The course of this disease is short and affected animals are usually found dead having shown no signs of illness. Once a farm becomes infected the disease is usually seen regularly in subsequent years.
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In Britain the distribution of Black Disease is not well-known and many farms where fluke is a problem are free of the disease. predominantly the autumn and early winter but occasionally in the early spring adult sheep appear more susceptible although lambs commencing their first winter have also been affected. Cases usually occur at the same time of year as acute liver fluke infection, i.e. novyi, is found mostly in soil, particularly in low-lying ground, and on pastures.īlack disease occurs on both hill and lowland farms which are infected by liver fluke.
Although any necrotic process in the liver can stimulate the bacteria to proliferate, field outbreaks of Black Disease are usually precipitated by invasion of the liver by immature liver fluke or sometimes by feeding changes which produce liver damage allowing entry of Clostridia. A generalised toxaemia of sheep, and occasionally cattle, caused by toxins of Clostridium novyi Type B which are produced in damaged liver tissue.
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