PROTECTION AGAINST MULTIPLY DRUG-RESISTANT AND GEOGRAPHICALLY DISTANT STRAINS OF HAEMONCHUS-CONTORTUS BY VACCINATION WITH H11, A GUT MEMBRANE-DERIVED PROTECTIVE ANTIGEN

H11 is a ''hidden antigen'' derived from adult Haemonchus contortus which is capable of conferring a high degree of protection against subsequent challenge. To be commercially useful, any vaccine based on this antigen must protect against field strains and drug-resistant worms. The results show that vaccination with H11 affords high levels of protection against the multiply drug-resistant (MDR) Lawes strain of Haemonchus contortus. Moreover, there was no difference in protection whether the H11 was extracted from drug-resistant or susceptible worms, indicating that multiple drug-resistance does not significantly alter the immunogenicity of H11. Ideally, a commercial vaccine based on this antigen should also be capable of protecting against strains from geographically separate areas, so that it is not necessary to manufacture ''region-specific'' vaccines. Vaccination with H11 purified from either Australian or U.K. Haemonchus contortus was effective in protecting against subsequent challenge with Australian larvae, indicating that one type of H11 should have world-wide application.