Increasing number of vectors implicated in transmission

Increasing number of vectors implicated in transmission

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Apr 01, 2007

Q. Please review bartonellosis in animals and humans.

A. Dr. Edward B. Breitschwerdt at the 2006 American College of Veterinary Internal Medical Forum in Louisville, Ky., lectured on "Bartonellosis: Legal and Medical Implications for Veterinarians." Here are some relevant points from his presentation:

The genus Bartonella is currently comprised of at least 20 species and subspecies of vector-transmitted, fastidious, gram-negative bacteria that are highly adapted to one or more mammalian reservoir hosts. Recent reports have provided additional evidence supporting intra-erythrocytic and endothelial localization of Bartonella, which provides a potentially unique strategy for bacterial persistence.

Based on recent research observations, the clinical and diagnostic challenges posed by Bartonella transmission in nature may be much more complex than is currently appreciated in either human or veterinary medicine.

As reviewed in several publications, numerous domestic and wild animals, including bovine, canine, feline, human and rodent species can serve as chronically infected reservoir hosts for various Bartonella species. In addition to the large number of documented reservoir hosts, an increasing number of arthropod vectors, including biting flies, fleas, keds, lice, sandflies and potentially ticks have been implicated in the transmission of Bartonella species.

In general, persistent bacteremia in a reservoir host does not induce obvious signs of disease or pathology. However, when a Bartonella species is transmitted from a reservoir host (a seemingly well-adapted association) to a non-reservoir host (a poorly adapted association) by a cat scratch, an animal bite or by an arthropod vector, infection can induce a diverse spectrum of clinical and pathological abnormalities.

Manifestations in humans

In people, Bartonella-induced disease manifestations can include fever of unknown origin, endocarditis, lymphadenopathy (cat-scratch disease), granulomatous hepatitis, encephalitis, and bacillary angiomatosis and peliosis hepatis, particularly in immunocompromised individuals.

Although not previously reported, our research group recently described putative bite transmission of Bartonella quintana from a feral barn cat to a woman followed by a second and unrelated episode of bite transmission of B. vinsonii berkhoffii from her pet dog. Dog and cat bites are a frequent cause of emergency-room presentations in the United States and may well represent an under-recognized source of Bartonella transmission to people.

These and other recent findings emphasize the potential environmental complexity associated with putative Bartonella bite transmission.

To date, four Bartonella species have been isolated from cats, including B. henselae, B. clarridgeiae, B. bovis and B. koehlerae. Based on well-documented publications or recent research abstracts, it is possible that all four of these Bartonella species can be zoonotic pathogens. In addition to the frequent cat-scratch transmission of B. henselae (cat-scratch disease) and potentially B. clarridgeiae, there is increasing evidence that cats may be involved in the transmission of B. quintana to people. Recently, B. quintana DNA was amplified from the dental pulp of a cat and from cat fleas (Ctenocephalides felis) in France.

Prior to these reports, a laboratory has also described two middle-aged female patients that had chronic peripheral or mediastinal adenomegaly, respectively, who were infected with B quintana. Both women had close contact with cats. Central nervous system infection with B. quintana was documented in two males from the southeastern United States, one of whom had experienced numerous scratches on the upper extremities by a kitten several weeks prior to the onset of seizures.