Epidemic Diarrhoea

NADIS disease forecasts are written specifically for farmers, to increase awareness of prevalent conditions and promote disease prevention and control, in order to benefit animal health and welfare. The forecasts are based on national trends and farmers are advised to discuss
their individual farm circumstances with their veterinary surgeon.

NADIS Pig Disease Focus – August 2005

Back before the late 1970’s scouring was regularly seen affecting the whole of a pig farm and the causes were specific viral infections producing either Transmissible Gastro Enteritis (TGE) or Epidemic Diarrhoea (PED). 

The former largely disappeared following effectively national immunisation of the herd by the related Porcine Respiratory Coronavirus (PRCV) and since the mid 1980’s reports of TGE have been, thankfully, rare – any stockmen or producers who experienced an outbreak is unlikely to ever forget it. However, the cause of PED is a separate coronavirus to which there is no cross immunity to PRCV and, as such, can still occur and the latest report from NADIS indicates that it is currently active.

Clinical Presentation
Scour is the main feature of PED and can occur at all ages (although there is a sub-strain of the virus which does not attack sucking piglets). The scour is often profuse and watery, often with a green tinge to it.  It can, thus, easily be confused with the now common problem in weaners of PMWS associated scour. Probably more significantly from a diagnostic point of view is vomiting – something that is not commonly seen other than in an isolated pig.

Inappetance for several days is also a key feature of the condition and, in growing pigs, this can affect 100% of animals. It is equally seen in sows and can then have knock on secondary effects to milking ability. Sows affected in early pregnancy can suffer high returns to oestrus or depressed litter size if they retain a litter.  Sows affected in late pregnancy are also likely to produce poor quality piglets.

Mortality is rare with PED – unlike TGE – although starvation in suckling pigs can occur and death due to secondary opportunist infection is likely in any herds other than those of the highest health status.

A herd will usually recover over a 4-6 week period, although this does depend on the nature of the herd e.g. an outdoor breeding herd may only see very slow spread through the sows, thus prolonging the outbreak.

In the longer term, sows become immune and pass on antibodies to the young piglets that will protect them as weaners. However, this protection will not last beyond 12 weeks of age and, in certain circumstances, the disease can become a long term problem in growers and finishers. This is particularly the case in permanently occupied accommodation, particularly with scrape through dung passageways or in systems where there is no regular cleaning and disinfection e.g. unwashed straw yards.

Introduction of Disease
The virus is likely to enter a farm either in infected pigs or by non pig carriers. Lorries, birds and rodents are all capable of mechanically transferring the virus from herd to herd and, thus, normal biosecurity measures are vital to keep the disease out. 

Control
Once the disease is present on the farm, it is vital that it spreads around as quickly as possible. The scour can be physically moved and introduced into unaffected groups but this should only be done under veterinary direction.

Once the major part of the outbreak is over, a cleaning programme, particularly in the feeding herd, is necessary to avoid the disease becoming a long term problem.

Diagnosis
Scouring is now common in both weaners and growers and PED must be considered in any outbreak of scour in these age groups; it may occur in conjunction with PMWS and as part of the grower scour complex.

Laboratory testing is needed to confirm a provisional diagnosis.

Costs
Even where no mortality occurs, affected pigs can take up to 14 days longer to reach slaughter.  For a 300 sow breeder feeder unit, this can mean that an outbreak can cost £6000 or £2.40 per pig in extra feed.

If the disease is allowed to become established in the farm, it can add 7 days to slaughter for all pigs – the disease generally being milder in its chronic herd form but this would mean an ongoing annual cost for the above herd of more than £8000 in extra food. The cost of failed biosecurity is high. 

Copyright NADIS 2005 
www.nadis.org.uk

While every effort is made to ensure that the content of this forecast is accurate at the time of publication, NADIS cannot accept responsibility for errors or omissions.
All information is general and will need to be adapted in the light of individual farm circumstances in consultation with your veterinary surgeon

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