Bartonellosis is emerging as a more important zoonotic disease than previously realized.

While Bartonella spp. are widespread and recognized in many species, the most significant clinical disease occurs in cats, dogs and people (cat scratch disease, CSD). Five species are now recognized in cats: Bartonella henselae, B. clarridgeiae, B. kochlerae, B. weissii and B. elizabethae. In dogs, the most common species is B. vinsonii, although B. henselae also is reported to cause illness. B. henselae is the most common species seen in people. Transmission vectors recently identified include the common domestic cat and dog fleas, and the deer tick. Concurrent infections with Lyme disease (Borrelia burgdorferi) and B. henselae have produced CNS disease in humans, and dogs have a high rate of co-infection with Ehrlichia spp. and Babesia spp.

Humans. Previously described diseases include: CSD, bacillary angiomatosis and peliosis, febrile bacteremia, lymphadenopathy, endocarditis, vegetative valvular disease, uveitis, neurological disorders, anemia, neuroretinitis, and osteomyelitis. Newly described diseases include: inflammatory bowel disease, mononucleosis-like syndrome, pulmonary infiltrates, meningoencephalitis, arthralgia, juvenile arthritis, cutaneous rash and purpura, cutaneous granuloma, and disciform keratitis.

Cats. There is a high prevalence of Bartonella spp. infection in cats, which are usually asymptomatic carriers. However, research has found an association between Bartonella infection and chronic oral disease (gingivitis, stomatitis, and oral ulcers), lymphocytic-plasmacytic conjunctivitis and uveitis, upper respiratory infection, inflammatory bowel disease, and chronic renal failure. Fleas transmit the infection among cats and the prevalence is higher among stray and shelter cats, and multicat households. Prevalence also varies geographically; the organism thrives in high heat and humidity where arthropod vectors are found. Infection can persist for years, and cats can become reinfected in the presence of Bartonella antibody.

Dogs. Bartonella spp. may cause endocarditis, granulomatous lymphadenitis, rhinitis, liver disease, dermatologic lesions, joint pain, uveitis, neurological disease, anemia, leukocytosis and thrombocytopenia.