Cat-scratch disease is an uncommon infection that typically results from a cat's scratch or bite. Most
Cat-scratch disease (also called cat-scratch fever) is caused by the Bartonella henselae bacterium, which is found in cats around the world and is transmitted from cat to cat by fleas. Researchers have discovered that large numbers of North American cats carry antibodies for the disease (meaning that the cats have been infected at some point in their lives). Some parts of North America have much higher rates of cat infection than others, however. Bartonella henselae is uncommon or absent in cold climates, which fleas have difficulty tolerating, but prevalent in warm, humid places such as Memphis, Tennessee, where antibodies were found in 71 percent of the cats tested. The bacterium, which remains in a cat's bloodstream for several months after infection, seems to be harmless to most cats, and normally an infected cat will not display any symptoms. Kittens (cats younger than one year old) are more likely than adult cats to be carrying the infection.
Bartonella henselae can infect people who are scratched or (more rarely) bitten or licked by a cat. It cannot be passed from person to person. Although cats are popular pets found in about 30 percent of American households, human infection appears to be rare. One study estimated that for every 100,000 Americans there are only 2.5 cases of cat-scratch disease each year. It is also unusual for more than one family member to become ill; a Florida investigation discovered multiple cases in only 3.5 percent of the families studied. Children and teenagers appear to be the most likely victims of cat-scratch disease, although the possibility exists that the disease may be more common among adults than previously thought.
Causes and symptoms
The first sign of cat-scratch disease may be a small blister at the site of a scratch or bite three to ten days after injury. The blister (which sometimes contains pus) often looks like an insect bite and is usually found on the hands, arms, or head. Within two weeks of the blister's appearance, lymph nodes near the site of injury become swollen. Often the infected person develops a fever or experiences fatigue or headaches. The symptoms usually disappear within a month, although the lymph nodes may remain swollen for several months. Hepatitis, pneumonia, and other dangerous complications can arise, but the likelihood of cat-scratch disease posing a serious threat to health is very small. AIDS patients and other immunocompromised people face the greatest risk of dangerous complications.
Occasionally, the symptoms of cat-scratch disease take the form of what is called Parinaud's oculoglandular syndrome. In such cases, a small sore develops on the palpebral conjunctiva (the membrane lining the inner eyelid) and is often accompanied by conjunctivitis (inflammation of the membrane) and swollen lymph nodes in front of the ear. Researchers suspect that the first step in the development of Parinaud's oculoglandular syndrome occurs when Bartonella henselae bacteria pass from a cat's saliva to its fur during grooming. Rubbing one's eyes after handling the cat then transmits the bacteria to the conjunctiva.
A family doctor should be called whenever a cat scratch or bite fails to heal normally or is followed by a persistent fever or other unusual symptoms such as long-lasting bone or joint pain. The appearance of painful and swollen lymph nodes is another reason for consulting a doctor. When cat-scratch disease is suspected, the doctor will ask about a history of exposure to cats and look for evidence of a cat scratch or bite and swollen lymph nodes. A blood test for Bartonella henselae may be ordered to confirm the doctor's diagnosis.
For otherwise healthy people, rest and over-the-counter medications for reducing fever and discomfort (such as acetaminophen) while waiting for the disease to run its course are usually all that is necessary. Antibiotics are prescribed in some cases, particularly when complications occur or the lymph nodes remain swollen and painful for more than two or three months, but there is no agreement among doctors about when and how they should be used. If a lymph node becomes very swollen and painful, the family doctor may decide to drain it.
Most people recover completely from a bout of cat-scratch disease. Further attacks are rare.
Certain common-sense precautions can be taken to guard against the disease. Scratches and bites should be washed immediately with soap and water, and it is never a good idea to rub one's eyes after handling a cat without first washing one's hands. Children should be told not to play with stray cats or make cats angry. Immunocompromised people should avoid owning kittens, which are
Acetaminophen—A drug used for pain relief as well as to decrease fever. A common trade name for the drug is Tylenol.
Acquired immunodeficiency syndrome (AIDS)—An infectious disease caused by the human immunodeficiency virus (HIV). A person infected with HIV gradually loses immune function, becoming less able to resist other infections and certain cancers.
Antibiotics—Drugs that are designed to kill or inhibit the growth of the bacteria that cause infections.
Antibody—A special protein made by the body's immune system as a defense against foreign material (bacteria, viruses, etc.) that enters the body. It is uniquely designed to attack and neutralize the specific antigen that triggered the immune response.
Bacteria—Singluar, bacterium; tiny, one-celled forms of life that cause many diseases and infections.
Hepatitis—An inflammation of the liver, with accompanying liver cell damage or cell death, caused most frequently by viral infection, but also by certain drugs, chemicals, or poisons. May be either acute (of limited duration) or chronic (continuing). Symptoms include jaundice, nausea, vomiting, loss of appetite, tenderness in the right upper abdomen, aching muscles, and joint pain. In severe cases, liver failure may result.
Immune system—The system of specialized organs, lymph nodes, and blood cells throughout the body that work together to defend the body against foreign invaders (bacteria, viruses, fungi, etc.).
Immunocompromised—A state in which the immune system is suppressed or not functioning properly.
Lymph nodes—Small, bean-shaped collections of tissue located throughout the lymphatic system. They produce cells and proteins that fight infection and filter lymph. Nodes are sometimes called lymph glands.
Pneumonia—An infection in which the lungs become inflamed. It can be caused by nearly any class of organism known to cause human infections, including bacteria, viruses, fungi, and parasites.
Pus—A thick, yellowish or greenish fluid composed of the remains of dead white blood cells, pathogens, and decomposed cellular debris. It is most often associated with bacterial infection.
Lex, Joseph R. "Catscratch Disease." eMedicine, December 30, 2003. Available online at <www.emedicine.com/emerg/topic84.htm> (accessed December 25, 2004).
Rosalyn Carson-DeWitt, MD