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Feline Scratch Disease (Bartonella henselae Infection)

Overview

Feline scratch disease (CSD) is a bacterial infection caused by Bartonella henselae. The organism lives in the blood of cats—especially kittens—and can be transmitted to humans through a scratch, bite, or even a flea bite that has been contaminated by infected cat saliva.

The disease most commonly affects children and young adults who have close contact with cats, but anyone who handles cats can become infected.

• Incidence: In the United States, an estimated 12,000–22,000 cases are reported each year, with higher rates in regions where feral cat populations are dense.<sup>1</sup>
• Geographic distribution: Worldwide, CSD occurs wherever domestic and stray cats live. Higher prevalence is noted in humid, temperate climates (e.g., Southern United States, Mediterranean countries).<sup>2</sup>
• Age & gender: About 60–70 % of cases occur in individuals under 20 years old; slight male predominance has been observed, likely reflecting pet‑ownership patterns.

Symptoms

Symptoms usually appear **1–3 weeks** after the cat scratch or bite. The presentation can range from a mild, self‑limited illness to a more systemic disease.

Typical (classic) presentation

• Regional lymphadenopathy – a tender, enlarged lymph node near the site of the scratch (often in the armpit, neck, or groin).
• Scratch or bite area – a small papule or pustule that may develop into a shallow ulcer within 3–5 days.
• Fever – low‑grade (<38 °C/100.4 °F) in most cases; higher fevers can occur.
• General malaise – fatigue, headache, and mild muscle aches.

Less common or atypical manifestations

• Conjunctivitis or ocular inflammation (conjunctival granuloma).
• Parinaud oculoglandular syndrome – eye redness, swelling of the lacrimal gland, and nearby lymphadenopathy.
• Skin lesions beyond the scratch site (e.g., erythema nodosum).
• Hepatosplenomegaly (enlarged liver or spleen) – more common in immunocompromised patients.
• Neurologic signs – headache, seizures, or encephalitis (rare).
• Endocarditis, osteomyelitis, or bacillary angiomatosis in patients with HIV/AIDS or other immune‑deficiency states.

Causes and Risk Factors

Etiology

The causative agent, Bartonella henselae, is a gram‑negative rod that resides in the erythrocytes and endothelial cells of cats. Fleas (especially Ctenocephalides felis) are the primary vector among cats, spreading the bacteria from cat to cat. Humans acquire the infection via:

• Direct scratch or bite from a cat.
• Contact of broken skin with cat saliva that is contaminated with flea feces.
• Less commonly, a flea bite on a human that has fed on an infected cat.

Who is at higher risk?

• Children aged 5–15 – they are more likely to play roughly with kittens.
• Owners of kittens – kittens have infection rates up to 50 % compared with 10–15 % in adult cats.<sup>3</sup>
• People with frequent exposure to stray or feral cats – shelters, veterinarians, animal control workers.
• Immunocompromised individuals – HIV/AIDS, organ‑transplant recipients, patients on chemotherapy, or those taking high‑dose steroids.
• People living in areas with high flea burdens – lack of regular flea control increases the reservoir.

Diagnosis

Diagnosis is based on a combination of clinical presentation, exposure history, and laboratory testing. No single test is 100 % sensitive, so clinicians often use a stepwise approach.

Clinical evaluation

• Detailed history of cat contact (type of cat, presence of scratches/bites, flea treatment status).
• Physical exam focusing on lymph node enlargement, skin lesions, and signs of systemic involvement.

Laboratory tests

1. Serology (IgG/IgM antibodies) – Enzyme‑linked immunosorbent assay (ELISA) or indirect fluorescent antibody (IFA). A four‑fold rise in IgG titers between acute and convalescent samples is diagnostic.
2. Polymerase chain reaction (PCR) – Detects bacterial DNA in blood, lymph node aspirate, or tissue biopsy. PCR is the most specific test but not always available.
3. Blood cultures – Rarely positive; requires prolonged incubation (up to 45 days).
4. Complete blood count (CBC) and inflammatory markers – May show mild leukocytosis, elevated ESR/CRP.

Imaging (when needed)

• Ultrasound or CT of enlarged lymph nodes to rule out abscess or malignancy.
• Chest X‑ray if respiratory symptoms suggest pulmonary involvement.

Treatment Options

Many cases of CSD are self‑limiting and resolve without antibiotics within 2–4 months. However, treatment is recommended for:

• Severe or progressive lymphadenopathy.
• Systemic disease (e.g., hepatic, neurologic, ocular involvement).
• Immunocompromised patients.

Antibiotic regimens

Condition	First‑line Antibiotic	Typical Dose & Duration
Mild–moderate CSD (skin + lymph nodes)	Azithromycin	500 mg orally on day 1, then 250 mg daily for 4 days (total 5 days)
Systemic disease or immunocompromised host	Doxycycline	100 mg orally twice daily for 4–6 weeks
Severe visceral involvement (e.g., endocarditis)	Combination therapy – Doxycycline + Rifampin	Both agents for 4–6 weeks; monitor liver enzymes
Pregnant or lactating women	Trimethoprim‑Sulfamethoxazole (TMP‑SMX)	800/160 mg orally twice daily for 4 weeks (avoid first trimester)

Adjunctive measures such as NSAIDs for pain and fever are often used. Surgical drainage is reserved for abscessed lymph nodes.

Supportive care

• Rest, adequate hydration, and balanced nutrition.
• Warm compresses to swollen lymph nodes for comfort.
• Elevation of the affected limb if a peripheral node is enlarged.

Living with Feline Scratch Disease

Most patients recover fully, but some experience lingering fatigue or enlarged nodes for weeks to months. The following tips help manage daily life during recovery:

• Monitor node size: Measure the longest dimension of the lymph node twice weekly. Report sudden increase (>1 cm) or rapid growth to a clinician.
• Pain control: Over‑the‑counter NSAIDs (ibuprofen 400 mg every 6 h) are effective unless contraindicated. Avoid aspirin in children.
• Activity modification: Limit vigorous exercise that strains the affected region (e.g., heavy lifting for axillary nodes) until pain subsides.
• Skin care: Keep the original scratch site clean; apply a thin layer of petroleum jelly to prevent cracking.
• Follow‑up appointments: Typically 2–3 weeks after starting antibiotics, then every 4–6 weeks until the node returns to normal.
• Psychological support: Children may feel anxious about visible swelling; reassure them that the condition is treatable and usually benign.

Prevention

Preventing CSD focuses on reducing cat‑to‑human transmission and controlling the flea reservoir.

1. Flea control – Treat all cats (including indoor pets) with veterinarian‑recommended flea preventatives (topical, oral, or collars). Keep the home environment clean; wash bedding weekly.
2. Cat handling practices
   • Wash hands with soap and water after petting, feeding, or cleaning a cat.
   • Avoid rough play that may lead to scratches or bites, especially with kittens.
   • Trim cats’ nails regularly (about every 2 weeks) or keep them filed short.
3. Prompt wound care – Clean any scratch or bite immediately with mild soap, apply an antiseptic (e.g., povidone‑iodine), and cover with a clean bandage.
4. Veterinary health – Have cats examined annually; discuss flea‑preventive protocols and consider testing high‑risk cats for Bartonella if they are frequently outdoors.
5. Education – Teach children to report any cat scratch or bite promptly, even if it seems minor.

Complications

When untreated or in high‑risk hosts, CSD can progress to serious complications:

• Parinaud oculoglandular syndrome – Conjunctivitis with pre‑auricular lymphadenopathy; may lead to corneal scarring.
• Neurologic involvement – Encephalitis, meningitis, or peripheral neuropathy; presents with headache, confusion, or focal deficits.
• Visceral organ involvement – Hepatosplenic granulomas, pneumonia, or myocarditis.
• Bacillary angiomatosis – Vascular skin lesions, often in immunosuppressed patients.
• Endocarditis – Rare but life‑threatening infection of heart valves.
• Chronic lymphadenopathy – Persistent enlarged nodes can mimic lymphoma, leading to unnecessary biopsies.

When to Seek Emergency Care

References

1. Mayo Clinic. “Cat Scratch Disease.” Updated 2023. https://www.mayoclinic.org
2. CDC. “Bartonella (Cat‑Scratch) Disease.” 2022. https://www.cdc.gov
3. Woldehiwet Z et al. “Prevalence of Bartonella henselae in cats and fleas worldwide.” *Veterinary Parasitology*, 2021; 292: 109‑117.
4. National Institutes of Health (NIH). “Bartonella Infections” – Review of clinical manifestations, 2020.
5. Cleveland Clinic. “Cat Scratch Disease (Bartonellosis).” 2023. https://my.clevelandclinic.org

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