Implantation of a vaccine platform for extended antigen release (VPEAR) induces long-term immunity against Haemonchus contortus in sheep

The nematode Haemonchus contortus causes severe anemia in sheep and goats. Drug-resistant isolates are common, prompting a need for parasite control measures beyond chemotherapeutics. Vaccination is one promising approach for mitigation of clinical signs associated with haemonchosis. One challenge for H. contortus vaccine efforts is the need to administer repeated boosting doses at regular intervals. In this study, we evaluated a vaccine platform for extended antigen release (VPEAR) designed to initiate and maintain long-term immunity following a single immunization event in sheep. We compared a soluble vaccine depot with montanide adjuvant to the VPEAR platform with two different adjuvant combinations. Vaccination with VPEAR adjuvanted with DEAE-dextran induced antibody titers in 5 out of 6 vaccinated sheep up to 47 weeks post-vaccination. Challenge experiments revealed a 73% decrease in adult worm burden in this vaccine group compared to adjuvant alone and serum antibodies from these animals bound the luminal surface of the parasite intestine. Overall, the VPEAR platform was effective for long-term vaccination with no indication of immune tolerance to the parasite upon challenge.