Ep.40 - The Real Sheep Detective (feat. Stephen D. White)

In this month's episode, Sue, John and Paul welcome Professor & Chief of Service (Dermatology) at UC Davis, Stephen D White to the podcast.

Chapter 1: Sheep Skin Detectives

(03:09) Sue sets the scope: primary-care perspective rather than rare autoimmune disease. Stephen confirms autoimmune skin disease is vanishingly rare in sheep (pemphigus foliaceus essentially unreported, bar one Barbary sheep case in a zoo).

(06:10) Sue asks whether clinical distribution helps localise the cause in a pruritic sheep the way it does in a dog or cat. Stephen explains it's less reliable — thick wool can mask hair loss even with significant pruritus, though rubbing behaviour is usually evident. Lice are visible with a hand lens; mites are not.

(08:07) Question on empirical response to treatment. Stephen notes lice usually respond well to licensed ectoparasiticides (mainly avermectins); isoxazolines are unlicensed in ruminants and unreported in sheep specifically (though used in camelids, and anecdotally a bighorn sheep). Repeat treatment at 2–4 weeks is usually needed to catch hatching eggs.

Chapter 2: Suspect Number 1 - Ectoparasites

(11:30) John asks for top differentials in a pruritic sheep, Stephen answers: “ectoparasites, ectoparasites, and ectoparasites” — mites, lice and sheep keds (which are insects, not mites). He stresses checking in-contact sheep, since one animal may be subclinical while another is severely affected.

(13:49) Sue asks why would a referral centre see an ectoparasite case at all? Stephen: usually a failed or incomplete owner-applied treatment, or a backyard sheep simply not monitored closely enough for early signs.

(15:29) On technique: always scrape if pruritic, using a medical-grade spatula rather than a blade (sheep are skittish; a slip with a blade causes injury). An otoscope with the cone removed doubles as a magnifier and light source. Dermatophytosis should also be considered — often presenting as facial alopecia rather than fleece loss — and can coexist with ectoparasitism.

(15:09) John ask about photosensitisation. Stephen distinguishes hepatogenous causes (impaired phylloerythrin metabolism from hepatotoxic plants, or a genetic defect in Corriedale lambs) from primary photodynamic plant ingestion (e.g. St John's Wort). Lesions favour the head and distal limbs. Flock-wide cases point to an environmental cause (send hay/pasture samples to the local extension lab); idiosyncratic reactions (as seen with clover in horses) may occur but are poorly documented in ruminants.

Chapter 3: Dermatological Movie Stars

(26:48) John introduces orf, referencing its cameo in Sheep Detectives. Stephen describes it as a parapoxvirus infection, usually self-limiting, but causing anorexia through oral pain — a problem in production settings. A non-resolving “super orf” form causes severe weight loss. Stephen shares data from the retrospective study: of ten orf-affected sheep, five were euthanised, due to generalised cutaneous lesions or concurrent Corynebacterium pseudotuberculosis abscesses — evidence that orf can significantly compromise immune function. One case of orf-associated facial alopecia resolved fully once the virus cleared.

(31:07) On zoonotic risk and management: gloves are essential when handling any crusting lesion in sheep or goats. Management includes moistening hay to ease painful feeding, antibiotics for secondary bacterial infection, and parenteral treatment or stomach tubing in severe anorexia.

(33:17) Sue asks about bacterial skin disease. Stephen identifies C. pseudotuberculosis and staphylococcal abscesses as the main presentations — often large, anywhere on the body, commonly peri udder in females. Internal abscessation (lungs, liver) is a key concern; aspirated purulent masses warrant involving a large-animal colleague, with caution against environmental contamination during drainage. Dermatophilosis is discussed as globally widespread and rain-associated, presenting dorsally, or interdigitally as “strawberry footrot.” Stephen references a 2008 paper (Norris) linking resistance to greasy, high-wax, low-pH, fine-fibre wool with higher suint content — traits that reduce moisture retention.

(41:10) Wrap-up: Stephen credits the study's primary author, a veterinary student, and flags Aidan Foster's JAVMA review of skin disease in alpacas, goats, pigs and sheep as further reading (both for show notes).

(42:00) Sue closes with a reflection that sheep dermatology follows the same diagnostic logic as small animal practice — FNA, impression smears, skin scrapes, hair plucks — and should feel less daunting to primary-care vets than expected.

Silly question to end: what's the most ridiculous thing you've done purely because everyone else was doing it?

References mentioned (from Sue’s closing remarks)

Lauth et al. (2025) – Skin disease in sheep (Ovis aries): a retrospective report of 299 cases at a university veterinary medical teaching hospital (1986–2020). Veterinary Dermatology. This is the retrospective study Stephen co-authored, discussed throughout the episode.

Wiley Online Library: https://onlinelibrary.wiley.com/doi/abs/10.1111/vde.13338

PubMed: https://pubmed.ncbi.nlm.nih.gov/40091266/

Foster AP (2023) – Challenges in the diagnosis and management of skin diseases in alpacas, goats, pigs, and sheep. Journal of the American Veterinary Medical Association, 261(S1). The review article flagged in the wrap-up as further reading.

AVMA Journals: https://avmajournals.avma.org/view/journals/javma/261/S1/javma.22.12.0572.xml

PubMed: https://pubmed.ncbi.nlm.nih.gov/36917614/