What Is Cat Scratch Fever, and How Common Is It?

Cats are playful, rambunctious pets that bring joy to many of us. They love to play, but even the most loving cat will sometimes bring their claws out on us. Maybe we bothered them when they wanted to be alone, or we did the unthinkable and tried to give them a bath. And one swipe of those sharp claws could lead to an infection called cat scratch fever, so should you be concerned? "Cats are indeed safe pets," assures Michael Koster, M.D, a pediatric hospitalist from Hasbro Children's Hospital. "Cat scratch fever is rare and, virtually, all cat owners need not worry."

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Cat scratch fever, also medically known as cat scratch disease (CSD), occurs when the organism Bartonella henselae gets into a person's bloodstream and travels toward the lymph nodes in the neck or armpits. This can cause painful swelling and discomfort. "Typically, the bacteria does not cause sepsis or fulminate disease and many people clear the infection without the need of antibiotics," explains Dr. Koster. "CSD most commonly happens in children, especially those under five years, but can occur in all ages."

Doctors will usually diagnose the disease without the need of a blood test by examination and history of the patient. If a patient says that a cat scratched them and there is indeed a scratch on their skin, then doctors are able to diagnose CSD based on this information and the presentation of the symptoms. A blood test, however, can confirm that the bacteria is there if an assessment is difficult or if additional confirmation is needed.

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Adults who have strong immune systems might never feel any ill effects from the bacteria; people with weakened immune systems could experience severe complications—still, it's very rare. "The hospital admission rates for this are about 0.75/100,000," says Dr. Koster. "Azithromycin is the antibiotic of choice for most infections and can help the gland swelling go away more quickly."

While the lymph node swelling is the most common way for cat scratch fever to appear, there are other ways that it can manifest. "CSD can also cause a myriad of other manifestations, most notably: hepatosplenic disease (small abscesses in the liver or spleen), and osteomyelitis (bone infection), with infections very rarely occurring in the eye, kidney, heart, joints, skin or nervous system," says Dr. Koster. These symptoms are, of course, very serious and may require care that treats the secondary issues of contracting the disease in addition to antibiotics that kill the bacteria.

It's worth noting that indoor cats are not likely to have Bartonella henselae lurking under their claws. According to Dr. Koster, the bacteria is transmitted by fleas and not by the cats themselves. An indoor cat that doesn't come into contact with fleas or has regular flea preventive will not become a carrier for the bacteria. Outdoor cats with fleas are more likely to have high rates of the disease. "Good flea prevention can help protect your cat from acquiring the bacteria," Dr. Koster says. And if you need to handle a stray or feral cat for some reason, wear protective gloves that can't be easily penetrated by claws and get to the veterinarian as soon as possible.