What is cat scratch fever?
Cat scratch fever, also called cat scratch disease (CSD), is a bacterial infection people catch from cats. The cause is Bartonella henselae, a bacterium that cats pick up from fleas and usually carry without looking sick.
The symptoms usually follow the same pattern. About 3 to 10 days after a scratch or bite, a small red bump (sometimes crusted or filled with pus) appears where the skin was broken. Within 1 to 3 weeks, a lymph node near the scratch swells and turns tender. Lymph nodes are the small glands you can feel in places like the neck, armpit or groin. Some people also run a low fever, feel tired, get a headache or lose their appetite.
Most cat scratches never cause this. And in healthy people, cat scratch fever usually clears up on its own.
Can I get cat scratch fever?
Yes. People usually get it from a scratch, especially a kitten's. Cats groom themselves, so infected flea dirt (flea feces) ends up on their claws and in their mouths. When a scratch carries that flea dirt into your skin, the bacteria come along. A bite can spread it too, and so can a cat licking an open wound.
It does not pass from person to person.
Children are the group most often affected, especially those under 15, although adults can get it as well. A US study of insurance claims from 2005 to 2013 estimated about 12,000 outpatient diagnoses and 500 hospital stays for cat scratch disease each year, with the highest rates in children aged 5 to 9 and in southern states (Nelson and colleagues, 2016). According to the CDC, most US cases happen in fall and winter.
Cat scratch fever symptoms in people
The common signs, in roughly the order they show up:
- A bump at the scratch or bite. Red, often painless, sometimes crusted or pus-filled. It appears within about 3 to 10 days.
- A swollen, tender lymph node. Usually the one closest to the scratch. It develops 1 to 3 weeks after contact with the cat.
- Low-grade fever.
- Tiredness, headache, poor appetite, and in some people sore muscles and joints.
The bump and any fever tend to fade fast. The swollen lymph node is the slow part: it can stay enlarged for a few weeks to a few months, and occasionally longer. A node can also fill with pus and drain.
Less common forms. Merck's professional manual reports unusual forms in about 11 to 12% of patients, more often in adults. About half of those involve the eye: red, irritated eye on one side with a swollen node in front of the ear (called Parinaud oculoglandular syndrome). Rarer still are sudden, painless vision loss in one eye (neuroretinitis), infection of the liver and spleen with lasting fever and belly pain, brain involvement with headache, confusion or seizures, and bone infection. B. henselae can also infect heart valves, mostly in people who already have a valve problem.
People with a weakened immune system (for example from advanced HIV, cancer treatment or another condition that suppresses immunity) face a higher risk of severe disease. In them the infection can spread through the body, and it can be life-threatening without treatment.
When should you see a doctor?
The CDC advises seeing a healthcare provider if you or your child develop:
- a fever,
- enlarged, tender lymph nodes 1 to 3 weeks after a cat scratch, or
- a pus-filled bump at the scratch site.
Tell your doctor about the cat. Contact with a cat or kitten plus the typical signs is often enough for a diagnosis, and tests are kept for severe or unclear cases. Get seen promptly if you have a weakened immune system, or if you notice changes in your vision, confusion or a seizure.
Your doctor decides on treatment. Most cases clear without antibiotics. The CDC says antibiotics may help the lymph node shrink faster and are recommended for everyone with a weakened immune system. Severe forms may need care from an infectious disease specialist. Healthy people who have had cat scratch disease generally don't get it again.
How can I protect myself from cat scratch fever?
You don't need to give up your cat. The CDC's prevention advice comes down to avoiding scratches and fleas:
- Skip rough play with cats, especially kittens, and don't let children play rough with them.
- Wash scratches and bites right away with soap and running water.
- Don't let cats lick open wounds or broken skin.
- Wash your hands after handling cats.
- Keep your cat on the flea control your veterinarian recommends.
- Keep cats indoors and away from stray cats.
- If your immune system is weakened, take extra care around kittens and strays, and choose a cat older than one year when adopting.
Declawing is not recommended to prevent cat scratch disease.
What animals can get cat scratch fever?
Cats, domestic and wild, are the main carriers of B. henselae and the main source of human infection. The CDC reports the bacteria in the blood of 30 to 40% of domestic and shelter cats. Kittens and cats under 2 years old are more likely to be infected than older cats, and stray and feral cats more likely than pet cats.
Cats are not the only hosts. Dogs can also carry B. henselae, though it is not known whether dogs pass it to people, and other Bartonella species live in many domestic and wild animals.
How does it affect my animal?
Usually it doesn't. Most infected cats carry the bacteria in their blood (bacteremia) and never look sick, which is why you can't tell which cat might pass it on.
Some cats get a short fever lasting 2 to 3 days. Call your veterinarian if your cat has:
- a fever lasting more than 3 days,
- vomiting,
- lethargy,
- red eyes,
- swollen lymph nodes, or
- a decreased appetite.
How can my animal get cat scratch fever?
Mostly through fleas, which carry the bacteria from cat to cat. Less often, cats are infected during fights with other infected cats or through a blood transfusion.
How can I protect my animal?
- Flea control. Ask your veterinarian which product suits your cat. Never put a product containing permethrin on a cat: it is in some dog flea products, and the CDC says it should never be used on cats. Our guide to external parasite prevention for cats covers the options to discuss.
- Keep your cat indoors. It cuts flea exposure and contact with stray cats. See the indoor vs outdoor cats trade-offs.
- No vaccine exists for cats against Bartonella.
Testing or treating a healthy cat for B. henselae is not recommended, even if someone in the home has a weakened immune system. Antibiotics have not been shown to clear the infection from cats reliably, so the CDC reserves treatment for cats that are actually sick. And you don't need to rehome a cat after someone in the family gets cat scratch disease.
Who should I contact if I suspect the disease?
- For a person: your doctor. Mention the cat contact and when the scratch or bite happened.
- For your cat: your veterinarian, if your cat shows any of the signs listed above. A healthy cat needs no testing for this.
Sources
- CDC: About Cat Scratch Disease
- CDC: Clinical Overview of Cat Scratch Disease
- CDC: Veterinary Guidance for Bartonellosis
- Center for Food Security and Public Health, Iowa State University: Cat Scratch Disease and Other Zoonotic Bartonella Infections (2023)
- Merck Manual Consumer Version: Cat-Scratch Disease
- Merck Manual Professional Version: Cat-Scratch Disease
- Cornell Feline Health Center: Zoonotic Disease: What Can I Catch from My Cat?
- Nelson CA, Saha S, Mead PS. Cat-Scratch Disease in the United States, 2005-2013. Emerging Infectious Diseases, 2016
This article is for general information and is not a substitute for advice from your doctor or your veterinarian.
