Photo by Anoushka, Toronto.

Cat scratch disease, sometimes known as cat scratch fever, is caused by an infection with a bacterium called Bartonella henselae (as well as other Bartonella species). It is spread from cat saliva to people through broken skin. People can get infected via scratches, bites or even a cat licking a person’s open wound or scab. Within three to 14 days of the scratch or bite, an infection can start to appear at the site of the bite or scratch. These signs include redness, swelling, warmth, pain or discharge (pus).

As the disease progresses and signs become systemic, the lymph nodes closest to the wound will enlarge and the person will experience generalized signs such as fever, exhaustion and lack of appetite. If left untreated, cat scratch disease can eventually affect the heart, brain and other organs. The disease is more likely to progress and become more serious in people who are immunocompromised (having a weakened immune system), such as children, the elderly or individuals with an autoimmune disease.

Cats become infected with Bartonella henselae via fleas: they may become exposed following a flea bite or from flea droppings that are deposited in the cat’s own wounds. When cats scratch at the fleas, they deposit the flea droppings (often called flea dirt) underneath their nails and in their mouths.

Cats can also get the infection through fighting with other infected cats. This is another reason why year-round flea control is important for all cats in Southern California, even those who remain indoors. Your veterinarian can help you decide on an appropriate product to use to prevent or treat flea infestations on your cat.

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According to the Centers for Disease Control and Prevention (CDC), up to 40 percent of cats carry the bacteria Bartonella henselae and can potentially cause a cat-scratch-fever infection through a bite or scratch. To make matters worse, cats that carry this bacteria typically do not show any clinical signs.

Occasionally, some cats with very severe infections may have difficulty breathing because the infection may affect the heart. Kittens under a year old are most likely to be infected and are most likely to spread the bacteria to people because they are likely to scratch and bite during play activities. However in most cases, you will not know if you are risk for the disease after a scratch or bite. Therefore, it is best to take all possible precautions to avoid a strike from a cat and foster a positive relationship with your pet.

You can learn about other types of internal parasites in cats (and dogs) on our website.