15 September 2000

Hopes of victory rise in battle to control PMWS

By Marianne Curtis

POST-WEANING Multisys-temic Wasting Syndrome (PMWS) may have been eclipsed by the recent outbreak of Swine Fever, but this puzzling disease is still quietly killing young pigs in East Anglia.

However, there are hopeful signs that mortality from the disease is less severe than it was, according to one Norfolk vet.

John Hayden, pig vet at Integra Veterinary Services, Thetford, Norfolk, has not seen any new herds in his practice area break down with the disease since April and is reasonably optimistic that units with a problem will see it largely disappear within nine to 18 months of the first case.

"PMWS has affected 30-40% of herds in East Anglia, but the number of cases seems to have stabilised. Evidence from Canada, which has had the disease since 1992, indicates that herds will see weaner pig mortality return to almost normal levels within nine to 18 months of the first case."

Although mortality levels appear to have fallen from 10% to 5% above normal, it is still a cost that hard-pressed pig producers can ill afford. But there are some steps that they can take which seem to reduce the severity of the problem, says Mr Hayden.

"It appears that sows are infected by PMWS sometime during mid-pregnancy and pass the disease to unborn piglets. New evidence obtained by tagging litter mates, shows that pigs from certain litters may be worse affected than those from other litters."

Because of this apparent susceptibility of certain litters, it makes sense to reduce fostering and keep litter mates together and isolated from other litters until two to three weeks after weaning.

"Resistance to PMWS develops with age and pigs that have experienced minimum challenge from other diseases and minimum stress may become resistant by seven weeks old. However, when they are mixed frequently and challenged by different bugs it may take until 70kg before they develop resistance."

Although pigs are likely to be born with the ability to develop the disease, wasting symptoms are usually not seen until six to seven weeks old. But they can spread the disease to other pigs from a much earlier age.

Other diseases also appear to be linked with PMWS, says Mr Hayden. "PMWS may have links with PRRS, Parvovirus or secondary bacterial infection."

Vaccinating against enzootic pneumonia (EP) also helps because it takes out another disease challenge, he says. "Continue vaccinating against EP, or start vaccinating against it if EP is present on your unit."

But take care when using needles, he warns. "When vaccinating pigs or injecting them with iron, change needles for each new litter to avoid spreading the disease between litters."

As the disease is passed from sows to piglets breeding stock introduction should also be undertaken conscientiously.

"Ensure that breeding stock comes from a source free from PMWS and isolate incoming stock for three to four weeks. Contact the supply farm before introducing animals to the main herd to check that it is still free from the disease."

But gilts entering a PMWS infected unit will be naive and the aim should be to build their resistance to the disease before they become pregnant, advises Mr Hayden.

"We are still unsure about how gilts and sows build resistance to the disease and whether they may still pass it to their offspring. The safest assumption is that it acts like other diseases, so they should be exposed to it by giving them bedding from weaner areas after an initial 3-4 week isolation period.

"After 3-6 weeks of bugging them up, give them three to four weeks to recover before service."

Certain litters of pigs are more susceptible to PMWS than others, says John Hayden.


&#8226 Keep litters separate.

&#8226 One needle a litter.

&#8226 Reduce all stresses.

&#8226 Treat secondary infections by vaccinating or medicating.

&#8226 Introduce breeding stock carefully.