EVALUATION OF ASPECTS OF THE PROTECTION AFFORDED TO SHEEP IMMUNIZED WITH A GUT MEMBRANE-PROTEIN OF HAEMONCHUS-CONTORTUS

Experiments were undertaken to evaluate the type of protection conferred against Haemonchus contortus by immunising sheep with H11, a 'hidden' integral gut membrane protein isolated from this parasite. A serial kill experiment showed that worms began to be lost from immunised lambs between seven and 14 days after challenge with a single dose of larvae and adult female worms were more susceptible than male worms. Seven-day-old juveniles survived immunisation even though their intestinal cells became coated with sheep antibody. Immunisation was equally effective against both benzimidazole-resistant and susceptible strains of H contortus. When immunised lambs were subjected to a trickle infection, they were largely protected against the anaemia and egg output observed in the challenge controls. Moreover, they grew as fast and as efficiently as uninfected lambs fed on the same high protein diet and acquired a natural immunity during the course of the trickle infection.