Preliminary observations on the potential of gut membrane proteins of Haemonchus contortus as candidate vaccine antigens in sheep on naturally infected pasture

In a trial lasting 11 months in South Africa, faecal egg counts and haemato crits of sheep vaccinated with gut membrane proteins of adult Haemonchus co ntortus were compared with unvaccinated controls grazing pasture contaminat ed with the parasite. Vaccination reduced egg output by > 82% on average du ring one 4 month period of the trial and simultaneously significantly reduc ed the degree of anaemia and deaths due to haemonchosis, Although vaccine i mmunity was not sufficiently long lasting to prevent a surge in egg output which occurred after the onset of a period of irrigation, re-vaccinating th e sheep at this point cleared their newly acquired infection and rapidly re stored protection to approximately the level observed beforehand. It was cl ear that a vaccine based on parasite gut membrane proteins could offer subs tantial benefits in the control of natural haemonchosis. (C) 2001 Published by Elsevier Science B.V.