Fipronil-induced cell death in salivary glands of Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) semi-engorged females

The tick Rhipicephalus sanguineus is currently considered an urban plague. For this reason many studies are intended to find methods to control these ectoparasites. Thus, the present study analyzed the ultrastructural modifications of the salivary glands cells of semi-engorged females of R. sanguineus resulting from their exposition to Fipronil (active ingredient of Frontline®). The studied individuals were divided into four groups. Group 1 was exposed to distilled water (control) and groups 2, 3 and 4 were exposed to 1, 5 and 10 ppm of Fipronil, respectively. The salivary gland of ticks subjected to the acaricide showed accelerated process of cell death by atypical apoptosis, as well as augmented cell damages as the concentration of the chemical compound was increased. The acaricide toxicity at cellular level was demonstrated by remarkable changes of elements of the cytoskeleton and spherocrystals (extremely hard inorganic structures). However, tick defense mechanisms, such as the observed autofagic vacuoles proved the cells attempt to preserve their integrity and minimize the devastating action of this chemical compound on the salivary glands.

The present study aimed to evaluate, at ultrastructural level, possible effects of different concentrations of fipronil (1, 5 and 10 ppm) in salivary glands of semi-engorged females of R. sanguineus ticks looking for morphophysiological changes induced by the acaricides. Furthermore, to understanding mechanisms used by the salivary gland cells in an attempt to preserve their integrity, even in the presence of the toxic compound. Research highlights► The salivary gland of ticks subjected to the acaricide fipronil showed the occurrence of atypical apoptosis. ► The destructive potential of the acaricide, reaching even mineral structures (spherocrystals) in the glandular tissue. ► The action of fipronil is not restricted to the ticks' nervous system, but also acts inhibiting the feeding process, considering that it damages one of the most important ticks' organs, the salivary glands.