Cat Scratch Disease: What Your Cat's Scratch Can Actually Do to You

The Most Common Reason a Cat Scratch Lands You at the Doctor

Most cat scratches heal without consequence. But when a cat infected with Bartonella henselae scratches you, the bacteria enter through the skin, and within 1-3 weeks, the lymph nodes draining that area (typically armpit for an arm scratch, groin for a leg scratch, neck for a face scratch) swell to 1-5 cm -- sometimes painful, sometimes not. Add a low-grade fever, headache, and fatigue, and you have classic cat scratch disease.

Bartonella henselae lives in cats' mouths and on their claws, deposited there through flea feces. Fleas defecate on cats while feeding; the cat grooms, the fecal material -- containing Bartonella -- coats the claws and mouth. Scratches and bites then transmit it to humans. The cat itself almost never shows signs of Bartonella infection -- your cat can be actively harboring and transmitting the bacteria while appearing completely healthy. This is why flea control is the primary prevention: reducing flea infestation reduces Bartonella prevalence in cats.

Who Is at Risk for Serious CSD

In immunocompetent (healthy immune system) adults and older children, CSD is self-limiting -- uncomfortable but not dangerous, resolving within weeks to months. Most people don't even need treatment beyond rest and monitoring. The risk picture changes dramatically for immunocompromised individuals: people with HIV, organ transplant recipients on immunosuppressive drugs, cancer patients, and people on long-term corticosteroids. In these patients, Bartonella can cause bacillary angiomatosis (vascular lesions throughout the body), peliosis hepatis (liver involvement), bacteremia, encephalopathy, and neuroretinitis -- sight-threatening infection of the optic nerve and retina.

Young children are at higher risk for more severe classic CSD simply because their immune responses are still developing and they're more likely to be scratched by cats during active play. Anyone in a high-risk category who is scratched by a cat and develops fever and lymph node swelling should see a doctor specifically and mention the cat exposure -- the antibiotic treatment window matters for these patients.

Diagnosis and Treatment

Classic CSD in healthy people is diagnosed clinically (history of cat exposure + typical signs) without specific testing. Blood tests for Bartonella antibodies are available if confirmation is needed. Diagnosis in immunocompromised patients is more urgent and may involve biopsy, PCR, or blood cultures.

Treatment in healthy adults: usually none needed. Azithromycin for 5 days accelerates lymph node resolution in some studies but doesn't change the eventual outcome significantly in healthy people. For children with significant lymphadenopathy, azithromycin is commonly prescribed. For immunocompromised patients: prolonged courses of doxycycline, often combined with rifampicin, with duration determined by the clinical picture and immune status -- weeks to months in severe cases.

Prevention

Year-round flea prevention on all cats in the household is the most effective prevention -- eliminating the flea transmission vector dramatically reduces Bartonella prevalence in cat populations. Beyond flea control: wash cat scratches with soap and water immediately. Don't let cats lick open wounds or mucous membranes. Trim cats' nails regularly to reduce scratch depth. Immunocompromised individuals should discuss cat ownership with their doctors; risk is manageable with flea prevention but is real. Adopt adult cats rather than kittens (kittens are more likely to scratch and bite during play) if you have a compromised immune system.