Exudative epidermitis is a generalized dermatitis that occurs in 5- to 60-day-old pigs and is characterized by sudden onset, with morbidity of 10%–90% and mortality of 5%–90%. The acute form usually affects suckling piglets, whereas a chronic form is more commonly seen in weaned pigs. It has been reported from most swine-producing areas of the world.
Lesions are caused by Staphylococcus hyicus, which can produce an exfoliative toxin but seems unable to penetrate intact skin. Both virulent and avirulent strains exist. Abrasions on the face, feet, and legs or lacerations on the body precede infection. Such injuries are usually caused by fighting or by abrasive surfaces such as new concrete. Other predisposing factors that may affect the severity and progress of the disease include immunity, hygiene, nutrition, and the presence of mange mites or anything that damages the skin. Mature sows that have acquired a high level of immunity from previous exposure will provide protection to piglets via their colostrum. The incidence is often higher in gilt litters and in newly established SPF herds in which most breeders are gilts.
Pigs develop resistance with age, but S hyicus may be recovered from the skin of older pigs, the vagina of sows, and the preputial diverticulum of boars. These inapparent carriers serve as a source of contamination for naive herds. Suckling pigs are usually infected by their dams, in some cases during birth from sows with vaginal infections, or from contamination in the farrowing unit. Suckling piglets are the most commonly and severely affected, but cross-infection occurs after mixing at weaning with a morbidity of as much as 80%. However, mortality is usually low in this age group. The incidence appears to have increased because of pig production units with high stocking densities and possibly earlier weaning. There are recent reports of exudative epidermitis associated with ST398 methicillin-resistant S aureus (MRSA) infections, but a causal role has not been clearly demonstrated.
The first signs are listlessness and reddening of the skin in one or more piglets in the litter. Affected pigs rapidly become depressed and refuse to eat. Body temperature may increase early in the disease but thereafter is near normal. The skin thickens, and reddish brown spots (macules) appear around the eyes, nose, lips, and ears from which serum and sebum exude. The lesions increase in size and develop a vesicular or pustular appearance.
The body is rapidly covered with a moist, greasy exudate of sebum and serum that becomes crusty. Accumulation of dirt gives the affected area a black color. Vesicles and ulcers may also develop on the nasal disk and tongue. The feet are nearly always involved, with erosions at the coronary band and heel; the hoof may be shed in rare cases. In the acute disease, death occurs within 3–5 days. In older animals, the chronic form of the disease is seen as thick, crusty lesions over the entire body or as discrete circumscribed lesions that do not coalesce. Mortality is low except in very young suckling piglets. However, recovery is slow and growth is retarded and often associated with diarrhea, emaciation, and dehydration.
Necropsy of severely affected pigs reveals marked dehydration, congestion of the lungs, and inflammation of the peripheral lymph nodes. Distention of the kidneys and ureters with mucus, cellular casts, and debris is common in peracute and acute forms of the disease. Differential diagnoses include sarcoptic mange (see Mange in Pigs), nutritional deficiencies including zinc (parakeratosis, see Parakeratosis), ringworm (see Dermatophytosis), and pityriasis rosea (see Pityriasis Rosea in Pigs (Porcine juvenile pustular psoriaform dermatitis).
The causative organism is inhibited by many antibiotics, including amoxicillin, ampicillin, erythromycin, lincomycin, penicillin, tylosin, trimethoprim-sulfonamide, the aminoglycosides, and cephalosporins. Successful treatment requires that the antimicrobial be given in high dosages early in the disease and for 7–10 days. Success is greatest when antimicrobial therapy is combined with daily applications of antiseptics to the entire body surface. Treatment is less effective in very young pigs and ineffective in advanced cases. In severe outbreaks, in-contact pigs should also be given antibiotics for several days. Sows due to farrow, and their housing, should be thoroughly disinfected to prevent outbreaks. Hygiene in the weaner accommodation and strategic in-water or in-feed medication for 3–5 days will help control outbreaks after weaning. Other procedures that may decrease the severity of an outbreak include clipping the needle teeth of newborn pigs, providing soft bedding, segregating infected animals, and avoiding mixing of animals to decrease the possibility of skin lesions due to fighting. Autogenous bacterins have been used with some success to reduce the incidence of disease in chronically infected herds.