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1.
Laboratory-reared larval Gulf Coast ticks (GCTs) (Amblyomma maculatum) were exposed experimentally and found to acquire Hepatozoon americanum infection while feeding on parasitemic dogs. These ticks supported gamogonic and sporogonic development of the apicomplexan, and oocysts from newly molted nymphs were infectious for a dog. Other nymphs from this cohort that were allowed to feed on a blood-parasite naive sheep molted normally; the resulting adult ticks contained oocysts that were infectious for another dog. Merogonic development of H. americanum in the dogs and the resulting lesions/disease appeared similar, irrespective of whether infectious oocysts were derived from nymphal or adult ticks that acquired infection as larvae. In the system previously known, nymphal ticks acquire infection and adults harbor infective oocysts, which vertebrate hosts ingest. Given that larval A. maculatum can acquire infection and nymphs can harbor viable oocysts as demonstrated by this study, the potential variety of vertebrate hosts that can alternate with GCTs in maintaining an endemic cycle is considerably expanded.  相似文献   

2.
Canine hepatozoonosis, caused by Hepatozoon americanum, is an emerging tick-borne disease of dogs in North America. In addition to the skeletal and cardiac myositis that are prominent features of the disease, there is disseminated periosteal bone proliferation in most dogs that manifest clinical disease. Each of six experimentally infected animals (four dogs and two coyotes) and seven of eight naturally infected dogs had gross or histopathologic osteoproliferative lesions. Experimental animals were 6-9 months of age when exposed. Naturally infected dogs were 8 months to 11 years old when subjected to necropsy. Lesions occurred primarily on the diaphysis of the more proximal long bones of the limbs; however, flat and irregular bones were frequently involved. Lesions involving metacarpals, metatarsals, and digits were infrequent. The earliest observed periosteal lesions were in an experimentally infected dog 32 days after exposure to sporulated oocysts of H. americanum. There were hypertrophy and hyperplasia of osteoprogenitor cells, and osteoblasts appeared in the cellular zone of the periosteum. Spicules of woven bone oriented perpendicularly to bone cortex followed. Later yet, periosteal new bone was remodeled and tended to become oriented parallel to the cortical bone. Horizontally oriented zones of remodeled, condensed bone sometimes occurred in multiple layers on the original cortex, forming "pseudocortices." The osseous lesions of American canine hepatozoonosis, with few variations, are remarkably similar to those of hypertrophic osteopathy in domestic dogs and other mammalian species, including humans.  相似文献   

3.
American canine hepatozoonosis is caused by Hepatozoon americanum, a protozoan parasite, the definitive host of which is the tick, Amblyomma maculatum. Infection of the dog follows ingestion of ticks that harbor sporulated H. americanum oocysts. Following penetration of the intestinal mucosa, sporozoites are disseminated systemically and give rise to extensive asexual multiplication in cells located predominantly in striated muscle. The parasitized canine cells in "onion skin" cysts and in granulomas situated within skeletal muscle, as well as those in peripheral blood leukocytes (PBL), were identified as macrophages by use of fine structure morphology and/or immunohistochemical reactivity with macrophage markers. Additionally, two basic morphologic forms of the parasite were observed in macrophages of granulomas and PBLs. The forms were presumptively identified as merozoites and gamonts. The presence of a "tail" in some gamonts in PBLs indicated differentiation toward microgametes. Recognition of merozoites in PBLs supports the contention that hematogenously redistributed merozoites initiate repeated asexual cycles and could explain persistence of infection for long periods in the vertebrate host. Failure to clearly demonstrate a host cell membrane defining a parasitophorous vacuole may indicate that the parasite actively penetrates the host cell membrane rather than being engulfed by the host cell, as is characteristic of some protozoans.  相似文献   

4.
American canine hepatozoonosis.   总被引：3，自引：0，他引：3  
Hepatozoon americanum infection is an emerging tickborne disease in the southern United States. This organism causes a very different and much more severe disease than does Hepatozoon canis, the etiologic agent of canine hepatozoonosis in the rest of the world. H americanum is transmitted through ingestion of the definitive host, Amblyomma maculatum (the Gulf Coast tick). Clinical signs of American canine hepatozoonosis tend to wax and wane over time and may include lameness, weakness, pain, muscle atrophy, fever, and mucopurulent ocular discharge. Radiographs typically reveal periosteal proliferation of various bones. Extreme leukocytosis is the most common laboratory finding, along with a mild elevation of serum alkaline phosphatase. Diagnosis is made by visualization of gamont-containing neutrophils or monocytes on examination of blood smears; observation of typical cysts, meronts or pyogranulomas on muscle biopsy; or detection of serum antibodies against H americanum sporozoites. Common complications of chronic infection include glomerulopathies, amyloidosis, and vasculitis. Although the prognosis for this disease in the past was guarded to poor, recent advances in treatment have increased the long-term survival rate of infected dogs.  相似文献   

5.
Canine hepatozoonosis caused by Hepatozoon americanum has periosteal proliferation on long bones, pelvis, vertebrae, and skull. The pathogenesis of the periosteal proliferation is unknown but may be similar to hypertrophic osteopathy. Objectives were to determine the time frame for onset of bone lesions, to characterize spatial distribution of early bone lesions, and to describe the scintigraphic appearance of bone lesions in six immature dogs infected with 400 H. americanum oocysts on day 0. 99mTc-MDP bone scintigraphy was performed before and after infection. The onset bone lesions noted using scintigraphy was before day 35/36 in three dogs, day 46 in one dog, day 53 in one dog, and between days 46 and 67 in one dog. Early bone lesions primarily occur proximal to the carpus/tarsus and on the axial skeleton. Bone lesions were diffuse, bilaterally symmetric, homogenous, high intensity regions of radiopharmaceutical uptake.  相似文献   

6.
The life cycles of filarioids of dogs presenting dermal microfilariae have been little studied. Following the recent retrieval of dermal microfilariae identified as Cercopithifilaria sp. in a dog from Sicily (Italy), this study was designed to assess the role of the brown dog tick Rhipicephalus sanguineus as an intermediate host of this filarial species. An experimental tick infestation was performed on an infected dog using 300 nymphs of R. sanguineus. Engorged nymphs were collected and examined by both microscopic dissection and molecular analysis at five time points (i.e., the same day of tick detachment and 10, 20, 30 and 50 days post-detachment) to detect the presence and developmental stage of filariae in the ticks. A total of 270 engorged nymphs were collected from the dog and developing filarioid larvae detected in 10 (5%) out of 200 ticks dissected. Infective third-stage larvae were observed in 4 (2%) of the all dissected ticks, 30 days post-detachment. Twelve (6.6%) out of 181 samples molecularly tested were positive for Cercopithifilaria sp. This study demonstrates that nymphs of R. sanguineus feeding on a dog naturally infected by Cercopithifilaria sp. can ingest microfilariae, which develop up to the third infective stage thus suggesting that this tick species might act as an intermediate host of this little known canine filarioid.  相似文献   

7.
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.  相似文献   

8.
Five laboratory studies were conducted to confirm that a single topical dose of the novel combination of fipronil, amitraz and (S)-methoprene, CERTIFECT? (Merial Limited, GA, USA), is efficacious for the rapid control of pre-existing infestations and the prevention of new infestations with Ixodes scapularis, Dermacentor variabilis, Amblyomma americanum and Amblyomma maculatum for at least 28 days on dogs. In each study, 8 male and 8 female purpose-bred, laboratory beagles were randomly assigned to one of two study groups (treated and untreated). Starting on the day before treatment, each dog was infested weekly with about 30 or 50 ticks, depending on the study. Treatment with the novel combination rapidly eliminated pre-existing infestations and controlled weekly re-infestations for at least 28 days. Pre-existing infestations with all four tick species were rapidly and effectively reduced, with post-treatment therapeutic efficacies ranging from 91.7 to 99.5% within 18-48 h post treatment. Amblyomma maculatum numbers were significantly (p<0.05) reduced on treated dogs from the first tick counts as early as 6h post-treatment. All subsequent infestations with each of the 4 tick species were quickly disrupted, with prophylactic efficacies greater than 90% within 18-48 h post-infestation for at least a full month. Because the combination of fipronil, amitraz and (S)-methoprene quickly starts disrupting and killing ixodid ticks within hours of treatment, with similar high levels of efficacy maintained for at least 28 days in these and other studies, the authors conclude that a single topical treatment with CERTIFECT may prevent the transmission of most infectious agents carried by ixodid ticks for at least one month.  相似文献   

9.
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.  相似文献   

10.
OBJECTIVE: To develop a method to experimentally induce Borrelia burgdorferi infection in young adult dogs. ANIMALS: 22 healthy Beagles. PROCEDURE: All dogs were verified to be free of borreliosis. Twenty 6-month-old dogs were exposed to Borrelia burgdorferi-infected adult ticks and treated with dexamethasone for 5 consecutive days. Two dogs not exposed to ticks were treated with dexamethasone and served as negative-control dogs. Clinical signs, results of microbial culture and polymerase chain reaction (PCR) testing, immunologic responses, and gross and histologic lesions were evaluated 9 months after tick exposure. RESULTS: Predominant clinical signs were episodic pyrexia and lameness in 12 of 20 dogs. Infection with B burgdorferi was detected in microbial cultures of skin biopsy specimens and various tissues obtained during necropsy in 19 of 20 dogs and in all 20 dogs by use of a PCR assay. All 20 exposed dogs seroconverted and developed chronic nonsuppurative arthritis. Three dogs also developed mild focal meningitis, 1 dog developed mild focal encephalitis, and 18 dogs developed perineuritis or rare neuritis. Control dogs were seronegative, had negative results for microbial culture and PCR testing, and did not develop lesions. CONCLUSIONS AND CLINICAL RELEVANCE: Use of this technique successfully induced borreliosis in young dogs. Dogs with experimentally induced borreliosis may be useful in evaluating vaccines, chemotherapeutic agents, and the pathogenesis of borreliosis-induced arthritis.  相似文献   

11.
This study evaluated the effectiveness of two topical spot-on formulations -- imidacloprid(8.8% w/w)-permethrin (44.0% w/w) and fipronil (9.8% w/w)-(S)-methoprene (8.8% w/w)--to repel, prevent the attachment of, and kill adult Ixodes scapularis and Amblyomma americanum on dogs. Twelve purpose-bred beagles were distributed into three groups of four dogs each; one group served as untreated controls, and each of the other two groups received one of the test products. Dogs were exposed to 25 adult ticks of each species for 10 minutes on posttreatment days 3, 7, 14, 21, and 28. Unattached or repelled ticks were collected and evaluated for viability, and on-dog tick counts were conducted at 3, 24, and 48 hours after tick exposure. The imidacloprid-permethrin formulation provided significant repellency against I. scapularis for up to 3 weeks after treatment, and both formulations provided good overall control of I. scapularis and A. americanum during the study period.  相似文献   

12.
Ehrlichia chaffeensis and Ehrlichia ewingii are agents of emerging human ehrlichioses in North America and are transmitted primarily by Amblyomma americanum ticks, while Ehrlichia canis is the globally distributed cause of canine monocytic ehrlichiosis (CME) and is transmitted by the brown dog tick, Rhipicephalus sanguineus. Although E. canis and Ehrlichia ruminantium are endemic in Africa, the presence of ehrlichial agents in dogs and ticks in Cameroon has not been investigated. The objective of this study was to determine the prevalence of ehrlichial infections in Cameronian dogs using a combination of serologic and molecular methods. Peripheral blood was collected, clinical signs and the presence or absence of ticks on dogs (n=104) presenting for various reasons at local veterinary clinics around the Mount Cameroon region were noted. IFA identified 33 dogs (32%) with antibodies reactive with E. canis, and reactivity of these sera with all major E. canis antigens (200, 140, 95, 75, 47, 36, 28, and 19-kDa) was confirmed by immunoblotting. Multicolor real-time PCR detected ehrlichial DNA (E. canis (15) and E. ewingii (2)) in 17 dogs (16.3%), all of which had attached ticks at time of presentation. The dsb amplicons (378 bp) from E. canis and E. ewingii were identical to gene sequences from North American isolates. This study identifies canine ehrlichiosis as a prevalent unrecognized cause of disease in Cameroonian canines.  相似文献   

13.
Neospora caninum is widely distributed in the world and this parasite is one of the major causes of abortion in cattle. Dogs and coyotes are definitive hosts of N. caninum and several species of domestic and wild animals are intermediate hosts. Dogs can become infected by the ingestion of tissues containing cysts and then excrete oocysts. It is not yet known whether sporulated oocysts are able to induce a patent infection in dogs, i.e. a shedding of N. caninum oocysts in feces. The objective of this study was to experimentally examine the infection of dogs by sporulated oocysts. The oocysts used in the experiment were obtained by feeding dogs with brain of buffaloes (Bubalus bubalis) positive for anti-N. caninum antibodies by indirect fluorescent antibody test (IFAT ≥200). Oocysts shed by these dogs were confirmed to be N. caninum by molecular methods and by bioassay in gerbils, and sporulated N. caninum oocysts were used for the oral infection of four dogs. The dogs were 8 weeks old and negative for antibodies to N. caninum and Toxoplasma gondii. Dogs 1 and 4 received an inoculum of 10,000 sporulated oocysts each; dog 2 an inoculum of 5000 sporulated oocysts and dog 3 received 1000 sporulated oocysts of N. caninum. The total feces excreted by these dogs were collected and examined daily for a period of 30 days. No oocysts were found in their feces. The dogs were monitored monthly for a 6-month period to observe a possible seroconversion and when this occurred the animals were eliminated from the experiment. Dogs 1 and 4 seroconverted 1 month after the infection with titer, in the IFAT, of 1600 and 800, respectively; the other two dogs presented no seroconvertion during the 6-month period. Dogs 1 and 2 were euthanized 180 days after infection and were examined for the detection of N. caninum in tissues (brain, muscle, lymph node, liver, lung, heart and bone marrow) by immunohistochemistry and PCR with negative results in both techniques. Bioassay in gerbils with brain of these dogs was also performed and again the results were negative. In conclusion, dogs infected with sporulated oocysts of N. caninum were not able to shed oocysts in feces. However, a higher dose of infection stimulated the production of antibodies against N. caninum in the dogs.  相似文献   

14.
Transstadial transmission of granulocytic Ehrlichieae in dogs was attempted using ticks, Amblyomma americanum and Dermacentor variabilis. Ticks were exposed by feeding as nymphs on acutely infected pups; adult ticks then fed to repletion on susceptible adult dogs that were monitored daily for signs of infection. Evidence of transmission was not observed in control dogs or in those exposed to D variabilis. In contrast, dogs exposed to A americanum developed serologic or clinical evidence of infection, but organisms were not seen in blood smears until corticosteroids were administered, causing recrudescence and accompanying parasitemia. At 12 days after subinoculation of blood obtained from donor adult dogs, before corticosteroids were administered, a febrile response, thrombocytopenia, and appearance of morulae in neutrophilic granulocytes were observed in 2 susceptible recipient dogs.  相似文献   

15.
A survey was carried out to investigate the occurrence of hard tick species (Acari: Ixodidae) infesting domestic dogs in Hungary. Forty veterinary clinics from a wide geographical area were asked to collect hard ticks from dogs and to complete a questionnaire. In total, 25 veterinary clinics submitted 900 ticks from 310 dogs. Intensity of infestation ranged from one to 78 per dog. The most preferred sites of tick attachment in decreasing order were head, neck and legs. The majority of ticks (91.7%) were adults, which were identified to species level, the others were nymphs. Six species were found: Dermacentor reticulatus (48.9%), Ixodes ricinus (43.2%), Ixodes canisuga (5.6%), Haemaphysalis concinna (2%) and there was one specimen of both Dermacentor marginatus and Ixodes hexagonus. Single species infestation with I. ricinus or D. reticulatus was found on 145 (46.8%) and 120 animals (38.7%), respectively. Mixed infestation caused by these two species was detected on 24 dogs (7.7%). I. canisuga and H. concinna were found on seven and five dogs, respectively. D. reticulatus and I. ricinus were collected almost throughout the year, except for a single month. The activity peaks were in spring and in autumn for both species. Based on clinical signs, canine babesiosis was diagnosed by the veterinarians in 66 (21.3%) tick infested dogs. These dogs were more frequently infested with D. reticulatus than the others. Our data contribute to the understanding of geographical and seasonal distribution of ixodid tick species infesting dogs in Hungary. The implication of these data, for the risk of canine tick borne diseases is discussed.  相似文献   

16.
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.  相似文献   

17.
This study was initiated to determine the degree of susceptibility of dogs to virulent and nonvirulent spotted fever-group rickettsiae and to evaluate dogs as sources of infection for ticks. Dogs were exposed either by inoculation (syringe) or by infective tick bite to the following rickettsial serotypes: (1) Rickettsia rickettsii (Wachsmuth and Sawtooth female 2 strains), (2) R montana (M/5-6 B strain), and (3) R rhipicephali (3-7-female 6 strain). Results indicated that dogs inoculated with 1,000 or 10,000 egg infective doses of virulent R rickettsii developed a rickettsemia that was detectable as early as 4 days after inoculation to as late as 10 days. Conversely, none of the dogs inoculated with R montana (M/5-6 B) or R rhipicephali (3-7-female 6) or exposed to ticks infected with these strains developed detectable rickettsemia, fever, or other observable clinical signs. None of the 394 ticks that fed on rickettsemic dogs (R rickettsii) infected by inoculation became infected, and only 3 of 348 ticks (0.9% infection rate) were infected after feeding on dogs which had been infected by tick bite. All ticks fed on dogs exposed to R rhipicephali and R montana were shown to be free of rickettsiae. The largest concentrations of plaque-forming units (PFU) in Vero cell culture from undiluted whole blood were found on day 6 and on day 7 in dogs that were inoculated with 10,000 and 1,000 R rickettsii, respectively, of the Sawtooth female 2 strain. The highest rickettsial concentration observed for the dog infected by tick feeding was on day 9.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

18.
We report previously undescribed, early lesions in skeletal muscle of dogs experimentally infected with Hepatozoon americanum by ingestion of laboratory-reared, infected Amblyomma maculatum. The earliest muscle lesion was recognized at the first interval of examination 3 weeks following exposure. The lesion consisted of a large, modified host cell whose cytoplasm frequently contained a demonstrable parasite. In skeletal muscle, the cell was consistently located between muscle fibers or in loose connective tissue adjacent to those fibers. Evidence suggesting that the parasite arrives in muscle and other tissue within the host cell cytoplasm is presented. Mucopolysaccharide encystment of the host cell, absent at this early stage, was acquired gradually and approached maximal development 26 weeks post exposure. Completion of the asexual cycle as evidenced by the presence of parasites entering vascular lumens within granulomas and also by the presence of gamonts in peripheral blood leukocytes, occurred within 28-32 days postexposure. Progression of the parasite cycle from meront to passage of zoites into vessel lumens of granulomas can occur in 11 or fewer days. The density with which parasitic lesions occur in one named skeletal muscle compared to other named muscles, although somewhat variable, was not significantly different in either experimentally induced or natural infections. The distribution of developmental stages of the parasite/lesion in four experimental infections (969 lesions) is compared with those in eight dogs with natural infections (557 lesions).  相似文献   

19.
Healthy, purpose-bred laboratory beagle dogs that had not been exposed to ticks and were seronegative for Borrelia burgdorferi and Anaplasma phagocytophilum were randomly assigned to four groups of eight dogs each. Control group 1 was not treated. Groups 2, 3 and 4 were treated with a single topical application of a new formulation of fipronil, amitraz and (S)-methoprene (CERTIFECT?, Merial Limited, GA, USA) at 28, 21 or 14 days prior to tick infestation, respectively. Each dog was infested with 25 female and 25 male field-collected adult Ixodes scapularis ticks that had infection rates of 66% for B. burgdorferi sensu stricto and 23% for A. phagocytophilum, as determined by polymerase chain reaction. Two and five days after tick infestation, control dogs had an average of 9.5 and 13.9 attached adult female ticks, respectively, whilst the 24 treated dogs remained tick-free aside from a single tick on the 2nd day after infestation. Serial serological tests demonstrated that the ticks successfully infected 8/8 control dogs with B. burgdorferi and co-infected 6/8 with A. phagocytophilum. B. burgdorferi infection also was confirmed in most control dogs by culture (6/8) and PCR (7/8) of skin biopsies. In contrast, CERTIFECT protected all 24 treated dogs against infection by both B. burgdorferi and A. phagocytophilum, as demonstrated by their negative serological tests throughout the study and the absence of any positive skin biopsy culture or PCR in these dogs.  相似文献   

20.
Rocky Mountain spotted fever   总被引：1，自引：0，他引：1  
Rocky Mountain spotted fever is an endemic tickborne disease found throughout the United States and other regions of the world. Exposure may result in a spectrum of disease from subclinical infection to severe or fatal multiorgan collapse. The disease is maintained in nature in Ixodid tick vectors and their hosts. The most important ticks in the United States are Dermacentor variabilis and Dermacentor andersoni. Small mammals are the natural reservoirs in the wild. Dogs become infected when a tick harboring Rickettsia rickettsii feeds on the dog. Dogs do not develop sufficient rickettsemia to act as a reservoir in the transmission of Rickettsia rickettsii. Thus, although dogs act as sentinels to the presence of the disease, they cannot directly transmit infection. Signs in early stages of disease often are nonspecific. The most characteristic laboratory abnormality is thrombocytopenia, but serologic testing is necessary for confirmation of infection. Tetracycline and chloramphenicol are effective antibiotics to treat infection. Treatment should continue for 14 to 21 days to allow host immune defenses to develop and eradicate the organism. Prevention requires avoidance of tick-infested areas and rapid removal of ticks should exposure occur.  相似文献   

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