Cat Scratch Disease
Cat scratch disease (CSD) is a subacute infection passed from animals to people (a zoonosis), caused by the fastidious Gram-negative bacillus Bartonella henselae. The bacterium lives in the blood and dental plaque of cats (especially kittens under a year old) and is spread between cats by the cat flea (Ctenocephalides felis). When a cat scratches, bites, or licks broken skin, the bacteria enter the dermis, causing a small bump at the site followed by painful, swollen regional lymph nodes that can last weeks to months. In most people with a normal immune system the illness settles on its own, but Bartonella henselae can still cause serious systemic complications, such as Parinaud oculoglandular syndrome, encephalitis, granulomatous hepatosplenic disease, or, in people with weakened immunity, bacillary angiomatosis.
At Haute-Derma, diagnosing and treating cat scratch disease combines lymph node ultrasound, serology or PCR testing, an antibiotic regimen to stop the bacteria multiplying, and cosmetic care to fade any marks or scars left after the infection.
Pathogenesis and Transmission
Vector and Route of Entry
- The flea–cat–human cycle: The cat flea (Ctenocephalides felis) feeds on an infected cat and leaves feces containing Bartonella henselae on the cat's fur and skin. As the cat grooms, the bacteria collect in its mouth and on its claws.
- How it enters: The bacteria pass directly into the superficial dermis through a scratch, a bite, or tiny breaks in the skin that the cat licks.
Immune Response and Granuloma Formation
- Lymphatic spread: From the entry site in the skin, the bacteria travel through the lymphatics to the regional nodes that drain that area (armpit, groin, or neck).
- Necrotizing granulomatous inflammation: The immune system sends macrophages and T lymphocytes to wall off the bacteria, forming granulomas with a pus-filled, necrotic center (suppurative granulomas).
Clinical Stages and Complications
Initial Skin Lesion (Inoculation Lesion)
- Appears 3–10 days after contact with the cat.
- A small papule, blister, or pustule 2–5 mm across on a red base. It is usually painless and not itchy, and it crusts over and disappears within 1–3 weeks, so it is easy to overlook.
Subacute Regional Lymphadenopathy
- Develops 1–3 weeks after the papule appears (roughly 2–4 weeks after the scratch).
- Persistent node swelling: The draining nodes (most often in the armpit, elbow, neck, and groin) become clearly enlarged, 1.5–5 cm in size, tender, and well defined.
- Suppuration: In about 10–20% of cases the node fills with pus and feels soft and fluctuant.
Atypical and Systemic Complications
- Parinaud oculoglandular syndrome: The bacteria enter through the conjunctiva (for example, rubbing the eyes with hands contaminated by cat saliva), causing granulomatous conjunctivitis with marked swelling of the lymph node in front of the ear.
- Systemic symptoms: Prolonged low-grade fever, fatigue, loss of appetite, headache, granulomatous liver and spleen involvement (hepatosplenic CSD), neuroretinitis, or bone lesions.
- Bacillary angiomatosis: Occurs in people with HIV/AIDS or severe immunosuppression, producing raised red-purple vascular nodules on the skin that are easily mistaken for Kaposi sarcoma.
Assessment and Diagnosis at Haute-Derma
Exposure History and Imaging
- We ask about owning, playing with, or being scratched or bitten by a cat in the previous 1–2 months.
- Dermoscopy of the papule at the original entry site, and color Doppler ultrasound of the nodes to assess their size and capsule and to detect pus-filled necrotic areas inside.
- Diagnostic tests: IgG/IgM antibodies to Bartonella henselae by indirect immunofluorescence (IFA), or PCR to detect bacterial DNA in fluid aspirated from the node.
Managing the Affected Lymph Nodes
- For tense, painful nodes that have filled with pus: ultrasound-guided fine needle aspiration (FNA) to drain the pus and relieve pressure and pain.
- Important: Formal incision and drainage is not recommended for cat scratch nodes, because opening the node tends to leave a chronic sinus tract that is very slow to heal and leaves a firm, unsightly scar.
Medical Treatment and Cosmetic Recovery at Haute-Derma
Antibiotic Treatment for Bartonella henselae
- First-line choice for typical disease (adults):
- Azithromycin 500 mg once on day 1, then 250 mg once daily on days 2–5. Clinical studies show azithromycin shrinks swollen nodes faster during the first month.
- Alternatives, or for severe or complicated infection:
- Doxycycline 100 mg twice daily for 2–4 weeks.
- Or ciprofloxacin 500 mg twice daily for 14 days.
- For eye, nervous system, or hepatosplenic granulomatous disease: doxycycline 100 mg twice daily combined with rifampin 300 mg twice daily for 4–6 weeks.
Cosmetic Care and Post-Inflammatory Scar Repair
- Once the nodes have settled and the skin papule has fully healed, apply a repair cream containing madecassoside, panthenol, and niacinamide to limit melanin buildup.
- For dark marks or scars at the scratch or FNA site: short-pulse fractional laser combined with an epidermal growth factor (EGF) serum to rebuild collagen and elastic fibers, fade hyperpigmentation, and prevent pitted scars.
