Makindo Medical Notes

Orf (Contagious Ecthyma)

🧠 Orf is a zoonotic parapoxvirus infection caught from sheep/goats, usually after the virus is inoculated into a small cut/scratch. Clinically it causes a solitary (or few) tender, red-blue “target-like” nodule on the hand/finger/forearm that can look “pus-filled” but is firm tissue if incised — so it’s often misdiagnosed as a bacterial abscess.

🦠 What is orf?

• Cause: Orf virus (a Parapoxvirus).
• Reservoir: infected sheep and goats (classically lambs with “scabby mouth”).
• Transmission: direct inoculation through broken skin from animal lesions, carcasses, contaminated bedding/fomites, or (rarely) animal vaccine exposure.

Teaching point: parapoxviruses replicate in the cytoplasm and drive a strong local inflammatory/proliferative response in skin, which is why the lesion can look dramatic yet remain localised. The “pseudo-pustule” appearance is a classic trap: cutting it open doesn’t release pus (and can delay healing and seed bacteria). In most immunocompetent patients, the immune response contains it and the lesion involutes over weeks.

🧭 UK context: who is at risk?

• 👩‍🌾 Farmers, shearers, vets, abattoir/meat workers, people bottle-feeding lambs.
• 🩹 Anyone with cuts/scratches handling infected animals or contaminated surfaces (e.g., bedding).
• 💉 Animal vaccination: sheep/goats can be vaccinated, and humans can still become infected after contact with recently vaccinated animals (live vaccine risk).

Orf is not on the routine notifiable diseases list in England, but clinicians can still notify/public health discuss if there’s an unusual cluster or significant risk concern.

🩺 Clinical features

• Incubation: typically ~3–7 days (often “about a week”).
• Site: usually fingers/hands/forearms; can occur on face (especially with animal-to-face contact).
• Lesion size: commonly 2–3 cm, can reach ~5 cm. }
• Systemic/local: may cause tenderness/itch, mild fever, lymphangitis and regional lymphadenopathy.

🧩 The 6-stage evolution (very exam-friendly)

• 1️⃣ Maculopapular (erythematous papule)
• 2️⃣ Target (targetoid nodule with halo)
• 3️⃣ Acute/weeping (oozes)
• 4️⃣ Regenerative (dries)
• 5️⃣ Papillomatous (warty/crusted surface)
• 6️⃣ Regression (involutes)

Each stage is often roughly a week, so the whole illness is usually 4–6 weeks (sometimes longer). This staged progression helps you distinguish orf from bacterial infection (which should improve quickly with appropriate antibiotics/drainage) and from herpetic whitlow (grouped vesicles, different tempo).

🚩 Red flags (escalate / discuss early)

• 🛡️ Immunosuppressed (giant, persistent, atypical lesions; higher complication risk). {index=7}
• 👁️ Peri-ocular/ocular involvement or facial lesions with eye symptoms.
• 🌡️ Significant systemic upset, rapidly spreading cellulitis, or severe pain.
• 🔁 Multiple lesions or extensive disease (consider alternative diagnosis or immune compromise).

🔍 Differentials (don’t miss these)

• 🐄 Milker’s nodules (parapoxvirus from cattle) — clinically very similar.
• 🧫 Bacterial abscess/cellulitis — usually lacks classic staged evolution; respond to antibiotics if true infection.
• 🦠 Herpetic whitlow — grouped vesicles, burning pain, healthcare exposure; avoid incision.
• ☣️ Cutaneous anthrax — painless eschar + marked oedema + relevant exposure history (urgent/public health).
• 🩸 Pyogenic granuloma/tumour mimic — especially if “giant orf” in immunosuppressed.

Key bedside clue: “looks pustular but isn’t drainable pus” + sheep/goat exposure = strongly think orf.

🧪 Investigations

• Usually clinical diagnosis with a clear exposure history.
• If uncertain or high stakes: send a PCR from lesion swab/scab/vesicular fluid (via microbiology/virology).
• Biopsy can support diagnosis if needed, but avoid unnecessary procedures if the story is classic.

🩹 Management (practical, ward-friendly)

• 🧼 Supportive care: clean, simple dressing, keep covered, analgesia.
• 🧤 Infection control: avoid touching lesion; hand hygiene after dressing changes; dispose of dressings safely.
• 🧫 Antibiotics only if there’s convincing secondary bacterial infection (spreading erythema, warmth, purulence + systemic signs).
• 🚫 Avoid incision & drainage unless you’re sure it’s a true abscess (often it is not).
• 🧑‍⚕️ For immunosuppressed/persistent/giant lesions: discuss with dermatology/ID — case-based options include topical agents (e.g., imiquimod) or other specialist approaches.

Mentoring pearl: reassuring the patient that “this looks ugly but is usually self-limiting” is therapeutic — and prevents the common spiral of repeated antibiotics and procedures. The main reason to escalate is not because most cases are dangerous, but because atypical disease in immunosuppressed patients can mimic malignancy and can genuinely become extensive.

⚠️ Complications

• 🧫 Secondary bacterial infection.
• 🩹 Erythema multiforme (often 1–2 weeks after lesion onset) and rarer bullous pemphigoid–like eruptions. }
• 📈 “Giant orf” / persistent lesions in immunosuppressed hosts.

🛡️ Prevention (for patients & staff)

• 🧤 Wear gloves when handling sheep/goats, carcasses, or bedding; cover cuts with waterproof dressings.
• 🧼 Wash hands after animal contact; avoid touching face/eyes while working.
• 💉 Be cautious around recently vaccinated animals (live vaccine exposure risk).

HSE highlights orf as a farm-related zoonosis and emphasises basic protective measures (gloves/hand hygiene) to reduce risk.

🩺 Mini-cases (teach your juniors)

• 👩‍🌾 “Not an abscess”: farmer with a targetoid weeping nodule on finger, tender nodes in axilla → supportive care + consider PCR if uncertain.
• 🍼 Bottle-fed lamb: parent bottle-feeding lambs; lesion on forearm; worried about “MRSA” → explain staged viral course, keep covered.
• 🛡️ Immunosuppressed patient: transplant recipient with rapidly enlarging exophytic lesion → urgent derm/ID (giant orf vs tumour mimic).

✅ One-liner to remember: “Sheep/goat exposure + target-like weeping nodule on the hand that evolves over weeks = Orf; reassure, dress, avoid I&D, and escalate if immunosuppressed or atypical.” :