B henselae can be found worldwide,4 and although cats are its primary reservoir,5,6 other animals (eg, dogs, raccoons, mongooses) may also be sources of infection.2 B henselae is transmitted among cats through flea feces (Ctenocephalides felis) and scratches from nails contaminated with flea feces.2,4,7,8 B henselae transmission to humans from dog bites2,9 and cat bites and scratches5,6 appears to be a low-risk source for human infection unless the animal is concurrently infested with fleas or the nails or saliva are contaminated with flea feces.2 Ticks, spiders, and mites may also play a role in transmission of B henselae to animals and humans.2,10,11 Bacteremia has been identified in various animals2; in cats (stray or pet), infection prevalence varies considerably by geographic area.6 Infection prevalence in cats is highest in warm, moist areas with high flea burdens.4,5,12 A North American study found seroprevalence rates to be higher in warmer regions as compared with cooler regions.12 Overall, 27.9% of cats tested in that study were seropositive. Bacteremia in cats can be intermittent,10 occurs primarily in cats younger than 2 years, and can last a year or longer.6,7 The seroprevalence rate of B henselae in dogs in the southeastern United States has been recorded to be 10% in healthy dogs and 27% in sick dogs.13 Broader studies have found 2% to 3.8% of dogs to be seropositive for B henselae.14,15
B henselae infection in humans and animals can be subclinical; this is particularly common in cats due to their coevolution with B henselae.2,7,16 Although association between infection and clinical signs in cats is equivocal,17 signs can include endocarditis,2,6 myocarditis,2,7 fever,18 lethargy,3,18 gingivostomatitis,19 uveitis, conjunctivitis, and others.3 In dogs, B henselae can cause fever, endocarditis, granulomatous hepatitis, peliosis hepatitis, lymphadenomegaly, panniculitis, and vasoproliferative lesions, as well as others.2,3,5,20
B henselae is the predominant cause of cat scratch disease (CSD) in humans.10,21 There are an estimated 500 hospitalizations and 12 000 outpatient cases of CSD each year in the United States.8 In humans, at the site of inoculation, a cutaneous papule or pustule develops 3 to 10 days after contact with an infected animal and may last 1 to 3 weeks.4 Accompanying signs may include regional lymphadenopathy, fever,18 fatigue, malaise, headache, sore throat, and/or rash.4 More severe signs may include neuralgia, endocarditis, osteomyelitis, Parinaud’s oculoglandular syndrome, pneumonia, hepatitis, splenitis, and/or encephalopathy.4 B henselae and B quintana are causative agents of bacillary angiomatosis, a neovascular disorder that occurs primarily in immunocompromised individuals and involves the skin, lymph nodes, and a variety of organs.4,22,23 Although CSD is often self-limiting, B henselae can cause chronic or intermittently clinical illness accompanied by persistent bacteremia.24