Controle dos parasitos do cão e avaliação do efeito carrapaticida do carvacrol

Abstract

Rhipicephalus sanguineus sensu lato (s.l.) is an important tick for animal and human health, being vectors of several pathogens. Given this scenario, it is essential to control this ectoparasite, which is essentially carried out with synthetic molecules. However, despite the guidelines on how to control parasites, these molecules are often used incorrectly, in addition to the fact that most have high toxicity for mammals and there are reports of selection of resistant ticks. In this context, the use of natural molecules, such as terpenes, is an important tool for tick control. Furthermore, information on recommendations for the control of parasites in dogs by veterinarians in Brazil is scarce. Thus, the objectives of this study were to investigate how the veterinarian recommends the control of parasites in dogs in Brazil and to evaluate the acaricidal effect of carvacrol on R. sanguineus s.l and its ability to alter the morphology of the tegument of nymphs. For the investigative study on the methods of controlling parasites in dogs used in Brazil, online questionnaires were applied to veterinarians throughout Brazil. The questions addressed control methods for helminths and ectoparasites, as well as medications, frequency of administration, and perception of medication ineffectiveness. Among these veterinarians, 71.4% (n = 288) stated that owners are concerned about parasite control. Preventive treatment against canine ectoparasites is the most recommended by veterinarians, and 46.6% (n = 188/403) frequently changed the chemical class of the antiparasitic. Prophylaxis for ectoparasites with a minimum monthly regimen (systemic, topical, and/or collars) was recommended by 21.5% of veterinarians (n = 87/403). These results show that the indiscriminate use of antiparasitic compounds and the perception of their ineffectiveness require guidelines for treating and controlling canine parasitic infections in veterinary clinics. Improving dog owner awareness requires the attention of veterinarians and a concerted effort by all professionals to implement effective parasite control strategies. Additionally, we investigated the in vitro and in vivo acaricidal effect of the natural compound carvacrol, through an in vitro bioassay on larvae and nymphs of R. sanguineus s.l. and oral administration in mice, looking for alterations on the tegument of the nymphs of R. sanguineus s.l. after treatment. To find the average lethal concentration CL50, larvae, and nymphs were immersed in carvacrol at different concentrations. The in vivo bioassay was performed by oral administration of carvacrol in Swiss mice artificially infested with R. sanguineus s.l. nymphs. The animals were allocated into three groups according to treatment: negative control (Sorbitol), carvacrol (60 mg/kg), and positive control (Lotilaner 20 mg/kg). The results of the in vitro bioassay showed that carvacrol had a LC50 of 0.94 mg/mL for immersion larvae and 1.81 mg/mL for nymphs. In the in vivo bioassay, carvacrol exhibited, 48h after treatment, nymph mortality of 17%. Histological alterations were observed in the tegument of the nymphs that fed on the animals treated with carvacrol (60 mg/mL), as the cubic cells of the epidermis showed a possible aggregation of protein granules between the epithelial and subcuticular layer. Our study demonstrated for the first time that carvacrol administered orally induces changes in the tegument, which may interfere with the development of the tick R. sanguineus s.l.