Bartonella henselae is the bacterium that causes bartonellosis in cats and cat scratch disease in people. The bacteria are usually transmitted from infected to non-infected cats through fleas. People contract the disease when they are scratched or bitten by a cat that has the bacteria around their nails or in their mouths. Immunosuppressed people are at a much higher risk for contracting cat scratch disease than is the general population. Many cats carry Bartonella henselae bacteria in and on their bodies without ever becoming sick themselves, while others may develop a fever, enlarged lymph nodes or chronic inflammation of their mouths and digestive tracts.
Diagnosing a cat with bartonellosis is difficult. Several different types of blood tests are available but none are perfect. Some tests only indicate that a cat has been exposed to the bacteria but do not determine if an animal's current illness is related to Bartonella bacteria or if it is likely to transmit cat scratch disease to people. Other tests can reveal the presence of an active infection but have a tendency to wrongly diagnose cats with low-level infections as being free from disease. It is generally not recommended that all cats be tested for bartonellosis due to the difficulty of interpreting the results.
Treating cats suspected of having bartonellosis is also difficult. The antibiotic azithromycin is the drug of choice, but it fails to completely clear the bacteria from many infected cats. Commonly, cats with chronic inflammatory diseases that are thought to be linked to Bartonella bacteria often improve with treatment but soon relapse after the antibiotic is stopped.
Written by: Jennifer Coates, DVM
Last reviewed: October 2, 2008