Cat scratch disease: Causes and treatment

What is cat scratch disease, and what are its symptoms?

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Robert Steele

Robert W. Steele, MD, is a board certified pediatrician at St. John's Regional Health Center in Springfield, MO. He graduated from medical... Read more

Cat scratch disease is an interesting infection because, while the disease has been known since 1931, it wasn't until relatively recently (about 1994) that the actual cause of it was identified. Cat scratch disease is identified primarily by typical symptoms and course of events.

The Typical Symptoms

  1. The person receives a scratch or bite from a cat. Sometimes an actual break in the skin is not recognized - but, interestingly, most of the cases involve kittens rather than adult cats (more on this later).
  2. About three to 10 days later, a non-painful, brownish-red, circular raised area around the scratch or bite develops. This lesion may last for days or even a couple of weeks.
  3. In a couple of weeks, a few lymph nodes near the area of the original scratch or bite enlarge. When the scratches are on the arms, the lymph nodes in the armpits or around the elbows are usually the ones that enlarge. When the legs are scratched, the nodes in the groin often get bigger, etc.
  4. These lymph nodes often hurt, and the swelling lasts for several weeks, after which they slowly decrease to their normal size.

Some people have other associated symptoms such as fever, feeling run-down, headaches and neck or abdominal pain.

The Unusual Symptoms

Uncommonly, two other manifestations of cat scratch disease can occur in the person who otherwise has a normal immune system:

Parinaud's Oculoglandular Syndrome - This is when the person gets one red eye (like pink eye) and swollen lymph nodes located in the back of the ear. This usually resolves without any special treatment. It is felt that this form of the infection is caused by the bacterium getting into the eye even though it hasn't been scratched.

Encephalopathy - This is a fancy word for when the brain seems to be affected by the disease. Symptoms of brain involvement include seizures, hearing loss, loss of function in certain muscle groups and coma. These symptoms are rare, and almost all children fully recover.

How Do We Get It from Cats?

As I mentioned, the bacterium that causes cat scratch disease (Bartonella henselae) was recently identified. This has led to an explosion of information concerning how infection occurs. It has been recognized for quite some time that being exposed to a kitten - as opposed to a cat - increases the risk of infection. This is because kittens have no immunity to the infection, so they are the ones who get the bacterium in their blood. While the bacterium is in their blood, they can easily transmit it to a person by scratching or biting. So, where do the kittens get this bacterium in the first place? There is a large body of evidence to suggest they get it from fleas. The fleas bite a kitten who has the bacterium and then transmit it to the next kitten they bite. There is no evidence to suggest the fleas are able to transmit the infection to people. Once the kitten has gotten the bacterium in its blood, the immune system is able to fight it off and make the kitten immune to future exposures to this bacterium. That is why older cats rarely transmit the disease to humans. The infection itself does not seem to cause any problems in kittens or cats.

Treatment

From what is currently known, it seems that antibiotics do not help in the typical course of cat scratch disease. For those that have the rare complications of the infection - or who have lymph nodes that do not heal within a few months - antibiotics may be helpful. The only instance in which antibiotics are clearly known to help is when the infection occurs in someone with a poor immune system, for example, people with AIDS or cancer patients.

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