Cat-scratch disease (also called cat-scratch fever) is an infection caused by the Bartonella henselae bacterium, which is found in cats around the world and is transmitted from cat to cat by fleas. It can infect people who are scratched or (more rarely) bitten or licked by a cat that carries the bacterium.

Researchers have discovered that large numbers of North American cats carry antibodies for the disease (meaning that the cats have been infected at some point in their lives). Bartonella henselae is uncommon or absent in cold climates, which fleas have difficulty tolerating, but prevalent in warm, humid places such as Memphis, Tennessee, where antibodies were found in 71% of the cats tested. The bacterium, which remains in a cat's bloodstream for several months after infection, seems to be harmless to most cats, and normally an infected cat will not display any symptoms. Kittens (cats less...