as environmental warming:
- Increases the rate at which infective free-living stages are ingested
- Decreases the duration of arrested stages
» More details are published in a June 2006 issue of Journal of Helminthology