Resumo

LARROZA, M. et al. Falla en la eficacia de dos formulaciones de ivermectina contra Psoroptes ovis (Hering, 1838) en ovinos. FAVE, Secc. Cienc. vet. [online]. 2020, vol.19, n.1, pp.23-29. ISSN 2362-5589.  http://dx.doi.org/https://doi.org/10.14409/favecv.v19i1.9292.

The current work evaluated the relationship between efficacy and pharmacokinetics of two commercial injectable formulations of ivermectin (IVM) in adult merino sheep artificially infested with Psoroptes ovis. Animals were treated subcutaneously with IVM 1% formulation (two doses on days 0 and 7) at 0.2 mg / kg or with a single dose of IVM 3.15% preparation at 1.05 mg / kg. Live mites were counted weekly by performing skin scrapings between days 0 and 28 post-treatment to determine the efficacy of each IVM formulation. Blood samples were taken up to 35 days post-treatment to measure IVM plasma concentrations. A significant decrease in mite counts was observed from day 14 post-treatment. However, live mites were found in all samples for both groups throughout the entire trial. After IVM 1% administration, the highest effcacy was observed on day 28 (93.3% whereas in the IVM 3,15% group was obtained on day 21 post treatment (95.9%). Higher IVM plasma concentrations were observed in animals treated with the IVM 3.15% formulation. Failure to obtain a parasitological cure after treatment with both IVM formulations may reflect the presence of resistant mites to this drug.

Palavras-chave : sheep scab; Psoroptes ovis; efficacy; resistance; ivermectin.

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