Cat scratch fever, formally called cat scratch disease, is a bacterial infection caused by Bartonella henselae. It typically develops after a scratch or bite from an infected cat and causes swollen lymph nodes near the wound site. Most cases resolve on their own within a few months, but a small percentage can lead to more serious complications affecting the eyes, nervous system, or internal organs.
How It Spreads
The bacterium lives in fleas, specifically cat fleas. When fleas feed on a cat, they leave behind infected feces on the cat’s fur and claws. If that cat scratches or bites you, the contaminated flea debris gets pushed into your skin. Cats can also transfer the bacteria by licking an open wound or scratch you already have. The key link in the chain is fleas: cats without flea exposure are far less likely to carry the infection, and the bacteria don’t spread from person to person.
Kittens are more likely to carry Bartonella henselae than adult cats, partly because they’re more prone to flea infestations and more likely to scratch during play. Infected cats almost never look sick themselves, so there’s no easy way to tell whether your pet is carrying the bacteria.
Symptoms and Timeline
The first sign usually appears 3 to 10 days after the scratch or bite. A small reddish-brown bump, roughly 3 to 5 millimeters across, develops at the wound site. It looks a lot like an insect bite, which is why many people don’t think much of it. Over the next one to three weeks, this bump may turn into a small blister or pus-filled spot before eventually healing on its own without leaving a scar.
The hallmark symptom comes next: swollen, tender lymph nodes near the site of the scratch. If you were scratched on the hand, the nodes in your armpit or elbow crease swell. A scratch on the face might cause swelling in the neck or behind the ear. These swollen nodes can be quite noticeable and sometimes painful. They typically shrink back to normal within two to four months, though in some cases they linger for six months to a year.
Along with swollen nodes, you may experience low-grade fever, fatigue, headache, and a general feeling of being unwell. These flu-like symptoms are usually mild and pass within a couple of weeks.
When It Becomes More Serious
Around 80 to 95 percent of cases follow the typical pattern described above and clear up without lasting problems. The remaining 5 to 20 percent develop atypical or more severe symptoms that can affect multiple organ systems.
Eye involvement is one of the more common complications. The infection can cause a condition called Parinaud oculoglandular syndrome, which leads to redness and swelling of the eye along with swollen lymph nodes near the ear. It can also affect the back of the eye, causing inflammation of the retina or optic nerve, which may temporarily blur vision.
Nervous system complications, while uncommon, include encephalopathy (a broad disruption of brain function that can cause confusion or altered consciousness), seizures, and nerve inflammation. The infection can also settle in the heart valves, bones, or liver and spleen. These atypical presentations are more likely in people with weakened immune systems, such as those undergoing chemotherapy, organ transplant recipients, or people living with HIV.
How It’s Diagnosed
Doctors often suspect cat scratch disease based on the combination of a recent cat scratch, a bump at the wound site, and swollen lymph nodes. Confirming the diagnosis with lab tests can be tricky. Blood tests that look for antibodies to the bacteria have limited sensitivity, and there’s cross-reactivity with related species, which can muddy the results. Molecular testing on blood samples also has low sensitivity, and it becomes even less reliable the longer you wait after the initial infection. In practice, many straightforward cases are diagnosed clinically, based on symptoms and exposure history, without extensive testing.
Treatment and Recovery
Most people with typical cat scratch disease don’t need antibiotics. The infection runs its course over weeks to a few months, and the swollen lymph nodes gradually return to normal. Over-the-counter pain relievers and warm compresses on tender nodes can help manage discomfort in the meantime.
Antibiotics are recommended for more severe cases, for people with weakened immune systems, and when the infection spreads beyond the lymph nodes. A short course of a common antibiotic, typically taken for five days, has been shown to speed up the shrinking of swollen nodes in mild to moderate disease. Disseminated infections involving the heart, retina, or liver and spleen require longer courses, sometimes with more than one antibiotic.
Occasionally, a lymph node becomes so swollen and painful that a doctor will drain it with a needle. This is uncommon and only done for comfort when the node isn’t resolving on its own.
How to Lower Your Risk
Flea control is the single most effective prevention strategy. Keeping your cat on a regular flea prevention product dramatically reduces the chance that it will carry the bacteria in the first place. The CDC recommends keeping cats indoors, which limits their exposure to fleas and contact with feral cats that may be infected.
Basic hygiene goes a long way too. If a cat scratches or bites you, wash the area immediately with soap and running water. Avoid rough play with cats, especially kittens, that makes scratches more likely. Don’t let cats lick any open wounds or broken skin. There is no vaccine available for cats or humans against this bacterium, so flea prevention and wound care remain the primary defenses.
People with compromised immune systems should take extra precautions. Adopting an adult cat rather than a kitten reduces risk, since kittens are more likely to carry the bacteria and more prone to scratching. If you’re in a higher-risk group and your cat scratches you, let your doctor know so they can monitor for early signs of a more serious infection.