Epidemiology

The most common Bartonella infection is cat-scratch disease (CSD), caused by Bartonella henselae, which is distributed worldwide. In the US, an estimated 12,000 people are diagnosed with CSD per year and a further 500 people are hospitalized with the disease.[16] Southern US states and children between 5-9 years were found to have the highest incidence of CSD.[16] It is generally transmitted from the bites and scratches of cats, particularly kittens.[17]​ The vector for transmission between cats is the cat flea (Ctenocephalides felis). In temperate areas, the highest incidence of CSD occurs in autumn and winter.[16][18]​​ In tropical regions, the incidence may be higher during the monsoon season.[19]

Carrion disease (Oroya fever and verruga peruana), caused by B bacilliformis, is geographically localized in some parts of South America (Peru, Ecuador, and Colombia) within the Andes mountains. It is transmitted by a sand fly vector (Lutzomyia verrucarum).[4][5]​​ Carrion disease is characterized by an initial life-threatening febrile phase, known as Oroya fever, followed by an eruptive phase, known as verruga peruana. In 2016, there were 786 cases of Carrion disease reported in Peru.[20]​ Verruga peruana accounted for around 30% of all Carrion disease cases.[20]

Trench fever, caused by B quintana, got its name when more than a million troops were infected in the trenches during World War I, then subsequently in World War II. This infection is transmitted by the human body louse (Pediculus humanus humanus) and humans are the only known reservoir. B quintana has a worldwide distribution and occurs most frequently in populations that lack access to adequate hygiene.​[17][21]​​ Outbreaks have been reported among homeless people in the US, Europe, and Japan.[21][22][23]​​ HIV infection, alcohol-use disorder, and other substance use disorders are frequently associated with B quintana infection.[21][22]

Since 1993, 45 Bartonella species have been described, some of which have been reported to cause human infections.[1][2][3]​ Human infections caused by other species of Bartonella (e.g., B vinsonii, B elizabethae, B clarridgeae, B grahamii, B alsatica, B rochalimae, B washoensis, and B koehlerae) do occur but are rare.[5][6][7][8][9][10][11]​ Although predominantly an animal species, B vinsonii subsp. berkhoffii has been noted to cause human disease.[12] Infections caused by B vinsonii subsp. arupensis in humans have been reported in France, Russia, and Nepal causing febrile illnesses, suggesting they are geographically widespread.[13]

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