Lyme Handbook

The Gram-negative bacterial genus Bartonella currently comprises roughly two dozen identified species, about half of which are known to infect humans. However, the clinical implications of many of these human infections are poorly understood, and it is possible that some of the species are non-pathogenic, at least in immunocompetent people. Until around 15 years ago, only three human diseases were recognized as clearly attributable to Bartonella organisms: cat scratch disease (CSD, also sometimes referred to as cat scratch fever), caused by B. henselae; Carrion’s disease, caused by B. bacilliformus (and limited to South America); and trench fever, caused by B. quintana. More recently, however, additional pathogenic Bartonella species have been discovered. The full clinical spectrum of all Bartonella infections remains to be elucidated, but includes conditions as diverse as hepatitis, endocarditis, encephalopathy and meningoencephalitis.

Bartonella are intracellular parasites that generally show preference for erythrocytes and endothelial cells in humans. The organisms are found in a wide range of both wild and domestic mammals, including cattle, rodents, dogs and cats. The various Bartonella species appear to be adapted to specific hosts. Cats are the main reservoir for B. henselae, which causes approximately 20,000 reported cases of cat scratch disease per year in the United States. (As with many reportable diseases, however, the true incidence of CSD is underreported and generally believed to be considerably higher.) Bartonella are also found in numerous arthropods, including fleas (a known vector of CSD), biting flies, lice and ticks.

The evidence for ticks as vectors of Bartonella organisms is circumstantial but fairly strong. Recent studies in both the United States and Europe have found that Ixodes ticks harbor B. henselae in addition to Borrelia, Babesia and Anaplasma organisms; in fact, a 2004 PCR analysis of I. Scapularis ticks in New Jersey discovered that a higher percentage of ticks were infected with B. henselae than any of these other pathogens. In addition, B. henselae has been detected in the spinal fluid of patients co-infected with Borrelia burgdorferi, the agent of Lyme disease. However, the ability of Ixodes ticks to actually transmit B. henselae has not been specifically demonstrated.

For more info:  http://columbia-lyme.org/patients/tbd_bartonella.html