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Feline Scratch Disease (Cat‑Scratch Disease)

What is Feline scratch disease?

Feline scratch disease (FSD), also called cat‑scratch disease (CSD), is a bacterial infection that humans acquire after a scratch, bite, or even a lick from a cat that carries the bacterium Bartonella henselae. The disease is usually mild but can lead to more serious complications in people with weakened immune systems. Most infections resolve on their own, yet a proper diagnosis helps to avoid unnecessary complications and to treat the infection quickly when needed.

According to the CDC, cat‑scratch disease is the most common cause of regional lymphadenopathy (swollen lymph nodes) in children and adolescents in the United States.

Common Causes

The primary cause is exposure to Bartonella henselae, but several related circumstances increase the risk of developing FSD. Below are the most frequent contributors:

• **Cat scratches** – especially from kittens whose claws are more likely to be contaminated.
• **Cat bites** – direct inoculation of bacteria into deeper tissue.
• **Licking of open wounds** – cats can deposit bacteria onto broken skin.
• **Fleas** – Ctenocephalides felis transmit B. henselae between cats; a flea‑infested cat has a higher bacterial load.
• **Kittens** – kittens under 12 months are 5–10 times more likely to be bacteremic than adult cats.
• **Indoor‑outdoor cats** – cats that roam outdoors acquire fleas and other infections more readily.
* **Immunocompromised hosts** – people with HIV, organ transplants, or on chemotherapy can develop severe disease.
• **Pregnancy** – although rare, infection during pregnancy can cause complications.
• **Recent exposure to other animals** – dogs or wild animals can also carry Bartonella spp., though cats remain the main reservoir.
• **Poor wound hygiene** – failing to clean a scratch or bite promptly raises infection risk.

Associated Symptoms

Symptoms typically appear 3–14 days after exposure and may last from a few weeks to several months. Common clinical features include:

• **Bump or papule** at the site of the scratch/bite (often 3–5 mm, may become a small ulcer).
• **Regional lymphadenopathy** – swollen, tender lymph nodes near the injury site (most often axillary, cervical, or inguinal).
• **Fever** – low‑grade (38‑38.5 °C) but can be higher in some cases.
• **Malaise, fatigue, and headache**.
• **Loss of appetite**.
• **Muscle aches (myalgias) or joint pain**.
• **Splenomegaly** (enlarged spleen) in a minority of patients.
• **Eye involvement** – Parinaud’s oculoglandular syndrome (conjunctivitis with nearby lymph node swelling).
• **Skin rash** – occasionally a papular or maculopapular rash appears distal to the scratch.

Most people experience only the first two signs (scratch site + swollen lymph nodes). Severe systemic symptoms are uncommon but more likely in immunocompromised individuals.

When to See a Doctor

While many cases resolve without medical intervention, you should seek professional care if you notice any of the following:

• Swollen lymph nodes that continue to enlarge after 2 weeks or become very painful.
• Fever > 38.5 °C (101.3 °F) lasting more than 3 days.
• Redness, warmth, or pus forming at the scratch/bite site – signs of secondary bacterial infection.
• Persistent headache, confusion, or neurological symptoms (e.g., weakness, numbness).
• Difficulty breathing, chest pain, or heart palpitations.
• Vision changes, eye pain, or swelling of the eyelids.
• Signs of liver or spleen enlargement (pain in upper abdomen, feeling of fullness).
• Any symptoms in a pregnant woman, newborn, or person with a known immune deficiency.

Diagnosis

Doctors rely on a combination of clinical history, physical examination, and laboratory testing.

Clinical evaluation

• Detailed history of cat exposure, including recent scratches or bites.
• Inspection of skin lesion and measurement of lymph node size.
• Assessment for systemic signs (fever, fatigue, organomegaly).

Laboratory tests

• Serology – detection of IgM and IgG antibodies against B. henselae. A rising IgG titer over 2–4 weeks confirms infection.
• Polymerase chain reaction (PCR) – identifies bacterial DNA in blood, tissue, or lymph node aspirate; highly specific.
• Complete blood count (CBC) – may show mild anemia or elevated white blood cells.
• Liver function tests – occasionally abnormal if the bacteria involve the liver.
• Imaging – ultrasound or CT scan of enlarged lymph nodes if the diagnosis is unclear or complications are suspected.

Differential diagnosis

Doctors must rule out other conditions that cause lymphadenopathy, such as:

• Staphylococcal or streptococcal skin infections
• Viral infections (EBV, CMV, HIV)
• Lymphoma or other cancers
• Tuberculosis
• Other Bartonella species infections

Treatment Options

Most healthy adults recover spontaneously within 4–6 weeks. Treatment decisions depend on symptom severity, patient age, and immune status.

Antibiotic therapy

• Azithromycin – 500 mg orally on day 1, then 250 mg daily for 4 more days. This regimen shortens lymph node swelling by ~50 % (studies from the New England Journal of Medicine).
• Doxycycline – 100 mg orally twice daily for 4–6 weeks; preferred for immunocompromised patients or when ocular involvement exists.
• Rifampin – used in combination with doxycycline for severe or disseminated disease.
• For infants and pregnant women, erythromycin is the safer alternative.

Supportive care

• Analgesics/antipyretics (acetaminophen or ibuprofen) for pain and fever.
• Warm compresses on swollen nodes to reduce discomfort.
• Adequate hydration and rest.
• Topical antiseptics (e.g., povidone‑iodine) on the scratch site to prevent secondary infection.

When antibiotics are NOT required

In otherwise healthy individuals with mild disease, doctors may adopt a “watchful waiting” approach, providing symptom relief while monitoring for progression.

Prevention Tips

Because cats are the natural reservoir, reducing exposure is the key.

• **Keep cats indoors** – limits flea infestations and reduces contact with other infected animals.
• **Regular flea control** – use vet‑recommended products (topical, oral, or collar).
• **Avoid rough play** – especially with kittens; use toys instead of hands.
• **Trim cat nails regularly** to lessen the depth of scratches.
• **Wash any scratch or bite promptly** with soap and water for at least 30 seconds.
• **Apply an antiseptic** (e.g., hydrogen peroxide) after cleaning.
• **Monitor pets for signs of flea infestation** (scratching, black specks of flea dirt).
• **Seek veterinary care** for cats with persistent fevers or lymph node swelling; they may need testing for B. henselae.
• **Educate children** about safe handling – no hugging or petting cats that are sleeping or agitated.
• **Pregnant women, newborns, and immunocompromised individuals** should avoid handling kittens or, at a minimum, wear gloves and wash hands thoroughly after any contact.

Emergency Warning Signs

Key Take‑aways

• Feline scratch disease is a bacterial infection caused by Bartonella henselae, transmitted through cat scratches, bites, or licks.
• Typical presentation includes a small skin lesion and swollen regional lymph nodes, often accompanied by low‑grade fever.
• Most healthy people recover without antibiotics, but azithromycin or doxycycline can speed up healing and prevent complications.
• Prevention focuses on flea control, safe cat handling, and prompt wound care.
• Seek urgent care if you develop severe systemic symptoms, eye involvement, or signs of a secondary bacterial infection.

For the most up‑to‑date information, consult reputable sources such as the CDC, Mayo Clinic, and the Cleveland Clinic.

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