What are Clostridial Diseases?
Clostridial diseases are a group of severe diseases seen in sheep caused by Clostridia spp. bacteria. These bacteria are widely recognised as pathogens in livestock, humans, and companion animals and can survive in spore form in the environment for long periods of time. Faecal contamination of pasture is the primary source of infections picked up from the environment. 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 and this 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 are caused when wounds become infected and bacteria enter the system, or through processes that are not yet well understood.
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
Five types of C. perfringens have been recognised (Type A, B, C, D, and E)1 and 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 and the rapidity of disease onset usually means that the first sign of a problem is a dead lamb. Some lambs show clinical signs prior to death 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 ingest spores of the bacterium which are retained in soils for upward of a year and the bacteria 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, is associated with a sudden change in diet, 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. The increase of nutrients in the intestine causes the bacterium to undergo explosive growth and release large amounts of toxins, producing the clinical signs 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 and sometimes seen in goats and cattle.3 It is caused by bacteria activation through damaged internal tissues. C. novyi spores which have been ingested 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 also thought to be caused by bacterial activation through the damaging of internal tissues. It is common in sheep populations in the UK, Ireland and areas of Northern Europe, and found commonly in calf populations in North America. Although the exact cause of braxy is unknown, it is closely associated with the consumption of frosted or frozen feed or milk.4Ice crystals damage the lining of the abomasum (fourth stomach) and this stimulate the spores of C. septicum to multiply and produce toxins. As such, this disease usually occurs during winter, although it can occur in bottle-fed animals if the milk they are fed is not sufficiently defrosted.
Blackleg and tetanus in sheep
Blackleg and tetanus in sheep are both caused by infection of wounds such as shearing cuts, dog bites, and 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, eventually culminating in death of the affected animal. While tetanus is found in almost all mammals, sheep are relatively susceptible to the disease and increased incidence is associated with warmer climates.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 vaccinations available for all of the major Clostridia bacteria and they are highly effective in almost all cases. While effective vaccination greatly reduces the incidence of diseases in adult sheep and provides protection for lambs whose dams have been vaccinated, there is relatively low uptake of vaccination programs in the UK, although this is increasing as the benefits, both economical and welfare, are great.6 Managing stress factors such as handling, drenching, shearing, and other disease management can all help in the prevention of clostridial disease and care should 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 prophylactic vaccination. Many vaccines are broad spectrum and cover a variety of different species of Clostridia, and the most appropriate vaccine should be selected 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 parturition. If not, two doses of the relevant clostridial vaccine should be administered 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 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 administration of vaccines to livestock.
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2. Lewis, C. J. Control of Important Clostridial Diseases of Sheep. Vet. Clin. North Am. Food Anim. Pract. 27, 121–126 (2011).
4. Glenn Songer, J. CHAPTER 18 – Clostridium novyi (Myonecrosis, Black Disease, and Bacillary Hemoglobinuria) and Clostridium septicum (Braxy) Infections. in Food Animal Practice (Fifth Edition) (eds. Anderson, D. E. & Rings, D. M.) 58–61 (W.B. Saunders, 2009). doi:10.1016/B978-141603591-6.10018-1.