Comparative Epidemiology of Bartonella Infection in Dogs and Humans

by Duncan, Ashlee Walker

Abstract (Summary)
The genus Bartonella is composed 20 species or subspecies of vector-transmitted, fastidious, gram-negative bacteria, which are classified as emerging pathogens in human and veterinary medicine. Due to their intracellular localization, successful microbiological isolation of Bartonella species is difficult to achieve and hinders the attribution of disease causation to Bartonella infection. Research was initiated to develop a pre-enrichment medium that would support the isolation of Bartonella species. The use of this novel medium, Bartonella/alpha-Proteobacteria Growth Medium (BAPGM), facilitated successful isolation of both single and co-cultures of multiple Bartonella species. Subsequently, a prospective study was designed to test the hypothesis that the detection and isolation of Bartonella in clinical samples, collected from dogs, are enhanced by pre-enrichment in liquid BAPGM prior to blood agar plating when compared to traditional diagnostic methods. No isolates were obtained when samples were cultured on a blood agar plate; however, refinements to the BAPGM method resulted in the successful isolation of single and co-infections with Bartonella species in clinical samples collected from sick dogs. This study resulted in the preliminary validation of a multi-faceted approach combining pre-enrichment culture with PCR amplification to identify and isolate Bartonella species from the blood of sick dogs.

Next, a study was conducted to assess the utility of the BAPGM-PCR combinational approach using blood samples collected from immunocompetent human patients with arthropod and occupational animal contact. Similar to results obtained in dogs, this multi-faceted method facilitated the detection and subsequent isolation of single and co-infections with multiple Bartonella species in the blood of human participants. To our knowledge, this study was the first to demonstrate concurrent infection with two Bartonella species or strains in the same individual.

In the final segment of the research presented, it was hypothesized that the development of lymphoma in Golden Retrievers may be associated with chronic infection with vector-borne pathogens. Using a matched, case-control study design and PCR analyses and DNA sequencing, single and co-infections with multiple Bartonella species were detected in the blood and lymph nodes of Golden Retrievers with lymphoma and in healthy Golden Retrievers; no Anaplasma or Ehrlichia DNA was detected in samples from any dog. There were no differences in the molecular prevalence of Bartonella infections or in the specific Bartonella species detected in the blood or lymph nodes of dogs with lymphoma (5/28 dogs, 17.9%) when compared to the clinically healthy controls (10/56 dogs, 17.9%). To our knowledge, this is the first report in which Bartonella DNA was detected in the lymph nodes of clinically healthy dogs or in dogs with lymphoma. Consistent with earlier reports, a significantly higher proportion of healthy Golden Retrievers were receiving monthly acaricide treatments (2.6 times higher), when compared to dogs with lymphoma. In addition, Golden Retrievers that were PCR positive for Bartonella species had prior tick exposure (odds ratio = 3.4) and were classified by their owners as indoor/outdoor dogs (odds ratio = 3.1), when compared to dogs that were PCR negative for Bartonella species. Based on these data, longitudinal studies should be conducted to determine whether Bartonella species can be transmitted by ticks, whether lymphatic infection is persistent, or whether these bacteria may contribute to the development of lymphoma.

The utilization of BAPGM for the isolation of Bartonella species from naturally infected patients represents an important contribution to worldwide research efforts to enhance the isolation and facilitate the microbiological study of these fastidious bacteria. Further, it appears that similar Bartonella species induce persistent blood-borne infections in humans and dogs. The current findings highlight the zoonotic potential of this genus and further validate Bartonella species as important, emerging pathogens in human and veterinary medicine.

Bibliographical Information:

Advisor:Stephanie K. Kordick; Robert M. Kelly; Maria T. Correa; Edward B. Breitschwerdt

School:North Carolina State University

School Location:USA - North Carolina

Source Type:Master's Thesis

Keywords:comparative biomedical sciences


Date of Publication:04/25/2007

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