Fluazuron-induced morphophysiological changes in the cuticle formation and midgut of Rhipicephalus sanguineus Latreille, 1806 (Acari: Ixodidae) nymphs

The present study demonstrated the effects of the arthropod growth regulator, fluazuron (Acatak®), in the formation of the integument and digestive processes of Rhipicephalus sanguineus nymphs fed on rabbits treated with different doses of this chemical acaricide. For this, three different doses of fluazuron (20, 40, or 80 mg/kg) were applied “pour on” to the hosts (groups II, III, and IV), as well as distilled water to the control group. On the first day after treatment (24 h), the hosts were artificially infested with R. sanguineus nymphs. After full engorgement (7 days), the nymphs were removed, placed on labeled Petri dishes, and kept in biochemical oxygen demand incubator for 7 days. The engorged nymphs were then taken for morphological, histochemical, and histological analyses. The results showed the occurrence of cytological, morphohistological, and histochemical alterations in the integument and midgut of nymphs from all the different treated groups. These alterations occurred at cuticular level in the subdivisions of the cuticle, related to the size of the digestive cells, amount of accumulated blood elements, and digestive residues, as well as the presence of vacuoles in the cytoplasm of the digestive cells. Thus, this study demonstrated that fluazuron acts on the integument and midgut cells of R. sanguineus nymphs fed on treated rabbits and pointed out the possibility of the use of this chemical—which is more specific, less toxic, and less harmful to the environment and nontarget organisms—in the control of R. sanguineus, at least in the nymphal stage of its biological cycle.     

Morphology of the midgut of Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) adult ticks in different feeding stages

The intestinal epithelial cells of ticks are fundamental for their full feeding and reproductive success, besides being considered important sites for the development of pathogens. Rhipicephalus sanguineus ticks are known for their great medical and veterinary importance, and for this reason, the knowledge of their intestinal morphology may provide relevant subsidies for the control of these animals, either by direct acaricidal action over these cells or by the production of vaccines. Therefore, this study aimed to describe the midgut morphology of male and female R. sanguineus ticks in different feeding stages, by means of histological analysis. Significant differences were observed between the genders, and such alterations may refer mainly to the distinct demands for nutrients, much higher in females, which need to develop and carry out the egg-laying process. In general, the midgut is coated by a thin muscle layer and presents a pseudostratified epithelium, in which two basic types of cells can be observed, connected to a basal membrane—generative or stem and digestive cells. The latter was classified as follows: residual, deriving from the phase anterior to ecdysis; pinocytic, with vesicles containing liquid or pre-digested components of blood; phagocytic, with entire cells or remnants of nuclear material inside cytoplasmic vesicles; and mature, free in the lumen. Digestion is presumably intracellular and asynchronous and corresponds to a process which starts with the differentiation of generative cells into pinocytic digestive cells, which subsequently start to phagocytize intact blood cells and finally detach from the epithelium, being eliminated with feces.     

Cytotoxic effects of andiroba oil (Carapa guianensis) in reproductive system of Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) semi-engorged females

The present study performed an analysis about the effects of andiroba seed oil (Carapa guianensis) in the ovary of Rhipicephalus sanguineus semi-engorged females; once, there are few studies about the action of natural products on the reproductive system, a vital organ for the biological success of this animal group. The results showed that andiroba oil is a potent natural agent which causes significant structural changes in the oocytes, such as the emergence of large vacuolated cytoplasmic regions, reduction in the number of yolk granules, changes in the shape of the cells, as well as impairment of genetic material. In addition, the ovary epithelium showed severe morphological changes, such as extreme structural disorganization, with highly vacuolated cells and picnotic nuclei, forming an amorphous mass. This study showed also that oocytes (mainly in the initial stages of development) and the ovary epithelium of R. sanguineus females subjected to different concentrations of andiroba oil presented morphological changes which became more numerous and intense as the concentration of the product increased. Based on the results, it can be inferred that although the defense mechanisms are developed by oocytes to recover the cellular integrity (presence of autophagic vacuoles), these cells are not able to revert the damage caused by this product. Thus, it can be concluded that although the damages caused to the oocytes by andiroba oil are comparatively less severe than the ones caused by synthetic acaricides, this product can be considered a potent natural agent that reduce and/or prevent the reproduction of R. sanguineus females, with the advantage of not causing environmental impact such as synthetic chemical acaricides.     

Ultrastructural analysis of the oocytes of female Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) ticks subjected to the action of Azadirachta indica A. Juss (neem)

The present study provides ultrastructural information about the acaricidal effects of neem (Azadirachta indica A. Juss) on the ovaries of R. sanguineus engorged females. In general, the main damage caused in the oocytes was alteration in the shape of the cell and of the germinal vesicle, ring-shaped nucleolus, cytoplasmic vacuolation, and disorganization of the organelles and of the cell membranes (including the chorion), all of which indicate that these cells could be in the process of death. The results showed that azadirachtin would be an efficient acaricide agent for inhibiting and/or neutralizing the reproduction process of R. sanguineus females, impairing the reproductive ability of this species.     

Zur Ökologie eines deutschen Stammes von Rhipicephalus sanguineus (Latreille, 1806)

Zusammenfassung Zur experimentellen Bewertung der ökologischen Toleranzkapazität von Rhipicephalus sanguineus wurden alle postembryonalen Entwicklungsstadien dieser Zeckenart im nüchternen und vollgesaugten Zustand verschiedenen Kombinationen von Temperatur- und relativen Luftfeuchtigkeitsbedingungen ausgesetzt, um den Einfluß dieser beiden abiotischen Faktoren auf ihre Entwicklung, Reproduktionskapazität sowie ihr Überleben zu untersuchen.In Untersuchungen zur ökologischen Reaktionsbreite von Rhipicephalus sanguineus konnte eindeutig nachgewiesen werden, daß die existentielle Sicherung dieser Zeckenart sowie deren Entwicklungs- und Reproduktionsvermögen von Temperatur und relativer Luftfeuchtigkeit bestimmt werden. Diese Beeinflussung ist dabei allgemein durch eine direkt proportionale Abhängigkeit von der relativen Luftfeuchtigkeit und eine umgekehrt proportionale Relation zur Temperatur gekennzeichnet.Das Propagationsvermögen zur enzootischen Manifestation ist nur im engen Temperaturbereich von 20–30° C und bei hoher relativer Luftfeuchtigkeit möglich. Diese Zeckenart ist jedoch in allen ihren Entwicklungsstadien für eine bestimmte Zeit fähig, selbst kritische Temperatur- und Feuchtigkeitsbedingungen zu tolerieren und damit ihren enzootischen Fortbestand zu sichern. Rhipicephalus sanguineus kann zwar auf Grund kritischer Makroklimabedingungen als Freilandzecke in Deutschland nicht bestehen, durch ihre besondere Wirtsprädilektion für Hunde wird dieser Zeckenart jedoch ein Biotop geboten, in dem alle ökologischen Voraussetzungen zur autochthon enzootischen Manifestation und epizootischen Ausbreitung gegeben sind.

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On the Ecology of a German Strain of Rhipicephalus sanguineus (Latreille, 1806)

Summary Experimental evaluation of the ecological tolerance of Rhipicephalus sanguineus was carried out by exposing all the postembryonic stages of development of this tick species to various combinations of temperature and relative humidity conditions, in both its fasting and replete phases, in order to investigate the influence of these two abiotic factors on their development and reproductive capacity, as well as on their ability to survive.Experiments into the degree of reaction to its environment showed unequivocally that the security of survival of Rhipicephalus sanguineus, as well its capacity for development and reproduction, are determined by temperature and relative humidity. These influences are characterized by a generally directly proportional relationship to relative humidity and an indirectly proportional relationship to temperature.The ability to propagate to the enzootic manifestation is only possible within the restricted range of temperature of 20–30° C and at a relatively high humidity. This tick is however capable of enduring critical temperature and humidity conditions for a given length of time, thus ensuring the continuation of the enzootic state. Rhipicephalus sanguineus is however unable to exist as a field tick due to critical macroclimatic conditions in Germany in its special predilection for the dog as a host this species is presented with a biotope in which all the ecological prerequisites are available for its autochthonous enzootic manifestation and its epizootic dissemination.

     

Histopathological study of ovaries of Rhipicephalus sanguineus (Acari: Ixodidae) exposed to different thymol concentrations

Thymol is a monoterpene with proven acaricide action for several tick species. In addition to killing these ectoparasites, thymol can also reduce oviposition and egg hatch rate. However, the effects of thymol on the morphophysiology of tick ovaries are still unknown. Thus, the aim of this study was to evaluate the morphophysiological changes caused by this active principle in ovaries of Rhipicephalus sanguineus after a 6-day feeding period, through the application of morphohistochemical techniques. After the feeding period, a total of 50 females were divided into five groups and immersed in the following solutions: (I) distilled water (control), (II) 30 % ethanol (control), (III) 1.25 mg/mL thymol, (IV) 2.5 mg/mL thymol, and (V) 5.0 mg/mL thymol. The experimental groups were kept in a climatic chamber (27?±?1 °C; RH 80?±?10 %) for 5 days. After this period, morphological (hematoxylin/eosin) and histochemical (von Kossa) techniques were applied after remotion of the ovaries. The morphological results revealed large vacuoles in germ cells at different developmental stages and invaginations that represent deformations in the chorionic membrane. From the results obtained in this study, it was concluded that thymol interfered with the development of oocytes, which showed degeneration signs. The treatment containing 5.0 mg/mL thymol affected more accentuately the morphological development. Moreover, thymol also altered the calcium content of yolk granules, which generally showed an intense staining for this element.     

Ultrastructural Analysis of the Oocytes of Female Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) Ticks Subjected to the Action of Azadirachta indica A. Juss (Neem)

The present study provides ultrastructural information about the acaricidal effects of neem (Azadirachta indica A. Juss) on the ovaries of R. sanguineus engorged females. In general, the main damage caused in the oocytes was alteration in the shape of the cell and of the germinal vesicle, ring-shaped nucleolus, cytoplasmic vacuolation, and disorganization of the organelles and of the cell membranes (including the chorion), all of which indicate that these cells could be in the process of death. The results showed that azadirachtin would be an efficient acaricide agent for inhibiting and/or neutralizing the reproduction process of R. sanguineus females, impairing the reproductive ability of this species.     

Prevalence of Ehrlichia canis (Rickettsiales: Anaplasmataceae) in dogs and Rhipicephalus sanguineus (Acari: Ixodidae) ticks from Brazil

The current study evaluated the prevalence of Ehrlichia canis Donatien and Lestoquard in domestic dogs, Canis familiaris L., and Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae) ticks from different areas of Brazil. In Monte Negro County (state of Rond?nia, Brazilian western Amazon), the indirect immunofluorescence assay detected E. canis-reactive antibodies (titer > or = 40) in 58/153 (37.9%) and 40/161 (24.8%) dogs from the urban and rural areas, respectively. These values were significantly different between the two areas. Ticks from a household in the urban area of Monte Negro, and from households in three other localities (162-165 adult ticks per household) in the state of S?o Paulo (SP) were tested by polymerase chain reaction (PCR) targeting an erlichial dsb gene fragment. The prevalence of infected ticks (given as minimal infection rate) was 2.3, 6.2, and 3.7% for populations 1 (Monte Negro), 2 (Jundiaí, SP), and 3 (S?o Paulo I, SP), respectively, which were statistically similar. In contrast, no infected tick was detected in population 4 (S?o Paulo II, SP). DNA sequences were determined for some of the PCR products generated from ticks and dogs from populations 1-3, being all identical to each other and to available sequences of E. canis in GenBank. These results reinforce previous records of E. canis-infecting dogs in Brazil. Natural infection of R. sanguineus ticks by E. canis is reported for the first time in Brazil, where this tick is the commonest species infesting dogs.     

Rhipicephalus sanguineus (Acari: Ixodidae) female ticks exposed to castor oil (Ricinus communis): an ultrastructural overview

Tick control has been accomplished through the use of synthetic acaricides, which has created resistant individuals, as well as contaminating the environment and nontarget organisms. Substances of plant origin, such as oils and extracts of eucalyptus and neem leaves, have been researched as an alternative to replace the synthetic acaricides. Ricinoleic acid esters from castor oil have recently been shown as a promising alternative in eliminating bacterial contamination during ethanol fermentation, by acting as an effective biocide. The same positive results have been observed when these esters are added to the food given to tick-infested rabbits. This study tested the effect of these substance on the reproductive system of Rhipicephalus sanguineus females, added to rabbit food, more specifically on oogenesis. For this, four groups were established: four control groups (CG1, CG2, CG3, and CG4) and four treatment groups (TG1, TG2, TG3, and TG4) with one rabbit in each (New Zealand White), used as hosts. After full 4 days feeding (semi-engorgement), the females were collected and had their ovaries extracted. In this study, it was observed that R. sanguineus females exposed to esters had their ovaries modified, which was demonstrated through transmission electron microscopy techniques. The addition of ricinoleic esters to the diet of tick-infested rabbits revealed how toxic such substances are for the cytoplasmic organelles of oocytes and pedicel cells. These compounds can change the morphophysiology of germ and somatic cells, consequently influencing their viability and, therefore, confirming that the ricinoleic acid esters from castor oil are a promising substance in the control of R. sanguineus.     

Climate and cuticular hydrocarbon variation inRhipicephalus sanguineus ticks (Acari: Ixodidae)

An association between the climate and variation of the cuticular hydrocarbon pattern was found for several populations ofRhipicephalus sanguineus ticks. Extreme parameters of climate (absolute minimal and maximal temperatures) correlated positively with six compounds (mainly methylalkanes) detected in cuticular hydrocarbon mixtures. In the light of work conducted on cuticular transpiration in arthropods and biochemical phase changes in cuticle lipids, it is suggested that the adaptation of ticks to potential colonization areas is accomplished by detectable changes in cuticular hydrocarbon relationships. These tick strains can be biochemically determined and their adaptation potential, analyzed.     

Focus of human parasitism by the brown dog tick, Rhipicephalus sanguineus (Acari: Ixodidae)

Throughout most of its range, the brown dog tick, Rhipicephalus sanguineus (Latreille), prefers dogs as a host, but human bites occasionally occur in the Mediterranean region and Central America; historically, this species has rarely bitten humans in the United States. A focus of 15 human bite cases by this tick is reported from four Air Force bases located within 200 miles of each other in north central Texas and southwestern Oklahoma. The sudden appearance of numerous documented bite cases indicates that either the species is becoming more anthropophilic in this area or than an introduction of a more human adapted population of R. sanguineus has occurred. The species is a known reservoir and vector of Ehrlichia canis, the causative agent of canine ehrlichiosis in dogs. The presence of an anthropophilic strain of R. sanguineus in the United States may lead to increased exposure to E. canis and thus an increase in the incidence of human ehrlichiosis.     

Evaluation of devices for removing attached Rhipicephalus sanguineus (Acari: Ixodidae).

Three types of forceps and a commercially available device, the Tick Solution, were used to remove adult brown dog ticks, Rhipicephalus sanguineus (Latreille), from dogs. The Tick Solution proved least effective at removing ticks, requiring significantly more removal attempts compared with forcep-removal methods. Medium-tipped angled forceps provided the best overall performance. Other advantages and disadvantages of the devices are discussed.     

Chemical characterization and acaricide potential of essential oil from aerial parts of Tagetes patula L. (Asteraceae) against engorged adult females of Rhipicephalus sanguineus (Latreille, 1806)

Rhipicephalus sanguineus, commonly known as the brown dog tick, is one of the most widely distributed species of tick. In dogs, it can cause anemia and provide the transmission of pathogenic microorganisms such as Babesia canis, Ehrlichia canis, Hepatozoon canis, Anaplasma platys, and Mycoplasma haemocanis. To man, it can transmit the intracellular parasites Rickettsia rickettsii and Rickettsia conorii, the causative agents of the Rocky Mountain spotted fever in the Americas and Mediterranean and spotted fever in Europe and North Africa. Its control is performed by applying synthetic formulations composed of pyrethroids; however, continued use of these products results in environmental damage and acquisition of resistance. Alternatively, studies with botanical insecticides have been increasingly recurrent. Therefore, this study aimed to test the efficacy of essential oil of Tagetes patula, a ruderal species widely described in the literature for its insecticidal properties, in engorged females of R. sanguineus by the adults immersion test (AIT) and impregnated paper disk test (IPDT). The essential oil used, through gas chromatography coupled to mass spectrometry, revealed the presence of 55 compounds, being the 4-vinyl guaiacol and gamma terpinene the majority ones. The AIT compared to the IPDT was more efficient in inhibiting oviposition of tick; however, the eggs laid by the females submitted to saturated atmosphere with essential oil, from IPDT, not hatched, interrupted their development cycle. Besides being a pioneer work, the results presented here contributes to new researches, aiming the incorporation of essential oil in an acaricide for use in the environment.     

Evaluation of the vectorial capacity of Rhipicephalus sanguineus (Acari: Ixodidae) in the transmission of canine visceral leishmaniasis

The vectorial capacity of Rhipicephalus sanguineus in the transmission of canine visceral leishmaniasis has been evaluated through a laboratory-controlled experiment. One healthy Leishmania-free dog and two dogs naturally infected with Leishmania were infested with R. sanguineus in various stages of development. Engorged larvae, unfed nymphs, engorged nymphs, unfed adults, engorged female adults and fed male adults were collected from the experimental animals and examined for Leishmania infection by optical microscopy, polymerase chain reaction (PCR) and parasite culture. Leishmania forms were not detected in any of the 433 smears prepared from engorged colonies nor in any of the 118 smears prepared from unfed colonies. However, one flagellate structure was identified in one of the smears. All pools of R. sanguineus that had fed on the infected dogs tested PCR-positive for Leishmania DNA, with the single exception of the pool of engorged larvae. In contrast, all pools of ticks that had fed on the Leishmania-free dog were PCR-negative. Leishmania growth was not observed in any of the tick colonies following incubation on culture medium. Considering that no Leishmania forms were identified in any of the meticulously analysed smears derived from engorged colonies of R. sanguineus, it appears somewhat unlikely that the maintenance and multiplication of Leishmania occurs within the tick.     

The dog factor in brown dog tick Rhipicephalus sanguineus (Acari:Ixodidae) infestations in and near human dwellings

Three cases of the tick Rhipicephalus sanguineus infiltration in or near human dwellings caused by dogs, and their influence on epidemiological features of human habitats have been investigated, (a) The observation of dogs kept indoors proved that single tick females could engorge and oviposit inside apartments followed by the development of subadults. (b) Abundant micropopulations of ticks were formed in small yards or gardens near the dwellings where dogs lived in kennels, (c) A huge field population of R. sanguineus was observed on a farm where watchdogs constantly patrolled along the farm perimeter. Tick abundance near the kennels and in the permanent resting sites of the dogs reached more than 30 adults per 10 min of collecting, while the number of adults on a dog reached 100. Unfed adult females under conditions of constant dog availability had a larger scutal index than females collected in the control field site. On the basis of circumstantial evidence it is possible to conclude that under the above conditions tick development may change from the normal 3-host cycle to a 2-host cycle. Ticks in the field had one complete generation per year. Ticks on the farm, as well as ticks in kennels, developed faster and a significant part of their population had two complete generations per year. R. sanguineus is the main vector and reservoir of a pathogen from the Rickettsia conorii complex, the causative agent of Israeli tick typhus. The described conglomerations of R. sanguineus create a great risk to humans who can be attacked by infected ticks in and around their homes, even in large towns. Such a feature of the tick life history most likely exists not only in Israel but in other countries as well.