[Parasitic specificity and development of stray parasites of animal origin in man]

As on introduction to the selected topic, the author, after conjuring up the problem of parasite specificity, describes the various biological behaviour of parasites of animal origin having got into man. So doing, he quotes two main types of parasitic zoonoses (1) holozoonoses, in which the parasites are able to pass from animals to man and back; (2) hemi-zoonoses, in which parasites cannot go back from man to animals. The latter are due: (a) either to the inability for the parasite to reach, in man, the stage which would enable it to follow on its life cycle; this is a biological phenomenon: man is a dead-lock for the parasite; (b) or to the necessity for a parasite having reached a suitable stage in man, to go back-to animal through predation of man by the animal; this is an ethological phenomenon: man is a cul-de-sac for the parasite.