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Bartonellosis (Cat-scratch Disease)

By: Dr. Arnold Plotnick

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There are several Bartonella subspecies that can infect humans. Bartonella organisms cause a wide range of clinical diseases in people including the following:

Bartonella henselae is the causative agent of cat-scratch disease in humans.

Bartonella vinsonii, Bartonella elizabethae, Bartonella washoensis may cause endocarditis in humans.

Bartonella clarridgeiae may cause cat scratch disease in humans.

Bartonella bacilliformis may cause Carrion's disease, Oroya fever and/or verruca peruana in humans.

Bartonella quintana may cause endocarditis, bacillary angiomatosis and or trench fever in humans.

Children and immunocompromised people may suffer severe disease when infected by these bacteria. Cats are considered the major reservoir for these bacteria, although fleas and some other mammals have also been shown to play a role in the disease. Most cats do not show clinical signs of illness when infected.

Cat-scratch disease was first described in 1950, but it was only in 1992 that the cause of the disease was identified. The organism responsible for the disease was called Rochalimaea henselae initially, but the organism was renamed Bartonella henselae shortly afterward.

In a study in 1993, children aged 5 to 14 years had the highest incidence of disease. Children younger than 18 made up 54 to 80 percent of CSD cases. The incidence of CSD is slightly higher in the southern United States and slightly lower in the western states. Sixty percent of cases occur from September through January.

Most cases of CSD begin with a cat scratch, although some cases have occurred in people who insist they haven't been exposed to cats or other animals. The variables most strongly associated with CSD include owning a kitten, owning a kitten with fleas, and/or being scratched by a kitten. There are a few reports in which dog scratches were implicated, and one case that may have occurred after a monkey scratch.

After a cat scratches a person, a small blister may appear 3 to 30 days later, and may or may not persist for as long as 5 months before healing. Five to 50 days after the scratch, lymph nodes near the region of the scratch enlarge and become painful. The enlargement may persist for as long as 4 months and is the main reason that people seek medical care. Atypical forms of CSD can also occur, including tonsillitis, encephalitis, and pneumonia, although this is fairly uncommon and occurs in only 5 to 8.5 percent of cases.

Neurologic signs occur more commonly in children. These usually begin with a headache, and can progress to delirium. Many patients have seizures. Recovery is usually rapid, and long-term neurologic deficits are rare. HIV-positive individuals are more likely to show signs of dementia after infection.

Bartonella organisms can cause other diseases in people. Bacillary angiomatosis and bacillary peliosis hepatis are two examples. Bacillary angiomatosis is a vascular disease of the skin that appears as multiple blood-filled cysts. It resembles Kaposi's sarcoma clinically. Bacillary peliosis hepatis is a vascular disease of the internal organs, causing fever, chills, vomiting and weight loss. These disorders tend to occur in people with advanced AIDS, and they tend to be refractory to treatment. One-third of patients with bacillary angiomatosis report no contact with cats. Studies have shown, however, that owning a cat and/or being scratched, bitten or licked by a cat are risk factors associated with both of these syndromes.

The prevalence of Bartonella infection in cats varies throughout the world. Twenty-five to 40 percent of pet cats are estimated to be healthy carriers of the organism. Feral cats have the highest likelihood of testing positive. Cats with a heavy flea burden are also more likely to test positive. Cats who test positive for the Feline Leukemia Virus or the Feline Immunodeficiency Virus are not more likely to test positive for bartonellosis.

Cats can have high levels of the Bartonella organism in their bloodstream and not show any clinical signs of disease. In experimental circumstances, mild clinical signs have been produced in cats after inoculating them with the organism. The signs seen were mild fever and lymph node enlargement that went away on its own.

Exactly how the organism is transmitted is still puzzling. Cats seem to get infected by flea infestation, or by blood transfusion from another infected cat. Fleas from cats who have the organism in their bloodstream have cultured positive for the organism as well. Pregnant cats that are infected do not seem to transmit the infection to their kittens transplacentally. Because fleas may carry the organism, human infection with Bartonella from fleas is theoretically possible; however, this has not yet been documented. Live Bartonella organisms are excreted in flea feces, and very recent research has shown that flea feces is the major transmitting agent from an infected and susceptible cat.

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