Diseases due to bacteria known as Clostridia are amongst the commonest causes of sudden death in cattle. Black disease is a disease of the liver caused by Clostridium novyi, which is usually seen as a sudden death with no previous signs.
What is Black disease?
Infection begins when bacterial spores are eaten (usually as result of eating soil, but occasionally from contaminated feed). These spores enter the bloodstream and travel to the liver and other organs in the body. The spores remain dormant in the liver, until its damaged. This results in areas of the liver with a reduced oxygen supply, which stimulates the spores to grow and develop. As they multiply the bacteria produce lethal toxins, which are absorbed leading to toxaemia and death.
The disease affects cattle of all ages, though like most clostridial diseases the peak age is between one and two years of age.
Clinical Signs
- Animals may be severely depressed and reluctant to move for up to two days before death
- Most cases though show NO signs before death.
Diagnosis
- A post mortem is essential to diagnose black disease. Many other diseases cause sudden death and need to be ruled out. The most important of these is anthrax, which must be ruled out by your vet before a PM is done
- The changes in the liver are characteristic, but may be difficult to see if the animal has been dead for more than a short while
- Further lab tests can be useful to confirm it is Cl. novyi
- Don’t do a PM on farm. Opening the carcass can liberate bacteria which will form spores to contaminate the ground and subsequently infect other cattle.
Prevention
As the bacteria are present in the soil, preventing access to soil by not grazing freshly sown pastures with youngstock can reduce the risk, but vaccination is really the only effective means of controlling black disease. With clostridial vaccines, like all vaccines, care should be taken to follow the manufacturers’ instructions. The best protection is a two-dose course followed by annual revaccination. Other regimes can be effective but check with your vet before using these. Vaccination takes 10-14 days to become effective, so it’s best to vaccinate before a problem occurs or a risk period is encountered.
As the bacterium requires liver damage to become active, it is almost always associated with liver fluke. Indeed the recent increase in the spread of liver fluke across the UK has been associated with an increase in the number of cases of black disease. Controlling liver fluke is thus an essential part of any black disease programme.
Article by Richard Laven PhD BVetMed MRCVS
