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, painless 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, particularly kittens, throughout the world are infected with Bartonella bacteria. Most infected cats have the bacteria in their blood but do not get sick or show signs of illness.
Cats are infected by fleas. Fleas transmit the Bartonella bacteria from one cat to another. People become infected by a cat bite or scratch, which does not need to be severe for infection to occur.
People also can become infected when a cat licks a person’s open wound.
Ticks, lice, and mosquitoes also may be able to infect people.
Children are most often affected.
Symptoms of Cat-Scratch Disease
At the site of a cat bite or scratch, a red, painless 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 of Cat-Scratch Disease
Blood tests
Sometimes blood culture and PCR test
Sometimes biopsy of a lymph node
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 of Cat-Scratch Disease
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.
People with a weakened immune system can avoid cat-scratch disease by avoiding domestic cats.
More Information
The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
Centers for Disease Control and Prevention (CDC): Cat-Scratch Disease: A resource providing information about cat-scratch disease, including prevention
