What exactly is cat scratch fever and how does a cat catch it?

Cat scratch disease (bartonellosis) in cats is an infection with Bartonella henselae, a bacterium that circulates between cats primarily through the cat flea, Ctenocephalides felis. The CDC estimates that roughly 40% of cats carry Bartonella species at some point in their lives, with prevalence highest in warm, humid regions where fleas thrive year-round (Centers for Disease Control and Prevention, 2024). Cats do not get infected directly from another cat's scratch; the bacterium actually needs to pass through a flea first.

The transmission chain is specific: fleas feeding on a bacteremic cat ingest the organism, then shed it in their feces, which accumulate in the cat's coat and under its claws during normal grooming and scratching. Another cat (or a person) becomes infected when flea dirt contaminated with the bacteria is inoculated into a wound, scratch, or mucous membrane. Cornell Feline Health Center notes that kittens under one year old and cats living in dense, flea-infested colonies are disproportionately affected because of their higher flea exposure (Cornell Feline Health Center, 2021).

Why do most infected cats never seem sick?

The majority of Bartonella-infected cats show no outward signs at all, which is part of what makes the disease easy to underestimate. The bacterium can persist in a cat's bloodstream for months to years in a low-grade, largely silent infection, and a healthy cat's immune system generally keeps bacterial numbers low enough to prevent clinical illness (Merck Veterinary Manual, 2023). This asymptomatic carrier state is precisely why routine, unexplained testing of healthy cats isn't recommended by most veterinary infectious disease specialists.

When illness does occur, it clusters in younger cats, cats with concurrent viral infections such as feline leukemia virus, and cats under significant stress, all of which can blunt immune defenses enough to let the bacteria multiply. The American Association of Feline Practitioners notes that clinical bartonellosis is uncommon enough in adult, healthy indoor cats that Bartonella is rarely the first differential considered for vague lethargy (American Association of Feline Practitioners, 2020).

What symptoms should make an owner suspect Bartonella in their cat?

When symptomatic, cats most often show nonspecific signs: intermittent fever, swollen lymph nodes (particularly under the jaw or in front of the shoulders), reduced appetite, and lethargy that comes and goes over days to weeks. Some cats also develop mild inflammation of the gums (gingivitis) or eyes (uveitis), reflecting the bacterium's tendency to seed tissues with rich blood supply (Merck Veterinary Manual, 2023).

Because these signs overlap heavily with viral upper respiratory infections, dental disease, and other tick- or flea-borne illnesses, owners often don't connect a lump under the jaw with a flea problem from months earlier. A cat that has a documented flea infestation and develops a persistently swollen lymph node warrants a veterinary visit, since lymphadenopathy in cats can also signal lymphoma or other serious disease that needs to be ruled out (Cornell Feline Health Center, 2021).

How do veterinarians actually confirm a Bartonella infection?

Diagnosis is trickier than a single blood test because antibody presence doesn't prove active disease — a cat can test seropositive from a past exposure yet have no current illness. Veterinarians typically combine serology (indirect fluorescent antibody testing) with PCR testing of blood to detect the bacterium's DNA directly, and interpret both alongside the cat's clinical signs, since PCR alone can also miss intermittent bacteremia (Merck Veterinary Manual, 2023).

Culture of the organism from blood is considered more definitive but is technically demanding and slow, so most general practices rely on commercial PCR/serology panels run through reference laboratories. The American College of Veterinary Internal Medicine's consensus statement on vector-borne disease testing emphasizes that a positive Bartonella test in a cat with vague signs should prompt investigation for other causes before treatment decisions are based on Bartonella alone (Sykes et al., as summarized by ACVIM, 2016).

What treatment does a cat with cat scratch fever actually need?

Not every cat with a positive Bartonella test needs antibiotics — treatment is generally reserved for cats showing clinical signs, since eliminating the organism from an asymptomatic carrier is difficult and doesn't reliably change outcomes. When treatment is indicated, azithromycin and doxycycline are the antibiotics most commonly used, typically for two to four weeks, though relapse after stopping antibiotics is well documented (Merck Veterinary Manual, 2023).

Supportive care matters just as much as antibiotics: aggressive flea control on the affected cat and every other pet in the household breaks the transmission cycle and reduces reinfection risk. Veterinarians will often recommend a fecal and bloodwork recheck a few weeks after finishing antibiotics to confirm the cat's lymph nodes and appetite have normalized rather than assuming the drug course alone cleared the infection.

Can this actually make a person sick, and how worried should pet parents be?

Yes — this is the zoonotic angle that gives the disease its common name. The CDC reports roughly 12,000 diagnosed cases of cat scratch disease in people annually in the United States, with about 500 people hospitalized each year, most commonly children under 15 who play roughly with kittens (Centers for Disease Control and Prevention, 2024). In otherwise healthy people, the infection typically causes a mild, self-limited swollen lymph node near the scratch site that resolves in a few weeks without treatment.

The real concern is for immunocompromised people — those with HIV/AIDS, on chemotherapy, or post-transplant — in whom Bartonella can cause more severe, disseminated disease. The CDC specifically advises immunocompromised individuals to avoid rough play with cats, wash any scratch or bite immediately with soap and water, and consider adopting an adult cat rather than a kitten, since kittens are more likely to be bacteremic (Centers for Disease Control and Prevention, 2024).

What's the best way to prevent it in a multi-cat household?

Year-round flea prevention is the single most effective control measure, since breaking the flea life cycle eliminates the primary transmission route between cats and to people. The Companion Animal Parasite Council recommends monthly, veterinarian-approved flea preventives applied consistently for every cat in the home, including indoor-only cats, because fleas can hitch rides in on other pets or on clothing (Companion Animal Parasite Council, 2023).

Keeping cats' nails trimmed, providing appropriate scratching posts, and keeping cats indoors — away from feral colonies where flea burdens and Bartonella prevalence run highest — further reduces exposure. Declawing is not recommended as a prevention strategy; the AVMA specifically discourages declawing for disease-prevention purposes given the procedure's welfare costs relative to the modest risk reduction it offers (American Veterinary Medical Association, 2022).