Assessment of sublethal effects of acetylcarvacrol in the oocyte morphology of Rhipicephalus microplus (Canestrini, 1888) and Rhipicephalus sanguineus sensu lato (Latreille, 1806) ticks (Acari: ixodidae)

Abstract

The ticks of the genus Rhipicephalus have two species with wide distribution in Brazil, namely R. sanguineus sensu lato (s. 1) and R. microplus. These ticks are of great medical and veterinary importance for transmitting pathogens to humans and dogs in the case of R. sanguineus (s. 1); and cattle, in the case of R. microplus. In addition, R. microplus is responsible for economic losses in the order of one billion dollars per year, only in Brazil. Therefore, these parasites are targets of different control methods, such as the use of acaricidal substances. Carvacrol, a phenolic monoterpene extracted from plants, shows high acaricidal action. Its semi-synthetic derivative, acetylcarvacrol, has been studied as nematicide, especially since it presents greater efficiency, greater stability and lower toxicity to the hosts, when compared to carvacrol. Based on this information, this study aimed to evaluate the effects of sublethal concentrations of acetylcarvacrol diluted in 3% dimethyl sulfoxide solution (DMSO) in the morphology of the ovaries of R. sanguineus (s. 1) and R. microplus ticks. In order to do this, the ticks were submerged, during five minutes, in different concentrations of acetylcarvacrol, based on previous experiments, according to procedure already established in the literature. After a period of seven days, the ticks were dissected for collection of the ovaries. The material was processed and included in historesin, sectioned, stained and evaluated by means of morphometry and a semiquantitative analysis protocol proposed in this study. The common morphological alterations in the ovaries of R. sanguineus s. l. and R. microplus were cytoplasmic vacuolization, ring-shaped nucleolus, irregular size and shape of germ cells and chorion detachment. For R. sanguineus (s. 1.), there was still a drastic alteration of oviduct epithelial cells, including the disappearance of young germ cells. For both species, higher concentrations of acetylcarvacrol caused statistically significant damages according to the proposed semiquantitative analysis. The results demonstrate the potential of acetilcarvacrol as a method for long-term control of these parasites’ reproduction.