Avaliação da biologia reprodutiva e histopatológica de fêmeas ingurgitadas de Rhipicephalus microplus submetidas a uma formulação contendo fipronil e fluazuron

Abstract

Rhipicephalus microplus is an important ectoparasite inside cattle breeding in tropical, subtropical and temperate region in the world. This tick is responsible for pathogens transmission, inducing a cattle pathological condition that can lead to a drop in meat and milk productivity. The R. microplus represents a great importance regarding to livestock cost, thus it is important control this ectoparasite which is done almost exclusively with chemical acaricide. Currently, there are commercial formulations for R. microplus control that contain, associated or not, fipronil and fluazuron. However there isn`t any information regarding cytotoxic effects of these molecules on ticks. Research on morphological changes caused by these two products allows a better understanding of how these active ingredients act in different tick organs. Thus, the objective of this study was to evaluate the reproductive biology and histological effects of a commercial formulation, containing fipronil and fluazuron on the ovary of R. microplus engorged females. Three calves were infested with approximately 5.000 larvae on days -24, -21, -19, -17, -14, -12, -10, -7, -5 and -3, considering day 0, the treatment day. The treatment consisted on the application of a commercial acaricidal formulation with fipronil (1,25 %) and fluazuron (2,5%) (Tick Gard®- MSD Saúde Animal). Before application of acaricidal formulation, 20 engorged females, naturally detached form the cattle, were recovered, to form the control group. After application of the commercial formulation, engorged females naturally detached from the animals were collected on days +5, +10 and +20 for reproductive biology monitoring and on days +4, +12 and +20 for ovaries histology evaluation. The females collected for reproductive biology monitoring were kept in a climate-controlled chamber for oviposition, subsequently incubating these eggs, while the females used for histological analysis were kept in a climate-controlled chamber for 4 days and then dissected. In reproductive biology evaluation, it was observed that females from the treated groups produced a smaller amount of eggs (p<0.05) and these eggs had a lower viability (p<0.5) when compared to the control group. All treatment group had considerable morphological change. In the histological analysis, many alterations were observed in the oocytes of females from all treated groups, including irregularly shaped oocyte, irregularly shaped germinal vesicle, yolk granules reduction, yok granules vacuolization and oocyte disruption. It was also observed a smaller number of oocytes in all stages of development (I, II, III, IV and V) and a greater number of indeterminate oocytes on ovaries of females from the treated groups (p<0.05), when compared with the control group. From these results, it is possible to conclude that the commercial formulation containing fipronil and fluazuron affected the reproductive biology and caused histological alterations in the ovaries of engorged females of R. microplus, leading to a reduction in the number of oocytes.