Bartonella Infections

Definition

Bartonella are vector-borne bacteria responsible for a wide spectrum of human acute and chronic diseases. More than 40 different bacterial species from this genus have been isolated from animals and humans. The human infections linked to these different bacteria include cat-scratch disease, Oroya fever, verruga peruana, trench fever, endocarditis, bacillary angiomatosis, and peliosis hepatis.

Epidemiology

More than 40 known Bartonella species have been isolated from both animals and humans. These bacteria are zoonotic, and the strains that are associated with human infections include B. henselae, B. quintana, B. bacilliformis, B. elizabethae, B. clarridgeiae, B. vinsonii subsp. arupensis, B. vinsonii subsp. berkhoffii, B. alsatica, B. tamiae, B. grahamii, B. washoensis, B. rochalimae, B. koehlerae, B. mayotimonensis , and B. ancashensis ( Table 291-1 ). The other Bartonella species have been isolated only from the blood of animals, including rodents, felids, canids, dolphins, bats, and ruminants. The route of transmission of Bartonella species in mammals and humans is by fleas, ticks, mites, and lice (see Table 291-1 ).

Almost all Bartonella species are vector-borne bacteria (see Table 291-1 ). Some are limited geographically, such as B. bacilliformis , which is found only in the Andes Mountains in South America at high altitudes, where its principal vector, Lutzomyia verrucarum , is distributed. Others have a worldwide distribution, such as B. henselae and B. quintana . Each Bartonella species is highly adapted to its mammalian reservoir, in which bacteria usually cause a long-lasting intraerythrocytic bacteremia that may be asymptomatic. Humans are the hosts and reservoirs for B. bacilliformis and B. quintana . B. quintana , which is transmitted by the human body louse by inoculation of arthropod feces through broken skin, is more common in homeless persons and in poorer countries. Cats represent the main reservoir hosts for B. henselae infection; this pathogen is the agent of cat-scratch disease in humans, caused by cat bites or scratches. In the United States, about 12,000 outpatients and 500 inpatients are diagnosed annually. B. henselae infection is transmitted from cat to cat by the cat flea. Cat fleas may also be infected by B. quintana . The role of dogs as reservoir hosts has been documented for several species, including B. vinsonii subsp. arupensis , B. vinsonii subsp. berkhoffii , and B. henselae . Wild rabbits are the reservoir hosts for B. alsatica , which is an agent of endocarditis and lymphadenopathy in humans in close contact with rabbits. For other Bartonella species known to cause diseases in humans, the pathogenic role and mode of transmission are not fully understood.

Pathobiology

A single Bartonella species can cause either acute or chronic infections and either vasculoproliferative or suppurative manifestations but with different pathogenetic mechanisms that mainly depend on the patient’s immune status. For example, B. henselae usually causes cat-scratch disease (a self-limited disease) in immunocompetent hosts, whereas it is responsible for bacillary angiomatosis in immunocompromised patients. B. quintana is responsible for trench fever as well as for endocarditis, bacteremia in the homeless population, and vasculoproliferative diseases, whereas B. bacilliformis is the agent of Carrión disease, which corresponds to either an acute intraerythrocytic bacteremic disease (Oroya fever) or a chronic vasculoproliferative disease (verruga peruana). B. bacilliformis (Oroya fever) and B. quintana (trench fever and bacteremia in the homeless) infect red blood cells, whereas B. henselae and B. koehlerae have been seen in erythrocytes of infected cats. B. henselae can cause granulomatous disease (i.e., cat-scratch disease), which affects lymph nodes, but it can also be responsible for other clinical manifestations or complications, such as endocarditis. Vasculoproliferative diseases include bacillary angiomatosis caused by B. henselae and B. quintana , peliosis hepatis caused by B. henselae , and verruga peruana caused by B. bacilliformis . In patients with a previous valvulopathy, any Bartonella infection may lead to endocarditis.

Clinical Manifestations

Bartonella infections can lead to a wide spectrum of either acute or chronic diseases. The status of the host immune response plays an important role in the development of the different manifestations. Four different groups of clinical syndromes may occur with Bartonella infections: (1) infection of red blood cells and erythrophagocytosis, (2) granulomatous disease controlled by the immune response, (3) bacteremia and blood culture–negative endocarditis, and (4) vasculoproliferative diseases (bacillary angiomatosis, peliosis hepatis, and verruga peruana) ( Table 291-2 ). In a recent French study, 89% of Bartonella infections were cat-scratch fever, 9% were endocarditis, and 2% were bacillary angiomatoses or peliosis hepatis.

Epidemiology and Pathobiology

The vector of B. bacilliformis is the mosquito Lutzomyia verrucarum , whereas B. quintana is transmitted via human body louse. In Oroya fever, B. bacilliformis invades up to 80% of erythrocytes and produces their massive lysis, which results in severe hemolytic anemia, the major symptom of the disease. Similarly, trench fever is characterized by intracellular erythrocyte parasitism by B. quintana , with the percentage of infected red blood cells ranging from 0.001 to 0.005% ( Fig. 291-1 ). Bacteria can also be seen extracellularly and in erythroblasts. This intracellular erythrocyte parasitism can presumably preserve the pathogens for efficient transmission by body lice, protect B. quintana from the host immune response, and contribute to decreased antimicrobial efficacy. During bacteremia in the homeless, B. quintana can also be seen in red blood cells.

Clinical Manifestations