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Edward Breitschwerdt, DVM, Bartonellosis, NorVect 2014

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Published on Dec 23, 2015

BARTONELLOSIS: A ONE HEALTH APPROACH TO AN EMERGING INFECTIOUS DISEASE

Bartonella species are recently rediscovered, fastidious Gram-negative bacteria that are highly adapted to a mammalian reservoir host and within which the bacteria usually cause a long-lasting intraerythrocytic bacteremia. These facts are of particular importance to physicians, veterinarians and other health professionals, as an increasing number of Bartonella species, known to induce persistent bacteremia in animal reservoir hosts, are being documented as a cause of disease in animals and people. Among numerous other examples, Bartonella henselae has co-evolved with cats, Bartonella vinsonii subsp. berkhoffii has co-evolved with dogs and wild canines, and Bartonella bovis has co-evolved with cattle. Importantly, the list of reservoir-adapted Bartonella species, including a large number of rodent species that might serve as “pocket pets,” continues to grow exponentially, as new Bartonella spp. are discovered in wildlife species. Prior to 1990, there was only one named Bartonella species, whereas there are currently 30 named and numerous yet to be named or Candidatus species. Seventeen Bartonella spp. have been associated with an expanding spectrum of animal and human diseases. Epidemiological evidence and experimental transmission studies support an important role for fleas in the transmission these bacteria among cats, which can be chronically bacteremic for months to years. Cats or their fleas can harbor four zoonotic Bartonella sp. Recent reports have identified an intra-endothelial, as well as intra-erythrocytic localization for these bacteria, which represents a unique strategy for bacterial persistence within the infected host. In addition to fleas, an increasing number of arthropod vectors, including biting flies, keds, lice, mites, sandflys, spiders, and ticks have been implicated in the transmission of Bartonella sp. among animals and people. Considering the diversity of newly discovered Bartonella sp., the large number and ecologically diverse reservoir hosts, and the spectrum of arthropod vectors; the clinical and diagnostic challenges posed by Bartonella transmission in nature may be much more complex than is currently appreciated in human or veterinary medicine. Clearly, a One Health Approach is needed to better define the medical relevance of this genus of bacteria as a cause of disease in animals and human patients and to develop preventive strategies so as to avoid Bartonella sp. infections in pets and their owners.
Because conventional microbiological techniques lack sensitivity, bartonellosis is usually diagnosed by PCR amplification of organism specific DNA sequences and/or through serological testing, which also lacks diagnostic sensitivity in dogs, horses and humans. Recently, the development of a more sensitive isolation/PCR approach, using BAPGM (Bartonella alpha Proteobacteria growth medium) followed by PCR amplification and DNA sequencing of organism-specific gene targets has greatly facilitated the isolation or molecular detection of Bartonella spp. DNA from the blood (tissues or other biological fluids) of sick or healthy animals, including cats, cows, dogs, horses, pigs and human beings. Most importantly, the use of this insect cell culture-based enrichment growth medium prior to PCR testing has allowed our research group to confirm that immunocompetent human patients, in particular veterinarians, animal workers and others exposed to arthropod vectors, can have chronic intravascular infections with Bartonella spp.
Due to extensive contact with a spectrum of animal species, veterinary professionals and others with arthropod and animal exposure appear to have an occupational risk of infection with Bartonella spp. As Bartonella spp. have been isolated from cat, dog or human blood, cerebrospinal fluid, joint fluid, aqueous fluid, seroma fluid and from pleural, pericardial and abdominal effusions, a substantial number of diagnostic biological samples collected on a daily basis in veterinary practices around the world could contain viable bacteria. In the context of disease causation, Bartonella sp. have been implicated in association with endocarditis, granulomatous inflammatory lesions, persistent bacteremia and vasoproliferative tumors in animals and people.

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