Bartonellosis and Cat Scratch Disease

Bartonellosis is an infection in humans that is caused by a group of bacteria called Bartonella. These bacteria can be spread from infected animals to people through scratches and bites, or possibly from any fleas or ticks that the animal may carry. Although Bartonella was first described in the early 1900s, it was only recently recognized as an important cause of disease in people and domestic animals, including cats and dogs. Bartonella species are now acknowledged as emerging zoonotic pathogens in all six inhabited continents and as the cause of many different diseases. At least eight species of Bartonella are either known or suspected of causing human illness. One of the most common types of bartonellosis in the United States is also known as cat scratch disease (CSD).

WHAT IS CAT SCRATCH DISEASE?

CSD is caused by Bartonella henselae and is the most common zoonotic Bartonella infection in people around the world. People can get CSD when they are bitten or scratched by a cat, or less commonly a dog, that is carrying the bacteria. Between 25% and 40% of cats carry these bacteria at some point during their lifetime, though they rarely show signs of illness when infected. In the United States, it is estimated that more than 20,000 new cases of CSD are diagnosed each year. Most cases occur in children and young adults, probably because they spend more time than adults do playing with cats and kittens.

WHAT ARE THE SIGNS AND SYMPTOMS?

Seven to twelve days after a scratch or bite, people with CSD usually develop a mild infection at the site of injury. They may also experience symptoms such as swollen lymph nodes around the head and neck, fever, headache, tiredness, and loss of appetite. Although infection in most people remains mild, sometimes without any noticeable symptoms, 5% to 9% of people with CSD develop more severe symptoms that may include anemia, infection of the eyes (conjunctivitis or retinitis), pneumonia, nervous system infection (encephalitis), or inflammation of the heart (endocarditis). People with compromised immune systems due to conditions such as HIV/AIDS and cancer are at greatest risk for developing severe CSD, and this population may be prone to developing raised skin lesions known as bacillary angiomatosis. Yet, even with severe symptoms, only one fatal case of CSD has been reported.

Most cats infected with Bartonella show no obvious signs of illness, but infected cats are more likely than noninfected cats to have swollen lymph nodes or inflamed gums and/or eyes. A small number of cats have been reported to develop severe complications from infection, including endocarditis.

Dogs do not typically carry the type of Bartonella that causes CSD, but they can become infected with it and develop severe illness, including liver and heart problems. Dogs are carriers of a different species (Bartonella vinsonii berkhoffii) that does not cause CSD but can lead to severe disease in some people and dogs by causing heart inflammation.

HOW IS BARTONELLOSIS DIAGNOSED AND TREATED?

Clinical diagnosis of CSD in people is based on the detection of swollen lymph nodes and an infected cat scratch or bite. In people with less typical forms of CSD, clinical diagnosis is not easy and usually requires laboratory tests that can confirm the presence or show evidence of Bartonella infection.

Because many cats show evidence of past exposure to Bartonella without posing a current risk of disease transmission, routine laboratory testing of cats is not recommended. However, veterinarians may perform laboratory tests for Bartonella infection in dogs that are ill and have a history of tick exposure.

Treatment for CSD in people depends on the types of symptoms that develop. In immunocompetent people with typical CSD, several types of antibiotics can be used for treatment. However, in most instances, antibiotics do not appear to shorten or improve the course of infection and symptoms resolve on their own in a few weeks. In immunocompromised individuals or those with severe complications from CSD, antibiotic treatment is usually administered for at least six weeks.

In cats, antibiotics have not been shown to be very effective in clearing the infection, which usually resolves on its own (although it may take weeks or even months). Supportive treatment may help lessen the symptoms in severe cases.

In dogs, treatment with antibiotics over a four- to six-week period may help reduce severe Bartonella infections; less severe infections generally aren't treated.

PREVENTION IN PETS AND PEOPLE

Cats likely acquire Bartonella infection from fleas (and dogs may acquire B. vinsonii berkhoffii from ticks), so using dependable flea and tick control products throughout the year is essential for limiting your pet's risk of carrying Bartonella. If you are concerned that your pet may be ill from Bartonella infection, contact your veterinarian.

How Can You Help Prevent These Diseases?

The best ways to reduce the risk of getting CSD are to:

• Keep fleas away from your pet by using veterinarian-approved flea and tick control products year-round
• Avoid activities such as "rough play" with cats, especially kittens, which may lead to scratches and bites
• Thoroughly wash any cat scratch or bite immediately with running warm water and soap
• Not let cats lick any open cuts or wounds
• Contact your physician if an infection develops at the site of a cat scratch or bite or if you develop symptoms such as fatigue, fever, headache, and swollen lymph nodes following the scratch or bite
• Ensure that people with compromised immune systems (such as those with HIV/AIDS, hepatitis, or cancer) take special care around young kittens to avoid exposure to Bartonella
• Keep cats' nails trimmed
• Keep cats indoors to minimize flea exposure