Blackleg disease in animals: Characteristics, diagnosis, and prevention

Blackleg disease is one of the most dangerous acute diseases in cattle and sheep, characterized by rapid progression and a high mortality rate. The disease not only causes severe economic losses in livestock production but also poses a challenge in herd management, especially on beef cattle and sheep farms. Let’s explore with Vemedim the pathogenesis, clinical signs, diagnosis, and control measures that are key to preventing and minimizing damage right below.

Causes of blackleg disease

The bacterium Clostridium chauvoei naturally exists in the intestinal tract of cattle and sheep, but its spores can survive in soil for many years, making it an important source of infection. Animals can become infected by ingesting spores from contaminated grass, water, or soil. After entering the body, the bacteria pass through the intestinal wall into the bloodstream, depositing mainly in the muscles, spleen, liver, and other tissues, where they remain in a latent state until disease-triggering mechanisms occur.

In cattle, blackleg is often endogenous, developing without any prior wound, although muscle trauma or overexertion can sometimes trigger it. Affected animals are usually healthy, fast-growing cattle, mainly 6–24 months old, but calves as young as 6 weeks or older cattle 10–12 years old can also be affected. The disease commonly occurs in summer and autumn.

In sheep, the disease is almost always associated with wound infection, such as after shearing, tail docking, castration, or tool-related injuries, allowing the bacteria to enter and multiply locally. Mortality in both cattle and sheep is often very high, even reaching 100%.

*Blackleg disease is caused by bacteria, and the mortality rate in affected livestock can be up to 100%*

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Clinical signs of blackleg disease

The disease has a sudden onset, and some animals may die without any warning signs. Common clinical signs include:

High fever at first, then temperature may return to normal or drop as the disease progresses.
Acute lameness, often affecting the hind limbs.
Swelling and edema of large muscles, especially the hip, shoulder, back, neck, and chest; initially localized, hot, and painful.
A crackling sound (crepitus) when palpating swollen muscles; the skin becomes cold and insensitive due to reduced circulation.
Weakness, trembling, sometimes the tongue may protrude, or the diaphragm and heart muscle may be affected, causing abnormal breathing.

Death usually occurs within 12–48 hours after symptoms appear. In sheep, muscle lesions are often small, deep, and easy to miss, while in cattle, the affected muscles are usually dark red, dry, spongy, infiltrated with gas bubbles, and show little edema.

*Blackleg disease causes fever, acute lameness, swollen and edematous muscles, ... in cattle*

Diagnosis of blackleg disease

Diagnosis is based on clinical signs and necropsy, combined with microbiological testing. Some key methods include:

Clinical examination: The presence of crepitus and swelling of large muscles is a suggestive sign.
Muscle ultrasound: Can detect abnormal muscle tissue, edema, and gas within the muscle.
Necropsy: Affected muscle samples are dark red to black, dry, spongy, with a sweet odor and gas bubbles. Muscles may include the tongue, diaphragm, and heart.
Anaerobic culture and biochemical identification: Confirmation of C. chauvoei in muscle tissue is the gold standard.
Immunoassays and PCR: Rapid detection of C. chauvoei in clinical tissue. However, environmental PCR is unreliable.

Note: Some other Clostridium bacteria (C. septicum, C. novyi, C. sordellii, C. perfringens) can cause tissue lesions similar to blackleg, especially if samples are collected more than 24 hours after the animal’s death.

*Blackleg disease will cause many losses for livestock farmers*

Prevention and control of blackleg disease

The main preventive measures are vaccination and environmental management. Specifically:

Cattle: Vaccinate calves at 2 months of age with 2 doses, 4 weeks apart, and revaccinate annually before the high-risk season (spring, early summer).
Sheep: Vaccinate ewes that have never had the disease with 2 doses, the second dose 1 month before lambing, and revaccinate annually. Vaccinate young sheep before turnout to pasture.
Outbreak prevention: During an outbreak, cattle and sheep can be vaccinated and given prophylactic penicillin treatment (10,000 IU/kg intramuscularly) for 14 days.
Pasture and housing management: Move animals away from affected pastures, avoid overgrazing, ensure sanitation, and limit the spread of spores.
Carcass disposal: Burn or bury deeply, with barriers to prevent spores from entering the environment.
Use of local vaccines: If commercial vaccines do not provide sufficient antigenic coverage, vaccines can be produced from identified local strains.

*The most effective way to prevent blackleg disease is regular vaccination*

Blackleg disease is a dangerous acute disease with a high mortality rate in cattle and sheep, especially under environmental conditions favorable for Clostridium chauvoei spores. Prevention through vaccination, environmental management, and carcass disposal is the most important measure to minimize economic losses and the risk of outbreaks. If you need support in disease control, please contact Vemedim for advice!