Safety and serologic response to a Haemonchus contortus vaccine in alpacas

Haemonchosis in camelids remains a challenging disease to treat, and prevention has become increasingly problematic due to widespread anthelmintic resistance. Barbervax^®is an adjuvanted vaccine containing natural H-11, H-gal-GP antigens obtained from Haemonchus contortus adults via a proprietary process and solubilized in Quil A. This vaccine is approved for use in Australia, after demonstrating its safety and efficacy in sheep and goats. There are no published studies evaluating Barbervax in other ruminants/pseudoruminants such as camelids which can be parasitized with H. contortus. The vaccine utilizes a mixture of the parasite gut mucosal membrane enzymes including H-gal-GP and H11, involved in digesting a blood meal from the host. This study monitored the safety profile of the Barbervax^® vaccine in a group of adolescent alpacas. Although designed into the original study of vaccine efficacy, the experimental infection with viable H. contortus third stage larvae could not be completed due to lack of detectable significant variation of infection following experimental challenge. Twelve alpacas (158 + 15 days) were randomized to vaccination with Barbervax^® or no treatment. Three doses of Barbervax^® were administered at 3 week intervals and investigators involved in animal monitoring and sample collection were blinded to the groupings. Clinical pathologic parameters were evaluated 7 days before vaccination, and 1 and 2 months post-vaccination. Daily clinical observations were made and specific observations regarding the injection site and rectal temperatures were monitored in each alpaca twice daily for 1 week following vaccination. Fecal egg counts, packed cell volume, and total protein were monitored following challenge with 1500 H. contortus larvae on days 42, 46, and 50. An increase in rectal temperature for a duration of 2 days (range 2-4 days) was observed post-vaccination. Vaccinated alpacas were lethargic for 2-3 days following vaccination; however, they maintained an appetite and no visible or palpable injection site reactions were observed. Following the first vaccination, all animals maintained normal clinical pathologic parameters throughout the study period. The vaccinated animals did develop titers to the H. contortus antigen as measured by ELISA. In conclusion, the Barbervax^® vaccine demonstrated safety in this small group of young, healthy alpacas, but additional studies are required to evaluate the efficacy of the vaccine under field conditions in protecting alpacas against infection with H. contortus.