Bartonella Henselae

Bartonella henselae is a small, rod-shaped, pleomorphic gram-negative bacteria. Domestic and feral cats are both the reservoir and vector for Bartonella henselae. Cats can be infested with fleas that carry B. henselae. The bacillus is transmitted to humans by domestic cat scratches, bites ,or licks that are contaminated with flea feces. B. Henselae infections occur most often in children under the age of 15.

Cat scratch disease begins as a low grade fever and cutaneous pustule that develops at the site of the scratch or bite within a week after contact. These symptoms are followed by regional lymphadenopathy, which is the predominant clinical feature of cat scratch disease. Most cases are self-limited, but B. henselae infection has been associated with:

• Cat scratch disease
• Bacillary angiomatosis
• Peliosis hepatitis
• Endocarditis

These complications are most common in patients with AIDS, organ transplant or another cause of immunosuppression. 

Traditionally, the diagnosis of Bartonella infections has been made by Warthin-Starry staining of tissue. B. henselae is a fastidious, slow-growing bacterium. Cultures should be held for a minimum of 21 days.

Serology can facilitate the diagnosis. The Euroimmun indirect immunofluorescence test is a standardized assay for the determination of specific antibodies against B. henselae. A positive IgM (titer >1:20) suggests a current infection. A positive IgG (titer >1:128) suggests a current or previous infection. Between 5 and 10% of healthy individuals have an IgG titer of 128. 

Because tissue staining and serology are nonspecific and may be falsely negative in early stages of disease, real time PCR testing for the citrate synthase gene of Bartonella species has become the preferred test. PCR is most reliable for testing lymph nodes or tissue samples. PCR is not recommend for testing blood. A positive PCR result does not differentiate between Bartonella henselae and B quintana.

Specimen requirement for serology is a red top tube of blood. 

Specimen requirement for PCR is:

• A lavender top tube of blood
• Fresh tissue frozen in a screw-capped sterile plastic container
• Paraffin block of tissue

Reference

Wolf LA, et al. EB. In pursuit of a stealth pathogen: Laboratory diagnosis of bartonellosis. Clin Micro News. 2014;36(5):33-39