The transmission of Syphacia muris (Nematoda: Oxyuroidea) in the laboratory rat

Abstract

During its transmission, Syphacia muris Yamaguti 1935, (Nermatoda: Oxyuroidea), undergoes 4 moults in the rat host to become an adult. Worms deposit up to 4000 eggs daily on the host's perianal region following a circadian rhythm. Most of the eggs are deposited in the day time, with a peak occurring around noon time. The rhythm is dependent upon the behaviour of the rat which is itself influenced by the lighting regime in the environment. Rats are nocturnal animals and normally feed and defaecate at night. Adult female worms of muris, therefore, release eggs during the day time when the rat is at rest so as to avoid the loss of eggs in the faeces at night. A technique is described to collect eggs from the perianal region of the rat for experimental infections. Eggs collected from around the peak of egg-laying activity produce the most worms in isolator-raised rats. In single infections, the worm burden increases with the dose size of eggs administered. But worm size is reduced in larger infections. Fecundity remains unaltered. In multiple infections a severe expulsion phase occurs in male rats. Females bear smaller worm burdens. An infection is transmitted to suckling rats about 12 days after birth so that litters already harbour worms on the day of weaning. The infection increases rapidly during the 32 days after weaning, thereafter it decreases and oscillates around a constant level. This oscillation may be attributed to periods of refraction and susceptibility to infection by the host. Infestation levels are remarkably similar in rats caged individually and in groups, indicating a degree of stability in the transmission strategy of Syphacia muris.