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Porcine Epidemic Diarrhoea (PED)

Background and history

Porcine Epidemic Diarrhoea (PED) is caused by a coronavirus named Porcine Epidemic Disease virus (PEDv). Two different types are recognised: PEDv Type I only affects growing pigs whereas PED Type II affects all ages including sucking pigs and mature sows. Type I is seen as a low level endemic disease in the UK with pro-active surveillance only detecting very low numbers annually. Type II is a more virulent strain that caused the death of over 1 million pigs in the USA in 2013-14, with up to 100% mortality seen in piglets less than 7 days old. The AHDB Pork and the APHA are monitoring all suspected cases of PED in the UK, offering a free testing service. The devastation of the disease in the pig industry in the USA prompted governments to make PED a notifiable disease in England and Scotland, by doing this identified cases of the virulent Type II PED can be prevented from spreading.

PEDv damages the villi (cell surface) in the pigs gut, reducing the amount of absorptive surface area which results in a loss of fluid, diarrhoea and dehydration. Up to 100% of sows in a herd may be affected, showing mild to watery diarrhoea after the PEDv enters a herd, but a strong immunity develops over two to three weeks and the colostrum then protects the piglets. The virus usually disappears spontaneously from small intensive breeding herds however in larger outdoor breeding herds not all the pigs may become infected the first time round and there may be recrudescence of the disease over a longer time frame.

PEDv is harmless to humans and other farm animals and is not a food safety risk.

Clinical signs

The clinical signs of disease are very age-specific and much more severe in younger animals. In very young piglets there is profuse, watery diarrhoea, without blood or mucus, which is usually yellow - green in colour, often accompanied with vomiting and anorexia which may lead to death in up to 100% of the piglets less than a week old. Pigs over a week of age typically recover but with growth rate losses of circa 10%. When older animals (nursery, grower, finisher, sows, boars) become infected they may go off feed for two to four days, have loose faeces or watery diarrhoea with no blood or mucus and vomit – dehydration is common. A death rate of 1 to 3% in the post-weaned animals is typical.

The incubation period is typically two to four days and the first clinical signs in a herd are seen approximately four days after PEDv enters the herd. When the virus is first introduced on to the farm there is a rapid spread of diarrhoea across all breeding (Type II) and growing pigs (Type I and II) with almost 100% morbidity (pigs affected) within 5 to 10 days, although in outdoor extensively kept pigs this time may be protracted.

There are other diseases that cause very similar clinical signs, such as; coccidiosis, transmissible gastroenteritis (TGE), rotavirus diarrhoea, Clostridium perfringens enterotoxaemia, and E. coli scours. It is now a legal requirement to contact your vet or the Official Veterinarian (OV) at your local APHA in such cases to rule out PED, they will submit samples to the APHA for a diagnosis.

In breeding adults there may be associated production losses such as; increase in returns to service if sows/ gilts are affected in early pregnancy; Agalactia (loss of milk production) in farrowed sows; reduced libido in boars; and abortions can occur.

As with many viruses, the disease tends to be more prevalent in the winter as the colder weather assists the survival of the PEDv in the environment, favouring the spread between and within farms.

Predisposing factors

The immunological status of the herd i.e. no immunity is a predisposing factor. If the breeding stock within the herd has recovered previously from PED then they will have a level of immunity. It is worth mentioning that pigs in the UK have no immunity to PED Type II should an incursion in the UK occur.

When susceptible pigs enter the herd then the disease may be perpetuated before they then recover and gain immunity.

NOTE: High mortality in piglets less than seven days old would be an early signal of virulent PEDv Type II currently not seen in the UK, but PEDv Type II appeared spontaneously in the USA so it makes sense to remain vigilant.

Diagnosis

This is based on the history, clinical signs in the different age groups and examination of faecal samples/dead piglets for evidence of PEDv Type I and Type II by laboratory diagnosis.

Causes

PEDv is transmitted primarily via the faecal-oral route and infected pigs shed enormous amounts of the virus for seven to nine days. Transmission may be through direct contact with infected pigs or indirectly by exposure to infected pigs faeces, which may persist in cool, damp organic matter for up to a month. The virus is killed by most common disinfectants such as Virkon S ™. PEDv may also be spread through the air, via semen and in blood plasma.

Prevention

Strict biosecurity and sanitation are the best means of prevention. A bio-security procedure with respect to visitors and vehicles is essential, especially the points of access to the farm by fell men and their vehicles. Controlling vermin, especially rats will assist in not un-doing your biosecurity efforts.

The infective dose of PED Type II has been researched and as few as 100 virus particles. To give you some idea of how low the infective dose is you could fit approximately 20 million virus particles on the head of a pin. It doesn’t take much contact with the faeces of an infected pig to cause disease and should PEDv Type II enter the country our bio-security plans are all we have to protect our herds.

A vaccine has been produced in the USA against PED Type II but its efficacy and how best it is used is still being evaluated. There are no vaccines licenced in the UK.

The AHDB Pork have produced a biosecurity guide for producers with many links to further information.

As our biosecurity plans are our only security in preventing our herds from the spread of PEDv then in the UK consider joining the AHDB Pork’s Significant Disease Charter with the aim of producers to sign up voluntarily to share information quickly in the event of an outbreak which will, in turn, make the control of disease faster and more effective. You can join up through the AHDB Pork Pig Hub.

Treatment

No specific treatment for PEDv is available. Affected pigs should be kept warm, dry, and well hydrated with oral electrolyte supplementation. In very young animals, treatment is usually futile. If secondary bacteria complicate the clinical disease or are likely to, then broad-spectrum antibiotics may be prescribed. If the virus enters the herd for the first time it is important to ensure that all the adult animals become infected at an early stage to allow an early immunity to develop. This can be achieved by exposing sows to the diarrhoea three times, two days apart via the drinking water, this practice is known as ‘feedback’. Mix scour or contaminated material into a bucket of water and use this as the source. The use of feedback technique must be performed under the rules laid down and detailed on the UK Pig Veterinary Society website under “controlled exposure”.