Gram-negative bacteria in the genus Bartonella. Human illness is primarily caused by Bartonella henselae (cat-scratch disease [CSD]), B. quintana (trench fever), and B. bacilliformis (Carrión disease). A variety of Bartonella spp. can cause culture-negative endocarditis; other clinical syndromes due to Bartonella spp. such as ocular disease, osteomyelitis, and encephalitis have been reported. Additional Bartonella spp. that cause human illness have been described recently.
B. henselae is contracted through scratches from domestic or feral cats, particularly kittens. Direct transmission to humans by the bite of infected cat fleas is likely to occur but has not yet been proven. B. quintana is transmitted by the human body louse. B. bacilliformis is transmitted by infected sand flies (genus Lutzomyia).
CSD and trench fever are distributed worldwide. In the United States, CSD is more common in children, southern states, and during the months of August through January. Trench fever typically occurs in populations that do not have access to proper hygiene, such as refugees and the homeless. Carrión disease has limited geographic distribution; transmission occurs in the Andes Mountains at 1,000–3,000 m (3,281–9,843 ft) elevation in Peru, Colombia, and Ecuador; sporadic cases have also been reported in Bolivia, Chile, and possibly Guatemala. Most cases are reported in Peru. Short-term travelers to endemic areas are likely at low risk.
CSD typically manifests as a papule or pustule at the inoculation site and enlarged, tender lymph nodes that develop proximal to the inoculation site 1–3 weeks after exposure. B. henselae infection may also cause prolonged fever, follicular conjunctivitis, neuroretinitis, or encephalitis. Trench fever symptoms include fever, headache, transient rash, and bone pain (mainly in the shins, neck, and back).
Some Bartonella spp. can cause subacute endocarditis, which is often culture-negative. Bacillary angiomatosis may present as skin, subcutaneous, or bone lesions and is caused by B. henselae or B. quintana; peliosis hepatis manifests as liver lesions and is caused by B. henselae. Both occur primarily in people infected with HIV.
Carrión disease has 2 distinct phases: an acute phase (Oroya fever) characterized by fever, myalgia, headache, and anemia and an eruptive phase (verruga peruana) characterized by red-to-purple nodular skin lesions.
CSD can be diagnosed clinically in patients with typical presentation and a compatible exposure history. Serology can confirm the diagnosis, although cross-reactivity may limit interpretation in some circumstances. Serology is available from some commercial laboratories, however, consultation is available from the CDC. B. henselae may also be detected by PCR or culture of lymph node aspirates by using special techniques.
Trench fever can be diagnosed by serology or blood culture for B. quintana. PCR may also aid the diagnosis of disseminated Bartonella infections when performed by clinical laboratories using validated methods. Endocarditis caused by Bartonella spp. can be diagnosed by elevated serology of the patient and by PCR or culture of excised heart valve tissue.
Oroya fever is typically diagnosed via blood culture or direct observation of the bacilli in peripheral blood smears, though sensitivity of these methods is low. PCR and serologic testing may also aid diagnosis.
Most cases of typical CSD eventually resolve without treatment, however antibiotics may shorten the course of disease. Azithromycin has been shown to speed the decrease in lymph node volume. A small percentage of people will develop disseminated disease with severe complications; however, it is unknown whether antibiotic treatment reduces the risk of progression to atypical disease.
Various antibiotics are effective against Bartonella infections, and regimens including agents such as tetracyclines, fluoroquinolones, trimethoprim-sulfamethoxazole, rifampin, and aminoglycosides have been used. Recommended regimens and duration of treatment vary by clinical disease.
Avoid rough play with cats, particularly strays and kittens, to prevent scratches. This is especially important for immunocompromised people. Flea control for cats and limiting outdoor roaming of cats also decrease the risk that they carry B. henselae. Wash hands promptly after handling cats. Protect against bites of sand flies and body lice (see Chapter 3, Mosquitoes, Ticks & Other Arthropods).