Cat scratch disease is an infection transmitted by cat scratches, cat bites or other exposure to cat saliva. Patients who are bitten experience swelling of the lymph nodes (round or oval-shaped immune system glands) near the site of the scratch. Cat scratch disease is one of the common sources of chronic lymph node swelling in children.

The bacteria Bartonella henselae are responsible for cat scratch disease. Cats infected with these bacteria are able to transmit the disease for only a few weeks. It is unclear exactly how cats acquire these bacteria, although it is believed that it may be due to contact with fleas. Younger cats seem to become infected more often than older cats, with kittens having the highest rates of infection. The infection lives in a cat’s saliva and experts believe about half of all cats become infected during their lives. Cats themselves do not become sick from exposure to these bacteria and do not display any signs or symptoms when infected. Therefore, there is no way to decipher which cats have the disease. 

Cat scratch disease is transmitted through exposure to cat scratches or bites. In addition, cat saliva can infect a person through contact with broken skin or the white of the eye. Some people may get the disease after petting a cat whose fur is covered with the bacteria, and then rubbing their eyes. In rare cases, the disease occurs from contact with other pets.

Although Bartonella henselae has been found in fleas, and contact with fleas is believed to cause the condition in cats, there is no research suggesting a bite from an infected flea can directly infect humans.

Cat scratch disease is found in all areas of the United States, but occurs most often in humid regions. Incidence levels are highest during the fall and winter months. Each year, about 22,000 cases are diagnosed, according to the American Academy of Family Physicians (AAFP). Children under 21 are most likely to be infected. Between 60 and 90 percent of cat scratch disease cases occur in children and young adults. In addition, males are more likely than females to contract the infection. Cat scratch disease cannot be transmitted from person to person.