Estudo da eficácia in vitro e in vivo de bioterápicos e produtos naturais no controle de Rhipicephalus microplus (Canestrini, 1887) e sua relação com o bem-estar animal

Abstract

Rhipicephalus microplus causes significant losses of cattle livestock and increase in proportion to the development of resistance to the main acaricides. In this scenery, homeopathy and herbal medicine have apperared as therapeutic possibilities for tick control. This study aimed to develop biotherapics, to perform screening of bioactive natural substances against R. microplus and evaluate the efficacy in artificially infested cattle. For this purpose four biotherapics of R. microplus, fourteen plant extracts from Brazilian Flora and three isolated substances were evaluated. In the first step, was investigated the efficacy of injectable biotherapic 30 DH, in calves submitted to artificial infestation. In the second, was evaluated three different biotherapics of living (MV), dried (MD) and calcined (MC) material at the potency 6 CH (2 x 10-11 mg/mL) administered orally to naturally infested calves. In the third step, were investigated in vitro larvicidal activity of plant extracts and isolated substances against R. microplus and the adult immersion test (AIT) was performed with the biomolecule that showed the highest larvicidal efficacy. In the fourth step, the effect of biotherapic MV 6 CH and eugenol 5% pour on was evaluated for R. microplus control associated with the study of hematic, leukocyte, biochemical, ultrastructural aspects and its relationship with animal welfare. In experiments with artificial infestation (first and fourth steps) Dutch male calves were used, with 8 months of age and with no previous contact with ticks. The efficacy of homeopathic formulation and eugenol was evaluated by counts of engorged females ( 4.5mm in length), present on the left side of the calves. Engorged females were collected for evaluation of oviposition, reproductive efficiency and hatchability larvae rate. Injectable biotherapic 30 DH administered once a week to calves showed acaricidal efficacy of -12.5 to 63.3% only with 6 applications. The biotherapics MV, MD and MC 6CH administered orally to naturally infested calves showed average efficacy respectively 33%, 25.8%, 27.5% and efficiency values that ranged from -50 to 74.7%, while the highest value was obtained with the MV biotherapic. In the third step, the fourteen plant extracts evaluated in vitro caused mortality rate in the R. microplus larvae ranging from 0 to 40.3%, while isolated substance nerolidol at the concentration of 30% occasioned 96.5% and 0.3% eugenol caused 100% of mortality. The AIT was performed with eugenol at concentrations 1, 2, 5, 10, 20 and 30% and since 5% showed inhibition of oviposition with 100% efficiency. The concentration of 30% resulted in 100% mortality of engorged R. microplus females. In the fourth experimental stage, the value of the efficacy biotherapic MV 6 CH ranged from -33.3% to 95.2%, emphasizing that the last week of treatment, the mean efficacy was 32.5%. The objective of homeopathic formulation is to produce a host response against R. microplus infestation, using the secondary reaction, differently of eugenol which is formulated by classical pharmacotechnique and have ponderal dose. The efficacy of eugenol 5% pour on in calves ranged from -66.6 to 53.5%. The biotherapic suggest inhibition of larval hatchability in 50% and efficiency of 45.8%, whereas, for eugenol 5% pour on was 12.03% on the 37th day of treatment. The biotherapic caused disruption in oocytes exocórion during vitellogenesis, showing possible interference in the reproduction of R. microplus, while eugenol pour on resulted in low interference of oviposition. Treatment with eugenol 5% pour on caused no changes in erythrocyte, leukocyte or deleterious effects to hepatic and renal calves. Calves treated with biotherapic demonstrated higher average values of acute phase protein haptoglobin during 48 hours after the start of treatment and increase of leukocytes throughout the experimental period unlike the control group, suggesting the primary action of the biotherapic. The mean values of haptoglobin and 1-acid glycoprotein in 21, 30 and 39 days were within the normal range for bovine parameters, whereas, mean value of transferrin decreased on 30 day after medium R. microplus infestation, demonstrating acute phase response and the importance of this parameter in R. microplus parasitism. The welfare of animals in the three groups was affected due to R. microplus infestation, demonstrating the need for more specific analyzes on cattle welfare protocols in endemic areas for this ticks. The group with the lowest rate of changes in the integumentary system was treated with the biotherapic of R. microplus 6 CH. Improvements in the formulation of the MV biotherapic 6 CH and studies in field conditions, for long periods should be performed, because this product has advantages of not contaminating milk and meat, neither cause environmental impact. Similarly, eugenol pour on at the concentration of 30% should be investigated in cattle, because it showed high efficacy against larvae and engorged in in vitro tests and significant potential for formulating ecofriendly product in the control of R. microplus.