Transmission of Ehrlichia canis to dogs by ticks (Rhipicephalus sanguineus).

Two strains of Rhipicephalus sanguineus acquired Ehrlichia canis by feeding as either larvae or nymphs on acutely infected dogs and, in subsequent instars, transmitted the agent to normal dogs. Three strains of R sanguineus transmitted E canis as adults after their larval and nymphal stages fed on infected dogs. More than 400 adult female ticks were fed on infected dogs as larvae or nymphs or both, but none transmitted E canis transovarially.     

Starvation and overwinter do not affect the reproductive fitness of Rhipicephalus sanguineus

Rhipicephalus sanguineus is the most widespread tick in the world, being able to survive under different climate conditions. In this study, the longevity of R. sanguineus was investigated under laboratory and natural climate conditions in southern Italy. Moreover, the reproductive fitness of females after overwintering was assessed. In the environment, unfed larvae, nymphs and adults were able to survive for up to 34, 40 and 385 days, respectively. However, the longevity of larvae (44 days), nymphs (54 days) and adults (584 days) in the laboratory was longer. Adult ticks that had overwintered under natural climate conditions were able to feed and give rise to viable larvae, after 40 weeks of starvation. Thereby, it is demonstrated that R. sanguineus is able to overwinter in southern Italy, without any prejudice to its fitness. These findings advance our knowledge on the natural history of R. sanguineus in nature and provide new insights into the epidemiology of certain tick-borne diseases in southern Europe as well as into the risk for their introduction in northern European countries.     

The brown dog tick, Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae): from taxonomy to control

Rhipicephalus sanguineus, commonly known as the brown dog tick, is a three-host tick that feeds primarily on dogs and occasionally on other hosts, including humans. R. sanguineus ticks are widely distributed around the world and they are known vectors of pathogens, such as Babesia canis, Ehrlichia canis, and Rickettsia conorii. The increasing number of cases of human parasitism by R. sanguineus ticks reported in the literature indicates that the interaction between humans and R. sanguineus ticks may be more common than it is actually recognized. The indiscriminate use of acaricides is an emerging problem worldwide and has led to the selection of acaricide resistant tick strains. In this article, the medical and veterinary importance, taxonomy, biology, and ecology of R. sanguineus ticks around the world are reviewed. It also discusses the current strategies for the control of R. sanguineus, highlighting the potential risks associated to the improper use of acaricides, such as environmental pollution and toxicity to humans and other non-target organisms (e.g., tick predators).     

Life cycle of the tick Amblyomma parvum Aragão, 1908 (Acari: Ixodidae) and suitability of domestic hosts under laboratory conditions

Amblyomma parvum is a widespread Neotropical tick found on several domestic animals and is known to harbor a Rickettsia species of yet unknown pathogenicity. However its life cycle on, and suitability of, several of these hosts has not been described. In this work the biology of A. parvum is presented when fed on seven domestic hosts (chicken, dog, rabbit, horse, guinea pig, cattle and goat). The complete life cycle of the tick varied from 96.8 to 102 days. Highest engorgement weight of larvae was from ticks fed on horses and that of nymphs from guinea pigs. Highest larval yield was from guinea pigs and that of nymphs from horses. Engorged female and egg mass weights, yield and conversion of female weight to eggs rates were the highest in dog ticks and the lowest in goat ticks. The highest egg hatching rate was seen in ticks from dogs and the lowest in ticks from cattle. Overall it was seen that dogs were the best host for adult A. parvum ticks, and guinea pigs for immatures. Horses were also shown to be a good host for all tick stages. It can thus be affirmed that A. parvum is a host generalist tick, and its distribution is probably determined by environmental requirements rather than by hosts.     

Experiments on transmission of an unidentified Theileria sp. to small ruminants with Haemaphysalis qinghaiensis and Hyalomma anatolicum anatolicum

Experiments on the transmission of an unidentified Theileria sp. infective for small ruminants by Haemaphysalis qinghaiensis and Hyalomma anatolicum anatolicum were carried out. Three Theileria-free batches of adult, larvae, and nymphs of laboratory reared H. qinghaiensis and Hy. a. anatolicum ticks were infected by feeding them on sheep infected with Theileria sp. The Theileria sp. was originally isolated from adult ticks of H. qinghaiensis, by inoculation of blood stabilates or tick transmission. H. qinghaiensis has been shown to be capable of transmitting the Theileria sp. infective for small ruminants transstadially to sheep and goats. The nymphs developed from the larvae engorged on the sheep infected with the parasite transmitted the pathogen to splenectomized sheep with prepatent periods of 30, 31 days, respectively; but the subsequent adult ticks of H. qinghaiensis derived from the nymphs did not transmit the pathogen to sheep. However, adults developed from the nymphs engorged on the sheep infected with the parasite transmitted the pathogen to sheep with prepatent periods of 24-27 days. The larvae, nymphs and adult ticks derived from female H. qinghaiensis ticks engorged on infected sheep were not able to transmit the parasite transovarially. The same experiments were done with Hy. a. anatolicum, but examination for presence of piroplasma of Theileria sp. from all animals were negative, demonstrating that Hy. a. anatolicum could not transmit the organism to sheep or goats.     

THE AUSTRALIAN BROWN DOG TICK RHIPICEPHALUS SANGUINEUS AS AN EXPERIMENTAL PARASITE OF CATTLE AND VECTOR OF ANAPLASMA MARGINALE

SUMMARY Experiments were done to explore the possible relationship between cattle, Australian dog ticks (Rhipicephalus sanguineus) and Anaplasma marginale. Calves' ears were exposed to larval, nymphal and adult ticks on 8, 9 and 7 occasions, respectively. The immature instars fed readily, but the adults attached very poorly to calves. Transtadial transmission of A. marginale was achieved on 6 occasions from 9 attempts: ticks infected as larvae or nymphs were able to transmit at the subsequent stage or stages. Transovarial transmission was not achieved. Six calves supported more than one infestation of ticks. Attached ticks caused the calves no apparent discomfort and calves developed no noticeable skin reactions. An abattoir survey of 200 hides detected no R. sanguineus.     

Striped mice, Rhabdomys pumilio, and other murid rodents as hosts for immature ixodid ticks as in the Eastern Cape Province

Striped mice, Rhabdomys pumilio, were trapped over a period of 17 months in the Thomas Baines Nature Reserve, and placed in cages, over water, until all the ticks they harboured had detached. The mice were then returned to the reserve. Four ixodid tick species were recovered from the mice of which the larvae and nymphs of Rhipicephalus follis and Rhipicephalus simus were the most numerous. Most larvae of R. follis detached from mice trapped from March to July, and most nymphs in March and from June to September. Most larvae of R. simus detached from mice trapped from December to March, and most nymphs from January to March and during May and June. Seven ixodid tick species were collected from striped mice, house rats, Rattus rattus, vlei rats, Otomys spp. and Praomys sp. captured in the vicinity of human dwellings or animal holding facilities in the Grahamstown district. The striped mice captured in the Thomas Baines Reserve harboured considerably larger numbers of ticks than any of the rodent species in the more urbanized localities.     

Evaluation of Rhipicephalus sanguineus as a potential biologic vector of Ehrlichia platys

The brown dog tick, Rhipicephalus sanguineus (Acari: Ixodidae), transmits several diseases among dogs including Ehrlichia canis infection. The role of Rhipicephalus sanguineus as a biologic vector for E platys, the rickettsial agent of infectious canine cyclic thrombocytopenia, was studied in dogs. Laboratory-cultured, pathogen-free nymph ticks were fed to repletion on dogs acutely infected with E platys. Tick engorgement coincided with the development of initial parasitemia and thrombocytopenia in the infected dogs. Following repletion, nymph ticks were allowed to molt under controlled conditions. One-month-old E platys-exposed adult ticks failed to infect naive dogs in animal transmission studies. The presence of E platys was not detected in midguts or salivary glands of similarly exposed adult ticks by use of light and transmission electron microscopy. These studies indicate that R sanguineus may not transmit E platys infection.     

Antibody and blood leukocyte response in Rhipicephalus sanguineus (Latreille, 1806) tick-infested dogs and guinea pigs

The dog is considered to be the natural host of Rhipicephalus sanguineus and is unable to develop appreciable resistance even after repeated feedings. The guinea pig develops strong resistance after one infestation with adult ticks. Antibody (IgG) titres against tick salivary gland antigens (SGAs) and blood leukocyte numbers in dogs and guinea pigs undergoing experimental R. sanguineus tick infestations were measured to detect a possible correlation with susceptibility or resistance of hosts. Since infested dogs develop an immediate hypersensitivity reaction to R. sanguineus antigens, total and anti-R. sanguineus SGA IgE levels were also measured in this host species. IgG and IgE antibody levels were determined by an enzyme-linked immunosorbent assay (ELISA) along three consecutive infestations of both hosts. Most dogs and guinea pigs displayed low IgG levels against R. sanguineus SGAs, though marked differences in individual response were observed. Although dog's total serum IgE levels increased significantly after infestations, no change in the amount of anti-salivary gland IgE was detected. Total and differential blood cell counts were determined in dogs and guinea pigs during primary and secondary infestation. In dogs, a tertiary infestation and a subsequent higher infestation level were also evaluated. Infested dogs did not display any alteration in blood leukocyte counts throughout the experiment. Guinea pigs, on the other hand, developed a significant basophilia during primary infestation which increased further during secondary infestation. These data reveal similarities and differences in the reactions of resistant and non-resistant hosts to ticks. They contribute for the understanding of such host-parasite relationships and will hopefully aid in the development of immune control of ticks.     

Survey of tick infestation and tick-borne ehrlichial infection of dogs in Ishigaki Island, Japan.

Twelve (54.5%) of 22 free-roaming dogs in Ishigaki Island had tick infestation identified as Rhipicephalus sanguineus. There were 121 ticks recovered and consisted of 28 females, 58 males, 22 nymphs and 3 larvae. Infection of dogs possibly with canine ehrlichial pathogens was examined by both indirect immunofluorescence assay and polymerase chain reaction (PCR). Two dogs of the 13 examined were sero-positive for the human granulocytic ehrlichia agent, and one of two dogs was PCR positive for Ehrlichia platys. This dog had platelet numbers slightly lower than normal value, however, no morulae were found within platelet on peripheral blood smear stained with Giemsa.     

Biological and DNA evidence of two dissimilar populations of the Rhipicephalus sanguineus tick group (Acari: Ixodidae) in South America

In this work, the biology, mitochondrial DNA and fertility of hybrids from two strains of Rhipicephalus sanguineus, from Brazil and Argentina, were compared. Engorged larvae, nymphs and adults from Argentina weighed more and the engorgement period of adult females was significantly longer than those of their Brazilian counterparts, whereas adult female tick yield rate was higher for the Brazilian strain. High intraspecific divergence of mitochondrial DNA was detected between R. sanguineus from Brazil and Argentina. On the other hand, a strong genetic relationship was detected between European and Argentinean R. sanguineus populations while the Brazilian population appeared to be related to the African Rhipicephalus turanicus. Adult hybrid females laid eggs, which were mostly unviable, whereas a mean of more than 1400 larvae hatched per egg mass from pure Brazilian and Argentinean strains. These results showed that differences between these strains are greater than previously assumed and that the biosystematic status of R. sanguineus ticks from South America should be re-evaluated. Wide variations, such as these might account for the reported worldwide differences in biology and vector capacity of this species.     

Infectivity rate and transmission potential of Hyalomma anatolicum anatolicum ticks for Babesia equi infection

The infectivity rate of Babesia equi in the salivary glands of Hyalomma anatolicum anatolicum was assessed. The hungry nymphs were fed on a donkey experimentally infected with B. equi. The engorged dropped-off nymphs were collected at different levels of parasitaemia and kept in BOD incubator. After ecdysis, the hungry adults were prefed on rabbits for different time intervals, thereafter the salivary glands were dissected out and acini were examined after methyl green pyronin (MGP) staining. A total of 134 male and 139 female ticks were dissected out. Average infected acini per tick were found to be significantly higher (p<0.05) in male as compared to the female ticks. Further, maximum infected acini in both male and female ticks were found at 24h of prefeeding on rabbits and overall infected acini per tick increased with rise in parasitaemia. The release of infected ticks on susceptible donkeys resulted in development of clinical babesiosis.     

The brown dog tick Rhipicephalus sanguineus and the dog as experimental hosts of Ehrlichia canis

Adult Rhipicephalus sanguineus ticks efficiently transmitted Ehrlichia canis to susceptible dogs for 155 days after detachment as engorged nymphs from a dog in the acute phase of ehrlichiosis. Adult ticks that had similarly engorged on a dog in the chronic phase of ehrlichiosis failed to transmit E canis to susceptible dogs. Infected but unfed adult ticks may be of greater importance than the chronically infected carrier dog as a natural reservoir of E canis.     

Experimental infection by capillary tube feeding of Rhipicephalus sanguineus with Bartonella vinsonii subspecies berkhoffii

It has been speculated that ticks may serve as vectors of Bartonella species. Circumstantial, clinical, epidemiological and serological evidence suggest that B. vinsonii subspecies berkhoffii (B. v. berkhoffii) might be transmitted by Rhipicephalus sanguineus. The purpose of the present study was to determine whether adult R. sanguineus ticks can be infected with a B. v. berkhoffii genotype II isolate via capillary tube feeding and whether the infection can then be transmitted from adult females to their eggs via trans-ovarial transmission. Furthermore, tick fecal material was also collected and screened as a possible source of infectious inoculum for canine infections. B. v. berkhoffii DNA was detected in 50% (7 of 14) of females that did not oviposit and in 14.3% (2 of 14) of female ticks that laid eggs, but not detected in egg clutches (100 eggs/female). DNA was also detected in tick feces collected on days 2 through 6 post-capillary tube feeding, however, dogs (n=3) did not become bacteremic or seroconvert when inoculated with tick fecal material. Therefore, trans-ovarial transmission of B. v. berkhoffii by R. sanguineus is unlikely, but further studies are needed to determine if tick fecal material can serve as a source of infection to canines.     

The prevention of attachment and the detachment effects of a novel combination of fipronil, amitraz and (S)-methoprene for Rhipicephalus sanguineus and Dermacentor variabilis on dogs

A novel combination of fipronil, amitraz and (S)-methoprene (CERTIFECT?, Merial Limited, GA, USA) was evaluated for the prevention of attachment of ticks and its ability to cause detachment of ticks. For the two prevention of attachment studies, 20 purpose-bred beagles were allocated each to two equal groups based on pretreatment tick counts (treated and untreated). Each dog was exposed to 50 adult Rhipicephalus sanguineus and Dermacentor variabilis weekly starting 24h after treatment. In study 1 infestations with R. sanguineus were discontinued after Day 7 but continued to Day 28 for D. variabilis in both studies. Counts of ticks by species were made 2, 4 and 24h after exposure to ticks. Ticks not attaching to dogs were evaluated for viability. For the evaluation of detachment study, 16 purpose-bred beagles were allocated each to two equal groups based on pretreatment tick counts (treated and untreated). Each dog was infested with 50 unfed R. sanguineus and D. variabilis adults on Day -2. Ticks were thumb counted without removal on all dogs on Day -1, and at 4, 12, and 24h after treatment. Ticks were counted and removed at 48 h after treatment. Dogs treated with the novel combination had significantly (p<0.05) lower total numbers of attached R. sanguineus and D. variabilis than untreated controls at 4h through Day 7. For R. sanguineus, percent reduction of attachment at 24h after infestation through Day 29 ranged from 94.5% to 100%. For D. variabilis, the percent reduction of attachment at 24h through Day 22 was above 98.0%. These studies demonstrate that novel combination can disrupt attachment of R. sanguineus and D. variabilis for up to 28 days following treatment. Of those ticks that are exposed to the treatment, even if they do not attach to the dog and remain in the environment, greater than 90% (p<0.05) die within 24h for 2-3 weeks following treatment. Also, for those dogs infested with ticks at the time of treatment, the novel combination causes significant detachment (p<.05) starting at 12h and reaching 98.9% by 48 h after treatment. This product provides an effective means for controlling ticks infesting dogs and limiting the spread of tick transmitted diseases. Additionally, the mortality of ticks exposed to CERTIFECT will reduce infestation of the dog's environment.     

Participation of Rhipicephalus sanguineus (Acari: Ixodidae) in the epidemiology of canine visceral leishmaniasis

The vectorial competence of the tick Rhipicephalus sanguineus is discussed in relation to the epidemiology of canine visceral leishmaniasis, taking into account its strict association with dogs and the low indices of natural infection presented by its known vector, the phlebotomine sand fly Lutzomyia longipalpis. In order to evaluate natural infection by Leishmania chagasi and the infectivity of these parasites in the tick, 39 specimens (6 females, 11 males and 22 nymphs) of R. sanguineus were removed from 21 dogs showing diverse symptoms of zoonotic visceral leishmaniasis (ZVL). Six ticks (15.4%) gave positive results for the genus Leishmania using the PCR technique. To determine the infectivity of the parasites, 36 hamsters were inoculated orally and peritoneally with macerates of ticks removed from nine dogs symptomatic for visceral leishmaniasis. After 6 months the hamsters were sacrificed and necropsied. Serum was removed for IFAT, as well as spleen and liver fragments to make imprint smears and for PCR. Eight (88.9%) of these dogs presented ticks that were infective for 14 hamsters (41.2%), 12 (85.7%) of them infected peritoneally and two (14.3%) orally. PCR revealed 27 smears (40.9%) to be positive, 20 (62.5%) of them infected peritoneally and seven (20.6%) orally. IFAT showed 14 positive animals (41.2%). Based on these findings, we suggest that the vectorial capacity of R. sanguineus for L. chagasi should be evaluated further, opening new perspectives in the epidemiology of ZVL.     

Transstadial and intrastadial experimental transmission of Ehrlichia canis by male Rhipicephalus sanguineus

The acquisition and transmission of rickettsial pathogens by different tick developmental stages has important epidemiological implications. The purpose of this study was to determine if male Rhipicephalus sanguineus can experimentally acquire and transmit Ehrlichia canis in the absence of female ticks. Two trials were performed where nymphal and male R. sanguineus were simultaneously acquisition fed on the same infected donor hosts, and transstadially or intrastadially exposed male ticks were fed on separate pathogen-free dogs as a test for transmission. A single-step p30-based PCR assay was used to test canine and tick hosts for E. canis infections before and after tick feeding. E. canis was detected after either intrastadial or transstadial passage in male ticks, the organism remained detectable in both tick groups after transmission feeding, and both tick groups transmitted the rickettsia to susceptible dogs. Infection of dogs via tick feeding resulted in milder clinical signs and lower antibody titers than intravenous inoculation of carrier blood, but further investigation is needed to understand the mechanisms responsible for this observation. These results demonstrate that male R. sanguineus can take multiple feedings, and that they can both acquire and transmit E. canis in the absence of female ticks. This tick development stage could be important in transmission of E. canis, and perhaps related pathogens, between vertebrate hosts under natural and experimental conditions.     

Histopathology of attachment sites of Amblyomma variegatum and Rhipicephalus appendiculatus on zebu cattle of varying resistance to ticks.

Mature, unimproved East African Zebu cattle (Bos indicus) naturally exposed to ticks from birth were ranked for resistance to ticks by repeated whole-body counts of infesting ticks. Four cattle of high resistance, four of low resistance and two of intermediate resistance were artificially infested with nymphs of Amblyomma variegatum and Rhipicephalus appendiculatus. Two Friesian cattle (Bos taurus) with less exposure to ticks were similarly infested. Biopsies of tick attachment sites were examined histologically. All attachment sites showed acute inflammatory lesions, and sites of both tick species on high resistance cattle showed delayed hypersensitive reactions with intra-epidermal pustulation and significant increases in the numbers of granulocytes. The predominant cells infiltrating attachment sites on high resistance cattle were eosinophils with A. variegatum and neutrophils with R. appendiculatus. Such differences need to be taken into account in developing immunological tests for selecting cattle for resistance but there are sufficient common features of reactions to the two infesting tick species to justify dermal hypersensitivity tests.     

First evidence and molecular characterization of Babesia vogeli in naturally infected dogs and Rhipicephalus sanguineus ticks in southern France

Babesiosis is an emerging tick-borne disease of animals and humans caused by intraerythrocytic protozoa of the genera Babesia and Theileria. In France canine babesiosis has a high prevalence with Babesia canis thought to be the main aetiological agent of the disease. Babesia vogeli has already been reported to occur in Europe and in other countries around the Mediterranean Sea. The tick Rhipicephalus sanguineus, the main known vector of B. vogeli, occurs in southern France. However, only one case of a B. vogeli infected dog has been reported to date in France. To gain further insight into the prevalence of Babesia and Theileria infections in dogs and ticks of the R. sanguineus complex, a study was conducted in a veterinary practice in the south of France from January to September 2010. Twelve bloods from dogs and 36 R. sanguineus ticks were analyzed using PCR and sequencing. For the analysis of ticks, a new primer was designed to specifically amplify the B. vogeli 18S rRNA gene. Four dogs (33.3%) and 8 ticks (22.2%) were found to be infected with B. vogeli. This approach has thus revealed for the first time a cluster of cases of canine babesiosis caused by B. vogeli in France and highlights the need to systematically screen for pathogens potentially responsible for canine babesiosis at the species level using suitable molecular tools.     

The Relative host status of rock elephant shrews Elephantulus myurus and Namaqua rock mice Aethomys namaquensis for economically important ticks

Several tick species of medical and veterinary importance occur in the southern Orange Free State. The purpose of the present study was to determine the host status of rock elephant shrews ( Elephantulus myurus) and Namaqua rock mice ( Aethomys namaquensis) for these ticks. Infestation levels were used as a criterion. The seasonal abundances of the ticks as well as the effects of landscape topography and sex of the host on infestation levels were also investigated. Incidental observations were made on the pouched mouse (Saccostomys campestris). No adult ticks were recovered from any of these small mammals. Seven tick species were found on the elephant shrews of which only Ixodes rubicundus and Rhipicephalus punctatus occurred in high numbers on a large proportion of the animals. Both these ticks cause paralysis in domestic stock. The Namaqua rock mice harboured eight tick species. Only Haemaphysalis leachi/spinulosa and R. punctatus had a relative abundance exceeding 15%. Three of the 10 pouched mice examined were infested with small numbers of ticks. The 132 rock elephant shrews examined harboured a mean total burden of 121 immature ticks compared to four on each of the 321 Namaqua rock mice. The larvae and nymphs of I. rubicundus occurred mainly in the colder months (April to September), while those of H. leachi/spinulosa preferred the warmer months (October to March). Large numbers of larvae of R. punctatus were present from December to July and nymphs from August to October. Infestation levels of I. rubicundus were consistently higher on animals trapped on southern slopes than on those trapped on northern slopes. The sex of the hosts seemed to have little effect on infestation levels.