Clostidia in the Horse: A Worry or Not

The species of clostridia bacteria cause a variety of diseases in horses including colitis, tetanus, botulism and liver disease. Some diseases are seen commonly whilst others are much more rare.

The most commonly seen disease caused by clostridial species is enterocolitis which presents as acute diarrhoea. Dullness, fever and inappetance may be observed before the onset of diarrhoea and can affect adults and young foals. Clostridium difficile toxin A/B and Clostridium perfringens ß toxin are the species commonly identified in horses. C.difficile diarrhoea can occur as a primary event however it is often associated with antimicrobial (antibiotic) use in both adults or foals. Vets are always concerned when a horse develops diarrhoea in association with or soon after systemic antimicrobials use because any systemic antibiotic has the potential for creating an upset of gut bacteria and an overgrowth of pathogens such as C.difficile. Clostridium perfringens also produces enterotoxins which can be associated with moderate to severe colitis in the horse and haemorrhagic diarrhoea (i.e. blood in the faeces) in foals.

Should clostridia be suspected as a cause of diarrhoea then faecal samples can be submitted for testing to identify if clostridial toxins are present. Whilst they can be difficult to culture/grow in a lab the toxins can be detected by a specific ELISA test. On ultrasound examination bright dots may be seen around the walls of the intestine which represents gas production by bacteria which although not exclusive to, can be a feature of clostridial diarrhoea.

Treatment of diarrhoea/colitis cases varies depending on the severity of the condition. The main aim is supportive care through fluid therapy and nursing alongside anti-diarrhoeals, intestinal adsorbents, anti-ulcers and pro/pre-biotics. Anti-inflammatory agents can be useful in improving fever, some of the side effects of sepsis and improve appetite. Generally anti-microbials are avoided however in the case of confirmed clostridial diarrhoea then a course of a specific oral antibiotic, metronidazole, is advised.

Clostridium tetani is the cause of tetanus aka 'lockjaw'. It is an anaerobic bacterium that is found in soil and gains entry into the horse via open wounds or hoof injuries. The incubation period varies from 3 days to 3 weeks however clinical signs are usually apparent after 7-14 days. Clinical signs include a general increase in muscle stiffness and spasm and prolapse of the third eyelid. Horses show restriction of jaw movements, erect carriage of the ears, flared nostrils, elevated head, unsteady stiff straddling gait, tail held out stiffly, increased heart or respiratory rate, fever, sweating, difficulty eating/swallowing, drooling, colic, constipation and urine retention. This can progress to recumbency and convulsions and ultimately death through asphyxiation due to tetany of respiratory muscles. Treatment can be attempted however the prognosis is guarded. Thankfully through the success of vaccination, cases are rarely seen although unvaccinated animals remain at risk.

Clostridium botulinum is the cause of botulism horses. This bacteria is also found in the soil or toxins can be ingested through contaminated feedstuffs, in particular silage. It is a disease characterised by progressive flaccid paralysis. Cases can present as decreased exercise tolerance, slowness to eat, dropping food from mouth, colic, muscle tremors (triceps/larger muscle groups), depression, progressing to weakness (e.g. reluctance to lift head) and recumbency. A subspecies (C.botulinum type C) is also thought to be a possible underlying cause of Equine Grass Sickness and formed the basis of the grass sickness vaccine trial.

Clostridium piliforme causes an acute bacterial infection of the liver known as Tyzzer's disease in foals usually between 7-42 days old. Clinical signs are non-specific and can present as a sudden death. The disease is highly fatal and diagnosis is made at post mortem.

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