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Cat Scratch Disease

Pet Tales  by Barry B. Burtis D.V.M.

Cat Scratch Disease

Zoonoses are diseases that are transmitted from animals to people. Veterinarians are often asked about zoonotic diseases because of our training and experience in dealing with illness in animals. There are not many such diseases that we can get from our pets but it is important to have an accurate understanding of the risk. Cat scratch disease (CSD), as the name suggests, is carried by cats.

The disease is caused by the bacterium Bartonella henselae. It usually is associated with either being scratched or bitten by a cat. One study in the U.S. estimated that as many as 22,000 - 24,000 cases of the disease occur in that country each year. In people affected, CSD causes lymph nodes near the site injured to become swollen and painful. A fever, muscle aches and general malaise is usually reported. More than 90 per cent of cases are mild and symptoms disappear without treatment in a few weeks to a few months. However, more severe problems, requiring hospitalization, sometimes occur. People who are HIV-positive or are immunocompromised for other reasons can develop more serious or even life threatening forms of the disease. A physician should always be consulted when serious scratches or bites from any animal happen.

We really do not know how many cats are infected with B. henselae. Prevalence in cats varies with geographic regions in North America. In some areas as many as 50% or more of the healthy cat population may be infected. Most infected cats are younger than 2 years of age. Feral or stray cats are more likely to harbour the illness than pet cats. It is most likely that fleas are responsible for spreading the disease between cats. The number of infected cats is highest in geographic areas with warm humid climates that are well suited to support large flea populations. Southern states in the U.S. have a much higher incidence of infection in cats than those states near us, in Ontario.

When cats are infected with the causative organism it can live in their bodies a long time but most animals develop few, if any symptoms. Sometimes they will develop some enlarged lymph nodes and a low fever, but there seem to be no lasting ill effects. Antibodies to the bacteria can be found in an infected cat. Occasionally the organism can be cultured from the cat's blood but diagnosis of the problem can be quite difficult. Unfortunately, there is no known effective way to treat the infection in cats. A number of different antibiotics have been evaluated for the treatment of infected cats and have proven to be unreliable Therefore, treating cats is not a method of preventing CSD in humans. Also, although most cases of CSD in people can be traced to a cat scratch, it can occur from bites or other means of spread. As a result, declawing a cat does not absolutely prevent infections either.

The most effective way of preventing B. henselae infections in pet cats is to keep the cats free of flea infestation. We are fortunate that we now have very effective medications to help us do this. These medicines are safe to use in kittens from a very early age. This is important since, as mentioned, it is they who are most susceptible to this infection. To begin this treatment promptly, if it is needed, is another reason why it is a good idea to have a kitten examined by a veterinarian as soon as possible after acquiring it. In addition, it is important to try and use every means possible to reduce scratches and bites by discouraging aggressive behaviour by cats. Cat owners should seek advice from their veterinarian when such behaviour is noticed. We should always avoid teasing kittens and not encourage rough play with them. If a bite or scratch does occur, the bite should be washed immediately with soap and warm water and covered to keep it clean. Cats should not be allowed to lick a human's open wound or broken skin.

The pleasure and benefits of cat ownership, in my opinion, far outweigh the risks of acquiring CSD from a cat, provided these steps to minimize the risk are taken.