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, although other staphylococci (S scurii, S chromogenes, S aureus) have also been sporadically implicated in outbreaks. There are recent reports of exudative epidermitis associated with ST398 methicillin-resistant S aureus (MRSA) infections, but a causal role has yet to be clearly demonstrated. Although S hyicus is best known as a swine pathogen, the organism also occurs commonly in birds and cattle, and a small number of human infections have been reported. Both virulent and avirulent strains of S hyicus exist but appear unable to penetrate intact skin. Virulence is linked to production of exfoliative toxins (five of which have been identified) that reduce cell-cell adhesion of keratinocytes in the superficial epidermis. 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 most commonly and severely affected, but cross-infection occurs after mixing at weaning, leading to morbidity of up to 80%. However, mortality is usually low in weaned pigs. The incidence appears to have increased because of high stocking densities and possibly earlier weaning.
The first signs of exudative epidermitis 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, but lesions are not pruritic. 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.
Usually, a presumptive diagnosis based primarily on clinical signs is sufficient, and bacterial culture of lesions can be used for those unique cases when confirmation may be necessary or when bacterial isolate is desired for production of an autogenous vaccine.
The causative organism of exudative epidermitis may be susceptible to many antibiotics, including amoxicillin, ampicillin, erythromycin, lincomycin, penicillin, tylosin, trimethoprim-sulfonamide, the aminoglycosides, and cephalosporins. However, antibiotic resistance has been described, particularly to beta lactams, and treatment selection should be guided by antibiotic susceptibility testing. Often successful treatment can be achieved with daily spraying of antiseptics (eg, 0.05% chlorhexidine solution, 1:50 dilution of 10% povidone iodine) to the entire body surface. In severe cases, treatment requires that antibiotic be given in high dosages early in the disease and for 7–10 days.
Because dehydration is a major feature of exudative epidermitis, administration of oral fluids and electrolytes is advisable for severely affected pigs. Treatment is less effective in very young pigs and ineffective in advanced cases. In severe outbreaks, in-contact pigs should also be sprayed with antiseptics and if sever enough, can be given antibiotics for several days. Sows due to farrow, and their housing, should be thoroughly disinfected in the face of outbreaks. Hygiene in the weaner accommodation and strategic in-water or in-feed medication for 3–5 days will help control outbreaks after weaning, together with appropriate ventilation to avoid high humidity.
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.
Exudative epidermitis is a common staphylococcal infection of young pigs, characterized by widespread, nonpruritic pustules.
Treatment should be based on antibiotic sensitivity testing, with antibiotics given at high dosages early in the course of disease.
Improved management may help control outbreaks.