Studies on immunity to Haemonchus contortus infection: the elimination of a challenge infection by immune sheep

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Abstract
Ten-month-old Blackface sheep double vaccinated with X-irradiated larvae of H. contortus were shown to be highly resistent to individual challenge with 50000 larvae. Compared to unvaccinated sheep, the percentage reductions in the numbers of worms established 6, 9, 12 and 16 days after challenge were 83, 90, 99 and 100 respectively. The immune response was directed against the 3rd and 4th larval stages.The author wishes to express his thanks to his colleagues at the Wellcome Laboratories for Experimental Parasitology for their co-operation and help during the period of this experiment.This work was supported by a grant from Allen and Hanburys Ltd., Ware, England.