A nonlinear model of stress hormone levels in rats-the interaction between pollution and parasites.

The impact of an infection with a parasite and a simultaneous cadmium exposure on the stress hormone levels of rats was studied. To this end, we introduce a nonlinear heteroscedastic model, which is able to describe the temporal evolution of cortisol concentrations in groups of rats treated by cadmium or parasite infection. A thorough analysis gives strong evidence that parasitic infection and cadmium exposure affect the stress hormone level of rats in an additive manner. Therefore, the host's response to environmental pollution should be studied in relation to parasite infections.