The route of administration affects ivermectin clinical efficacy against resistant nematodes in sheep.

LLOBERAS, M.; ENTROCASSO, C.; LIFSCHITZ, A.; ALVAREZ, L.; BORDA, B.;VIRKEL, G.; LANUSSE, C.

Calgary, Canada

Conferencia; 22 International Conference of the World Association for the Advancement of Veterinary Parasitology; 2009

Asociacion Mundial para el avance de la Parasitología Veterinaria

Macrocyclic lactone compounds are administered by the subcutaneous and oral routes to sheep and goats. Optimized drug treatment is necessary to deal with resistant nematodes. The aim of this work was to compare the efficacy of ivermectin (IVM) against resistant nematodes following its subcutaneous and intraruminal administration to lambs. Eighteen (18) lambs naturally infected with IVM resistant gastrointestinal nematodes were used. Animals were allocated into three (3) experimental groups (n=6): untreated control, IVM subcutaneously injected (SC) (IVOMEC® Merial Argentina) (0.2 mg/kg) and IVM intraruminally administered (IR) (ORAMEC® Merial Uruguay) (0.2 mg/kg). Individual fecal samples for egg counts were collected at 0, 9 and 15 days post treatment. Post-mortem examination was done at day 15 post-treatment. Adult nematodes recovered from the digestive tract were count and identified by species. The Kruskal Wallis test was applied. IVM effectiveness percentage by genus was always higher after the IR treatment. Efficacies against abomasal parasites were 52.4 % (SC) and 81.9 % (IR). Treatments showed 95.2 % (SC) and 99.9 (IR) of efficacy against intestinal nematodes. The adult nematode counts of Teladorsagia spp., T. axei. and T. colubriformis were statistically different (p≤0.05) between groups. H. contortus showed be highly resistant after the IVM treatment by both administration routes. The enhanced IVM concentrations recovered at the sites of gastrointestinal nematodes location account for the higher effectiveness obtained after the IR treatment. This advantageous efficacy pattern against resistant nematodes obtained for the oral/IR route should be considered to optimize IVM efficacy.