Swine dysentery is usually easily recognisable on farms, if displaying the classical blood, mucus and diarrhoea (see Photo 1) and is still one of the most severe causes of loss, if uncontrolled. Over the last decade, farmers in Europe have seen the number of products for controlling this disease dwindle, following the removal of carbadox, olaquindox, dimetridazole, ronidazole and now the growth promoter salinomycin, which seems to have exerted an inhibitory effect on some susceptible strains of Brachyspira hyodysenteriae, the cause of the disease. The remaining therapeutic products tylosin, lincomycin, tiamulin and valnemulin are all that are left and resistance development to these antibiotics has been reported in the EU and is a real concern to farms that are surviving with the disease. Now is the time to take a serious look how we keep our pigs and try to reduce the infectious challenge or if possible eliminate it.
Photo 1. Swine dysentery - typically diarrhoea with
blood
Dysentery has been in pig production for a long time and I remember it well in my early days in practice in the seventies in West London, the weaner producers and swill feeders supplying heavy hogs to the factory in Acton frequently had outbreaks of the disease. Since the proposed ban on growth promoters in the UK, a number of producers have taken them out and tried to adjust but many promptly went back onto them until the end in December. I expect to see a rise in the incidence of the disease and speaking to the three main Veterinary Investigation Laboratories involved with pigs, already one has seen an increase overall last year, one an increase in the last quarter and one no increase so far but it is still early days.
Why is dysentery so difficult to get rid of? The infection is spread from faeces to mouth so any increase in faecal contact increases the risk. In the photograph one can see a solid floor, liquid in the dunging channel (bacteria like moisture not dryness) and the presence of straw as bedding. Pigs walk in the dunging channel through the muck, go back into the straw, which they eat and infect themselves. The more bacteria they eat, the more likely they will break down with the clinical disease.
Survival of the organism is also critical. Chia and Taylor (1978) looked at the survival of B. hyodysenteriae in solid faeces or in a mixture of faeces and water, to simulate slurry (see Graph 1). The bacteria can survive upto 7 and 9 weeks in faeces and faeces plus water respectively, during cold wintry temperatures of 0°C. In summer temperatures (20°C), the survival time falls dramatically to under 2 weeks. This is why the summer is preferred for swine dysentery eradication, as the temperature can help reduce the organism's survival, thereby farm and pen contamination and risk of re-infection
Graph 1. Maximum, minimum and mean survival time of B. hyodysenteriae stored in solid faeces at various temperatures
(Source: Chia and Taylor, 1978)
As well as being temperature sensitive, B. hyodysenteriae are also sensitive to most disinfectants, so this is also another way of controlling their survival. Cleaning and disinfection between batches of pigs is also helpful but only if you are bringing in clean, dysentery-free pigs.
Scrape-through systems also can spread the disease from pen to pen, so slatted-floor systems, which remove/reduce the liquid and faecal contact and permit drying, will help reduce environmental contamination, challenge and the risk of infection.
The organism has been found in mice, rats and dogs, and flies can also carry the organism. Control of these is also important in any programme.
The main spread of the disease is an infected pig. The organism can live in a carrier pig for at least 90 days after clinical recovery from the disease. Usually, the incubation period for the disease in the field is between 7-60 days but in high challenge situations or artificial model infections it is 4-14 days (Taylor, 1999).
If you have an uninfected herd, keeping the disease out is the key, so biosecurity is a critical prevention strategy and if purchasing replacement stock, ensure they are from accredited swine dysentery-free herds. Quarantining them away from the main herd on arrival is also very important in case of breakdowns.
If you have an infected herd, controlling the disease by improving the hygiene and reducing faecal contamination is essential. The use of antimicrobials will help reduce the level of disease and infection, tiamulin and valnemulin remain the most effective, but serious consideration to eradication during the summer should be planned for now with your veterinarian, so that you can use nature to help you eliminate the infection.
References: Taylor, D.J. (1999) Swine Dysentery. In 'Pig Diseases' 7th Edition, Ed. Taylor D.J., Glasgow, UK, pp 157-169
Chia, S.P. and Taylor, D.J. (1978) Factors affecting the survival of Treponema (Brachyspira) hyodysenteriae in dysenteric faeces
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