Cat scratch disease (CSD) is an infection that is thought to be caused by bacteria carried in cat saliva. Humans can get it if they are scratched, bitten or otherwise exposed to the saliva of an infected cat.
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The disease is usually not serious. It typically involves swollen lymph glands and
flu-like symptoms that resolve within a few weeks.
What causes cat scratch disease?
Many recent studies have implicated the bacterial organism Bartonella henselae (also called cat scratch disease bacillus) as the primary (but not the sole) cause of cat scratch disease. Other Bartonella species may also be involved in CSD.
Cats do not become ill when they are infected and act only as vectors of the disease, carrying the bacteria on their claws or teeth. Once infected, cats carry bacteria in their blood for many months but seem to be able to transmit the infection only for a few weeks. Kittens appear to be more likely to carry the bacteria than older cats and households with kittens have higher rates of human infection. If the kittens have fleas, the infection rate is 29 times higher than if they are flea-free. In rare instances, the disease may also be contracted from dogs.
The disease is spread to humans through contact with the saliva of an infected cat as a result of a cat bite or scratch, or if cat saliva makes contact with broken skin or the conjunctiva (membrane lining the eye and inner eyelid). You can get the infection from a cat scratch because the cat contaminates its paws by licking them. You can get the bacteria in your eyes if you stroke a cat that has the bacteria on its fur (also from licking) and then rub your eyes. You can also become infected if you scratch yourself on a surface contaminated with infected cat saliva.
Some people with cat scratch disease do not remember being scratched or bitten by a cat, and some have had no contact with cats at all. This makes it likely that there are other modes of transmission, such as environmental sources of the bacteria or from other animals.
Who gets cat scratch disease and who is at risk?
Despite widespread presence of Bartonella henselae in cats and the fact that cat scratch disease is found all over the world, it appears that CSD is not easily acquired. One estimate by the Centres for Disease Control found that there were only 2.5 cases of CSD per 100,000 people a year in the United States. While multiple cases of CSD in one household can occur, this situation is rare. One study found that more than one member of a family contracted CSD only 3.5% of the time.
The majority of individuals who contract CSD are under the age of 17 and are usually under the age of 12. Children are most commonly infected with cat scratch disease because they are most often the victims of a scratch or bite. CSD is possibly the most common cause of chronic lymph node swelling in children.
CSD is rarely a severe illness in people who are healthy. However, it can be a problem for people with weakened immune systems, for example those who are receiving chemotherapy for cancer, diabetics or people with AIDS.
Symptoms and signs of cat scratch disease
Typical symptoms of cat scratch disease include the following:
A history of contact with a cat, together with a scratch or injury.
In about half of all cases of CSD, a persistent crusting sore or blister, that looks similar to a boil, occurs at the site of the scratch or bite. This is usually the first sign of CSD infection. The sore might not appear immediately - it might take three to 10 days after the bite or scratch to appear. The sore may take a long time to heal. The most common site of a cat scratch is on the hands, arms and face and therefore is the most common place for a CSD infection.
Painful lymph node swelling occurs in the area close to where the skin was infected (bitten, scratched, etc.) about two to three weeks after exposure and may persist for months. Swelling may occur at the site of the initial infection followed by enlarged lymph nodes along the lymph drainage route from the injury site. For example, if the infection is from a cat scratch on your arm, the glands in your armpit may become tender and swollen. Occasionally nodes may form a fistula (opening) through the skin and drain.
About one third of people with CSD also get a low grade fever and feel like they have flu, with possible weakness, fatigue, nausea, chills, loss of appetite and headaches.
Less common symptoms:
Weight loss
Enlarged spleen (splenomegaly)
Sore throat
Rash
Bone or joint pain
Abdominal pain (without fever, vomiting or diarrhoea)
How is cat scratch disease diagnosed?
If you remember that you were bitten or scratched by a cat and then got painful, swollen lymph nodes, your doctor will probably be able to diagnose the illness based on this history. In some cases, physical examination also shows an enlarged spleen.
When the diagnosis is not clear, diagnostic tests may help your doctor make the diagnosis.
Tests used in the diagnosis of cat scratch disease:
Bartonella henselae IFA test (uses fluid or tissue from a lymph node)
CSD skin test: the cat scratch disease antigen (a characteristic protein) is injected just under the skin to determine if your immune system is able to react to the antigen. A positive result indicates that you may have CSD.
A lymph node biopsy (tissue sample) to rule out other causes of swollen glands. Other diseases, such as tuberculosis, brucellosis, and lymphoma, can cause similar symptoms.
How is cat scratch disease treated?
In most people, cat scratch disease is mild and resolves without treatment and with no after-effects. Sometimes, the symptoms will last several months and then clear up.
Medication
Antibiotics may be needed when infected lymph nodes stay painful and swollen for more than two or three months. Antibiotics may also help if you have a fever for a long time or if the infection is in your bones, liver or another internal organ. Antibiotics which have been shown to be effective against the presumed causative bacteria include: erythromycin (E-Mycin), sulfamethoxazole and trimethoprim, doxycycline and rifampin combined with another agent. However, their efficacy in humans is doubtful.
Lymph node drainage
If a lymph node is very large or painful, your doctor may drain it to help relieve the pain. The lymph node is drained by putting a needle through normal skin to the side of the node and then moving the needle to the swollen node. The needle is then inserted into the node and the fluid is drained out. This is not recommended routinely.
What is the outcome of cat scratch disease?
Cat scratch disease is mild and self-limiting in the majority of patients and lasts for about two to four weeks, although it may take some months for the swollen lymph nodes to return to normal. In rare cases, it may persist for a period of up to two years. Prognosis in healthy people is excellent.
People with compromised immune systems, such as AIDS and cancer patients, are most at risk and can become seriously ill, although treatment with antibiotics generally leads to recovery.
In a very small number of cases, CSD can develop serious complications, when parts of the body such as the bones and internal organs become infected. There have been rare cases of severe infection that have led to serious illnesses such as pneumonia, encephalitis, hepatitis and even death due to CSD.
Can cat scratch disease be prevented?
A common-sense approach is the best way to safeguard against CSD. Avoiding contact with cats helps to prevent the disease. Where this is not feasible, good hand washing after handling your cat, avoiding scratches, bites and cat saliva minimises the risk of infection. If you do get bitten or scratched, wash the wound immediately with antiseptic soap and hot water. Children should be taught not to tease or annoy cats and rough play should be discouraged. Some people use a glove when 'play-fighting' with their cat. Keep your pets free of fleas.
CSD is primarily a concern in homes with immunocompromised people. Since kittens are more likely to carry Bartonella henselae than adult cats, it is recommended that people with compromised immune systems adopt cats older than one year of age as pets to reduce the risk of contracting CSD. Any cat suspected of carrying Bartonella henselae should be isolated from sick or immunocompromised individuals.
There is no reliable and available diagnostic test to determine if a cat is a carrier of Bartonella henselae. Since carrier cats are usually healthy and multiple cases of CSD within a household are rare, euthanasia of a suspected carrier is not warranted. De-clawing is also not recommended as infection can occur without a cat scratch.
When to call the doctor
Call your doctor if you notice any of the following:
A cat scratch or bite that does not heal in the usual length of time
An area of redness around a cat scratch or bite that continues to spread for more than two days after the injury
Fever that lasts for several days after a cat scratch or bite
Painful and swollen lymph nodes for more than two or three weeks
Bone or joint pain, abdominal pain, or an unusual degree of tiredness for more than two or three weeks.
(Reviewed by Dr Andrew Whitelaw, University of
Cape Town and Groote Schuur Hospital)
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