). Efficacy of nitroxynil and closantel against Haemonchus contortus. Comparative parenteral treatments in lambs.

SUAREZ, G.; CASTELLS, D.; ALVAREZ, L.; BERRETTA, C.; BETANCUR, DAMIAN, J.; LANUSSE, C.

Buenos Aires

Conferencia; 23 International Conference of the World Association for the Advancement of Veterinary Parasitology; 2011

AAVP

Helminth infections are the most important cause of productivity losses in livestock. Drug-based treatments remain as the main tool to control parasitism in different animal production systems. Both nitroxynil (NTX) and closantel (CLS) are flukicidal compounds which have been shown to have good activity against the haematophagous sheep abomasal nematode Haemonchus contortus. However, the development of resistance to the available anthelmintic drugs is a seriously increasing problem. Resistance to anthelmintics from different chemical families (different mode of action) is widespread in sheep nematodes in Uruguay. The current trial describes the comparative clinical efficacy of nitroxynil (NTX) and closantel (CLS) against a CLS-resistant H. contortus strain in lambs. The CLS-resistant H. contortus strain was previously isolated from naturally infected lambs, where an efficacy failure was observed after oral CLS treatment. The isolated CLS-resistant strain was used to artificially infect (8000 L3/lamb) fifteen (15) non-parasitized lambs. Twenty eight (28) days post-infection, the lambs were randomly allocated into three (3) experimental groups (n= 5), including an untreated control and those subcutaneously treated (10 mg/kg) with either NTX (NTX-treatment) or CLS (CLS-treatment). The efficacy estimation was performed by the faecal egg count reduction test (FECRT). Additionally, all animals were sacrificed at 13 days post-treatment to assess the comparative efficacy against adult H. contortus according to the WAAVP guidelines. Interestingly, while the FECRT reached a 39% for the NXT-treated lambs, a 100% reduction was observed in lambs treated with CLS at the same dose rate. Following a similar trend, the efficacy against CLS-resistant H. contortus was 99% after CLS treatment but only reached a 57% following NTX administration to infected lambs. An enhanced CLS systemic availability has been observed after parenteral compared to its oral administration to sheep. Thus, a subcutaneous injection at 10 mg/kg may have reached a CLS pharmacokinetic profile sufficient to kill the resistant strain, which has previously survived after the oral administration of the drug. Further work is required to understand the low efficacy observed for NTX, a drug usually active against susceptible H.contortus.