Monepantel é a mais nova molécula anti-helmíntica disponívelpara ovinos no mercado mundial. Por possuir mecanismo de ação diferente (não muito...) das demais moléculas, apresenta elevada eficácia contra populações de Nematoda extremamente resistentes. Porém, em artigo publicado neste mes, pesquisadores neozelandeses relataram sua ineficácia contra Teladorsagia circumcincta e Trichostrongylus colubriformis em ovinos necropsiados nove dias após o tratamento. Este é o primeiro relato de resistência ao monepantel somente dois anos após seu lançamento naquele país.
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Este é o resumo do artigo:
Lack of efficacy of monepantel against Teladorsagia circumcincta and Trichostrongylus colubriformis
Scott, I., Pomroy, W.E., Kenyon, P.R., Smith, G., Adlington, B., Moss, A., Lack of efficacy of monepantel against Teladorsagia circumcincta and Trichostrongylus colubriformis, Veterinary Parasitology (2013), http://dx.doi.org/10.1016/j.vetpar.2013.07.037
Reports of the apparent failure of monepantel to reduce the egg counts of goats on a farm in the lower North Island of New Zealand, faecal egg count reduction tests were conducted in goats and lambs resident on the property, and a confirmatory, slaughter study was conducted using 12 sheep, sourced elsewhere, that were grazed on the farm for approximately 5 weeks. In the egg count reduction test in goats, 8 animals were given monepantel at 3.9mg/kg (just over 1.5x the sheep dose rate of 2.5mg/kg), whilst four received 7.7mg/kg (just over 3x the sheep dose). In the egg count reduction test in sheep, 15 lambs were treated with 3.0mg/kg of monepantel. For the confirmatory study, the sheep were housed indoors for two weeks before half were treated with 2.9mg/kg monepantel and the animals were killed for worm counts 9 days later. There was no evidence of efficacy in either egg count reduction test, and in the goats, the two dose rates used appeared equally ineffective. Likewise, there were no significant reductions in egg counts or worm burdens in the slaughter study. Monepantel was ineffective against at least two gastrointestinal nematode species, Teladorsagia circumcincta and Trichostrongylus colubriformis. These findings represent the first report from the field of resistance having developed to the anthelmintic monepantel with severe resistance developing in more than one species after being administered on 17 separate occasions to different stock classes and in less than two years of the product first being used on the farm in question.