Rhythmic behaviour of intestinal helminths in rodents

Intestinal helminths exhibit two types of circadian rhythms, either involving the migration of adults worms ( Hymenolepis and Syphacia ) within the gut or periodic release of eggs by female worms ( Aspiculuris and Heligmosomoides ) to the exterior of the host to maximize transmission efficiency. By modifying the feeding regimes of rodents, there is clear evidence that these rhythmic processes are directly linked with the digestive and defaecating activities of the host with neurohormonal control mechanisms likely to be involved at least in the migratory behaviour of adult worms. Furthermore, in Heligmosomoides polygyrus rhythmic egg output appears to be dependent upon parasite age and the population density of the host and parasite. A brief reference is also made to studies on long-term rhythms of egg output by intestinal nematodes and their effect on patterns of host faecal production.