Trichostrongylus colubriformis and Heligmosomoides polygyrus: relationship between infectivity and exsheathment during ageing of infective larvae.

Infective larvae of two trichostrongyle parasites of the small intestine were stored from 0 to 22 weeks at 24 degrees C for T colubriformis and from 0 to 82 weeks at 4 degrees C for H polygyrus. A loss in infectivity with ageing was observed in vivo as well as a decrease in the exsheathment potential (number of larvae exsheathed in vitro after 20 min of incubation). A linear regression was established between the number of larvae exsheathed in vitro within 20 min and the number of adult worms developed in vivo.