Studies on the Resistance of Pigs to Infestation with Hyostrongylus rubidus (Hassall & Stiles, 1892): I. Infection Experiments in Non-sensitised and Previously Sensitised Growing Animals

Abstract

SUMMARY Single infections and reinfections with variable numbers of H. rubidus larvae have been studied in growing pigs. Clinical symptoms of infection have only been seen following infection with 200,000 or 500,000 larvae. Worm counts following similar infection rates were higher in colostrum deprived S.P.F. pios than in conventionally reared M.D. pigs. Initial infections became patent in 18 to 21 days and reinfections from 32 to 35 days. Reinfection of pigs which had had initial infections of 200,000 or 500,000 larvae did not become patent. Reinfections of animals which had initially been infected with 20,000 larvae or less became patent though egg production was low and of short duration. Worms recovered from a 3 to 5 week initial infection were significantly longer than worms from 10-week-old infections or 4½-week-old reinfections. Evidence is provided which shows that the degree of immunity following initial infection is related to the level and persistence of that infection. Worms may be inhibited in development as either fourth or fifth stage larvae and the fecundity of established worms considerably reduced in the immune animal. There is also a gradual elimination of worms as infection progresses.