Cat scratch disease is a self-limiting infection caused by a bacillus called Bartonella henselae. It is transmitted to cats by the bite of a flea and cats act as reservoir for the disease. Though most people get the disease from cats, it may also be caused after exposure to dogs, goats, squirrels, and even barbed wire. There is usually a history of bite or scratch to the head, neck, or upper limb. Within a few days there may be a small skin lesion and by 2 weeks the local lymph gland becomes enlarged and painful. This may be accompanied by malaise &/or loss of appetite. Fever occurs in about 1/3rd individuals.
The diagnosis is made by testing the blood for IgG and IgM antibodies. The presence of IgM antibodies suggests recent infection but low levels may persist for more than a year following an infection. IgG antibody is suggestive of current or past infection. Generally, no treatment is required as the disease resolves spontaneously but antibiotics may be needed if complicated skin infections are present.
Other conditions like mononucleosis, TB, chronic granulomatous disease etc. need to be excluded.