Infection-avoidance behaviour in humans and other animals

• The biology of host resistance and tolerance is better understood than infection avoidance behavior.
• Parasite avoidance behaviour in animals and humans is governed by the disgust adaptive system.
• Animals can defend themselves against parasites using four fundamental avoidance strategies.
• Avoidance behaviour is first in a continuum of resistance and tolerance responses.

Compared with living free, the parasitic way of life has many attractions. Parasites create problems for all animals. Potential hosts can respond by learning to live with parasites (tolerance), actively fighting them (resistance), or they can avoid becoming infected in the first place (avoidance). I propose here a new classification of avoidance behaviour according to the epidemiology of infection risk, where animals must avoid (i) conspecifics, (ii) parasites and their vectors, (iii) parasite-rich environments, and (iv) niche infestation. I further explore how the disgust adaptive system, which coordinates avoidance behaviour, may form a continuum with the immune system through the sharing of signalling pathways, sites of action, and evolutionary history.