Cat Scratch Disease Causative Organism
Cat scratch disease (cat scratch fever) is caused by Bartonella henselae, a gram-negative, facultative intracellular bacterium 1, 2.
Key Microbiological Characteristics
Bartonella henselae is a:
- Gram-negative, rod-shaped bacillus
- Facultative intracellular organism
- Fastidious bacterium (difficult to culture)
- Non-motile, pleomorphic organism 3, 4
Transmission and Epidemiology
The bacterium is transmitted to humans primarily through:
- Cat scratches (most common route) - when claws become contaminated with flea feces containing B. henselae 1
- Cat bites
- Contact with cat saliva on broken skin 5
The cat flea (Ctenocephalides felis) serves as the vector that transmits B. henselae among cats, with up to 50% of pet cats in some U.S. areas carrying bacteremia 1, 3.
Clinical Significance
In immunocompetent individuals, B. henselae causes classic cat scratch disease with:
- Papule or pustule at inoculation site (3-30 days post-exposure)
- Regional lymphadenopathy (approximately 3 weeks after inoculation)
- Self-limited course (resolves within 1-6 months) 2, 6
In immunocompromised patients (particularly those with HIV and CD4+ counts <100 cells/µL), B. henselae can cause:
- Bacillary angiomatosis
- Bacillary peliosis hepatis
- Chronic bacteremia
- Systemic disseminated disease 1
Important Clinical Caveat
While Bartonella quintana can also cause disease in humans (trench fever, bacillary angiomatosis), only B. henselae is associated with classic cat scratch disease transmitted via cat scratches 1. B. quintana is associated with body louse infestation rather than feline exposure.