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Gangrenous dermatitis is often characterized by a sudden increase in flock mortality, with affected birds exhibiting dry necrosis of the skin over the wings, thighs, breast, and head. In addition, extensive cellulitis can often be observed under the necrotic skin. Gangrenous dermatitis occurs worldwide and has been reported most commonly in chickens 4–16 wk old and occasionally in turkeys.
Etiology, Transmission, and Epidemiology
Gangrenous dermatitis usually occurs as the result of a skin wound that has become contaminated by one or more types of bacteria, including Clostridium septicum, Staphylococcus aureus, and Escherichia coli. Infections involving more than one type of bacteria are often more severe. The resulting cellulitis is due to the release of bacterial toxins that cause necrosis of the underlying tissue. Mortality is due to septicemia and the resulting toxemia. Immunosuppressed birds (eg, those with infectious bursal disease) may be more prone to gangrenous dermatitis.
Clinical Findings
The first sign of gangrenous dermatitis is a sudden increase in mortality, with overall mortality ranging from 10–60%. Affected chickens are depressed, often prostrate, and succumb to the disease within 8–24 hr. Red to black areas of moist, gangrenous skin are seen over the breast, abdomen, wing tips, or thighs. Feather loss or sloughing of the skin is common. If Clostridium spp are involved, crepitation due to gas bubbles in the subcutis and musculature is common.
Lesions
Lesions observed at necropsy include the accumulation of serosanguineous fluid in the subcutis of affected tissue. Enlargement of internal organs is noted, including the liver, spleen, and kidney, which could also contain infarcts or necrotic areas. Because affected birds are often immunocompromised, there is often atrophy of the bursa of Fabricius.
Diagnosis
Gangrenous dermatitis can be tentatively diagnosed based on flock history, signs, and necropsy findings. Confirmation is achieved via histopathologic examination of necrotic tissues to demonstrate the presence of the causative bacteria. Bacterial culture will identify the species of bacteria involved. Differential diagnoses for gangrenous dermatitis include exudative diathesis, avian pox, and other skin diseases.
Treatment and Control
Because a variety of bacteria can be involved, a broad-spectrum antibiotic, such as penicillin, erythromycin, or a tetracycline (eg, oxytetracycline), is preferred until a bacterial culture can confirm the causative bacteria and its antimicrobial susceptibility. Immunosuppressed birds are predisposed to gangrenous dermatitis; therefore, a vaccination program for diseases such as infectious bursal disease will add further protection. Any factors that can lead to skin wounds (eg, trauma, wet litter, feather picking, and cannibalism) may provide entry sites for the bacteria and should be eliminated.
Zoonotic Risk
There are currently no known human health risks associated with gangrenous dermatitis.
Last full review/revision March 2012 by Teresa Y. Morishita, DVM, MPVM, MS, PhD, DACPV
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