Disease outbreaks may be acute or chronic, and clinically inapparent infections also occur. Acute outbreaks are characterized by sudden and unexpected deaths, febrile episodes, inappetence, painful joints, and skin lesions that vary from generalized cyanosis to the often-described diamond skin (rhomboid urticaria) lesions. Chronic erysipelas tends to follow acute outbreaks and is characterized by enlarged joints and lameness. A second form of chronic erysipelas is vegetative valvular endocarditis. Pigs with valvular lesions may exhibit few clinical signs; however, when exerted physically they may show signs of respiratory distress, lethargy, and cyanosis, and possibly suddenly succumb to the infection.
The acute and chronic forms of swine erysipelas may occur in sequence or separately. Pigs that succumb to the acute septicemic form may die suddenly without previous clinical signs. This form occurs most frequently in growing and finishing pigs. Outbreaks may be related to stressful conditions, such as extreme heat during transportation. Acutely infected pigs are depressed, febrile (104°-108°F [40°-42°C]), and reluctant to stand and move. Affected pigs squeal excessively when handled, require assistance to stand, and prefer to lie down soon after being forced to stand. Affected pigs may also walk stiffly on their toes and shift weight from limb to limb when standing. Anorexia and thirst are common, and febrile pigs will often seek wet, cool areas to lie down. Skin discoloration may vary from widespread erythema and purplish discoloration of the ears, snout, and abdomen, to diamond-shaped skin lesions almost anywhere on the body, but particularly on the lateral and dorsal regions. The lesions may occur as discrete, pink or purple areas of varying size that become raised and firm to the touch within 2-3 days of illness. They may disappear over the course of a week or progress to a more chronic type of lesion, commonly referred to as diamond skin disease. If untreated, necrosis and separation of large areas of skin can occur, and the tips of the ears and tail may become necrotic and slough.
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Clinical disease is usually sporadic and affects individuals or small groups, but sometimes larger outbreaks occur. Mortality is variable (0-100%), and death may occur up to 6 days after the first signs of illness. Acutely affected pregnant sows may abort, probably due to the fever, and lactating sows may show agalactia. Untreated pigs may develop the chronic form of the disease, usually characterized by chronic arthritis, vegetative valvular endocarditis, or both. Such lesions may also be seen in pigs with no previous signs of septicemia. Valvular endocarditis is most common in mature or young adult pigs and is frequently manifest by death, usually from embolism or cardiac insufficiency. Chronic arthritis, the most common form of chronic infection, produces mild to severe lameness. Affected joints may be difficult to detect initially but eventually become hot and painful to the touch and later visibly enlarged. Dark purple, necrotic skin lesions that commonly slough may be seen. Mortality in chronic cases is low, but growth rate is retarded.
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