21 January 2000

Diseases pose serious threat

By James Garner

PIG producers are being warned to be extra vigilant over two diseases whose increased incidence in recent months is causing anxiety for pig health experts.

Experts agree that both diseases are serious threats to financially struggling pig units. Both can cause high levels of pig mortality or prolonged performance loss for 18 months – and it appears in many recent cases that the two diseases are linked.

Porcine dermatitis and nephropathy syndrome (PDNS) and post-weaning multisystemic wasting syndrome (PMWS) have been reported in at least 30 cases in south east England, causing 20-25 herds to be shut down while diagnosis was confirmed.

This action has had to be taken in herds with fresh outbreaks of PDNS in south-east England, said VLA Weybridges Stan Done, speaking at a press briefing organised by Tom Alexander of Cambridge Vet School, Cambridge.

"In these cases it is difficult to differentiate between PDNS and classical or african swine fever and we cant afford to miss a case of this.

"We cant rule out swine fever because PDNS has become more complicated and harder to diagnose."

Tests for classical swine fever take three to four days, and seven to 10 days for african swine fever, which can cause finishing units some loss of production.

Experts fear that as many as 100 herds, which several breeding companies supply, are affected by either disease. Most recent cases have been reported in south east England.

Despite the serious nature of both diseases, there are gaps in experts knowledge. Questions remaining unanswered include what causes infections, how they spread and whether PDNS and PMWS are linked.

Norfolk pig vet John Hayden says PDNS follows PMWS. "I am convinced PMWS sets the whole thing off and PDNS follows."

Vets who have come across recent incidences on farm agree that both diseases are linked. Richard Potter of the Larkmead Vet Group believes there is an increased chance of PDNS occurring in herds with PMWS. Clinical symptoms of PDNS are easily spotted, with pigs developing gross lesions. It typically occurs in pigs between 30-70kg, which are normally healthy. Those with acute skin lesions suffer weight loss and will die after one to three days illness.

Still a mystery

Its cause is still a mystery, although Jill Thompson, based at SACs Bush Estate, said links have been made with porcine circovirus 2 (PCV-2), especially in Spain, where a strong case for association between diseases has been made.

"Increases in PDNS cases may be concurrent with a rise in PCV-2." But there may be other viruses involved and more research work is needed to find the cause, she added.

In serious infections mortality rates can be as high as 80%, although it is normally about 15%. Post-mortem often reveals swollen lymph nodes and haemorrhages on kidneys, said Dr Thompson.

PMWS affects younger pigs, according to Dr Done. Infection often occurs at eight to 12-weeks-old, normally peaking about 12 weeks of age in the late nursery stage. Usual mortality is about 7%, although levels can be far higher.

Typical symptoms are chronic wasting, pale skin colour, cough and enlarged lymph nodes. How many weaners become infected varies, but mortality in those could be high, depending on secondary infection, warned Dr Done.

There was little advice for producers in face of outbreak of either disease: Bury St Edmunds-based vet Jake Waddilove said that as neither disease responded to treatment, management solutions might offer some solutions.

"Do not mix pigs from different systems. All-in and all-out may be the best option. Keep pigs at optimum temperatures, and reduce stress."

Mixing pigs increased challenges, agreed Dr Done. "Mixing at birth, at weaning and at finishing is three sets of challenges to pigs whose immune systems could be compromised by these diseases."

One industry source believes questions may be raised about breeding stock. But there is little evidence so far to suggest that one breeding company is the source of infection.

PIC customers have been sent information packs about the disease and advised to improve biosecurity. The companys marketing manager Martin Whiting says its breeding stock will not be tested for infection until a proven test is available. &#42

PDNS/PMWS

&#8226 Devastating diseases.

&#8226 Knowledge is incomplete.

&#8226 Treatment unknown.