Black Disease
Black disease, also known as infectious necrotic hepatitis, is a serious condition in sheep caused by the bacterium Clostridium novyi type B. This disease is often associated with liver fluke infestations and is prevalent in areas with wet conditions, such as parts of the UK, New Zealand, and Australia. It typically affects sheep aged 2 to 4 years, especially during late summer and autumn.
Symptoms and Diagnosis of Black Disease🩺
Unfortunately, clinical signs of black disease are rarely observed because affected sheep are often found dead. When symptoms do appear, they include sudden dullness, unsteadiness, collapse, and rapid death. Post-mortem examinations reveal rapid decomposition of the carcass, darkening of the skin, and liver necrosis.
Diagnosis is primarily based on necropsy findings and the presence of large Gram-positive rods in liver smears. However, since C. novyi B can be a normal inhabitant of the liver, additional tests such as FAT techniques are used for confirmation.
Treatment of Black Disease💊
Sadly, black disease is not amenable to treatment. Once symptoms appear, the disease progresses rapidly, leading to death. Therefore, treatment options are limited, and focus is placed on prevention.
Prevention of Black Disease🛡️
Prevention is key in managing black disease. Vaccination is the most effective method, with polyvalent vaccines available that protect against multiple clostridial diseases. It's recommended to vaccinate lambs at around 3 months of age with two doses 30 days apart, followed by an annual booster. Ewes should be vaccinated one month before lambing to provide passive immunity to their lambs.
Controlling liver fluke infestations is also crucial, as they create the anaerobic conditions that allow C. novyi to thrive. Effective flukicides can help reduce the incidence of liver fluke and, consequently, black disease.