Cat-Scratch Disease

by Charles H. Booras, MD


What is cat-scratch disease, and how do people get it?

Cat-scratch disease is an infection caused by bacteria (germs) carried in cat saliva. The bacteria can be passed from a cat to a human. Cats may get the bacteria from ticks and fleas, although this hasn't been clearly proven yet. Studies in the early 1990's found that the Bartonella henselae bacterium is responsible for the disease. Approximately 38% of household cats tested positive for the bacterium in one study from 1992.

You can get cat-scratch disease from a cat bite or cat scratch. You can get the infection after a cat scratches you if the cat's paws have the bacteria on them. A cat can get the bacteria on its paws when it licks itself. Then, when the cat scratches you, the bacteria on the cat's paws and claws may be passed on to you. With a cat bite, the cat can pass the bacteria to you in its saliva. You can also get the bacteria in your eyes if you pet a cat that has the bacteria on its fur and then rub your eye with the hand you used to pet the cat. You are at higher risk if your cat sleeps with you, licks you, or is allowed outdoors.

The symptoms of cat-scratch disease develop about six to eight weeks after a cat scratch, bite, or other direct contact with a cat or it's saliva. Many people who get cat-scratch disease do not ever remember being scratched or bitten by a cat.

Cat-scratch disease is not a severe illness in people who are healthy. But it can be a problem in people with weak immune systems. People with weak immune systems include those who are receiving chemotherapy for cancer, those who have diabetes or those who have acquired immunodeficiency syndrome (AIDS).

What are the signs of cat-scratch disease?

A sore may develop where a cat has bitten or scratched you. The sore might not happen right away. It may take three to 10 days for the sore to appear after the bite or scratch. It will usually look like a small red bump; similar to a pimple, but usually without the white "head".

The sore may take a long time to heal. An infection of the lymph nodes (also called lymph glands) also develops, most often in the glands that are near the place where you got the cat scratch or cat bite. For example, if the infection is from a cat scratch on your right arm, the glands in your right armpit (not the other side of the body) may become quite tender and swollen. The lymph nodes may swell to an inch or more in size. Fever and flu-like symptoms such as fatigue, malaise and headache are often present. These symptoms can last weeks to months. Rarely, nodes remain enlarged for as long as 24 months.

Cat-scratch disease can occur in other parts of the body. Some people get the infection on an eyelid or underneath an eyelid. Other people get a rash over their entire body. Still other people get an infection of the liver or spleen or an infection of the bones or the joints.

What tests are needed to diagnose cat-scratch disease?

If you remember that you were bitten or scratched by a cat, your doctor will probably be able to diagnose the illness based on the fact that you were bitten or scratched and then got painful, swollen lymph nodes. In children, CSD is the most common cause of prolonged swelling of lymph nodes in a localized area. 80% of all cases occur in persons under the age of 21. When the diagnosis is not clear to your doctor, a blood test may help your doctor make the diagnosis.

How is cat-scratch disease treated?

In most people, cat-scratch disease is a benign, self-limited illness and clears up without treatment. However, antibiotics (medicines that kill bacteria) may be needed when infected lymph nodes stay painful and swollen for more than two or three months. Antibiotics may also help if you have a fever for a long time or if the infection is in your bones, liver or another organ. Your doctor can determine if treatment with an antibiotic is necessary. More rapid reduction in lymph node swelling has been noted with antibiotic therapy. If treatment is deemed necessary, the antibiotic will often be continued for six or more weeks. Treatment is usually discontinued once the lymph node has decreased in size and all fever and flu-like symptoms have resolved for five to ten days.

Sometimes surgery to drain the node is needed if it is very large or painful. This is usually done by the simpler needle drainage rather than incision and drainage.

Can cat-scratch disease be prevented?

Avoiding cats is the simplest way to prevent the disease, but it is not usually necessary to get rid of your cat. Having your cat declawed stops your cat from being able to spread the infection if your cat scratches you or one of your family members. Washing your hands carefully after handling your cat is another way to prevent the infection. Getting rid of fleas on your cat may also help prevent you and your family members from catching the infection.

Cats only seem to be able to transmit this infection for a few weeks. Young cats seem to be more susceptible to carrying the bacteria than older cats. Households with kittens have higher rates of infection. If the kittens have fleas, the infection rate is 29 times higher than if the kittens do not have fleas.

Should cats be treated?

Cats require no treatment. The bacteria doesn't cause a sickness in cats. They merely carry the bacteria that causes cat-scratch disease in people.

Should your doctor be seen if you are bitten or scratched by a cat?

See your doctor if you notice any of the following problems:

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