Cat scratch disease is a disease spread by cats, but that affects only humans; it's also called cat scratch fever. It is most commonly diagnosed in the colder winter and fall months of the year for reasons scientists don't understand; it's possible that cats are more likely to be indoors at this time, raising the chance of human exposure overall.
Cat scratch disease is caused by bacteria called Bartonella henselea that generally lives in the mouths of cats. They spread it to their claws through routine grooming. Interestingly, cat scratch disease is not spread through cat bites, only through cat scratches.
Most Americans have been exposed to cat scratch disease, and 5% of the US population has antibodies in their blood but no history of clinical illness. Because antibodies are only made in response to the invasion of a disease, it is clear that they were exposed to Bartonella directly. It is possible that they did not subsequently become ill, or that the disease was mistaken for the flu.
Cat scratch disease does present with flu-like symptoms. The most common symptoms include fever, chills, and lethargy, but they last for only a few days, much shorter than most flu’s.
There is a more severe form of cat scratch disease that causes high fever, anorexia, weakness, and badly swollen lymph nodes, particularly in the armpits and groin area. Sometimes the lymph swelling gets so bad that the swelling spontaneously ruptures; at other times, doctors choose to surgically drain them to prevent the rupture and relieve the pain.
Typically, the most serious form of the disease is seen in younger children and the elderly and people with compromised immune systems, such as those who have HIV, are receiving chemotherapy, or who have been the recipient of an organ donation. When the serious form of the disease presents itself, the consequences for the victim can be disability or even death.
If the disease in humans is treated immediately with antibiotics, the outcome is usually good, but it's very hard to diagnose because it's so similar to flu and because it is not a common disease. Cat scratch disease is often overlooked in its earliest stages, and only caught when the lymph nodes are involved. Almost every verified case of cat scratch disease follows a cat scratch wound; a few occur after a bite, and a few even crop up with no obvious cause.
Another oddity of cat scratch disease is that only rarely are adult cats involved in the transmission. Generally, a kitten scratch passes the disease. This does not mean you should not worry about it with an older cat, but only that you should worry more about the kittens. It is contagious for only about two or three weeks in a kitten, after which it goes dormant. It can recur, however.
Kittens can be diagnosed as cat scratch disease carriers through a simple blood test, and positive kittens can be treated successfully with antibiotics. Because this disease can come back, however, this is not a silver bullet for preventing cat scratch disease. Declawing kittens at an early age is the best way to prevent infection. You should be aware of the ramifications to the cat before declawing it, however. Not only can it be dangerous for the cat to go outside, it can also be psychologically traumatic and cause unexpected complications like arthritis.
There are a few alternatives to declawing your cat, such as claw covers or trimming back their claws, but you will have to be vigilant if you are in a home with an immunocompromised person.
Fewer than ten percent of family members scratched by a cat carrying cat scratch disease will develop the disease, and very serious illness from the disease is rare. If you've had cat scratch disease once, you are almost certainly immune to it afterward.
Cat scratch disease should not be confused with another cat-borne disease, toxoplasmosis. Toxoplasmosis is deadly to a pregnant woman's fetus, but presents in different ways and is more likely to be inhaled when a woman changes her cat's litter box. Cat scratch disease can be dangerous to a pregnant woman as well, but in an entirely different way.