the effects of psychological stress and other environmental factors on incidence of diseases

the main purpose of this paper has been to discuss the effects of psychological stress and other environmental factors on incidence of diseases. we were specifically concerned with stress that increased susceptibility of uninfected hosts when exposed to infection. if such stresses also reduced resources, fecundity and/or survivorship, there was a reduction in the host carrying capacity. in addition, stress that increased parasite mortality decreased disease. the opposing effects of stress on disease dynamics made it difficult to predict the response of disease to environmental stress. stress can simultaneously increase parasite mortality and impair host vital rates, making it more likely that parasites will be extirpated by stress. stress may have multiple effects on hosts and parasites such as increasing susceptibility to disease while decreasing host vital rates, such as reproduction. the knowledge about stresses help clarify predictions about the interaction between environmental stress and disease in natural populations