What is Cat scratch?

Cat scratch disease is an infection transmitted by cat scratches, cat bites or other exposure to cat saliva. Patients who are bitten experience swelling of the lymph nodes (round or oval-shaped immune system glands) near the site of the scratch. Cat scratch disease is one of the common sources of chronic lymph node swelling in children.

The bacteria Bartonella henselae are responsible for cat scratch disease. Cats infected with these bacteria are able to transmit the disease for only a few weeks. It is unclear exactly how cats acquire these bacteria, although it is believed that it may be due to contact with fleas. Younger cats seem to become infected more often than older cats, with kittens having the highest rates of infection. The infection lives in a cat’s saliva and experts believe about half of all cats become infected during their lives. Cats themselves do not become sick from exposure to these bacteria and do not display any signs or symptoms when infected. Therefore, there is no way to decipher which cats have the disease.

Cat scratch disease is transmitted through exposure to cat scratches or bites. In addition, cat saliva can infect a person through contact with broken skin or the white of the eye. Some people may get the disease after petting a cat whose fur is covered with the bacteria, and then rubbing their eyes. In rare cases, the disease occurs from contact with other pets.

Although Bartonella henselae has been found in fleas, and contact with fleas is believed to cause the condition in cats, there is no research suggesting a bite from an infected flea can directly infect humans.

Cat scratch disease is found in all areas of the United States, but occurs most often in humid regions. Incidence levels are highest during the fall and winter months. Each year, about 22,000 cases are diagnosed, according to the American Academy of Family Physicians (AAFP). Children under 21 are most likely to be infected. Between 60 and 90 percent of cat scratch disease cases occur in children and young adults. In addition, males are more likely than females to contract the infection. Cat scratch disease cannot be transmitted from person to person.

In most cases, cat scratch disease does not pose a serious health threat to the patient. However, patients with compromised immune systems may be at greater risk. This includes people with diabetes or HIV/AIDS, and patients undergoing chemotherapy treatment for cancer. People who have a bout of cat scratch disease develop immunity to the condition thereafter.

Signs and symptoms of cat scratch disease

A bump (papule) or blister (pustule) at the site of injury is the first sign of cat scratch disease. It may take anywhere from three to 10 days before this sore appears, at which point it often is mistaken for an insect bite. Sores most often appear on the arms, hands, neck, head or scalp and are not usually painful. Sores related to cat scratch disease may take several days or months to heal. They do not typically leave a scar.

About two to three weeks after infection, the patient will begin to experience swelling of the lymph nodes near the infection site. For example, a patient bitten on the arm will experience swelling of the lymph nodes in the elbow or armpit. Redness, warmth and draining pus may also be associated with the swollen lymph node. This swelling may continue for months or years and may spread to other lymph nodes in the drainage route connected to the lymph nodes at the injury site. Lymph nodes of the upper arm are most often affected, followed by the head, neck and groin.

About one-third of patients will develop a fever related to cat scratch disease, followed by fatigue, headache and a feeling of overall discomfort. Less frequently, patients may experience loss of appetite (anorexia) and weight loss, an enlarged spleen and a sore throat.

In most cases, cat scratch disease resolves on its own and does not require treatment. However, rare cases should receive medical attention. In some cases, the swollen lymph nodes may form a fistula (an abnormal passage) to the skin. Infection can sometimes spread to the liver, spleen, bones or lungs. In rare cases, patients may also develop an eye infection known as parinaud oculoglandular syndrome. This is characterized by a small sore on the conjunctiva (the membrane lining the eye and inner eyelid), redness of the eye and swollen lymph nodes in front of the ear. Inflammation of the brain may also trigger seizures.

Another rare complication of Bartonella henselae infection is bacillary angiomatosis. This condition is characterized by the appearance of purple or bright red patches on the skin. Most often seen in HIV patients, the condition can lead to disorders of the liver and spleen.

Anyone experiencing symptoms of these complications is urged to seek medical attention.

Other symptoms that indicate a need for medical care include:

• Cat scratches or bites that do not heal
• Redness around a cat scratch or bite that increases for more than two days
• Fever that lasts for several days following a bite
• Painful and swollen lymph nodes for more than two weeks
• Bone or joint pain
• Abdominal pain
• Fatigue that lasts for more than two weeks

How is it diagnosed?

A physician will perform a complete physical examination and compile a thorough medical history in diagnosing cat scratch disease. During the exam, the physician will look for a characteristic scratch or injury and the presence of an enlarged spleen (splenomegaly). In many cases, cat scratch disease can be diagnosed solely on the basis of a patient’s report of being bitten or scratched by a cat.

Blood tests may be ordered to look for the presence of the Bartonella henselae bacteria. In addition, a Bartonella henselae immunofluorescent antibody (IFA) test may allow the physician to examine fluid or tissue from a lymph node. In some cases, a lymph node biopsy may be performed to rule out other causes of swollen glands.

At one time, a cat scratch disease skin test was the chief method used to test for infection. In the skin test, the cat scratch disease antigen is injected under the skin of the forearm. This causes a small lump to form and the site is labeled. Between 48 and 72 hours later, the site will be checked to determine whether or not a positive reaction has occurred. However, this test has been largely replaced by blood tests and the IFA test.

How is it treated?

In most cases, medical treatment is not needed for cat scratch disease. Scratches or bites should be washed with soap and water, and patients can usually take an over-the-counter pain reliever to lessen any discomfort associated with the injury. Patients should not take any medication without first consulting a physician. Children should never be given aspirin, as it is associated with a potentially life-threatening condition called Reye syndrome. Warm, moist compresses can be used to treat swollen lymph nodes.

Severe forms of the disease – such as swelling that lasts for more than two to three months – may require medical treatment, such as a course of antibiotic medications. Antibiotics may also be used to treat patients with immune system problems, or those with long-term fever or infection in the bones, liver or another organ.

Lymph nodes that are painfully swollen and those that fail to regress after weeks or months may benefit from fine needle aspiration. In this procedure, a needle is inserted into the node and the fluid is removed. Lymph nodes may need to be drained multiple times.

Cat scratch disease poses no danger to cats, and felines with the condition do not require treatment.

Medications

What might complicate it?

In rare instances, encephalitis may occur.

Predicted outcome

The prognosis for this infection is excellent. Full recovery is expected, even in individuals with impaired immune systems.

Alternatives

Lymphoma and other malignancies, tuberculosis, lymphogranuloma venereum, and acute bacterial infection may mimic the lymph node involvement. Cat scratch fever may be differentiated on the basis of nodal biopsy.

Appropriate specialists

Infectious disease specialist.

Last updated 27 June 2015