Ação anti-helmíntica de diferentes formulações de lactonas macrocíclicas em cepas resistentes de nematódeos de bovinos

As lactonas macrocíclicas (LMs) (avermectinas e milbemicinas) são endectocidas amplamente utilizados em animais e em algumas parasitoses humanas. Em bovinos, a resistência parasitária às LMs é emergente, e o surgimento de formulações que diferem nas suas propriedades farmacológicas tornou complexa a escolha da droga mais indicada a cada caso. Com o objetivo de avaliar possíveis alternativas para recuperar a eficácia de LMs sobre cepas resistentes de nematódeos gastrintestinais, testaram-se, neste estudo, dez diferentes tratamentos a base de LMs sobre uma população de nematódeos gastrintestinais de bovinos a qual, sabidamente, sofrera pressão de seleção por avermectinas a 1%. Adicionalmente, testou-se um benzimidazol. A eficácia das drogas foi calculada com base na redução de ovos por grama de fezes (OPG) dos bovinos. A resistência de cada gênero foi avaliada por meio de identificação de larvas, obtidas de cultivos nas fezes, pré- e pós-tratamentos. Não se obteve a eficácia desejada com o emprego de avermectinas de longa ação - com alta concentração e em associação - ou mesmo, com a aplicação de superdoses. Os gêneros Cooperia spp., Haemonchus spp. e Trichostrongylus spp. foram resistentes às avermectinas, e Ostertagia spp. à ivermectina. Observou-se que, uma vez estabelecida a resistência parasitária a LMs a 1%, a aplicação de fármacos, deste mesmo grupo químico, ainda que em formulações mais concentradas, asso-ciações ou superdoses, pode não resultar na eficácia esperada.The macrocyclic lactones (MLs) (avermectins and milbemycins) are endectocides broadly used in livestock and in some parasitic diseases of humans. In cattle, parasite resistance to MLs is emerging, and the appearance of formulations that differ in their pharmacological properties become complex the choice of the most appropriate drug to each case. In order to evaluate possible alternatives to restore the effectiveness of MLs on resistant strains of gastrointestinal nematodes, were tested, in this study, ten different treatments based on the MLs on a population of gastrointestinal nematodes of cattle which, known, was under pressure of selection by 1% avermectins. Additionally, was tested a benzimidazole. The efficacy of the drugs was calculated with basis on the reduction of eggs per gram of feces (EPG) of cattle. The resistance of each genus was evaluated by identification of the larvae, obtained from culture in the feces, pre- and post-treatments. The desired efficacy was not obtained using long action avermectins - with high concentration and in association - even with the application of high doses. The genera Cooperia spp., Haemonchus spp. and Trichostrongylus spp. were resistant to avermectins, and Ostertagia spp. to ivermectin. It was observed that, once established parasite resistance to the 1% MLs, the application of drugs, of this same chemical group, even in formulations of high concentration, association or in high doses, may not result in the expected efficacy

The efficacy of eprinomectin extended-release injection against naturally acquired nematode parasites of cattle, with special regard to inhibited fourth-stage Ostertagia larvae

AbstractThe efficacy of eprinomectin in an extended-release injection (ERI) formulation in the treatment of cattle harboring naturally acquired nematode populations (including inhibited nematodes) was evaluated. Five studies were conducted under a similar protocol in the USA, the UK, and in Germany. All study animals were infected by grazing naturally contaminated pastures. The adequacy of pasture infectivity was confirmed by examining tracer calves prior to allocation and treatment of the study animals. The cattle were of various breeds or crosses, weighing 79–491kg, and aged approximately 6–15 months. In each study, 20 animals were infected by grazing, and then removed from pasture and housed in a manner to preclude further nematode infections for 8–16 days until treatment. Animals were blocked based on descending pre-treatment body weight and randomly allocated to one of two treatments: ERI vehicle (control) at 1mL/50kg body weight or eprinomectin 5% (w/v) ERI at 1mL/50kg body weight (1.0mg eprinomectin/kg). Treatments were administered once on Day 0 by subcutaneous injection in front of the shoulder. For parasite recovery and count, all study animals were humanely euthanized 14/15 days after treatment. Cattle treated with eprinomectin ERI had significantly (p<0.05) fewer of the following nematodes than the controls with overall reduction of parasite counts of ≥94%: adult Dictyocaulus viviparus, Capillaria spp., Cooperia oncophora, Cooperia pectinata, Cooperia punctata, Cooperia surnabada, Haemonchus placei, Nematodirus helvetianus, Oesophagostomum radiatum, Ostertagia lyrata, Ostertagia ostertagi, Trichostrongylus axei, Trichostrongylus colubriformis, Trichuris discolor, Trichuris skrjabini, and Trichuris spp.; developing fourth-stage larvae of Ostertagia spp. and Trichostrongylus spp.; and inhibited fourth-stage larvae of Cooperia spp., Haemonchus spp., Nematodirus spp., Oesophagostomum spp., Ostertagia spp., and Trichostrongylus spp.Animal treatments were well accepted, with no adverse reactions to treatment observed in any study animals. The results of this series of controlled studies demonstrated high therapeutic efficacy and acceptability of eprinomectin ERI against pulmonary nematodes and a wide range of gastrointestinal parasitic infections, including inhibited gastrointestinal nematodes, in cattle