BLACK QUARTERS/LEG: A DISEASE OF CATTLE

This is an acute infectious disease of cattle caused by Clostridium chauvei. It is characterized by inflammation (puffiness) of muscles, toxaemia and high mortality. It is a relatively common disease of cattle which generally leads to rapid degeneration and death. It is caused by Clostridium chauvei although occasionally other organisms such as Clostridium novyi and Clostridium septicum may be implicated. Spores of Clostridium chauvei occur in soil of problem areas most frequently due to contamination by the decomposing body of earlier cases. It is probable that infection takes place by ingestion of spores but how the organism reaches the musculature and why there may be a sudden stimulus from the proliferation of organism is not known. The disease is seen in cattle and sheep.
Clinical signs
In most cases, black leg results in sudden death. If live cases are encountered, death follows within 12-24 hours. In very early cases, there is profound depression and high fever. The most commonly affected site is the upper limb which suffered lameness or complete loss of limb function. On closer examination, there will be extensive pain and hot swelling although this quickly changes to cold painless stage in a dry bluish black discoloration of the skin.

Finally, there is emphysematous crackle around the site on palpation. At this stage, the animal is almost completely recumbent and near death. Other sites affected include the throat, neck and thoracic inlet. The back of animal and loin and occasionally in newly calved animals, vulva, vagina and perineal areas are affected. Many animals die without showing clinical sign.
Immunity
It is believed that animals recovering from blackleg are resistant to the infection for the rest of their lives.
Diagnosis
In many instances, use of laboratory animals for confirmation of blackleg is not necessary because the clinical, epidemiological and pathological attributes of the blackleg are characteristic.
Moreover, bacterial examination should be carried out on tissue samples from recently diseased animals because rapid putrefaction leads to massive invasion of many other clostridia from alimentary tract.
Prevention and control
Whenever possible, carcasses of animals known or strongly suspected of blackleg should be burnt or deeply buried. In addition, certain farm areas known to be endemic for the disease should be put to alternative or cultural use or grazed only with vaccinated animals. A bacterin/ vaccine prepared from a local strain of Clostridium chauvei is preferable. The strategy of the control must be according to local conditions but in general, it is recommended that the first dose of the vaccine given 6 weeks and second dose 2 weeks before the onset of the period of maximum risk. When faces with an outbreak, vaccination of all animals should be carried out immediately and the group at risk moved to an alternative grazing area. Blackleg antiserum or long acting penicillin is recommended at the time of vaccination because does not protect for about 2 weeks. Clinical cases of the disease should be given high doses of procain penicillin intramuscularly and around the infected sites. In areas where other clostridia are known to be responsible for the disease, it is recommended that a mix vaccine containing Clostridium chauvei, Clostridium novyi and Clostridium septicum be used.