Bartonella henselae is a gram-negative bacterium that is passed on to kittens and young cats by fleas, or possibly other biting insects. Older cats generally do not carry Bartonella henselae because their immune systems are well developed and better able to clear the infection. Kittens and young cats usually do not get sick from the bacteria, but humans can become seriously ill when bitten or scratched by an infected cat.
Cat scratch disease is especially threatening to people with compromised immune systems; for them, symptoms of the illness may remain for an extended period of time. Individuals with normal immune systems, however, are usually resistant to infection, or are able to fight off the bacteria in a couple of weeks to months.
