Antibodies to Ehrlichia canis, Ehrlichia platys, and spotted fever group rickettsiae in Louisiana dogs

Development of a Multiplex PCR and Magnetic DNA Capture Assay for Detecting Six Species Pathogens of the Genera Anaplasma and Ehrlichia in Canine, Bovine, Caprine and Ovine Blood Samples from Grenada, West Indies

Infections with tick-borne pathogens belonging to Anaplasma/Ehrlichia in various vertebrate hosts are a persistent problem resulting in nonspecific clinical signs during early infection. Diagnosis of single and multi-infections with these pathogens, causing diseases in companion/agricultural animals and people, remains a challenge. Traditional methods of diagnosis, such as microscopy and serology, have low sensitivity and specificity. Polymerase chain reaction (PCR) assays are widely used to detect early-phase infections, since these have high sensitivity and specificity. We report the development and validation of an assay involving PCR followed by magnetic capture method using species-specific oligonucleotides to detect six Anaplasma/Ehrlichia species pathogens in canine, bovine, caprine, and ovine blood samples. Overall, the assay application to 455 samples detected 30.1% (137/455) positives for one or more out of six screened pathogens. Single-pathogen infections were observed in 94.9% (130/137) of the positive samples, while co-infections were detected in 5.1% (7/137). Anaplasma marginale infection in cattle had the highest detection rate (34.4%), followed by canines positive for Anaplasma platys (16.4%) and Ehrlichia canis (13.9%). The assay aided in documenting the first molecular evidence for A. marginale in cattle and small ruminants and Ehrlichia chaffeensis and Ehrlichia ewingii in dogs in the Caribbean island of Grenada.

Sensitivity and specificity levels of two rapid assays for antibodies to Anaplasma spp. in dogs

Canine anaplasmosis is a tick-borne disease of dogs that results following infection with Anaplasma phagocytophilum or Anaplasma platys. The SNAP 4Dx Plus test (IDEXX Laboratories) and the VetScan Canine Anaplasma Rapid test (Abaxis) are commercial in-house rapid tests for the detection of antibody to these 2 antigenically related Anaplasma species. We evaluated 2 tests using serum and whole blood samples obtained from reference laboratories and veterinary hospitals. Samples were obtained from regions of the country known to be habitats of the primary tick vectors. The A. phagocytophilum sample set comprised 236 dog sera from the northeastern and midwestern United States; the A. platys sample set comprised 179 sera from dogs living in the southwestern United States. An indirect immunofluorescent antibody (IFA) test and an A. platys species-specific ELISA were used as reference assays for the A. phagocytophilum and A. platys samples, respectively. The SNAP test demonstrated significantly higher sensitivity (84.7% for A. phagocytophilum and 83.1% for A. platys), compared to the VetScan test (39.0% for A. phagocytophilum and 57.6% for A. platys). The specificity of the SNAP test (95.8% for A. phagocytophilum and 99.2% for A. platys) was significantly greater than the VetScan test (85.6% for A. phagocytophilum and 82.5% for A. platys). In a separate clinic study, conducted within an A. phagocytophilum-endemic state (Minnesota) using 154 whole blood samples from client-owned dogs, the VetScan test was negative for 22 of 39 SNAP and IFA seropositive samples.

Anaplasma platys Immunoblot Test Using Major Surface Antigens

Anaplasma platys is an uncultivable tick-borne obligatory intracellular bacterium, which is known to infect platelets of dogs. A. platys causes infectious canine cyclic thrombocytopenia in subtropical and tropical regions throughout the world. Several cases of human infection with A. platys infection have also been reported. However, seroprevalence of A. platys exposure and infection has not been determined in most of the regions, in part, due to lack of a simple and reliable assay method. Furthermore, A. platys antigens recognized by dogs are unknown. We previously sequenced gene encoding A. platys major outer membrane proteins P44 and Omp-1X. In the present study, we obtained purified recombinant A. platys P44 and Omp-1X proteins, and using them as antigens in immunoblotting examined seroreactivity in dogs. Of 34 specimens from Venezuela where A. platys infection was previously reported, 25 specimens (73.5%) reacted to rAplP44 and/or rAplOMP-1X. Neither Anaplasma phagocytophilum-seropositive (N = 10) nor A. phagocytophilum-seronegative canine specimens (N = 10) from the geographic regions where A. platys infection has never been reported, reacted rAplP44 or rAplOMP-1X. The result indicates a high A. platys seroprevalence rate in tested dogs from Venezuela and suggests that the immunoblot analysis based on recombinant A. platys major outer membrane proteins can provide a simple and defined tool to enlighten the prevalence of A. platys infection.

Host surveys, ixodid tick biology and transmission scenarios as related to the tick-borne pathogen, Ehrlichia canis

The ehrlichioses have been subject to increasing interest from veterinary and public health perspectives, but experimental studies of these diseases and their etiologic agents can be challenging. Ehrlichia canis, the primary etiologic agent of canine monocytic ehrlichiosis, is relatively well characterized and offers unique advantages and opportunities to study interactions between a monocytotropic pathogen and both its vertebrate and invertebrate hosts. Historically, advances in tick-borne disease control strategies have typically followed explication of tick-pathogen-vertebrate interactions, thus it is reasonable to expect novel, more sustainable approaches to control of these diseases as the transmission of their associated infections are investigated at the molecular through ecological levels. Better understanding of the interactions between E. canis and its canine and tick hosts would also elucidate similar interactions for other Ehrlichia species as well as the potential roles of canine sentinels, reservoirs and models of tick-borne zoonoses. This article summarizes natural exposure studies and experimental investigations of E. canis in the context of what is understood about biological vectors of tick-borne Anaplasmataceae.

Serologic evidence for exposure to Rickettsia rickettsii in eastern Arizona and recent emergence of Rocky Mountain spotted fever in this region

During 2002 through 2004, 15 patients with Rocky Mountain spotted fever (RMSF) were identified in a rural community in Arizona where the disease had not been previously reported. The outbreak was associated with Rickettsia rickettsii in an unexpected tick vector, the brown dog tick (Rhipicephalus sanguineus), which had not been previously associated with RMSF transmission in the United States. We investigated the extent of exposure to R. rickettsii in the local area through serologic evaluations of children and dogs in 2003-2004, and in canine sera from 1996. Antibodies to R. rickettsii at titers > or = 32 were detected in 10% of children and 70% of dogs in the outbreak community and 16% of children and 57% of dogs in a neighboring community. In comparison, only 5% of canine samples from 1996 had anti-R. rickettsii antibodies at titers > or = 32. These results suggest that exposures to RMSF have increased over the past 9 years, and that RMSF may now be endemic in this region.

PCR detection of Anaplasma platys in blood and tissue of dogs during acute phase of experimental infection

Four dogs were experimentally infected with Anaplasma platys to determine changes in real-time TaqMan PCR detection in blood and tissue, microscopically detectable parasitemia, and platelet concentrations during the first 28 days of infection. Buffy-coat blood cells were PCR positive for A. platys DNA at 4 days after inoculation and remained positive in all dogs until day 14. Marked thrombocytopenia and low parasitemia occurred in dogs during that initial period. During 17 and 28 days post-inoculation, the PCR results on buffy-coat blood cells were intermittently negative in each dog with marked thrombocytopenia and no microscopic evidence of parasitemia. Bone marrow and splenic aspirates collected from the A. platys-infected dogs were tested by real-time TaqMan PCR. Two dogs were PCR positive in spleen and marrow at 28 days post-inoculation, when PCR results for buffy-coat blood cells were negative. Spleen and/or bone marrow samples should be considered as additional samples for PCR testing of dogs, particularly when blood samples are PCR negative during the acute phase of A. platys infection.

Multiplex Detection of Ehrlichia and Anaplasma Pathogens in Vertebrate and Tick Hosts by Real-Time RT-PCR

Tick-borne rickettsial infections are responsible for many emerging diseases in humans and several vertebrates. These include human infections with Ehrlichia chaffeensis, Ehrlichia ewingii and Anaplasma phagocytophilum. As single or co-infections can result from a tick bite, the availability of a rapid, multiplex molecular test will be valuable for timely diagnosis and treatment. We recently described a muliplex-molecular test that can detect single or co-infections with up to five Ehrlichia and Anaplasma species. We reported that the test has the sensitivity to identify single infections in the canine host with E. chaffeensis, E. canis, E. ewingii, A. phagocytophilum, and A. platys and co-infection with E. canis and A. platys. In this study, ticks were collected from different parts of the state of Kansas during summer months of the year 2003 and tested for the presence of infection using the molecular test. The analysis revealed a minimum of 3.66% of the ticks to be positive for either E. chaffeensis or E. ewingii in A. americanum and Dermacenter species. This assay will be valuable in monitoring infections in dogs and ticks, and with minor modifications it can be used for diagnosing infections in people and other vertebrates.

Multiplex detection of Ehrlichia and Anaplasma species pathogens in peripheral blood by real-time reverse transcriptase-polymerase chain reaction

Tick-borne infections are responsible for many emerging diseases in humans and several vertebrates. These include human infections with Anaplasma phagocytophilum, Ehrlichia chaffeensis, and Ehrlichia ewingii. Because single or co-infections can result from tick bites, the availability of a rapid, multiplex molecular test will be valuable for timely diagnosis and treatment. Here, we describe a multiplex molecular test that can detect single or co-infections with up to five Ehrlichia and Anaplasma species. The test protocol includes the magnetic capture-based purification of 16S ribosomal RNA, its enrichment, and specific-pathogen(s) detection by real-time reverse transcriptase-polymerase chain reaction. We also report a unique cloning strategy to develop positive controls in the absence of a pathogen's genomic DNA. The test was assessed by examining blood samples from dogs suspected to be positive for ehrlichiosis. The dog was chosen as the model system because it is susceptible to acquire infections with up to five pathogens of the genera Ehrlichia and Anaplasma. The test identified single infections in the canine host with E. chaffeensis, E. canis, E. ewingii, A. phagocytophilum, and A. platys and co-infection with E. canis and A. platys. The multipathogen detection and novel positive control development procedures described here will be valuable in monitoring infections in people, other vertebrates, and ticks.

Serologic evidence of Rickettsia akari infection among dogs in a metropolitan city

OBJECTIVE

To determine whether dogs in New York, NY are naturally infected with Rickettsia akari, the causative agent of rickettsialpox in humans.

DESIGN

Serologic survey.

ANIMALS

311 dogs.

PROCEDURE

Serum samples were obtained from dogs as a part of a study on Rocky Mountain spotted fever and borreliosis or when dogs were examined at area veterinary clinics for routine care. Dog owners were asked to complete a questionnaire inquiring about possible risk factors at the time serum samples were obtained. Samples were tested for reactivity to spotted fever group rickettsiae by use of an enzyme immunoassay (EIA). Twenty-two samples for which results were positive were tested by use of an indirect immunofluorescence antibody (IFA) assay followed by confirmatory cross-absorption testing.

RESULTS

Results of the EIA were positive for 24 (7.7%) dogs. A history of tick infestation and increasing age were significantly associated with whether dogs were seropositive. Distribution of seropositive dogs was focal. Seventeen of the 22 samples submitted for IFA testing had titers to R rickettsii and R akari; for 11 of these, titers to R akari were higher than titers to R rickettsii. Cross-absorption testing indicated that in 6 of 7 samples, infection was caused by R akari.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that dogs can be naturally infected with R akari. Further studies are needed to determine the incidence of R akari infection in dogs, whether infection is associated with clinical illness, and whether dogs can serve as sentinels for human disease.

Ancillary diagnostic techniques for the lame patient

The cause of lameness is usually identified through evaluation of signalment, history, and physical examination. Radiographic evaluation provides a definitive diagnosis in many cases; however, laboratory evaluation may prove useful in the characterization of certain conditions or in the prognostication of the condition. In some instances where the definitive diagnosis remains elusive, arthroscopic examination is a minimally invasive diagnostic tool that may be more affordable and available than computed tomography. This article reviews laboratory evaluation of the lame patient and arthroscopic evaluation of joint abnormalities.

Post-therapy antibody titers in dogs with ehrlichiosis: follow-up study on 68 patients treated primarily with tetracycline and/or doxycycline

The clinical and serological responses to therapy were evaluated for at least 1 year in 68 dogs with antibody titers positive for Ehrlichia canis. Treatments were of variable periods with primarily tetracycline hydorchloride and/or doxycycline. Sixteen dogs had initial titers of 1:20 and, at the end of the year, were asymptomatic, no longer receiving medication, and had negative serology. The average length of treatment with tetracycline HCl and/or doxycycline was 85 days (range, 14 to 360 days). Of 39 dogs with initial titers of 1:2,560 or greater, 1 died, 25 were asymptomatic, and 13 were lost to follow-up at the end of the study. The average length of treatment was 210 days (range, 21 to 630 days). Twenty-seven dogs were seropositive at > or = 1:2,560 when the sera was last tested. Thirteen dogs had initial titers of 1:80 to 1:1,280. Of these 13 dogs, 2 died, 2 were lost to follow-up, and 9 were asymptomatic and had titers ranging from negative to > or = 1:2,560 at the end of the study. The persistence of antibodies, prolonged subclinical phase, and delayed relapses despite long-term medication, suggest inadequate chemotherapeutic agents or may be natural features of latency of ehrlichiosis in dogs.

Serologic evidence of canine and equine ehrlichiosis in northeastern United States

In a retrospective study, indirect fluorescent-antibody staining methods were used to detect immunoglobulins to Ehrlichia canis and Ehrlichia risticii in canine and equine sera that had originally been analyzed for antibodies to Borrelia burgdorferi. Analyses of 60 dog serum specimens collected in Connecticut and New York State during 1986 revealed antibodies to E. canis in 7 (11.7%) specimens; titration endpoints ranged from 1:40 to 1:320. Three of these dogs had anemia. Of the 187 equine serum specimens obtained in Connecticut during 1985 and analyzed by indirect fluorescent-antibody staining methods, 17 (9.1%) contained antibodies to E. risticii. Maximal antibody titers of 1:1,280 were recorded for serum specimens collected from three equids during May and July. We conclude that canine and equine ehrlichiosis coexist with Lyme borreliosis in Connecticut and the lower Hudson River Valley of New York State.

The tribe Ehrlichieae and ehrlichial diseases

The tribe Ehrlichieae consists of gram-negative minute cocci that are obligate intracellular parasites classified in the family Rickettsiaceae. Although ehrlichial organisms have been observed in leukocytes for many years, only a few species have been cultured in quantities sufficient for biochemical and molecular analyses. Recents studies on 16S-rRNA sequence analysis and energy metabolism showed that the genus Ehrlichia is closely related to the genus Rickettsia. There is, however, no antigenic cross-reactivity between these genera. Ehrlichial organisms cause a disease called "ehrlichiosis," a noncontagious infectious disease known to be transmitted by a tick in several cases and by a fluke in one case. Ehrlichia spp. infect dogs, ruminants, horses, and humans. Recently, two new ehrlichial diseases, Potomac horse fever and human ehrlichiosis, were discovered in the United States. The etiologic agent of Potomac horse fever, Ehrlichia risticii, is closely related to the known human pathogen Ehrlichia sennetsu. The etiologic agent of human ehrlichiosis is related to Ehrlichia canis, a canine pathogen. In contrast to the genus Rickettsia, members of the tribe Ehrlichieae reside primarily in the cytoplasmic vacuoles of monocytes or granulocytes and cause hematologic abnormalities, lymphadenopathy, and other pathologic changes in the host. However, the actual mechanisms whereby Ehrlichia spp. infect leukocytes, multiply in them, and produce various forms of systemic disease have not been defined. Depending on the ehrlichial species involved, serologic or direct microscopic observation of stained blood smears is currently used to diagnose ehrlichial disease.

Ehrlichial diseases of dogs

Ehrlichial diseases of dogs currently are recognized to be caused by Ehrlichia canis, Ehrlichia platys, Ehrlichia equi, and Ehrlichia risticii. Information on each disease's history, transmission, pathogenesis, clinicopathologic findings, diagnosis, therapy, and prevention is presented in this article. Ehrlichia canis is the most common cause of clinical illness. Case reports are included to illustrate common presentations of Ehrlichia canis infections.

Platelets and coagulation

Hemostasis is a multiple-component system. In order to function properly it has become highly integrated with several strategies of control. Failure of the system or its control can result in life-threatening hemorrhage requiring transfusion. It is hoped that the information provided in this article has enhanced the reader's understanding of hemostasis in animals, and will enable the reader to make a more educated choice concerning transfusion therapy for the bleeding patient.

Rocky Mountain spotted fever

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.