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. have also been reported. For example, in 2007, a newly recognized species of Bartonella (B. rochalimae) was identified in an ill traveler returning from Peru.
CSD is contracted through scratches from domestic or feral cats, particularly kittens. Direct transmission to humans by the bite of infected cat fleas is likely but has not yet been proven. Trench fever is transmitted by the human body louse. Carrión disease is transmitted by sand flies (genus Lutzomyia) that are infected with B. bacilliformis.
CSD and trench fever are distributed worldwide. In the United States, CSD is more common in children, and the incidence peaks from September 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 1–3 km (0.6–1.9 miles) elevation in Peru, Colombia, and Ecuador; sporadic cases have 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 symptoms include fever, a papule or pustule at the inoculation site, and enlarged, tender lymph nodes that develop ipsilateral 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 signs and symptoms of subacute endocarditis, which is often culture-negative. Bacillary angiomatosis (caused by B. henselae or B. quintana) and peliosis hepatis (caused by B. henselae) occur primarily in people infected with HIV. Bacillary angiomatosis may present as skin, subcutaneous, or bone lesions.
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. B. henselae DNA may also be detected by PCR or culture of pus or lymph node aspirates by using special techniques.
Trench fever can be diagnosed by isolating B. quintana from blood or by serology. 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 CSD eventually resolve without treatment, but a small percentage of people will develop disseminated disease with severe complications. The use of antibiotics to shorten the course of disease is debated, although azithromycin speeds the decrease in lymph node volume.
Various antibiotics are effective against Bartonella infections, including penicillins, tetracyclines, cephalosporins, and aminoglycosides. Recommended antibiotic regimens and duration of treatment vary by clinical disease.
Avoid rough playing with cats, particularly strays and kittens, to prevent scratches. This is especially important for immunocompromised people. Wash hands promptly after handling cats. Protect against bites of sand flies and body lice (see Chapter 2, Protection against Mosquitoes, Ticks, & Other Arthropods).