Veterinary Handbook Disease Finder

Blackleg And Malignant Oedema

Species

Other Names

  • Clostridial Diseases
  • Malignant Oedema

Syndromes

Description

Blackleg is an acute infection of heavy muscles caused by Clostridium chauvoei; malignant oedema is an acute infection of wounds usually caused by Clostridium septicum, although other clostridia may be involved. Clostridia are present in the soil and gut of farm animals and are a constant threat to unvaccinated animals in the live export process. Once ingested, spores may be absorbed and then spread in the blood to various tissues in the body.

Blackleg can be caused by ingested spores that have lodged in muscle tissue, and possibly remained dormant there for a long time. Injury to muscle following vaccination, transport or rough handling may trigger germination resulting in extremely rapid bacterial multiplication and the production of toxins and gas. Multiple animals are usually affected. Most cases are found dead.

There is a risk of black leg occurring in unvaccinated livestock in the live export process as a result of the intensive animal handling associated with export processes.

Malignant oedema occurs when skin wounds are infected by Clostridial sp. leading to bacterial proliferation and production of toxins. Specific risk factors may include shearing cuts, head butting or fighting behaviour in penned animals (particularly intact males), and possibly intramuscular injections.

Clinical Signs and Diagnosis

Affected animals are usually found dead or dying. Infected animals found alive will be severely depressed and have obvious swelling or lameness. The typical lesions are readily seen but may be obscured by rapid post mortem decomposition.

In blackleg, there may be an area over the shoulder, back or rump that is swollen, and has darkened skin, and gas bubbles may be detected by gentle finger pressure. At necropsy, the affected muscle is black and dry, and gas bubbles will have spread between the muscles. The lesion may be in any muscle including tongue or heart and may be quite small.

In malignant oedema, tissues around the inciting wound will be soft, swollen, and pit on finger pressure. At necropsy, tissues surrounding the wound will be wet and large quantities of dark brown exudate will have spread out under the skin.

Differential diagnoses include bloat and anthrax.

Specimens for laboratory confirmation must be taken from freshly dead animals. These include smears of affected muscle or wound exudate for bacteriology; sections of affected muscle, collected aseptically, and submitted chilled for bacteriology; and sections of affected muscle or tissue adjacent to an affected wound, in buffered formalin for histology.

Treatment

Treatment with antibiotics (procaine penicillin, or oxytetracycline) may be attempted but infection is likely to be overwhelming. To stop an outbreak, all susceptible animals in the mob should be vaccinated and treated with antibiotics (procaine penicillin, erythromycin, or oxytetracycline).

Prevention

Vaccination provides effective protection against clostridial diseases. Handle animals gently to avoid bruising and overexertion.