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Cat-Scratch Disease

(Cat-Scratch Fever)

By

Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Last full review/revision Feb 2020| Content last modified Feb 2020
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NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
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Topic Resources

Cat-scratch disease is infection caused by the gram-negative bacteria Bartonella henselae and transmitted by a scratch or bite from an infected cat, often causing a crusted bump and swollen lymph nodes.

  • People with cat-scratch disease have a red bump at the site of the scratch, and some have a fever, headache, poor appetite, or swollen lymph nodes.

  • In people with a weakened immune system, the infection may spread throughout the body and, without treatment, may result in death.

  • Doctors do blood and fluid tests to check for the bacteria.

  • Usually, applying heat to the infected area and taking pain relievers are all that is needed, but if people have a weakened immune system, doctors give them antibiotics.

(See also Overview of Bacteria.)

Most domestic cats throughout the world are infected, but most show no signs of illness. Fleas transmit the Bartonella bacteria from one cat to another. People become infected by a cat bite or scratch, which need not be severe for infection to occur.

Symptoms

At the site of a cat bite or scratch, a red bump develops within about 3 to 10 days. The bump usually has a crust and sometimes contains pus. Within 2 weeks (sometimes after the scratch has healed), nearby lymph nodes swell and become tender and filled with pus. People may have a fever, headache, and poor appetite. Sometimes pus drains from the swollen lymph nodes.

Usually, people have no other symptoms, and cat-scratch disease resolves on its own. But in people with human immunodeficiency virus (HIV) infection, AIDS, or another condition that weakens the immune system, infection can spread throughout the body and, without treatment, can be fatal.

Diagnosis

  • Blood tests

  • Sometimes blood culture

  • Sometimes lymph node fluid aspiration or biopsy

To diagnose cat-scratch disease, doctors measure antibodies to the bacteria in the blood. (Antibodies are proteins produced by the immune system to help defend the body against a particular attacker, such as the bacteria that cause cat-scratch disease.) In very sick people or people with a weakened immune system, doctors may also take a sample of blood and send it to a laboratory to grow (culture) and identify the bacteria. Or doctors may insert a needle in an infected lymph node to remove a sample of fluid. Doctors then use the polymerase chain reaction (PCR) technique on this sample to increase the amount of the bacteria's DNA, so that the bacteria can be detected quickly.

If the diagnosis is unclear, particularly if cancer is suspected, doctors take a sample of tissue from a swollen lymph node and analyze it (lymph node biopsy).

Treatment

  • Heat and pain relievers

  • Sometimes an antibiotic

For people with a healthy immune system, applying heat to the infected area and taking pain relievers are usually adequate.

Sometimes doctors also give antibiotics such as azithromycin to reduce swelling in the lymph nodes and to keep the disease from spreading.

If people with a weakened immune system (particularly those with HIV infection or AIDS) have an infection that has spread, they need to take antibiotics. Antibiotics that may be used include ciprofloxacin, gentamicin, and doxycycline. These antibiotics need to be taken for weeks to months.

People with a weakened immune system can avoid getting the infection by avoiding domestic cats.

More Information

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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