Clostridial Diseases in Sheep
What are Clostridial Diseases?
Clostridial diseases are a group of severe diseases seen in sheep caused by Clostridia spp. bacteria. These bacteria are known to be pathogens in livestock, humans, and companion animals. They can survive in spore form in the environment for long periods of time and so are very dangerous. The primary source of infections picked up from the environment is faecal contamination of pasture. At the same time, it is normal for many of these bacteria to inhabit the intestines of healthy animals.
The problem arises when stress factors cause a sudden change in the chemistry of the intestines. This then triggers the bacteria to multiply rapidly. They then release potent toxins which cause extreme deleterious effects in the animal and can cause death. Other clostridial diseases can occur when wounds become infected and bacteria enter the system. Although these are well-known diseases, there are some methods of infection that we still don’t understand.
The six main clostridial diseases in sheep are:
- Lamb dysentery (bloody scours) caused by C. perfringens
- Pulpy kidney or enterotoxemia (overeating disease) caused by C. perfringens
- Black disease caused by C. novyi
- Braxy caused by C. septicum
- Blackleg caused by C. chauvoei
- Tetanus (lock jaw) caused by C. tetani
There are five types of C. perfringens (Type A, B, C, D, and E).1 All are pathogenic to some extent. The different types vary in which toxins they produce, their prevalence, and the species which are susceptible to infection. Types B and D both produce the highly necrotising and lethal toxin which is responsible for the symptoms seen in both lamb dysentery and in pulpy kidney respectively.
Lamb dysentery is seen predominantly in lambs that are less than 3 weeks old. The rapidity of disease onset usually means that the first sign of a problem is a dead lamb. Some lambs show clinical signs such as a lack of interest in nursing, listlessness and bloody diarrhoea. These lambs usually come out of unvaccinated ewes and thus have not received sufficient antibodies through the maternal colostrum to be able to fight the infection. They eat spores of the bacteria which are able to live in soils for upwards of a year. The bacteria then rapidly multiplies in their intestines, causing disease. The exact trigger of rapid multiplication is unknown for this disease.2
Pulpy Kidney in Sheep
Pulpy kidney, also known as enterotoxaemia, can happen when there is a sudden change in diet. This is usually to a feed that is higher in protein, starch, or sugar. Most healthy animals have a small population of C. perfringens in their intestines, however there are not enough bacteria to cause a problem. Bacteria can undergo explosive growth in response to extra feed and release large amounts of toxins. This is what then causes the symptoms and eventual death of the animal. Primary signs of pulpy kidney are lethargy and going off feed, clear indicators of stomach pain such as vocalisations and kicking at their bellies, and occasionally diarrhoea. As the disease progresses, the toxin begins to effect the brain of the animal and they can lose the ability to stand and show muscle spasms and contortions.
Black disease and Braxy in Sheep
Black disease, or infectious necrotic hepatitis, is common in sheep. Sometimes goats and cattle can catch it, but it’s not that common.3 It is caused by bacterial activation through damaged internal tissues. Ingested C. novyi spores can remain inactive in the liver for long periods of time. If the liver tissue becomes damaged, usually through movement of migrating liver fluke, the spores become activated and quickly begin multiplying and producing toxins. Clinical signs are rarely seen in animals with this disease, and death is usually sudden. Affected animals are often healthy, 2-4 years old, and always infected with liver fluke. As such, a management technique for this disease is to try and control the incidence of liver fluke in a flock, however this is not always possible.
Braxy is similar to other clostridial diseases with sudden death as the most likely sign of the disease. It is common in sheep populations in the UK, Ireland and areas of Northern Europe, and found in calf populations in North America. Although the exact cause of braxy is unknown, it is often seen after animals have eaten frozen feed or milk.4 Ice crystals damage the lining of the abomasum (fourth stomach) and this stimulates the spores of C. septicum to multiply and produce toxins. As such, this disease usually occurs during winter. It can occur in bottle-fed animals if the milk they are fed is not properly defrosted.
Blackleg and Tetanus in Sheep
Blackleg and tetanus in sheep are both caused by infection of wounds. These might be as shearing cuts, dog bites, or castration where an open wound becomes contaminated. Bacteria in the wound produce toxins that cause a wide range of effects from necrosis of tissues to paralysis and muscle spasms. This eventually culminates in death of the affected animal. While tetanus almost all mammals can catch tetanus, sheep are relatively susceptible to the disease. Additionally, animals living in warmer climates tend to catch it more.5
Unlike other clostridial diseases these diseases tend to show clinical signs before sudden death of the animal. The most common symptoms are stiffness of limbs and difficulty walking, and in tetanus, muscle spasms. Few lambs recover from these diseases, and there is currently no effective treatment.
How can clostridial diseases be prevented?
The primary defence against clostridial diseases in sheep is vaccination. There are vaccines available for all of the major Clostridia bacteria and they are highly effective in almost all cases. Good vaccination greatly reduces the occurrence of diseases in adult sheep. Lambs from vaccinated dams are also protected. In spite of this, there is relatively low uptake of vaccination programs in the UK. It is, however, becoming more popular, as there are many benefits.6 Managing stress factors such as handling, drenching, shearing, and other disease management can all help in the prevention of clostridial disease. Care should also always be taken when moving livestock from one feed to another, as this can be a major risk factor.
As lambing season approaches, the best way to prevent an outbreak of any clostridial disease in a flock is vaccination. Many vaccines are broad spectrum and cover a variety of different species of Clostridia. You should always select the most appropriate vaccine based on local conditions and the prevalence of diseases. If a breeding ewe has already had vaccines for these diseases, all she needs is a booster vaccine two to eight weeks before lambing. If not, two doses of the relevant vaccine should be given at an appropriate interval with the final dose four to six weeks before lambing.* This will provide protection for the dam during this period of high stress and provide protection for the lamb through the colostrum it receives.7 Consult your veterinary professional for flock-specific information and a more tailored vaccination programme.
*This information is correct for Lambivac, Bravoxin and Covexin according to the NOAH Compendium 2020. However, specific information should always be researched before giving vaccines to livestock.
Research at Ridgeway
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- Clostridium difficile and C perfringens Infections – Generalized Conditions. Veterinary Manual.
- Lewis, (2011). Vet. Clin. North Am. Food Anim. Pract. 27, 121–126.
- Infectious Necrotic Hepatitis – Generalized Conditions. Veterinary Manual.
- Glenn Songer, J. Food Animal Practice (Fifth Edition) (2009).
- Tetanus – Generalized Conditions, Veterinary Manual
- NADIS Animal Health Skills – Clostridia and Pasteurella Vaccination
- How to protect your flock from clostridial diseases and pasteurella. Farmers Weekly.