Blackleg has been recognized as a livestock disease since before medieval times, and today we often use the term loosely to describe several diseases caused by organisms in the Clostridium class of bacteria. However, there are more than 60 different types of Clostridium bacteria, and not all cause disease.
What we commonly call blackleg is a highly fatal infection caused by Clostridium chauvoei, resulting in a gas gangrene in the muscle of young cattle, usually occurring between 4 months and 2 years of age. Blackleg seldom affects cattle older than 2 years of age, most likely due to immunity induced by vaccines or natural exposure. However, sporadic cases do occur in cattle older than 2 years and are often associated with the reuse of needles for multiple injections. Blackleg can also be a problem in cattle less than 4 months old that do not receive adequate passive immunity through colostrum. Some of the other clostridial diseases are not as restricted to younger animals as is seen with blackleg.
What are other clostridial diseases?
Some diseases caused by other clostridial bacteria include lockjaw (tetanus), botulism, enterotoxemia, red water (bacillary hemoglobinuria), and malignant edema. The type of disease depends on the particular type of Clostridium and the type and location of toxins produced.
In a case of tetanus caused by Clostridium tetani, the toxins from bacteria growing in contaminated wounds cause uncontrollable muscle spasms. With botulism, caused by Clostridium botulinum, the ingestion of toxins in contaminated food or water causes paralysis, a profound weakness, and death. In enterotoxemia caused by Clostridium perfringens, the organisms in a young animal’s gut overgrow the normal microflora and form toxins that cause severe poisoning and death. In the case of red water, the spores of Clostridium hemolyticum grow in the animal’s liver, usually in areas damaged by liver fluke parasites. These spores sometimes cause the animal to pass dark red urine and may cause severe sickness and death. With malignant edema, caused by a number of different clostridial bacteria, muscle or skin is infected with bacteria, toxins are produced, and death can result. Malignant edema is very similar to blackleg in that it results in gas production in the muscle, followed by severe swelling in body tissues.
Different species of animals have different susceptibilities to clostridial disease. Blackleg is probably the most common clostridial disease seen in cattle in the southeastern United States, while tetanus is the most common clostridial disease in horses. Tetanus does occur in cattle, particularly in older steers after castration, but it is not very common.