Brachyspira hyodysenteriae

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Also known as: Swine Dysentery

Brachyspira hyodysenteriae
Phylum Spirochaetes
Class Spirochaetes
Order Spirochaetales
Family Brachyspiraceae
Genus Brachyspira
Species B. hyodysenteriae

Introduction

Swine dysentery 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 prevalent in the United Kingdom and can be important economically. Recently new isolates called Brachyspira hampsonii have been isolated in the United States that are genetically distinct, but have strong hemolysis and are associated with clinical cases of dysentery.

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 dysentery is spread by the faeco-oral route and is carried by pigs and rodents. B. hyodysenteriae survives several weeks in moist faeces. Carrier pigs shed B. hyodysenteriae for up to 3 months, acting as a source of infection for healthy pigs.

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 prevalent 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 to show organisms in the epithelium of the mucosa. The bacteria can also be cultured on blood agar with added antibiotics for at least 3 days at 42 degrees under anaerobic conditions. The best samples are from colon of clinically ill pigs, rectal swabs are not sensitive. - B. hyodysenteriae causes complete haemolysis whereas other spirochaetes cause partial haemolysis. This is called a "strong beta" reaction, where complete beta hemolysis is visible, especially after removing a plug of agar. This is called a ring phenomenon and is indicative of a pathogenic Brachyspira infection.

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. However, the gold standard and method of definitevely diagnosing Brachyspira is the presence of a strong beta hemolysis organisms isolated using selective media.

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. However, this is a difficult task as the organisms can remain viable for months in manure pits and lagoons. It can also be spread and maintained in rodent populations.

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.



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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




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