Malignant edema is caused by a fatal anaerobic gram-positive rod shaped bacteria called Clostridium septicum. All ages and species of animals are susceptible and the disease occurs worldwide. Clostridium septicum is found in the soil and intestinal tracts of animals. Typically infection occurs through contamination of wounds by the bacteria. Wounds caused by lacerations, injections, head butting, shearing, tail docking, castration and parturition may become infected. Once the organism gains entry into a wound the bacteria can release toxins that cause severe local tissue necrosis and systemic signs.
- 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 cows have dormant spores present in muscle tissues.
- Signs such as anorexia, intoxication and high fever as well as local lesions, develop within 6–48hrs 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 infiltrates 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 or may not 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 hr.
- The characteristic swelling and high mortality rate is what gives this infection its name, Malignant Edema.
Prevention and control
- 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. Two doses 2–3 week apart generally give protection. In high-risk areas, annual vaccination is indicated, as is revaccination after severe trauma.
- Treatment with high doses of parenteral penicillin, tetracyclines, or broad-spectrum antibiotics is indicated early in the disease. Although injection of penicillin directly into the periphery of the lesion may minimize spread of the lesion, the affected tissues usually slough.
- Supportive therapy with 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 will need supportive treatments such as IV perfusion.