Immunopathology of Bartonella vinsonii (berkhoffii) in experimentally infected dogs.

Following natural infection with Bartonella, dogs and humans develop comparable disease manifestations including endocarditis, peliosis hepatis, and granulomatous disease. As the immunologic response to infection in these hosts has not been clearly established, data presented here was derived from the experimental infection of six specific pathogen free (SPF) beagles with a known pathogenic strain of Bartonella. Six dogs were inoculated intravenously with 10(9)cfu of B. vinsonii ssp. berkhoffii and six control dogs were injected intravenously with an equivalent volume of sterile saline. Despite production of substantial levels of specific antibody, blood culture and molecular analyses indicated that Bartonella established chronic infection in these dogs. Flow cytometric analysis of monocytes indicated impaired bacterial phagocytosis during chronic Bartonella infection. There was also a sustained decrease in the percentage of CD8+ lymphocytes in the peripheral blood. Moreover, modulation of adhesion molecule expression (downregulation of L-selectin, VLA-4, and LFA-1) on CD8+ lymphocytes suggested quantitative and qualitative impairment of this cell subset in Bartonella-infected dogs. When compared with control dogs, flow cytometric analysis of lymph node (LN) cells from B. vinsonii infected dogs revealed an expanded population of CD4+ T cells with an apparent naïve phenotype (CD45RA+/CD62L+/CD49D(dim)). However, fewer B cells from infected dogs expressed cell-surface MHC II, implicating impaired antigen presentation to helper T cells within LN. Taken together, results from this study indicate that B. vinsonii establishes chronic infection in dogs which may result in immune suppression characterized by defects in monocytic phagocytosis, an impaired subset of CD8+ T lymphocytes, and impaired antigen presentation within LN.

Cyclic CD8+ lymphopenia in dogs experimentally infected with Bartonella vinsonii subsp. berkhoffii.

Until recently, it was presumed that Bartonella vinsonii only infected voles, a species of North American rodents. In April of 1993, however, our laboratory isolated a novel subspecies of B. vinsonii (B. vinsonii subsp. berkhoffii) from the blood of a dog diagnosed with vegetative valvular endocarditis. Subsequently, based on a seroepidemiologic survey of dogs from North Carolina and Virginia presenting for a variety of medical problems, we found evidence supporting a potentially important association between B. vinsonii and Ehrlichia canis co-infection in dogs. In the following study, eight dogs were infected with B. vinsonii: four specific pathogen free dogs and four dogs that had previously been infected with E. canis. Flow cytometric analysis of peripheral blood lymphocytes revealed a cyclic elevation of the CD4/CD8 T-cell ratio that correlated with cyclic CD8+ lymphopenia in all dogs infected with B. vinsonii, regardless of prior exposure to E. canis.

Granulomatous disease associated with Bartonella infection in 2 dogs.

Shortly after removal of an engorged tick from the left ear, a 4-year-old Greyhound was referred for evaluation of fever and a rapidly enlarging mass in the region of the left submandibular lymph node. Histopathologic evaluation of the lymph node resulted in a diagnosis of severe granulomatous lymphadenitis. An 11-year-old mixed-breed dog was referred for evaluation of a 6-week history of serous nasal discharge. Histologic examination of a surgical biopsy from a nasal mass indicated multifocal granulomatous inflammation with fibrosis. Serum samples obtained from both dogs were reactive by immunofluorescent assay to Bartonella vinsonii subsp. berkhoffii antigens (reciprocal titers of 128). Although Bartonella organisms were not isolated by lysis centrifugation blood culture, Bartonella DNA was amplified from tissue samples obtained from each dog (lymph node biopsy from dog 1 and nasal biopsy from dog 2) using primers that amplify a portion of the 16S rRNA gene followed by Southern blot hybridization using a genus-specific probe. Additionally, restriction fragment length polymorphism (RFLP) analysis of a Bartonella-specific citrate synthase gene product obtained from dog 2 resulted in a restriction pattern identical to B. vinsonii subsp. berkhoffii. This is the 1st report of granulomatous disease in dogs associated with Bartonella infection.

Epidemiologic evaluation of the risk factors associated with exposure and seroreactivity to Bartonella vinsonii in dogs.

OBJECTIVES: To determine seroprevalence to Bartonella vinsonii subsp berkhoffii in a population of sick dogs from North Carolina and Virginia and to evaluate potential risk factors associated with increased likelihood of exposure to the organism. SAMPLE POPULATION: Serum samples from 1,920 sick dogs. PROCEDURE: An indirect fluorescent antibody assay was performed on each sample, and the end-point antibody titer was recorded. A case (seropositive) was defined as a dog with reciprocal titer > or = 64, and a control (seronegative) was defined as a dog with reciprocal titer < 16 that was referred within 0 to 3 days of referral of a corresponding case. From this population, 207 dogs (69 cases and 138 controls) were included in a case-control seroepidemiologic study. RESULTS: 3.6% (69/1,920) of the dogs were seropositive to B vinsonii subsp berkhoffii. Results of the case-control study indicated that seropositive dogs were more likely to live in rural environments, frequently on a farm, were free to roam the neighborhood, and were considered to be predominantly outdoor dogs. Moreover, seropositive dogs were 14 times more likely to have a history of heavy tick exposure. After analysis of the case-control study, a more detailed examination of banked sera from dogs with known tick exposure was performed. High correlation was found between sero-reactivity to B vinsonii and seroreactivity to E canis or B canis (36.0 and 57.1%, respectively). Sera derived from dogs experimentally infected with E canis or R rickettsii did not cross react with B vinsonii antigen. CONCLUSIONS AND CLINICAL RELEVANCE: Several potential risk factors are associated with canine exposure to B vinsonii. Rhipicephalus sanguineus, the tick vector for E canis and B canis, may be involved in B vinsonii transmission among dogs.