Cytotoxic effects of permethrin in salivary glands of Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) semi-engorged females

Repellent activity of acetylcarvacrol and its effects on salivary gland morphology in unfed Rhipicephalus sanguineus sensu lato ticks (Acari: Ixodidae)

Rhipicephalus sanguineus sensu lato (s.l.), commonly known as brown dog tick, is a widely distributed tick species that is substantially important for human and veterinary medicine. Therefore, it is the target of different control methods. Carvacrol and its semisynthetic derivative, acetylcarvacrol, are promising chemical compounds for alternative tick control. Thus, this study aimed to compare the repellent activities of carvacrol and acetylcarvacrol at different concentrations and drying times. Additionally, morphological alterations found in salivary glands were evaluated through histological techniques after exposure to acetylcarvacrol. The impact of the morphological changes on the development and survival of acini/cells in salivary glands was measured by a semiquantitative analysis. The repellent action of both compounds did not differ when evaluated at different concentrations, although acetylcarvacrol increased its effects as the concentration raised. Regarding the different drying times, acetylcarvacrol maintained its effects after 3 hours of exposure, while the efficacy of carvacrol decreased during this time period. Salivary glands of unfed R. sanguineus s.l. females showed dose-dependent alterations in the size and shape of acini as well as cytoplasmic vacuolization. Loss of the acinar cell limit, rupture of secretory granules and nuclear changes in the cells were also observed in the treated groups. Thus, our results demonstrated the potential of acetylcarvacrol to act as repellent against R. sanguineus s.l. Additionally, the morphological alterations found in salivary glands may interfere with the feeding process of ticks, which contributes to mitigate infestation by this species.

Morphophysiological analysis of the salivary glands of Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) exposed to ozonated water: A control strategy

The tick Rhipicephalus sanguineus sensu lato has great medical and veterinary importance, mainly because the ability to transmit many diseases, causing harm to pets but also risks to public health. The blood spoliation and transmission of pathogens occur because of the immunosuppressive action of these ticks' saliva, a potent mixture of bioactive substances that is secreted by the salivary glands, one of the organs responsible for their biological success, and hence the target of studies for their control. Ozone has promise for use as an alternative acaricide, due to its proven efficiency in controlling agricultural and food pests, besides posing no risk of environmental contamination or to animal and human health. Therefore, this study evaluated the acaricidal potential of exposure of females of R. sanguineus s.l. to ozonated water at many concentrations and analysed the morphophysiological alterations of the salivary glands, employing histological and light microscopic techniques. The results demonstrated that the ozonated water at the concentrations investigated caused severe alterations in the salivary glands, bringing a new perspective for control of R. sanguineus s.l., through an ecologically correct method due to the absence of harm to non-target organisms and the environment.

Thymol: Effects on reproductive biology and Gene's organ morphology in Rhipicephalus sanguineus sensu lato engorged females (Acari: Ixodidae)

Thymol is a monoterpene with proven acaricidal activity on different tick species and life stages. The objective of this work was to evaluate the effect of thymol on the reproductive biology of engorged females of Rhipicephalus sanguineus sensu lato and the morphological changes caused in the cells of the tubular and accessory glands of Gené's organ. The females were exposed to thymol by immersion. Seven groups were established: group I (distilled water), group II (30% ethanol), group III (thymol 1.25 mg/mL), group IV (thymol 2.5 mg/mL), group V (thymol 5.0 mg/mL), group VI (thymol 10.0 mg/mL), and group VII (thymol 20.0 mg/mL), with 20 replicates for each treatment. The ticks were kept in a BOD incubator at 27 ± 1 °C and RH > 80 ± 10%. Ten females from each group were evaluated daily until death, and the remaining ten were kept in the incubator under the same conditions for five days and then dissected for the removal of Gené's organ to note possible damage to cell morphology by scanning electron microscopy (SEM) and hematoxylin-eosin (HE) techniques. Thymol demonstrated 63% and 98% efficacy in groups VI (10.0 mg/mL) and VII (20.0 mg/mL), respectively. In these groups, the cells of the tubular and accessory glands of Gené's organ showed signs of damage: irregular eosin staining, rupture and deformation of the cellular limit, presence of fragmented nuclei, changes in cytoplasmic homogeneity and areas with deformation (folds) in the basal region.

Thymol action on cells and tissues of the synganglia and salivary glands of Rhipicephalus sanguineus sensu lato females (Acari: Ixodidae)

Thymol is a monoterpene present in plants of the families Lamiaceae, Verbenaceae and Apiaceae. Despite its proven acaricidal activity, little is known about the mechanism of action of thymol in ticks. Thus, the aim of this study was to perform a morpho-histochemical analysis of the synganglion and salivary glands of partially engorged females of the brown dog tick, Rhipicephalus sanguineus sensu lato (s.l.), exposed to thymol at different concentrations. Five groups were established: Control Group I (distilled water), Control Group II (ethanol 30%), Group III (thymol 1.25 mg/mL), Group IV (thymol 2.5 mg/mL) and Group V (thymol 5.0 mg/mL). The females were exposed to the treatments by the immersion method and subsequently kept in a climatic chamber (27 ± 1 °C and relative humidity 80 ± 10%) for five days. After this period, the synganglion and salivary glands were removed, and the hematoxylin/eosin morphological technique was applied. The von Kossa staining method with counterstaining neutral red was performed on the salivary glands. The results showed that females exposed to thymol had damaged synganglia, with pyknotic nuclei and vacuoles in the cortex and subperineurial regions, as well as rupture of the neural lamellae. The salivary glands showed type I acini with a dilated lumen. Cells with extremely vacuolated cytoplasm and fragmented nuclei were observed in type II and III acini. Type II acini of the females exposed to thymol revealed different calcium staining when compared to the Control Groups I and II. We therefore conclude that the salivary glands and synganglion are subject to changes in morphology and calcium levels when exposed to thymol at concentrations of 1.25, 2.5 and 5.0 mg/mL, demonstrating that this monoterpene has acaricidal potential on partially engorged females of R. sanguineus (s.l.).

Ultrastructural analysis of salivary glands in a phytophagous stink bug revealed the presence of unexpected muscles

The exceptional abilities of stink bugs (Hemiptera: Pentatomidae) to colonize a diverse group of plants have been attributed to the feeding behaviors and the functions of the salivary complex of these insects. Here, we describe the ultrastructure of the salivary glands of the Neotropical brown stink bug, Euschistus heros, which is a major component of the pentatomid pest complex on soybeans, Glycine max, in the neotropics. Our results revealed a salivary gland complex consisting of two lobes (i.e., anterior and posterior), with a constriction between them (i.e., the hilum), in which the salivary and accessory gland ducts are inserted. The principal gland epithelium has a single layer of cells lining an enlarged lumen filled with saliva, and these cells are cuboidal, rich in rough endoplasmic reticulum and secretory vesicles, with well-developed nuclei, all of which are typical features of protein-secreting cells. We report, for the first time in insects, the presence of a layer of muscle cells surrounding the columnar hilum epithelium. The accessory salivary gland cells are cuboidal with nuclei containing condensed chromatin and cytoplasm rich in vacuoles and rough endoplasmic reticulum, indicating the potential involvement of these glands in water transport/secretion. The lumen content of each lobe of the principal gland suggests that the lobes produce different compounds. Thus, our results suggest that the E. heros salivary complex might have unconventional mechanisms to mix/release saliva, which might help explain the polyphagous abilities of these insects.

Detrimental effect of deltamethrin on the central nervous system (synganglion) of Rhipicephalus sanguineus ticks

Ticks are ectoparasites of medical and veterinary importance, which transmit many infectious agents, causing significant damage to the hosts. The "dog tick" Rhipicephalus sanguineus is responsible for transmitting several pathogens to dogs, motivating researchers to investigate efficient and sustainable control methods. Currently, chemical acaricides currently in use target the central nervous system (synganglion), which is responsible for controlling all the systemic functions of the ticks. Here, the neurotoxic potential of deltamethrin on the synganglion of unfed R. sanguineus female ticks was investigated. The results showed that the synganglion of the females belonging to the control group presented intact morphological characteristics; however, the ones from the treatment group (exposed to 1.5, 3.12 and 6.25 ppm of deltamethrin) displayed alterations, which were increasingly intense as the concentration increased. Observed alterations were mainly in the cortex region and in the neuropile, indicating that the deltamethrin is neurotoxic.

Dinotefuran-induced morphophysiological changes in the ovaries and midgut of semi-engorged females Rhipicephalus sanguineus Latreille, 1806 (Acari: Ixodidae) ticks

The present study demonstrated the effects of dinotefuran (active compound of the Protetor Pet® acaricide) in germ cells and the digestive processes of semi-engorged females of R. sanguineus exposed to different concentrations of the chemical. For this purpose, 120 semi-engorged females were divided into four treatment groups with 30 individuals each: group I or control (distilled water), group II (5000 ppm), group III (6250 ppm), and group IV (8334 ppm of dinotefuran). All ticks were immersed in different concentrations of dinotefuran or in distilled water for 5 min and then were dried and stored in biological oxygen demand (BOD) incubator for 7 days. The results show the action of this compound, exhibiting morphohistologic and histochemical changes in the oocytes and the midgut cells of individuals of different groups, which were compared with those of group I (control). The alterations occurred mainly in relation to the size of the germ cells and yolk granules; presence, quantity, size, and location of vacuoles found in the cytoplasm of these germ cells; the damage occurred in the generative cells of the midgut; the size of the digestive cells; the quantity of blood elements captured, accumulated digestive wastes and digestive vacuoles found in the cytoplasm of the digestive cells of the midgut, as well as the amount and distribution of proteins, polysaccharides, lipids of all cells in both organs. So, it has demonstrated the effectiveness of dinotefuran in the reduction of fertility and digestive processes of semi-engorged females of R. sanguineus, data that points the possibility of employing this chemical to control these ectoparasites.

The effect of synthetic pyrethroids on the attachment and host-feeding behaviour in Dermacentor reticulatus females (Ixodida: Amblyommidae)

BACKGROUND

The high competence of D. reticulatus in transmission of tick-borne pathogens prompts investigations of the effect of chemicals used as repellents and acaricides on the behaviour of the tick on the host. Therefore, this paper presents the effect of permethrin and deltamethrin on the attachment and feeding in this tick species.

FINDINGS

Attachment to rabbit skin of D. reticulatus females sprayed with pyrethroids and the effect of different doses thereof on feeding were assessed at a temperature of 20 ± 3 °C and 50% humidity. The dynamics of attachment of D. reticulatus females varied in a dose-dependent manner after the application of both pyrethroids. Within the first 0.5 h of the experiments, there was an over six-fold and over twelve-fold increase in the number of females attached to host skin after application of permethrin concentrations of 0.3906-0.7812 μg and 1.5625-3.1250 μg/1 specimen, respectively. In the case of deltamethrin, females treated with the dose of 0.0390 μg of the compound were able to attach to host skin only 4 hours after the infestation. The toxic activity of both pyrethroids increased the duration of the feeding period and decreased the body weight of engorged females and the feeding efficiency index.

CONCLUSIONS

The accelerated attachment of D. reticulatus females caused by sublethal permethrin doses and delayed or inhibited attachment caused by deltamethrin suggest a necessity of careful selection of the type and dose of pyrethroids to protect hosts from tick attacks.

One-month comparative efficacy of three topical ectoparasiticides against adult brown dog ticks (Rhipicephalus sanguineus sensu lato) on mixed-bred dogs in controlled environment

This study was designed to compare the therapeutic and residual efficacy for 1 month of three topical ectoparasiticides on mixed-bred dogs against the brown dog tick, Rhipicephalus sanguineus. Adult dogs (n = 32, 10.8-18.4 kg BW) were allocated to 4 groups (n = 8) and infested with 50 adult ticks on days -8, -2, 7, 14, 21, and 28. Within each group, dogs were treated topically on day 0 with a control solution (CS), Vectra 3D (DPP), Frontline Plus (FM), or K9 Advantix (IP). Ticks were enumerated on dogs 24 h after treatment and each subsequent tick infestation by in situ thumb count assessment without removal and at 48 h by combing and removal. Acaricidal efficacy was calculated using arithmetic means for all 24 and 48 h tick count assessments. From 42 to 56% of the total, infested ticks were found on dogs 48 h post-challenge in the CS group. Therapeutic efficacy for all treatments ranged from 45.5 to 64.6% after 48 h of infestation. Residual efficacy after FM treatment was consistently lower compared to DPP or IP treatments at the 24 h assessments on days 8, 22, 23, and 29. Residual efficacy measured at this last time point was 94.8% for DPP, 83.1% for IP, and 46.9% for FM. This study demonstrates that permethrin-based formulations (DPP and IP) provided a quicker onset of residual protection against brown dog ticks compared to FM. Although DPP and IP are both permethrin-based formulations, DPP exhibited consistently higher residual acaricidal efficacies and was the only treatment that provided >90% protection for 1 month at 24 h post challenge.

Changes in the synganglion of Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) female ticks exposed to permethrin: an ultrastructural overview

This study performed the ultra-structural analysis of the changes caused by permethrin in the synganglion of semi-engorged Rhipicephalus sanguineus females, aiming to understand the toxic action of this substance at cellular level. The results showed that the neural lamella had its structure changed, allowing the influx of the toxic agent into the nervous tissue. The glial cells of the perineurium, as well as the neural cells of the cortex showed great changes, such as: irregular nuclei with chromatin margination, cytoplasmic vacuolation and degenerating mitochondria. These changes showed that the permethrin would be able to induce the degeneration of the synganglion through an atypical death process, involving apoptosis and autophagy. In addition, a dilated rough endoplasmic reticulum was observed in the neural cells, suggesting an intense synthesis of the hydrolytic enzymes that would be used in the processes of degradation of the damaged cellular structures (formation of lysosomes). The subperineurium and the neuropile also showed changes in their structures. Thus, it is suggested that permethrin is a dose-dependent compound able to impair the metabolism of the organism as a whole, once all the other organs and body structures are directly dependent of the neural control. The information obtained in this study can be used in the improvement of the control methods which use permethrin as active substance, helping in the creation of a really efficient acaricide product to fight this important urban plague.

The occurrence of autophagic cell death in the tegument of rabbits pre-infested with Rhipicephalus sanguineus and exposed to selamectin (active principle of acaricide Pfizer Revolution®)

Ticks of Rhipicephalus sanguineus species have great medical and veterinary importance for being a vector of various diseases. In an attempt to minimize their action on the host, people have resorted to chemical control by using various acaricides, such as selamectin. Although previous studies have demonstrated its toxic action in domestic animals, no studies focused on the detection of cell death when exposed to selamectin. For this reason, the technique for detecting autophagic cell death was used in order to demonstrate the responses of rabbits' skin tissues pre-infested with R. sanguineus and exposed to different concentrations of selamectin. The obtained results when exposed to 100 and 80% concentrations of selamectin showed a strong mark of acid phosphatase on the cells of the connective tissue of the dermis and hair follicles, whereas the ones exposed to the 50% concentration had a weak mark on the cells of the connective tissue of the dermis and moderate staining in hair follicles. It became clear that, when used at high concentrations (100 and 80%), selamectin is capable to induce a large scale occurrence of the autophagic cell death process. On the other hand, the concentration of 50% causes minor morphophysiological changes in the skin of rabbit hosts when evaluated the cell death process. Therefore, the data confirms that selamectin is a powerful dose-dependent toxic agent causes increased activity of the enzyme acid phosphatase.

Action of permethrin on Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) semi-engorged females: morpho-physiological evaluation of salivary glands

Currently the most effective method of tick control is the use of acaricides, among which stands out permethrin (active ingredient of acaricide Advantage(®) Max3, Bayer), a neurotoxic pyrethroid. However, assessments of their effects on other tick systems such as glandular are still scarce. Thus, this study provides information, through histochemical techniques, about the toxic effect of this pyrethroid on the morphophysiology of salivary glands of semi-engorged Rhipicephalus sanguineus females exposed to different concentrations of permethrin (206, 1031, and 2062 ppm). The results showed that permethrin caused significant changes in the salivary gland metabolism accelerating the process of glandular degeneration, an event which would occur naturally and with great intensity only in the final engorgement stage. Furthermore, this study pointed out that permethrin reduces the salivary gland secretion ability through a drastic reduction of proteins, lipids, and polysaccharides in acinar cells. These changes impair the females to finalize the feeding process, what indirectly affects the reproductive process.

Ecdysteroid levels changed by permethrin action in female Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) ticks

As recent studies have shown that ecdysteroids may play a major role in the regulation of vitellogenesis in Ixodidae, the present study quantified, by means of a radioimmunoassay, the levels of ecdysteroids present in the hemolymph of semi-engorged females of Rhipicephalus sanguineus ticks obtained from control females (exposed to distilled water) and those exposed to increasing concentrations of permethrin. The levels of ecdysteroids decreased significantly as the concentration of permethrin increased, suggesting that this compound could be an inhibitor of ecdysteroids secretion, and consequently interfering with the reproductive ability of these ticks, since this hormone is responsible for the synthesis and incorporation of vitellogenin by oocytes. This study complements the previous results with R. sanguineus semi-engorged females, showing that permethrin is a potent agent causing major morphological changes in tick oocytes, such as the appearance of large vacuoles in the cytoplasm, reduction in the amount of yolk granules and a decrease in oocyte size, thus culminating in cell death and consequently reducing or preventing reproduction in treated females. The findings that permethrin leads to a decrease in ecdysteroid titers could represent an entry step into this scenario.