Cat Scratch Disease

How it spreads

Up to about 4 in 10 cats carry Bartonella at some point, most often kittens under a year old and cats with fleas. Infected cats look healthy. The bacteria live in flea droppings in the cat's fur and claws. People are infected when:

• a cat scratches or bites them
• a cat licks an open wound or scab
• infected flea droppings get into broken skin or the eye (for example, rubbing the eye after petting a cat)

It does not spread from person to person. Cases peak in fall and winter, and children and teenagers are most often affected.

Symptoms

Typical cat scratch disease

1. Skin bump: 3 to 10 days after the scratch, a small, raised, red or brown bump or blister appears at the site. It can be easy to miss.
2. Swollen lymph nodes: 1 to 3 weeks after exposure, one or more lymph nodes near the scratch become swollen and tender, most often in the armpit, neck, or groin. Nodes can be 1 to 5 cm (half an inch to 2 inches) or larger. See swollen lymph nodes.
3. General symptoms: mild fever, tiredness, headache, poor appetite and aches in some people.

In about 1 in 10 cases, the node fills with pus and may drain.

Eye involvement: Parinaud oculoglandular syndrome

If bacteria enter the eye, the result is a red, irritated eye (conjunctivitis) on one side, often with a granular lump on the inner eyelid, and a swollen lymph node in front of the ear on the same side. It usually resolves, but needs medical assessment.

Neuroretinitis

Less commonly, Bartonella inflames the optic nerve and retina, causing sudden painless blurred vision in one eye, often with a star-shaped pattern visible on eye examination. Most people recover good vision, often with antibiotic treatment.

Other uncommon forms

• prolonged fever without a clear source, with liver or spleen lesions
• encephalopathy: confusion, seizures, coma, mostly in children; recovery is usually complete
• bone infection, heart valve infection (endocarditis)
• in people with weakened immunity, such as advanced HIV infection: bacillary angiomatosis (red-purple skin lumps) and liver lesions, which need prolonged antibiotics

Diagnosis

Doctors suspect it in someone with swollen lymph nodes and recent cat or kitten contact, especially with a scratch bump. Tests:

• Bartonella henselae antibody blood test (serology)
• PCR on fluid from a lymph node or tissue
• Ultrasound of the swollen node
• Biopsy if the diagnosis is unclear or other causes such as lymphoma or tuberculosis need to be ruled out

Treatment

• Mild cases: many resolve without antibiotics. Warm compresses and acetaminophen (paracetamol) or ibuprofen at the label dose help pain. Do not give aspirin to children or teenagers.
• Moderate to severe lymph node swelling: a 5-day course of azithromycin can speed shrinking of the nodes.
• Pus-filled nodes: needle drainage relieves pain. Surgical cutting and draining is avoided because it can cause a lasting draining tract.
• Eye, nerve, liver, bone or heart involvement, and immunocompromised patients: longer courses of antibiotics such as doxycycline, rifampin, or combinations, under specialist care.

Recovery and outlook

Most people recover fully. Swollen nodes typically shrink over 2 to 4 months, though some take longer. Lifelong immunity is usual after infection. Serious complications are rare in people with healthy immune systems.

Prevention

• Wash scratches and bites promptly with soap and water.
• Avoid rough play with kittens that encourages scratching.
• Do not let cats lick open wounds, eyes or the mouth.
• Keep cats indoors and use flea control for all pets.
• Wash hands after handling cats.
• People with weakened immune systems should consider adopting an older cat rather than a kitten.

Removing the cat is not necessary.

Frequently asked questions

What are the symptoms of cat scratch disease?

A small bump at the scratch site is followed 1 to 3 weeks later by tender swollen lymph nodes near the scratch, often in the armpit or neck. Mild fever, tiredness and headache are common. Rarely, the eyes, liver, brain or heart are affected.

Can cat scratch disease cause conjunctivitis?

Yes. When bacteria enter the eye, they can cause Parinaud oculoglandular syndrome: a red, irritated eye with a swollen lymph node in front of the ear on the same side. It needs medical assessment and sometimes antibiotics.

How long does cat scratch disease last?

The illness is usually mild, but the swollen lymph nodes can take 2 to 4 months, or occasionally longer, to go down completely. Antibiotics may speed recovery in more significant cases.

Do I need to get rid of my cat?

No. Most adult cats have already been exposed. Flea control, avoiding scratches and washing any wounds lower the risk. People with weak immune systems should take extra care, especially with kittens.