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 conferr ed against Haemonchus contortus by immunising sheep with H11, a 'hidde n' integral gut membrane protein isolated from this parasite. A serial kill experiment showed that worms began to be lost from immunised lam bs between seven and 14 days after challenge with a single dose of lar vae and adult female worms were more susceptible than male worms. Seve n-day-old juveniles survived immunisation even though their intestinal cells became coated with sheep antibody. Immunisation was equally eff ective against both benzimidazole-resistant and susceptible strains of H contortus. When immunised lambs were subjected to a trickle infecti on, they were largely protected against the anaemia and egg output obs erved in the challenge controls. Moreover, they grew as fast and as ef ficiently as uninfected lambs fed on the same high protein diet and ac quired a natural immunity during the course of the trickle infection.