Bartonella

Bartonella is a genus of small, gram-negative, facultative intracellular bacteria in the order Rhizobiales. Members are zoonotic pathogens that infect humans and a range of animals. The most clinically significant species include Bartonella henselae, Bartonella quintana, and Bartonella bacilliformis.

Transmission and hosts: B. henselae is associated with domestic cats and cat fleas; cats act as reservoirs and humans typically acquire infection through scratches or bites contaminated with flea feces containing the organism. B. quintana is transmitted by body lice, and B. bacilliformis is transmitted by sandflies in the Andean region. Other Bartonella species can involve a variety of hosts and vectors.

Clinical features: In humans, cat scratch disease presents with regional lymphadenopathy, fever, and malaise and is usually self-limited in healthy individuals. Immunocompromised patients can develop bacillary angiomatosis and peliosis hepatis. Bartonella quintana causes trench fever and can be associated with endocarditis. Endocarditis is a rare but important manifestation for several Bartonella species and can be culture-negative. Oroya fever, caused by B. bacilliformis, is an acute hemolytic anemia with potential severity.

Diagnosis: Detection relies on serology (such as immunofluorescence assays), PCR from blood or tissue, and specialized culture techniques; histopathology may reveal bacilli on Warthin-Starry or related stains. Culture is slow and technically challenging, contributing to diagnostic difficulty in some cases.

Treatment and prevention: Mild cat scratch disease often requires no antibiotics, but azithromycin is commonly used; alternatives include doxycycline, rifampin, or trimethoprim-sulfamethoxazole. Bacillary angiomatosis and endocarditis require longer courses and specific regimens, often with macrolides or doxycycline, sometimes with rifampin. Prevention focuses on vector control and reducing exposure to reservoirs, such as flea control in cats and minimizing cat scratches or bites.