Hibernation and parasitism : recent developments and some theoretical consideration [Hibernation et parasitisme : développement récents et quelques considérations théoriques].

Résumé

Not enough is yet known about the relation of metazoan parasites to hibernating hosts to make extensive generalization possible. Considering the wide range of host and parasite species involved, there is no real reason to assume any overall generalizations will develop. I would suggest the following tentative conclusions, more to stimulate further observation than to establish dicta. (1) Adaptation of a parasite to host hibernation may be active or passive. Active in the sense of a compensating biochemical change to meet the stress of an altered environment, or a passive avoidance of the stress by overwintering outside the host in some stable developmental stage; (2) Seasonal reduction of infection level in hibernators does not necessarily mean the parasites are unable to withstand the altered host-environment. The strongly seasonal behavioral and ecological aspects of the life cycle of hibernating animals may make natural reinfection difficult or impossible during the hibernating season; (3) The concept that hibernation increases the resistance of the host seems to be supported by experimental work using abnormal host-parasite systems. Where normal systems are used there is some evidence of adaptation of the parasite to hibernation. (4) Those metazoan parasites which are adversely effected by hibernation are more sensitive during developmental stages. Gastrointestinal parasites seem to be more sensitive than tissue parasites; (5) As with many other problems in helminth parasitology, work would be greatly stimulated by the development of adequate methods of in vitro cultivation of parasites. Because of available culture methods, the protozoa would appear to be a more rewarding group to study at present if any attempt is made to determine the biochemical basis of cold sensitivity or the mechanisms of adaptation to hibernation in animal parasites.