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Swine Dysentery (SD)

(456) Swine dysentery (SD), which is caused by a small snake-like bacteria called Brachyspira hyodysenteriae can be one of the most expensive diseases of the growing pig. There are two other similar bacteria, one called B. innocens which is non pathogenic and the other B. pilosicoli, associated with colitis. Disease is common in pigs from 12 to 75kg weight and occasionally in sows and piglets. It is spread entirely by the ingestion of infected faeces or from carrier pigs that shed the organism in faeces for long periods. It may enter the farm through the introduction of carrier pigs or mechanically from infected faeces via equipment, boots or birds. The disease has a marked depressant effect on feed conversion and daily gain with symptoms appearing intermittently often associated with stress, such as the movement of pigs which increases the output of organisms. The organism survives in slurry for up to eight weeks. Continual exposure to infected faeces is a major factor in the maintenance of disease in a herd

The costs of disease are associated with mortality (low), morbidity (high), inefficient production and continual in-feed medication. Disease often appears in cycles and previously affected pigs will still transmit infection to susceptible ones for at least 10 to 12 weeks. SD can be spread by flies, mice, birds (starlings) and dogs, all these species shedding the organism for up to 21 days. SD will survive outside the pig for up to eight weeks in moist conditions particularly in cold slurry but it dies out in two to three days when allowed to dry.

Clinical signs

The incubation period is normally 2 to 14 days but can be much longer. The pig may develop a sub-clinical carrier state first and then break down with clinical disease when put under stress or when there is a change of feed.

The early symptom is a sloppy diarrhoea, which stains the skin of the perineum under the anus, and a rapid hollowing of the flanks. Initially the diarrhoea is light brown and contains jelly-like mucus. As the disease progresses, blood may appear in increasing amounts turning the faeces black and tarry. The pig's appetite is decreased, it rapidly loses condition, becomes dehydrated and takes on a gaunt appearance. Spread through the herd is slow, building up in numbers as the dose rate of the causal agent builds up in the environment. Sudden death sometimes occurs mainly in heavy finishers.

Post-mortem examinations show the lesions are confined to the large bowel and sometimes the greater curvature of the stomach.


This is based on the history, the clinical picture, post-mortem examinations, gram-stained faecal or colonic smears, fluorescent antibody tests on faecal smears and the isolation and identification of B. hyodysenteriae. Specific identification of B. hyodysenteriae to distinguish it from other similar colonic spirochetes requires specialised procedures which are not available in every laboratory.

Similar diseases

These include non-specific colitis, bloody gut (PHE) and acute salmonella infection particularly by S. choleraesuis. Heavy infections of the whip worm, trichuris can also simulate swine dysentery.


  • The following medicines have an activity against B. hyodysenteriae: (*very active + not available in some countries )
    • Carbadox * +
    • Chlortetracycline.
    • Dimetridazole *.+
    • Lincomycin *.
    • Monensin *.+
    • Ronidazole *.+
    • Salinomycin.
    • Tiamulin *.
    • Tylosin *.
    • Valnemulin *
    • Virginiamycin +
      NOTE Some strains of B. hyodysenteriae have become resistant to some of these medicines.
  • With the first signs of disease medicate the drinking water with either lincomycin, tiamulin or tylosin for at least 7 days.
  • Inject badly affected individual pigs daily for 4 days with either lincomycin, tiamulin or tylosin.
  • In-feed medication may be used to suppress clinical disease for treatment. The following medication could be used; lincomycin - 110g / tonne, tiamulin - 100g / tonne or valnemulin 75g / tonne could be used.
Management control and prevention
  • If the herd is not infected with swine dysentery carry out all the biosecurity measures discussed in chapter 2 to prevent its entry. Transmission usually requires a moderate dose of infected faeces so it can usually be kept out successfully even in pig dense areas.
  • In infected herds control is aimed at preventing the movement of the organism between groups of pigs. Management procedures should therefore be directed towards all-in all-out systems with cleansing and disinfection between each batch. The organism is sensitive to most disinfectants and in particular phenol based ones.
The following specific management procedures should be adopted:
  • Develop an all-in all-out housing system with disinfection. Slurry channels should be separate.
  • Where solid dung passages are used it may be necessary to depopulate the whole house, clean and disinfect and bring in new pigs at weaning time that have not been contaminated.
  • Control flies, they can transmit the organism from one group of pigs to another
  • Carry out strategic medication, for example post-weaning using either lincomycin (110g/tonne) or tiamulin (100g/tonne) for a period of three weeks. This should produce a dysentery-free pig and provided this pig moves into further accommodation which as not been exposed to the organism it becomes possible to break the cycle. Segregate the herd into believed clean and infected areas and prevent transmission of faeces between them as much as possible.
  • Use liberal disinfectant foot baths dispersed around the farm particularly when personnel move from one batch of pigs to another.
  • Reduce the movement and handling of pigs to as little as possible particularly at weighing time when transfer of faeces is likely to take place and stress is likely to cause clinical flare ups.
  • Do not overcrowd pigs and endeavour to keep a dry environment, the organism will die out quickly on drying. Poor sanitation and wet pens enhance the disease.
  • One of the greatest risks is the introduction of the disease into a finishing system. This is likely when pigs have been brought in from unknown sources. Isolate incoming pigs for a period of three weeks and strategically medicate with dimetridazole 800g/tonne, lincomycin 220g/tonne or tiamulin at 100g/tonne for a period of two weeks. Water medication could also be used. This should eliminate the organism if it is present or at least lower it to a manageable level.
  • A common source of infection is from infected pigs that are present on the vehicle which calls at your farm to collect your pigs. Infected faeces are carried back into the buildings on boots.

Swine dysentery is a disease that no producer can afford to live with. There are therefore two options in the medium to long term: either to depopulate and repopulate the herd or attempt to eradicate the disease without depopulation. Eradication has been carried out on a number of farms successfully, although depending on farm circumstances, the success rate may only be as high as 80%. In the breeding finishing herd eradication commences with the treatment of the sow herd to eliminate the organism and produce and wean a dysentery-free pig. Such pigs must not be allowed to come into contact with any other infected pigs or their faeces on the farm. There are a number of programmes that can be adopted from this principle (Fig.9-36).

There are however some rules that need to be noted:

  1. Do not start an eradication programme until clinical disease is reduced to an absolute minimum by management control and continuous preventative in-feed medication; 60g/tonne tiamulin, 55-100g lincomycin or 100g monensin could be used.
  2. Maintain the preventive medication throughout the whole period of the eradication and for two months afterwards.
  3. The numbers of growing pigs on the farm should be reduced to a minimum thereby reducing the susceptible population. Ideally this should start at weaner weight with all the grower pigs being sold off the farm.
  4. An alternative would be to carry out segregated weaning for a period of weeks depending upon the availability of accommodation. Whilst this is going on the pigs from weaning through to slaughter can be marketed at their suitable weights.
  5. One or more weaner houses should be totally emptied washed, disinfected and left empty for four weeks to give a break between clean and dirty pigs. This gap is maintained throughout the programme. Strict isolation procedures must be adopted between cleaned and infected houses.
  6. As each house is emptied it should be completely cleaned down, all evidence of faeces removed and faeces channels totally emptied. Slurry channels become the most dangerous area because the organism can survive for up to eight weeks. However in practice disinfection can be carried out with individual buildings left emptied for a period of four weeks only, but this is a less reliable method.
  7. Always attempt eradication during the warm summer months since the organism dies out in a matter of hours under dry conditions, whereas it can survive for weeks in cold wet conditions.
  8. Prior to the commencement of the eradication programme the sow herd should be medicated for at least six weeks to remove any possible carrier state.
  9. As the elimination procedures continue mice, rats and flies should be dealt with accordingly. The organism can persist for long periods of time in mice.
Medicines that have been used successfully for the eradication of swine dysentery.


    Period of medication up to 8 weeks:
    Dimetridazole 500 to 800g/tonne feed.
    Tiamulin 100g/tonne feed.
    Lincomycin 110g/tonne feed.
    Monensin 100g/tonne feed.


    Period of in-feed medication three weeks.
    Lincomycin 110-220g/tonne of creep feed.
    Tiamulin 100g/tonne of creep feed.


    Lincomycin 55 to 110 g/tonne.
    Tiamulin 60 to 100 g/tonne.
    Monensin 100 g/tonne.

One note of warning, eradication is not always successful but it can be more cost effective than total herd depopulation and repopulation. Discuss this with your veterinarian.

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