Cat Scratch Disease - Causes

Authored by Dr Jacqueline Payne, 19 Jun 2017

Patient is a certified member of
The Information Standard

Reviewed by:
Dr Colin Tidy, 19 Jun 2017

Cat scratch disease is caused by a germ (bacterium) called Bartonella henselae (B. henselae). It used to be called Rochalimaea henselae.

Most cats in the world are infected by B. henselae at some point in their lives, usually when they are kittens less than a year old. It doesn't cause them any problems at all, except very rarely. They catch it from fleas that have picked it up from another cat. They can also catch it directly from an infected cat if they have been fighting.

Most people who get cat scratch disease have caught it from a cat and can remember a scratch, bite or a lick from a cat in the previous week to two months. Very occasionally the affected person doesn't remember any contact with a cat. It is possible they have caught it from an infected cat flea. Some people think it can be caught from other animals such as dogs and rabbits, but this hasn't been proven.

Cat scratch disease is quite rare. In a study from the Centers for Disease Control and Prevention (CDC) in the USA, it was estimated that one person out of every 20,000 to 25,000 seeks medical advice for cat scratch disease every year. It was more frequent in people who lived in the Southern USA, where cat fleas are more common as it is warmer.

Anyone can get it, but it particularly affects children aged 5-9. This may be because they are more likely to play with a cat or kitten in a way that encourages it to scratch them.

It seems that it is more likely to follow a scratch from a kitten than from a cat. This is because, although most cats are likely to pick up the germ that causes it at some point, they are most likely to be infected with it when they are kittens. Their immune system then gets rid of it, so they no longer have it when they are older. Kittens are also more likely to scratch than older cats, as they learn how to catch prey.

Further reading and references

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