Clostridium septicum dermatitis, cellulitis, and myositis (malignant edema) in swine

Clostridium septicum dermatitis, cellulitis, and myositis (malignant edema) in swine

Josepha DeLay, Margaret Stalker, Đurđa Slavić, Clint Lichty, Greg Wideman

Animal Health Laboratory, University of Guelph, Guelph, ON (DeLay, Stalker, Slavić); South West Ontario Veterinary Services, Stratford, ON (Lichty, Wideman).

AHL Newsletter 2019;23(3):10.

Sudden (unexpected) death was reported in several grow-finisher pigs from 2 unrelated herds. Most of the affected pigs had well-demarcated 30-50 cm diameter raised purple skin lesions involving mainly the ears, neck, and ventral trunk. Subcutaneous emphysema was palpable in some lesions. Similar skin lesions in a few live pigs expanded rapidly and the pigs’ clinical condition deteriorated, culminating in death or euthanasia. Those pigs treated very early in the disease course, with clinical signs of lethargy and ≤5 cm skin lesions, did survive.

A range of tissue samples, including samples from the margin of affected and non-affected skin and underlying skeletal muscle, were examined histologically, and significant lesions were confined to skin. Epidermis was necrotic (infarcted); dermis and subcutis were expanded by edema, fibrin, and neutrophils; and myocyte bundles were degenerate and surrounded by fibrin and neutrophils. Many long bacilli compatible with Clostridium spp. were visible among the inflammatory debris. Clostridium septicum was cultured in low-to-moderate numbers from skin swabs from each of 4 sampled pigs. Malignant edema caused by C. septicum was confirmed based on the combination of clinical history, gross appearance of skin lesions, histologic lesions, and isolation of the causative bacterium from lesions.

Infection with the anaerobic bacillus C. septicum is an uncommon cause of disease and death in swine, and literature reports of this condition are sparse. C. septicum cellulitis and myositis is known as malignant edema, gas gangrene, or ‘pseudo-blackleg’ due to the clinical and pathologic similarity of the condition to blackleg (clostridial myositis, C. chauvoei) in ruminants. Clostridial exotoxins, particularly alpha toxin (ATX), cause localized tissue necrosis and inflammation, and systemic toxemia results in death. Fibrinohemorrhagic peritonitis and pulmonary edema are present in some animals. Wound infection is considered the main portal of entry for bacteria, although activation of dormant intramuscular clostridia and bacteremia secondary to gastrointestinal mucosal injury are also possible. Concentration of lesions in the head and neck area of these pigs supports contamination of fighting wounds in this case. Lesions may also be associated with injection sites. Both histopathology and bacterial culture are important for confirmation of a diagnosis of C. septicum cellulitis and myositis, because the organism may also be present in tissues as a postmortem invader unassociated with lesions. Penicillin is the antibiotic of choice for treatment of animals with suspected C. septicum-associated disease.   AHL

References

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Uzal FA, Songer JG. Clostridial diseases. In: JJ Zimmerman et al, ed. Diseases of Swine. 2019:799-801.