The effects of a novel vaccine candidate against Haemonchus contortus on the worm burden of infected sheep

Haemonchus contortus is a highly pathogenic gastrointestinal nematode affecting small ruminants. Its Pathomechanism includes blood-feeding in the abomasum, leading to anaemia, oedema, loss of productivity and in severe cases even death of the animals, resulting in serious economic consequences for the livestock industry worldwide. Due to an extensive anthelmintic resistance and the restricted availability of vaccines, new approaches to control H. contortus are required. This research project aimed to evaluate the efficacy of two new recombinant vaccine candidates against H. contortus in sheep, focusing on their impact on worm burden in the abomasum of infected sheep. A total of 35 male lambs were divided into five groups, including negative and positive controls, one group receiving a commercial vaccine (Barbervax®) two groups receiving either a glyco-engineered antigen cocktail (GErH11) or a non-glyco-engineered antigen cocktail (nGErH11). Following a standardised vaccination (three doses, administered s.c.) and challenge protocol using one dose of 5,000 infective L3 larvae administered orally per sheep, worm counts were assessed post mortem. Barbervax® resulted in a significant 86.36 % reduction in worm burden (p < 0.01), while GErH11 and non-GErH11 vaccines decreased the worm burden in the abomasum by 25.36 % and 13.72 %, however both results were not statistically significant. While Barbervax® reduced the ratio of female-to-male worms from 1.29 (pos. control) to 0.59, the recombinant vaccines had no significant effect on the ratio of female-to male worms, which is a valuable measure of parasite transmission. The study concludes that although there was partial efficacy against H. contortus demonstrated by the two tested recombinant vaccine candidates (GErH11 and nGErH11), they were unable to match the efficacy of the commercial vaccine (Barbervax®). Therefore, further optimisation of antigen design is needed to enhance immunogenicity and field efficacy.