Combined effects of parasites and contaminants on animal health: parasites do matter.

The cumulative effects of multiple stressors are becoming a priority concern for ecotoxicologists, ecologists and conservation biologists working to understand threats to ecosystems and species. In that context, parasites and pathogens are increasingly a focus of attention. Parasites interact with natural and anthropogenic stressors to increase mortality and reduce animal health in myriad ways in a wide spectrum of host and parasite taxa. The combined effects of parasites and other stressors can reduce either resistance or tolerance to infection. Recommendations are provided to guide further research.