Experimental Ehrlichia canis infection in the dog does not cause immunosuppression

A carrier state develops in some Ehrlichia canis-infected dogs due to ineffective host defenses. The subsequent development of immune-mediated diseases or opportunistic infections in chronic ehrlichiosis suggests dysregulation of immunity; however, the immunobiology of this infection has not been well characterized. In this study, eight dogs were infected with E. canis, and changes in seroreactivity, serum immunoglobulin (Ig) concentrations, peripheral blood T cell subsets, lymphocyte blastogenesis (LBT), and lymphokine-activated killer (LAK) activity were evaluated over 4 months. Infection, which was documented by seroconversion, polymerase chain reaction, and blood culture, caused self-limiting fever and thrombocytopenia. Infected dogs developed an anti-E. canis antibody response but were not immune to re-infection. Serum IgM, IgG, and IgA concentrations were unaffected by E. canis. The percentage of circulating CD4(+) T cells was similar in uninfected and infected dogs at all points. Infected dogs developed a CD8(+) lymphocytosis 6 weeks after inoculation that subsequently subsided, despite organism persistence. Functional defects of cell-mediated immunity, measured as suppression of LAK activity or mitogen-driven LBT, were not observed. These results suggest that immune responses are not grossly impaired in young dogs during the first several months following experimental E. canis infection.     

Development and evaluation of a PCR assay for the detection of Cytauxzoon felis DNA in feline blood samples

Cytauxzoonosis is an emerging tick borne infectious disease of domestic cats in the United States, caused by the organism Cytauxzoon felis (C. felis). In naturally infected domestic cats the disease is almost always fatal. Currently there are no commercially available molecular or serologic tests to facilitate the antemortem diagnosis of C. felis infection. Clinical and pathological diagnosis of cytauxzoonosis is based on microscopic identification of parasites in tissues or on blood smears. We have developed and evaluated the sensitivity and specificity of a polymerase chain reaction (PCR) based assay for the diagnosis of C. felis infections in feline blood samples. The assay is sensitive enough to detect one copy of a cloned fragment of the C. felis 18S rRNA gene. This PCR assay can be used for the rapid clinical diagnosis of cytauxzoonosis and for epidemiological studies that will better define the geographic distribution of C. felis infection in cats.     

Comparison of an indirect immunofluorescence assay, western blot analysis, and a commercially available ELISA for detection of Ehrlichia canis antibodies in canine sera

OBJECTIVE: To examine the correlation between results for an indirect immunofluorescence assay (IFA) that uses Ehrlichia canis antigen as a substrate (ie, E canis-IFA), 2 western blot (WB) analyses, and a commercially available ELISA in the detection of E canis antibody in dog sera. SAMPLE POPULATION: 54 canine serum samples that were reactive on E canis-IFA and 16 canine serum samples that were E canis-IFA nonreactive. PROCEDURE: Serum samples were evaluated by use of 2 WB analyses and a commercially available ELISA. Correlation between results of the 3 testing modalities (ie, IFA, WB analyses, and the ELISA) was examined by use of nonreactive (E canis-IFA reciprocal titer, < 20), low-titer (reciprocal titer, 80 to 160), medium-titer (reciprocal titer, 320 to 2,560), and high-titer (reciprocal titer, 5,120 to > 20,480) serum samples. RESULTS: For all serum samples in the nonreactive (n = 16), medium-titer (17), and high-titer (18) groups, correlation of results among IFA, WB analyses, and the commercially available ELISA was excellent. A poor correlation was found between IFA results and those of WB analyses and the ELISA for serum samples in the low-titer group (19), with only 4 of the 19 serum samples having positive results on both WB analyses and the commercially available ELISA. CONCLUSIONS AND CLINICAL RELEVANCE: The discrepancy between E canis-IFA, WB analyses, and the commercially available ELISA results for the low-titer serum samples may be related to a high IFA sensitivity or, more likely, a lack of specificity associated with cross-reactivity among Ehrlichia spp.     

Prevalence of Bartonella species antibodies and Bartonella species DNA in the blood of cats with and without fever

The purpose of this study was to determine whether there are associations between Bartonella species antibody (enzyme-linked immunosorbent assay (ELISA) and Western blot (WB)) and polymerase chain reaction assay results in cats with and without fever. Afebrile control cats (39/93; 42.0%) were more likely to have Bartonella species antibodies than cats with fever (29/93; 31.2%). The difference in prevalence of Bartonella species deoxyribonucleic acid (DNA) in blood of cats with fever (14/81; 17.3%) as compared to afebrile control cats (6/81; 7.4%) approached statistical significance (P=0.0571). Bartonella species ELISA or WB results frequently did not correlate to the presence or absence of Bartonella species DNA in blood. The results of this study indicate that in cats, Bartonella species antibody tests cannot predict whether fever is due to Bartonella species infection and should not be used to determine the Bartonella species infection status.     

Vascular permeability and coagulation during Rickettsia rickettsii infection in dogs

The vascular permeability of the ocular fundus, alterations in the coagulation system, and plasma concentrations of thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) were studied in dogs following intradermal inoculation with 5 x 10(5) TCID50 of Rickettsia rickettsii. Twenty-four to 48 hours after the onset of fever and rickettsemia, multifocal areas of retinal vasculitis were evident, which corresponded to areas of altered vascular permeability demonstrated by fluorescein angiography. The number and intensity of retinal vessels with sodium fluorescein leakage peaked during the second week after inoculation, and retinal vascular permeability remained altered during the third week of infection, well past the phase of clinical and clinicopathologic recovery. Development of retinal vasculitic foci was associated with thrombocytopenia, increased concentrations of circulating fibrinogen, and slight prolongation of activated partial thromboplastin time. Increased concentrations of fibrin/fibrinogen degradation products were detected in 4 of 9 dogs. Despite the degree of vascular endothelial damage evident on fluorescein angiographic and histologic studies in these dogs, plasma TXB2 and 6-keto-PGF1 alpha concentrations were not increased.     

Monoclonal Gammopathy Associated With Naturally Occurring Canine Ehrlichiosis

Clinical, hematologic, and immunologic findings for 14 dogs with Ehrlichia canis monoclonal gammopathy were studied retrospectively. Epistaxis, anemia, thrombocytopenia, hypoalbuminemia, hypergammaglobulinemia, and proteinuria were documented in the majority of these dogs. The serum protein electrophoresis pattern was characterized by a distinct narrow-base monoclonal spike, by a broad-base monoclonal spike, or by a monoclonal spike superimposed on a polyclonal gammopathy. The monoclonal spike disappeared following tetracycline treatment for ehrlichiosis. The long-term prognosis following treatment was generally good. The diagnostic features of monoclonal gammopathy due to myeloma were compared with those of E. canis monoclonal gammopathy. Owing to numerous similarities in clinical, hematologic, and immunologic findings, we conclude that an E. canis antibody titer should be determined in all dogs in which a diagnosis of benign monoclonal gammopathy is contemplated or definitive evidence of myeloma, leukemia, or macroglobulinemia is lacking.     

Bartonella spp. DNA in cardiac tissues from dogs in Colorado and Wyoming

Background: Several Bartonella species (spp.) have been identified in dogs diagnosed with infectious endocarditis (IE) or myocarditis. Objective: To interrogate cardiac tissues of dogs with suspected IE for the presence of Bartonella spp. DNA of dogs in the Rocky Mountain states. Animals: Nine dogs with a clinical diagnosis of endocarditis from January 1990 to June 2008 were included. Methods: In this retrospective study, medical records at the Veterinary Teaching Hospital were searched. Animals were excluded if there was no diagnosis of IE in the original necropsy report. Paraffin embedded tissue blocks and medical records were available from 9 dogs. Total DNA was extracted from the cardiac tissues and assessed for Bartonella spp. DNA by 3 polymerase chain reaction (PCR) methods. For positive samples, the Bartonella spp. were determined by genetic sequencing or fluorogenic real‐time PCR. Results: Bartonella henselae DNA was amplified from the tissues of 7 dogs; Bartonella vinsonii subsp berkhoffii DNA was amplified concurrently from 3 dogs. Six dogs were from Colorado and 1 was from Wyoming. Flea or tick infestations were reported in 2 dogs. Conclusions and Clinical Importance: Bartonella spp. should be on the differential list for dogs in the Rocky Mountain states. The results emphasize the need for routine use of external parasite control products even in regions perceived to have low risk for flea and tick infestations.