Porcine Juvenile Pustular Psoriasiform Dermatitis

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Porcine Juvenile Pustular Psoriasiform Dermatitis (Pityriasis rosea)


  • Pityriasis rosea is a self‑limiting inflammatory disease of young pigs.
  • The disease is of unknown etiology.
  • There is a predilection for the white breeds, especially the Landrace, and suggestions of a hereditary link.
    • Although the mode of inheritance is not simple, it is clear that swine that have had this condition are more likely to produce affected progeny.
  • The condition is noncontagious.
    • Experimental attempts at transmitting the disease, and attempts to demonstrate any significant microorganisms have failed.
    • The disease has been observed in cesarean‑derived SPF pigs.
  • The condition most frequently occurs in young pigs, 3‑14 weeks of age, and often more than one member of a litter is affected.
  • Although this condition had been previously called pityriasis rosea, clinically and pathologically it is nothing like pityriasis rosea in humans!

Clinical Signs

  • There are usually no systemic signs. Skin lesions may be preceded by anorexia, vomiting, & diarrhea.
  • There is no fever.

Gross Lesions

  • Primary lesions are seen on the ventral abdomen or medial thighs, and appear as symmetric, sharply defined, red raised plaques up to 6 mm in diameter.
  • These expand centrifugally, often coalescing to produce whorling mosaic or serpiginous patterns, and may extend up the sides and perineum.
  • As they expand, lesions become scaly and heal from the center outward, producing ring‑shaped lesions with a center of scaly or normal appearing skin surrounded by a zone of elevated erythematous skin and scales.
    • The term pseudo-ringworm has been used to describe this condition.
  • Lesions are nonirritant and usually resolve spontaneously in 2 ‑ 10 weeks.

Microscopic Lesions

  • Skin biopsy reveals superficial perivascular dermatitis with psoriasiform epidermal hyperplasia.
  • The superficial dermis usually shows mild to moderate mucinous degeneration, and eosinophils and neutrophils are the predominant inflammatory cell types.
  • Intra-epidermal pustules containing eosinophils and neutrophils are prominent in early lesions.
  • Parakeratotic hyperkeratosis is usually prominent.

Differential Diagnosis

  1. Dermatophytosis ‑ (etio: Tr. mentagrophytes, M. canis, Tr. verrucosum var. discoides, M. nanum, Tr. rubrum) Ruled‑out due to lack of mycotic organisms.
  2. Exudative epidermitis (greasy pig disease) ‑ (Staphylococcus hyicus) Early lesions may appear as red plaques, but soon become exudative and ulcerated; R/O based on culture, lesion distribution, histopathology.
  3. Dermatosis vegetans ‑ Systemic, erythematous maculopapular dermatitis caused by the inheritance of a autosomal recessive, semilethal factor. Skin, coronary band and hoof lesions, giant cell pneumonia, fatal.
  4. Swinepox ‑ Ballooning degeneration and intracytoplasmic inclusion bodies.



IL-3 is involved... Vet Path (2007) 34: 45-43