Estudo da resistência anti-helmíntica de bovinos aos nematódeos gastrintestinais: uma meta-anàlise

Abstract

Infections caused by gastrointestinal nematodes in cattle are common; they can prejudice the health and welfare of animals, resulting in losses in milk and meat production. As the transmission of these parasites occurs in the pasture, what is usually found are mixed infections, that is, more than one nematode genera parasitizing the same animal. The anthelmintics have been used to control these parasites for years. The indiscriminate use, the utilization of the same chemical compound without alternation, the underdosage, are factors that can cause the anthelmintic resistance. Due to the increase in the reports of resistance to these compounds in cattle, the objective of the study was to estimate through the metaanalysis the anthelmintic resistance in cattle by gastrointestinal nematodes. Data for the composition of the database were obtained from articles and short communications published in index databases. They were carefully evaluated according to their quality and importance according to the meta-analysis objectives. It were tabulated information about the bibliographic, anthelmintic, animal, reduction method, days after application, type of infection, parasite genera, type of application and dosage. The final data base was composed of 80 articles between 1986 and 2016, making a total of 9516 animals. The graphical analysis was used as a first step to observe the data distribution, followed by analysis of variance and comparisons by the Tukey test. Prediction equations were performed from the coefficients obtained in the variance-covariance analyzes. In order to demonstrate the summary value of the meta-analysis, the "forest plot" was performed. The type of application interfered in the efficacy of anthelmintics in cattle (P<0.05), oral application was superior to injectable and pour on. In the chemical groups and active principles, the associated group presented better mean of efficacy (>95%), macrocyclic lactones and ivermectin showed the worse means (P<0.05). The associated use showed superiority in relation to unique use (P<0.05). The type of infection, reduction method, age and racial group did not show interference (P>0.05) in the efficacy of anthelmintics. In relation to nematode genera, levamisole presented the highest average of efficacy for the genera Cooperia spp. and Trichostrongylus spp. differed from Ostertagia spp. with the worse average (P<0.05), ivermectin showed the highest average for Ostertagia spp. and Trichostrongylus spp., Cooperia spp. and mixed infection presented worse average (P<0.05), doramectin presented the highest average for Ostertagia spp., and the worse for Cooperia spp. (P<0.05). In the active principles listed in the category "others" the highest average was recorded in the genera Ostertagia spp. differing from Haemonchus spp. with the worse average (P <0.05). Associated active principles and moxidectin, did not show significance between the nematode genera (P>0.05). Prediction equations showed that for the levamisole the efficacy of the drug increases proportionally according to the dose, and that the efficacy decreases as the days pass after the application. The forest plot showed high heterogeneity among the data, being the summarized value classified as resistant (P>0.05). This study evidences the anthelmintic resistance in cattle on several continents, where only the associated use showed efficacy. Therefore, there is a need to replace the schemes based on the exclusive use of chemical compounds in order to decrease the selection pressure.