What is cat scratch disease and what causes it?
Cat Scratch Disease (CSD) or Cat Scratch Fever is a disease of humans, not of cats. Although a cat scratch may be associated with the development of disease, this is not believed to be the means by which infection occurs. A microorganism called Bartonella henselae is the most common cause of this disease. It is now believed that Bartonella organisms are transmitted by arthropods such as fleas and mites. The typical symptoms of CSD are mild fever, chills and lethargy accompanied by enlarged lymph nodes and skin or conjunctival lesions. Most symptoms last for a few days, but the enlarged lymph nodes may persist for weeks or months. In a minority of people, a more severe disease can develop, with various combinations of high fever, weight loss, arthritis, enlarged liver and spleen, pneumonia and neurological signs. These more serious forms of the disease occur in people with immunodeficiency states, such as in HIV-infected people or individuals undergoing chemotherapy.
"The typical symptoms of CSD are mild fever, chills and lethargy accompanied by enlarged lymph nodes and skin or conjunctival lesions."
How common is cat scratch disease?
It is not possible to give accurate estimates of the prevalence of cat scratch disease since not all cases are diagnosed or reported, but it is probably a rare disease. Surveys carried out in the USA indicate that about 5% of the human population may have been exposed to infection, but only a small proportion of these develop the disease.
It is likely that many infections are without symptoms and go unnoticed, or are of a trivial nature, mimicking a "cold".
"Cats that carry B. henselae do not show any signs of illness."
One report suggests that as many as 40% of cats may have been exposed to B. henselae at some time in their lives. Cats that carry B. henselae do not show any signs of illness; even cats with extremely high levels of B. henselae organisms in their blood do not show any signs of disease. Mainly younger cats and kittens carry the infectious organism. Although they do not show signs of illness, they can be a source of infection to humans until they clear the infection from their blood. Once a cat clears the infection, it appears to be resistant to re-infection.
How do humans become infected?
Although some cases of Cat Scratch Disease follow a scratch from a cat, this is not always the case. Recent evidence suggests that a fleabite is the major source of infection with B. henselae. Infected cats carry the microorganism in their blood, where it can be present in extremely high numbers. When a flea feeds on an infected cat it ingests large numbers of the Bartonella henselae organisms, some of which may be inoculated into a human if the flea takes a blood meal from the human. There are no reported cases of any human being infected more than once.
Is there a vaccine or treatment for Cat Scratch Disease?
There is no vaccine available against Cat Scratch Disease, either for cats or for people. Bartonella henselae is sensitive to a number of antibiotics, including doxycycline and azithromycin. The disease is usually self-limiting, and mild cases will resolve without recourse to antibiotics.