Biochemical Determinants of Drug Resistance in Haemonchus contortus Infection in Small Ruminants in South East Nigeria: An Analytical Study

Anthelmintic resistance in Haemonchus contortus is a serious threat to small ruminant production in Nigeria, yet the biochemical mechanisms underlying resistance development in local parasite populations have not been analytically examined. This study characterised the biochemical determinants of anthelmintic resistance in Haemonchus contortus-infected goats in Imo and Anambra States, South East Nigeria. Eighty West African Dwarf goats confirmed infected with H. contortus by larval development assay and in vivo egg reduction tests were classified as exposed to drug-resistant (faecal egg count reduction below 90%) or drug-susceptible isolates. Serum glutathione-S-transferase, cytochrome P450 enzyme activity, superoxide dismutase, catalase, and acetylcholinesterase activity were measured in both host serum and worm protein extracts obtained from abomasa of goats slaughtered for parasite recovery. Drug-resistant parasite isolates showed significantly higher glutathione-S-transferase and cytochrome P450 activities in worm extracts compared to susceptible isolates, consistent with enhanced detoxification-mediated resistance. Host serum acetylcholinesterase was not significantly different between groups, confirming that resistance resides in the parasite biochemistry rather than host response. Superoxide dismutase was elevated in the resistant parasite group, suggesting enhanced oxidative defence in drug-resistant worms. These novel biochemical findings contribute to understanding H. contortus resistance mechanisms in South East Nigeria and support the design of resistance-breaking anthelmintic combinations targeting detoxification pathways. Keywords: Haemonchus contortus, anthelmintic resistance, glutathione-S-transferase, biochemical mechanisms, South East Nigeria.