Bartonella henselae and Cat Scratch Disease (CSD)

Background

Cat scratch disease (CSD) is a zoonotic infection (i.e. acquired from animals) caused by the bacterium Bartonella henselae. Cats are the main reservoir for B. henselae and humans usually become infected after being scratched or bitten by a cat. CSD occurs worldwide. Although anyone can become infected, the disease is more frequently seen in children and young adults.

Symptoms

CSD often begins with a small papule developing at the site of cat scratch or bite within 3-14 days of the infection. Nearby lymph node become swollen and can persist for several months. They normally appear in the neck, axillary (underarm) or groin areas. It may take up to 50 days for the enlarged lymph nodes to appear, therefore individuals do not always recall any cat scratch or bite. Other symptoms include fever, fatigue, malaise, headache and poor appetite.

Approximately 5-10% of patients may develop other forms of CSD. The commonest is an eye infection characterised by conjunctivitis and swollen lymph nodes near the ear. Other complications may include rash, liver and spleen enlargement, or more rarely encephalitis (inflammation of the brain) or retinitis. Generally, patients completely recover without any long term effect.

In healthy individuals, CSD is a mild and self-limiting illness. However, patients with a weakened immune system may develop more severe disease, such as bacillary angiomatosis. This is a deeper infection of the skin and underlying tissues that may spread to other organs, and can be life-threatening if not treated.

Transmission

Humans usually become infected after being scratched or bitten by a cat. There is no transmission from person to person. Cats can carry the infection in their blood for a long period of time (up to one year), but often do not present any sign of illness. Seroprevalence surveys have shown that up to 40% of domestic cats in the UK have been infected by B. henselae at some stage in their lives. Kittens are more likely to be infected. The infection is transmitted between cats by their fleas (Ctenocephalides felis).

Treatment

In healthy patients presenting with mild symptoms, antibiotics are generally not recommended. Antimicrobial therapy has not proven effective in the treatment of typical CSD cases. Moreover, all symptoms generally resolve spontaneously. Supportive therapy such as pain killers may help to relieve symptoms. Occasionally, when lymph nodes become too large and painful, the accumulated fluid inside is removed by needle aspiration. For unusual or complicated cases of CSD, antibiotics may be prescribed.

Diagnosis

Clinical diagnosis is based on physical examination as well as history of cat contact. Laboratory tests are used to confirm the diagnosis. Usually this is by a blood test to detect the presence of B. henselae antibodies. See here for laboratory information and here for UK data

Prevention

General advice for preventing CSD includes avoiding rough play with cats, particularly kittens. Cat scratches and bites should be washed immediately with water and soap and cats should not be allowed to lick open wounds. Cats should be treated for fleas in order to reduce the chance of them becoming infected.

Last reviewed: 24 May 2010