JPC SYSTEMIC PATHOLOGY
INTEGUMENT
August 2022
I-B09
SIGNALMENT (4066662-00): 8 week old neutered male, crossbreed pig (Sus scrofa)
HISTORY: Pig developed “blotchy” skin lesions and became lethargic, moribund, and ultimately passed away. Staphylococcus aureus was isolated from the skin.
HISTOPATHOLOGIC DESCRIPTION: Haired skin: The epidermis is diffusely expanded by moderate orthokeratotic to parakaratotic hyperkeratosis and acanthosis. The stratum corneum and stratum granulosum are infiltrated by large numbers of neutrophils which occasionally aggregate into intraepidermal pustules. Inflammatory cells transmigrate all layers of the epidermis and extend into dilated hair follicle ostia (luminal folliculitis). Portions of the stratum corneum are lost (erosion) and replaced by a serocellular crust composed of abundant degenerate neutrophils, cellular debris, fibrin, few macrophages, lymphocytes, plasma cells, fragmented hair shafts, lakes of eosinophilic serum, and few small colonies of 1µm basophilic cocci. The hyperplastic epidermis forms anastomosing rete ridges and has moderate intercellular edema and prominent bridging (spongiosis) and intracellular edema. Within the subjacent superficial dermis, there is abundant clear space (edema) separating collagen bundles and admixed with moderate numbers of neutrophils, eosinophils, lymphocytes and plasma cells.
MORPHOLOGIC DIAGNOSIS: Haired skin: Epidermitis, exudative and proliferative, diffuse, subacute, severe, with dermal edema and colonies of intracorneal cocci.
ETIOLOGIC DIAGNOSIS: Staphylococcal epidermitis and folliculitis
CAUSE: Staphylococcus hyicus
CONDITION: Exudative epidermitis (EE)
SYNONYMS: Greasy pig disease, impetigo contagiosa suis, seborrhea oleosa
GENERAL DISCUSSION:
- EE is a common, worldwide acute, exudative superficial pyoderma in young pigs (5-35 days old); can cause mild disease in older pigs
- Tends to affect all piglets in a litter; morbidity 10-90%; mortality 5-90%
- Most commonly caused by hyicus subsp. Hyicus; may be associated with S. chromogenes. S. aureus and S. sciuri
- An autogenous vaccine exists
- EE is divided into acute, subacute, and chronic forms (see below)
PATHOGENESIS:
- S. hyicus is part of healthy pig flora with highest concentrations within the conjunctiva, snout, ears, and vagina; obtained at birth
- The most pathogenic strains possess exfoliative toxins (ExhA, ExhB, ExhC, ExhD, SHETA, SHETB); Exh toxins digest desmoglein-1 in the epidermis of porcine skin, disrupting cell-cell adhesion
- Thought that trauma breaches the skin barrier, allowing for the pathogenic bacteria to flourish
- Other predisposing factors may include agalactia of the sow, concurrent infections (i.e. porcine circovirus 2, parvovirus), nutritional deficiencies, large-size production units, high stocking densities, and poor husbandry
- Mortality occurs due to dehydration, electrolyte imbalances, negative energy balance, and septicemia
TYPICAL CLINICAL FINDINGS:
- Acute: few day old piglets with abrupt onset of skin lesions around the eyes, snout, chin, ears, and medial aspect of the legs which then spread rapidly and become generalized within 24-48 hours
- Subacute: course more protracted
- Chronic: older piglets with mild skin lesions confined to the head and ears
- May cause abortions in sows
TYPICAL GROSS FINDINGS:
- Acute: peeling skin with underlying red, glistening moist areas with become covered with a greasy, dark brown malodorous exudate; erosions of the coronary bands and heels; conjunctivitis with eyelids matted shut; usually die
- Subacute: thick, wrinkly skin with exudate that becomes dry, hard, and cracked producing fissures and a furrowed appearance
- Chronic: erythema and waxy brown crusts; stunted growth; subcutaneous abscesses; polyarthritis; necrosis of the ears and tail
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Skin: subcorneal vesicular to pustular dermatitis with extension into the hair follicles (luminal folliculitis) that quickly progress to thick crusts of orthokeratotic to parakeratotic keratin, lakes of serum, neutrophils, necrotic debris, and microcolonies of gram-positive cocci; elongated rete ridges and acanthosis; dermal edema and congestion +/- inflammation (in ulcerated areas)
- Draining lymph nodes: lymphadenitis
- Kidneys: Degeneration and exfoliation of collecting duct and renal pelvis epithelium, tubular casts (with or without bacteria present); purulent pyelonephritis (if bacteria present)
DIFFERENTIAL DIAGNOSIS:
- Porcine juvenile pustular psoriasiform dermatitis (pityriasis rosea; I-M14) – young Landrace pigs (3-14 weeks) with symmetrical round, red raised papules and plaques with scales that coalesce into a mosaic or serpiginous pattern
- Sarcoptic mange (Sarcoptes scabiei var suis; I-P06) – young pigs with papules and crusts on the ears, head, neck, and legs; intensely pruritic
- Zinc responsive parakeratosis (I-M18) – symmetrical, erythematous macules on the lower limbs, face, scrotum and tail +/- dry brown crust up to 2-3mm thick
- Ringworm (I-F11) – uncommon, crusting
COMPARATIVE PATHOLOGY:
- Cattle: hyicus often associated with concurrent psoroptic mange.
- Goats: Has been isolated from young pygmy goats with chronic generalized seborrheic dermatitis and alopecia
- See I-B02 for information on aureus/botryomycosis and other Staphylococcal spp
References:
- Mauldin EA, Peters-Kennedy J. Integumentary System. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed. Vol. 1. Louis, MO: Elsevier; 2016: 630-631.
- Welle MM, Linder KE. The Integument. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1167, 1230-1231.
