Swine Dysentery

Introduction

Swine dysentry is an infectious disease caused by the anaerobic spirochete, Brachyspira hyodysenteriae, seen in pigs worldwide. It causes a severe mucohaemorrhagic colitis of pigs, causing dysentry with variable amounts of mucous and necrotic material passed in the faeces. It is quite prevelant in the United Kingdom and can be important economically.

The disease is not systemic and is localised to the large intestine only- in particular, the spiral colon. It predominantly affects pigs post weaning, at around 4 months of age, but all the herd will show signs of the disease. It can be particularly severe in sows mid- late lactation. If a herd becomes infected there is usually around 90% morbidity and 50% mortality.

Swine dysentry is spread by the faeco- oral route and is carried by pigs and rodents.

 

Clinical Signs

The first apparent signs are twitching of the tail and signs of abdominal discomfort, along with reduced appetite and a slight reddening of the skin. Pyrexia then often occurs but usually disappears at the first signs of diarrhoea. Initial white scour becomes a liquid dirty red / brown scour with a foul smell and contains poorly digested focal shreds of mucosa and fibrin strands. Later, mucous covered faeces is the most prevelant clinical sign.

All affected pigs will be depressed, inappetant, have sunken eyes, hairy coats and dull skin.

 

Diagnosis

Characteristic clinical signs and history along with post mortem findings are used for diagnosis.

Post mortem findings include; a shiny appearance of the serosa of the spiral colon, which will also be turgid and oedematous. Haemorrhage is sometimes seen. Characteristically in this disease, the small intestine is not affected. Fibrinous deposits are seen on the mucosa as the disease progresses and the mucosa underneath is eroded to expose blood vessels in lamina propria.

Samples can be taken to perform silver stains show organisms in the epithelium of the mucosa. The bacteria can also be culturedon blood agar with added antibiotics for at least 3 days- B. hyodysenteriae causes complete haemolysis whereas other spirochaetes cause partial haemolysis.

Immunofluorescence, DNA probes and biochemical tests can also be used though this is usually not cost effective.Serology using ELISA can be used on a herd basis as well as PCR, immunofluorescence or electron microscopy.

 

Treatment and Control

Treatment is usually administered via drinking water as this is a herd condition. If animals are inappentant then parenteral administration may be required. Tiamulin and Lincomycin are the antibiotics of choice for this anaerobic infection. All in contact animals should also be treated prophylactically with these drugs. Supportive treatment such as fluid therapy may be required in severe cases, or an electrolyte solution can be put into the drinking water if animals are not inappetant.

Control measures include improved hygiene, managements strategies such as all in all out systems and keeping a closed herd. Therapeutic levels of medication used to treat the disease may be given as a preventative measure at weaning and if mixing groups of animals. This has variable degrees of success.

There is currently no vaccination for this disease.

Complete eradication of the herd followed by scrupulous disinfection and cleaning can be undertaken in cases of farms wishing to improve or maintain their herd health status.

 

Prognosis

Affected animals often recover, but have a low feed conversion ratio for sometime.

There are three outcomes to infection; the animal may:

Die, recover or become chronically infected.

 

References

Cowart, R.P. and Casteel, S.W. (2001) An Outline of Swine diseases: a handbook Wiley-Blackwell
Jackson, G.G. and Cockcroft, P.D. (2007) Handbook of Pig Medicine Saunders Elsevier
Straw, B.E. and Taylor, D.J. (2006) Disease of Swine Wiley-Blackwell
Taylor, D.J. (2006) Pig Diseases (Eighth edition) St Edmunsdbury Press ltd