Attempts to detect synergy between vaccination and anthelmintic against a drug resistant isolate of Haemonchus contortus

Abstract

An experiment was conducted to determine whether any synergistic activity could be detected between an experimental vaccine and anthelmintic treatment against a drug resistant strain of Haemonchus contortus, i.e. would the combined effect of both interventions be greater than the sum of either alone. Two groups of 14 worm-free sheep were immunised twice, either with Haemonchus galactose containing glycoprotein complex (H-gal-GP) in QuilA as adjuvant or with adjuvant alone. All were challenged with 5000 Haemonchus L3 from the White River isolate which were resistant to ivermectin and fenbendazole. By 26 days post-challenge the H-gal-GP vaccinated sheep had shed 89% fewer nematode eggs than the adjuvant only controls, indicating that this antigen did indeed protect against the anthelmintic resistant isolate. Twenty six days after challenge seven vaccinates and seven control sheep were drenched with ivermectin, but over the next 11 days the mean egg count of either group did not differ significantly from those of the corresponding untreated groups of sheep. On day 37 the drenched sheep were treated with fenbendazole. This time the egg counts of both treated groups fell significantly compared to those of the corresponding untreated groups, but again there was no suggestion that the drug was more effective in the vaccinated sheep. It was concluded that there was no evidence for synergy between a gut membrane protein vaccine and ivermectin or fenbendazole against an anthelmintic resistant isolate of H. contortus.