Bartonella
henselae (gram-negative, curved bacterial
rod) Bartonella
henselae (gram-negative, curved bacterial
rod)
Bartonella henselae is an intraerthrocytic bacterium. Cats are reservoirs for Bartonella, which can be transmitted by arthropod vectors (i.e. fleas) between cats. Transmission does not occur in the absence of arthropods (fleas) between cats. It is currently unknown whether the flea serves as a biological/mechanical vector of B. henselae to humans. Human exposure to B. henselae occurs via cat scratches or bites and exposure to fleas or ticks.
Veterinarians have a 6% higher rate of Cat Scratch Disease than the general public.
Kittens are at greater risk than adult cats. More than 90% of patients with Cat Scratch Disease have had contact with cats. But there have been several reports of CSD in people associated with contact with a dog with B. henselae, though the connection is not well established. B. henselae is also a health concern for the dog itself where it can cause peliosis hepatis and serosanguinous peritoneal effusion. Bartonella henselae is considered an emerging disease due to the increasing recognition of the disease in humans and is an especially increasing concern in AIDS patients.
Cats
B. henselae causes a self-limiting transient febrile illness for 48-72 hours, often accompanied by anorexia and lymphadenopathy. Infection is often subclinical but bacteremia persists for months. Clinical signs can appear with chronic infections when the animal is under stress or with concurrent disease.
Diagnosis: Serologic testing does not diagnose active infection just exposure to the organism. A negative serologic test is accurate and useful for testing cats for exposure. Blood tissue culture is best for the most accurate diagnosis of active infection in a cat.
 B. henselae in blood |
 B. henselae on agar |
 Electron micrograph of B. henselae from human bloodstream infection 33,000 X |
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Treatment: Doxycycline, amoxicillin, enrofloxacin, and rifampin have all proven to be variably effective in reducing the level and possibly the duration of bacteremia in the infected cat. Follow up cultures should be done at 2-4 week intervals to check treatment efficacy. Treatment is not always necessary but should definitely be pursued if the owner is immunocompromised.
Humans
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Most patients feel well despite the enlarged lymph nodes. The scratch itself may also persist as a non-healing lesion. In addition to Cat Scratch Disease, B. henselae can also cause bacillary angiomatosis in the skin, angiomatous lesions in other organs, peliosis hepatitis, endocarditis, osteomyelitis and prolonged bacteremia and fever. In AIDS patients, B. henselae may also cause encephalopathy. Immunocompetent individuals are able to keep the infection localized to regional lymph nodes where the bacteria incite pyogranuomatous lymphadenitis. In the immunocompromised human bacteremia and dissemination of the bacteria can occur. This often manifests itself as bacillary angiomatosis which is a vascular proliferative disease of the skin characterized by multiple, blood-filled, cystic tumors. Bacillary angiomatosis can also spread to the rest of the body. Fever, malaise, anorexia and weight loss are found in both immunocompetent and immunocompromised humans.
Diagnosis: Usually the diagnosis of CSD in humans is made by assumption with a history of unexplained lymphadenopathy and association with cats without a definitive positive serologic test or blood tissue culture. It is still debated whether infections in humans are responsive to antibiotic therapy.
Treatment: See your physician for treatment.
