Cat scratch fever — medically known as cat scratch disease (CSD) — is a bacterial infection caused by Bartonella henselae, a bacterium carried by cats (particularly kittens) and transmitted to humans through a scratch, bite, or lick on broken skin. Despite its alarming name, cat scratch fever is usually a mild, self-limiting illness in healthy people, but can be serious in immunocompromised individuals. Understanding how it spreads, what symptoms to watch for, and how to reduce your risk is important for every cat owner.
What Causes Cat Scratch Fever?
The causative agent is Bartonella henselae, a gram-negative bacterium. Cats — especially kittens under 12 months — become infected with B. henselae through flea bites. Infected fleas defecate on the cat’s fur; when the cat scratches itself, flea feces get under its claws. When that cat scratches a human, the bacteria are introduced into the wound. The bacterium can also be transmitted if a cat licks an open wound or scratch on a person’s skin.
Importantly, cats themselves are almost never sick from carrying B. henselae. An infected cat looks and acts completely normal — there is no way to tell if your cat is a carrier just by looking at it. Studies suggest that up to 40% of cats carry B. henselae at some point in their lives, with higher rates in warm, humid climates where fleas are more prevalent, and in kittens and stray cats.
Symptoms of Cat Scratch Fever in Humans
Symptoms typically appear 3–14 days after the scratch or bite. The classic progression is:
- A small bump or blister at the site of the scratch, which may appear within 3–10 days and is often mistaken for a regular wound
- Swollen lymph nodes — the most recognizable symptom; nodes near the scratch site enlarge and become tender, often dramatically so. A scratch on the arm causes swelling in the armpit or elbow; a face scratch may cause neck swelling.
- Fatigue, mild fever, and headache — general flu-like malaise that typically lasts 1–3 weeks
- Loss of appetite in more significant cases
In healthy people, the illness resolves on its own within 2–4 months, though swollen lymph nodes may persist for several months. In rare cases, nodes become so enlarged they require drainage.
Who Is at Risk for Serious Complications?
People with weakened immune systems — including those with HIV/AIDS, organ transplant recipients, people undergoing chemotherapy, and those on long-term corticosteroids — are at risk for severe forms of cat scratch disease. These include:
- Bacillary angiomatosis: Skin and organ lesions caused by uncontrolled Bartonella proliferation; requires antibiotics
- Peliosis hepatis: Blood-filled cysts in the liver and spleen
- Bacteremia: Bacteria in the bloodstream causing prolonged fever
- Neuroretinitis: Inflammation of the optic nerve and retina, causing vision changes — rare but can occur in otherwise healthy people
- Encephalopathy: Neurological complications in a small percentage of cases
Immunocompromised individuals should discuss cat ownership and safety precautions with their healthcare provider.
Diagnosis and Treatment
Diagnosis is typically clinical — based on a history of cat contact and the characteristic swollen lymph nodes following a scratch. Blood tests (serology for Bartonella henselae antibodies) or PCR testing can confirm the diagnosis. A skin biopsy of lymph node tissue may be taken in atypical or severe cases.
In healthy individuals, treatment is usually supportive — rest, hydration, and over-the-counter pain relievers for fever and discomfort. Antibiotics (typically azithromycin, doxycycline, or ciprofloxacin) may be prescribed to shorten the duration in moderate cases or for patients with larger lymph nodes. Immunocompromised patients require prolonged antibiotic therapy and close medical management.
How to Reduce Your Risk
Prevention focuses on flea control and safe cat-handling habits. Keep cats strictly on flea prevention year-round — this is the most important step, as fleas are how cats become infected with Bartonella. Wash cat scratches immediately with soap and water. Avoid rough play that encourages scratching and biting, especially with kittens. Do not allow cats to lick open wounds or mucous membranes. Wash hands after handling cats, especially before touching your face.
You do not need to rehome your cat if you get cat scratch disease. Simply follow safe handling practices and ensure rigorous flea control. Declawing is not recommended as a prevention strategy — it causes chronic pain and behavioral problems and is banned or discouraged in many countries.