Malignant edema is an acute, generally fatal toxemia affecting all species and ages of animals and is usually caused by Clostridium septicum. Other clostridial species have been isolated, indicating mixed infections. Additional clostridia implicated in wound infections include C chauvoei, C perfringens type A, C novyi type A, and C sordellii. The disease occurs worldwide.
C septicum is found in soil and intestinal contents of animals throughout the world. Infection ordinarily occurs through contamination of wounds containing devitalized tissue, soil, or some other tissue debilitant, or through activation of dormant spores. Wounds caused by accident, castration, docking, insanitary vaccination, and parturition may become infected. Potent clostridial toxins cause local and systemic signs, often resulting in death. Local exotoxins cause excessive inflammation, resulting in severe edema, necrosis, and gangrene. Risk factors include IM injections in horses; shearing, docking, and lambing in sheep; and traumatic parturition and castration in cattle. Horses and probably cattle have dormant spores present in muscle tissues.
General clinical signs, such as anorexia and high fever, as well as local lesions, develop within 6–48 hours after predisposing injury or activation of dormant spores. The local lesions are soft swellings that pit on pressure and extend rapidly because of the formation of large quantities of exudate that infiltrate the subcutaneous and intramuscular connective tissue of the affected areas. The muscle in such areas is dark brown to black. Accumulations of gas in subcutaneous tissue and along muscle fascias may be present. These muscle infections are extremely painful, and systemic toxemia may evolve. Extensive local sloughing of skin and tissues is often seen in progressed states of malignant edema. Severe edema of the head of rams develops after infection of wounds inflicted by fighting. Malignant edema associated with lacerations of the vulva at parturition is characterized by marked edema of the vulva, severe toxemia, and death in 24–48 hours.
Similarity to blackleg is marked, and differentiation based on necropsy examination is unreliable for diagnosis; laboratory confirmation via samples is the only certain method. Horses and pigs are susceptible to malignant edema but not to blackleg. An important differential diagnosis in these species is anthrax.
C septicum also causes braxy in sheep, a highly fatal infection characterized by toxemia and inflammation of the abomasal wall. This disease seems to be confined mostly to European sheep fed on “frosted” pasture.
Diagnosis can be confirmed rapidly on the basis of fluorescent-antibody staining of C septicum from a tissue smear. However, C septicum is an extremely active postmortem invader from the intestine, and its presence in a specimen taken from an animal that has been dead for ≥24 hours is not significant. Immunohistochemical testing has also been used to identify the bacteria. PCR assay can be used for direct identification and differentiation of clostridia associated with malignant edema. The presence of type III echinocytes or spheroechinocytes in blood smears may help diagnose immune-mediated hemolytic anemia associated with clostridial infections in horses. Fine-needle aspirates and Gram stain may confirm the presence of gram-positive rods before confirmation by anaerobic culture.
Proper carcass disposal helps to prevent soil contamination; however, vaccination is the main tool to prevent malignant edema. Bacterins are used for immunization. C septicum usually is combined with C chauvoei in a blackleg/malignant edema vaccine and is available in multivalent vaccines. In endemic areas, animals should be vaccinated before they are castrated, dehorned, or docked. Calves should be vaccinated at ~2 months of age. Administration of two doses of vaccine 2–3 weeks apart generally gives protection. In high-risk areas, annual vaccination is indicated, as is revaccination after severe trauma.
Treatment with administration of high doses of parenteral penicillin, tetracyclines, or broad-spectrum antimicrobials is indicated early in the disease course. Although injection of penicillin directly into the periphery of the lesion may minimize spread of the lesion, the affected tissues usually slough. Supportive treatment with administration of NSAIDs (flunixin meglumine for cattle and horses) is recommended. Local treatment includes surgical incision of skin and fascia to allow drainage. Animals with systemic toxic signs need supportive treatments such as intravenous perfusion.
Malignant edema is an acute, generally fatal toxemia affecting all species and ages of animals and is usually caused by Clostridium septicum.
Infection ordinarily occurs through contamination of wounds containing devitalized tissue, soil, or some other tissue debilitant, or through activation of dormant spores.
Proper carcass disposal and vaccination prevent malignant edema.
Odani JS, Blanchard PC, Adaska JM, Moeller RB, & Uzal FA. Malignant Edema in Postpartum Dairy Cattle. J Vet Diag Invest. 2009;21(6):920–924.
Peek SF, et al. (2003) Clostridial myonecrosis in horses (37 cases 1985–2000). Equine Vet J. 2003;35:86–92.
Also see pet health content regarding malignant edema in horses.