Cat scratch fever spreads when bacteria called Bartonella henselae enter your body through a break in the skin, almost always from a cat’s claws or teeth. The bacteria don’t originate in the cat itself. They come from fleas, and the chain of events that leads to infection is more specific than most people realize.
How the Bacteria Gets on a Cat’s Claws
The process starts with fleas. When fleas feed on a cat’s blood, they produce large amounts of feces (often called “flea dirt”) that accumulate in the cat’s fur. If the fleas carry Bartonella henselae, their feces contain the bacteria too. Cats pick up the bacteria on their claws by scratching flea bites or grooming themselves, essentially coating their claws in contaminated flea debris. Cats can also develop high levels of the bacteria circulating in their blood, which means their claws can become contaminated with infected blood when they scratch at irritated skin.
This is why the infection is tied so closely to scratches. The claws act as tiny delivery devices, pushing bacteria directly into the wound they create. A bite can do the same thing if the cat has licked its paws or has bacteria in its saliva.
The Moment of Infection
You get cat scratch fever when a cat breaks your skin and deposits the bacteria beneath the surface. The most common scenarios are a scratch during play, a bite, or a cat licking an open wound or area of broken skin. The scratch doesn’t need to be deep. Even a superficial scrape can be enough if the claws carry enough contaminated material.
Symptoms typically begin 3 to 10 days after the scratch or bite. The first sign is usually a small bump or blister at the wound site, which can look like a bug bite or minor skin irritation. Within one to three weeks after that initial bump appears, the lymph nodes closest to the scratch swell. If a cat scratched your hand, the lymph nodes in your armpit or elbow area might become tender and visibly enlarged. If the scratch was on your face, you might notice swollen nodes near your neck or ears.
Why Kittens Are Higher Risk
Kittens are more likely to transmit the infection than adult cats for two overlapping reasons. First, kittens are at greater risk of carrying Bartonella henselae in their bloodstream. Their immune systems are still developing, so they tend to harbor higher concentrations of the bacteria for longer periods. Second, kittens bite and scratch more often during play. Their claws are sharp, their coordination is imperfect, and rough play is normal kitten behavior. The combination of higher bacterial loads and more frequent skin-breaking contact makes kittens the primary source of human infections.
Adult cats can still carry and transmit the bacteria, but they’re generally less likely to be actively infected and less likely to scratch you during everyday interactions.
Who Gets It Most Often
An estimated 12,000 outpatient cases are diagnosed in the United States each year, with about 500 people hospitalized. Children ages 5 to 9 have the highest infection rate at roughly 9.4 cases per 100,000 people, likely because young kids play more roughly with cats and are less careful about cleaning scratches afterward. Cases are also more common in the southern United States, where warmer climates support larger flea populations year-round.
What the Infection Feels Like
For most people, cat scratch fever is uncomfortable but not dangerous. The swollen lymph nodes can be quite painful and may stay enlarged for several weeks or even a few months. You might also feel generally run down, with a low fever, fatigue, headaches, and body aches. The illness resolves on its own in the majority of cases without any specific treatment.
In rare situations, the bacteria can cause complications beyond the lymph nodes. One example is Parinaud oculoglandular syndrome, which happens when the bacteria enter through the eye, usually from rubbing your eye after handling an infected cat. This causes painful, red, watery eyes with small bumps forming on the inner eyelid, along with swollen lymph nodes near the ears. People with weakened immune systems face higher risks of the infection spreading to the liver, spleen, bones, or other organs.
How It’s Diagnosed
Doctors often suspect cat scratch fever based on the combination of a recent cat scratch and swollen lymph nodes. Confirming the diagnosis, however, can be tricky. The most common lab test checks your blood for antibodies against the bacteria, but these results aren’t always reliable. The antibodies can cross-react with other infections, leading to false positives, and some people don’t produce detectable antibody levels early in the illness.
Growing the bacteria in a lab culture is another option but has low success rates because Bartonella henselae is slow-growing and difficult to cultivate. Newer molecular tests that detect the bacteria’s DNA directly from blood or tissue samples are more precise and can identify the specific species involved, but they aren’t available at every lab.
Preventing Cat Scratch Fever
Since fleas are the root cause, flea control is the single most effective prevention strategy. Keeping your cat on year-round flea prevention kills adult fleas and stops new ones from hatching, which breaks the cycle that puts Bartonella on your cat’s claws in the first place. Talk to your vet about which flea product is appropriate for your cat’s age and weight.
Beyond flea control, a few practical habits reduce your risk:
- Wash scratches and bites immediately with soap and running water. This is the simplest way to reduce the bacterial load before it can establish an infection.
- Avoid rough play with cats, especially kittens. If a kitten is in a biting and scratching mood, redirect with a toy rather than using your hands.
- Don’t let cats lick open wounds or broken skin.
- Keep cats indoors when possible, since outdoor cats have more flea exposure and more contact with stray animals that may carry the bacteria.
You cannot catch cat scratch fever from another person. The bacteria requires a cat (or, very rarely, a flea bite directly) as the transmission route. Dogs, while they can theoretically carry Bartonella, are not considered a meaningful source of human infection.