Signalment:  

7 to 8-week-old pig (Sus scrofa)Skin rash.

Gross Description:  

Multifocal to coalescing skin lesions with mild to severe crusting were present over the entire body surface. Lesions were slightly raised. Periocular crusting was so severe the eyes appeared permanently closed. Generalized moderate lymphadenopathy was also present. This pig also had a large, reducible umbilical hernia.

Histopathologic Description:

Within sections of skin, there is multifocal subcorneal pustular dermatitis with mild to moderate epidermal acanthosis and hyperkeratosis (Fig. 1-1). Many cocci bacteria are present (Fig. 1-2). Multifocal epidermal ulceration and suppurative folliculitis are evident in some areas (not present in every slide). Within the superficial dermis there is congestion, edema and multifocal hemorrhage. There is also mild perivascular to interstitial infiltration of the superficial dermis by lymphocytes. The dermal inflammation is more pronounced in areas of epidermal ulceration.

Morphologic Diagnosis:  

Haired skin: Dermatitis, subcorneal, pustular and proliferative, acute to subacute, multifocal, mild to severe, with multifocal ulceration, and multifocal folliculitis due to Staphlococcus hyicus

Condition:  

Staphylococcus hyicus

Contributor Comment:  

Exudative epidermitis (greasy pig disease) is caused by Staphlococcus hyicus and is most common in pigs 535 days of age.^1,2 Although S. hyicus is a member of the normal skin flora of healthy pigs, trauma resulting in a breach of the skin barrier may predispose pigs to developing skin lesions.^1,2 S. hyicus produces exotoxins which cause intra-epidermal cleavage, resulting in separation of epidermal cells and lesions typical of exudative epidermitis.¹

The presence of cocci bacteria in the epidermal pustules of pigs affected by exudative epidermitis makes this condition similar to human bullous impetigo. Human bullous impetigo is an infection caused by staphylococcal exotoxins and characterized by epidermal pustules which contain many cocci bacteria.¹

JPC Diagnosis:  

Skin: Epidermitis, exudative and proliferative, multifocal, moderate with ulceration and mild superficial dermatitis and intracorneal cocci

Conference Comment:  

Staphylococcus hyicus causes a fatal generalized exudative epidermitis in neonatal pigs. The exotoxins produced by S. hyicus are metalloproteases that target the stratum granulosum, causing cleavage between the stratum corneum and stratum granulosum. In addition to the cutaneous lesions, piglets can have conjunctivitis, oral lesions and renal lesions. Renal lesions range from epithelial vacuolation, degeneration and exfoliatin of the cells lining the renal pelvis and collecting ducts that can lead to uretheral occlusion to suppurative pyelonephritis. Older pigs may develop subcutaneous abscesses, polyarthritis, necrosis of the ears and tail, abortion and mastitis. S. hyicus is the proposed cause of flank-biting and necrotic ear syndrome of pigs, which results in large ulcerated and crusty lesions in early weaned pigs.²

Exudative epidermitis of pigs is similar to two human conditions: staphylococcal scalded skin disease and bullous impetigo. Both of these conditions have exfoliotoxins that cause separation between the stratum spinosum and stratum granulosum. However, in bullous impetigo the cocci are present within the intact pustules like in exudative epidermitis, whereas in scalded skin syndrome the cocci are located at a distant often extracutaneous site.² Staphylococcus intermedius exfoliotoxins cause impetigo, bullous impetigo and superficial spreading pyoderma in dogs.³

Review of this slide led to a discussion of various cutaneous lesions in swine. Sarcoptes scabiei causes erythematous allergic dermatitis with secondary self trauma and crusting. Lesions are primarily located on the rump, flank and abdomen.² Zinc-responsive dermatosis in swine occurs in 2-4 month old growing pigs, and causes thick, dry scales and crusts that can produce deep fissures. Roughly symmetrical lesions are often found on the lower limbs, around the eyes, ears, snout, scrotum and tail. The microscopic lesion is marked hyperplastic dermatitis with parakeratotic hyperkeratosis.² Dermatosis vegetans is an inherited disorder in Landrace pigs that results in vegetating skin lesions, hoof malformations and giant cell pneumonia. Skin lesions range from brown-black plaques with a raised border and depressed center to dry-horny papillomatous lesions. The head is typically spared.² Erysipelothrix rhusiopathiae causes septicemia with cutaneous vasculitis and rhomboidal dermal infarcts, and is also known as diamond back skin disease. Additional lesions in acute cases include fibrinoid glomerular necrosis, renal intracapsular hemorrhage and fibrinous polyarthritis. The most common lesions in chronic cases include vegetative valvular endocarditis, chronic proliferative arthritis and diskospondylitis.⁶ Blue discoloration of the ears, tail and snout are due to venous thrombosis most commonly caused by Salmonella cholerasuis, but also other septicemic and viral infections such as Erysipelothrix rhusiopathiae, porcine pestivirus (Classical swine fever) and porcine asfarvirus (African swine fever).¹ Porcine dermatitis and nephropathy syndrome causes a systemic necrotizing vasculitis with hemorrhagic dermal infarcts, exudative glomerulonephritis and interstitial nephritis in feeder pigs. Skin lesions typically occur on the perineal area of the hindquarters, limbs, dependent areas of the abdomen and thorax, and ear margins. The condition has been associated with Porcine circovirus-2 and Porcine reproductive and respiratory syndrome virus (PRRS).5 Porcine juvenile pustular psoriasiform dermatitis is most common in weaned Landrace pigs, and causes erythematous serpigenous plaques on the ventral abdomen and inner thighs. Histological lesions include eosinophilic perivascular inflammation, spongiform pustules and psoriasiform hyperplasia.² Swinepox is caused by suipoxvirus. Typical poxviral lesions include proliferative and necrotizing skin lesions with large eosinophilic intracytoplasmic inclusions. Lesions primarily occur on the ventral and lateral abdomen, lateral thorax and medial legs of young, growing pigs. Mucosal surfaces are rarely affected. Hematopinus suis, the sucking louse, acts as a mechanical vector.² Melanomas are often congenital in the Duroc, Sinclair minipig and in Hormel crosses.²

References:

1. Brown CC, Baker DC, Barker IK: Alimentary system. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed., vol. 2, pp.196-197. Saunders, Edinburgh, Scotland, 2007
2. Ginn PE, Mansell JEKL and Rakich PM: Skin and appendages. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed. Vol. 1, pp. 591-744. Saunders, Edinburgh, Scotland, 2007
3. Gross TL, Ihrke PJ, Walder EJ, Affolter VK: Skin Diseases of the Dog and Cat, 2nd ed., pp. 4-9. Blackwell Publishing, Ames, Iowa, 2005
4. Taylor DF: Exudative epidermitis. In: Diseases of Swine, eds. Leman AD, Straw BE, Mengeling WL, et al., 7th ed., pp. 522 525. Iowa State Press, Ames, Iowa, 1992
5. Thibault S, Drolet R, Germain M-C, DAllaire S, Larochelle, and Magar R: Cutaneous and systemic necrotizing vasculitis in swine. Vet Pathol 35:108-116, 1998
6. Thompson K: Bones and Joints. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed., vol. 1, pp.163-164. Saunders, Edinburgh, Scotland, 2007

Click the slide to view.

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1-1. Pig, haired skin.

1-2. Pig, haired skin.

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