Ultrastructural characterization and quantification of hemocytes in engorged female Amblyomma sculptum ticks.

Amblyomma sculptum (formerly Amblyomma cajennense) ticks have been implicated in the transmission of pathogens that cause diseases in animals and humans. Their wide geographic distribution and high impact on animal health and zoonotic disease transmission highlight the importance of studying and implementing effective control measures to mitigate the risks associated with this tick species. The aim of this study was to quantify and characterize the morphology and the ultrastructure of different types of hemocytes in the hemolymph in engorged A. sculptum females fed on rabbits. The hemolymph samples were collected by perforation of the cuticle in the dorsal region. Hemocyte types, sizes, and differential counts were determined using light microscopy, while ultrastructural analysis of hemocytes was performed using transmission electron microscopy. The average number of total hemocytes in the hemolymph was 1024 ± 597.6 cells µL-1. Five morphologically distinct cell types were identified in A. sculptum females: prohemocytes (6 % ± 8.8), plasmatocytes (10 % ± 7.7), granulocytes (78 % ± 12.2), spherulocytes (5 % ± 4.48), and oenocytoids (1 % ± 1.6). In general, prohemocytes were the smallest hemocytes. The ultrastructural morphology of A. sculptum hemocytes described in the present study agrees with the findings for other hard ticks. This is the first study to investigate ultrastructural characteristics of hemocytes of female A. sculptum ticks.

Evaluation of the susceptibility to fipronil of Rhipicephalus microplus larvae from egg masses incubated at different times of oviposition.

The objective of this work was to evaluate the susceptibility of R. microplus larvae from different oviposition times to fipronil. The LPT was performed in sextuplicate, at concentrations of 18.75, 37.5, 75, 150 and 300 µg.mL-1. The LC50 found for the egg masses incubated with +7, +14 and +21 days were respectively 105.87, 110.71 and 121.22 µg.mL-1. The larvae originating from egg masses from the same group of engorged females, incubated on different days, presented similar mortality rates compared to the evaluated fipronil concentrations, facilitating the maintenance of laboratory colonies of this tick species.

O objetivo deste trabalho foi avaliar a susceptibilidade de larvas de R. microplus oriundas de diferentes momentos da oviposição frente ao fripronil. O TPL foi realizado em sextuplicata, nas seguintes concentrações 18,75; 37,5; 75; 150; 300 µg.mL-1. Não houve diferença estatística entre as mortalidades das larvas oriundas de posturas incubadas nos dias mais sete, +14 e +21, expostas ao fipronil. As CL50 encontradas para as posturas incubadas com +7, +14 e +21 dias foram respectivamente 105,87; 110,71 e 121,22 µg.mL-1. Observou-se que as larvas oriundas de posturas, do mesmo grupo de fêmeas ingurgitadas, incubadas em dias diferentes apresentam taxas de mortalidade parecidas frente as concentrações de fipronil avaliadas, facilitando a manutenção das colônias laboratorias desta espécie de carrapato.

Oral pharmacokinetic profile of fipronil and efficacy against flea and tick in dogs.

Fipronil (FIP) is an ectoparasiticide of the phenylpyrazole class, used in veterinary medicine in topical form. Supported by evidence of uncontrolled human exposure to FIP and environmental damage caused by commercially available formulations, its use by oral administration has become promising. The effectiveness of FIP against the flea Ctenocephalides felis felis and the tick Rhipicephalus sanguineus and its pharmacokinetics and main active metabolite, fipronil sulfone (SULF) were evaluated after single oral administration of tablets in three different doses (2, 4, and 6 mg/kg) in dogs. Through the plasma concentration curves, it was possible to observe that the FIP showed rapid absorption and metabolization and slow elimination. The values of Cmax (ß = 0.7653) and AUC0- t (ß = 0.3209) did not increase proportionally with increasing dose. At 48 h after treatment, doses of 4 mg/kg (AUC0- t  = 442.39 ± 137.35 µg/ml*h) and 6 mg/kg (AUC0- t  = 421.32 ± 102.84 µg/ml*h) provided 100% and 99% efficacy against fleas, and 95% and 98% against ticks, respectively. The estimated EC90 of FIP +SULF was 1.30 µg/ml against C. felis felis and 2.16 µg/ml against R. sanguineus. The correlation between the FIP pharmacokinetic and efficacy data demonstrated its potential for oral administration in the form of tablets for the control of ectoparasites in dogs, as a safer alternative for animals, humans, and the environment, aligned with the One Health concept.