African swine fever diagnosis can be difficult

Infected pigs often die without any previous signs of trouble; sows appear fine in the evening and are dead by morning


BANFF, Alta. — African swine fever can lurk undetected in hog herds for weeks before producers identify it. That’s one of the reasons it has taken such lethal hold on hogs in China, Asia and parts of Europe.

Klaus Depner, head of the German National Reference Laboratory at the Friedrich-Loeffler Institute in Riems, said infected pigs often die without any previous signs of trouble. Sows appear fine in the evening and are dead by morning.

“It’s so fast, you don’t have time to see it,” he told those at the Banff Pork Seminar Jan. 9.

Other pigs lick and nibble on the dead one and the virus is transmitted. That seems simple, but in fact ASF is not particularly contagious, said Depner. Infected pigs don’t shed much virus and it is spread by direct contact or ingestion of contaminated material such as meat and blood.

Left on its own, ASF does not spread quickly. Animals that do survive the illness are not necessarily carriers, and carriers do not shed the virus.

ASF is not a hazard to people, but people have been the main perpetrators in spreading the disease across large distances in Asia and Europe by inadvertently transporting infected meat and meat products that enter the hog food chain through swill feeding or other means.

ASF is a tenacious virus that can live in frozen meat, dry meat, fat and carcasses for long periods.

Depner said ASF can go undetected because producers initially attribute hog deaths to other causes. If the number of dead animals is within the usual range, no alarm is raised. This was the scenario in at least one European case.

“We missed it for weeks, and this farm was still trading,” he said.

Random sampling of pigs will be useless in terms of surveillance. Only tests of sick or dead animals can reveal the situation.

Once ASF is found in even one pig, European Union legislation demands that all pigs in the herd be slaughtered. When vast numbers are not ill and risk of contagion is not great, it is hard to convince farmers and the public that slaughter is necessary, Depner said.

ASF has not been found in Germany, though cases have been identified in Poland only a few miles from the border. Germany is now testing all dead wild boars, which are potential carriers of the disease.

As Depner pointed out, wild boars running around the country are not the ones with the virus. Infected ones are those already dying or dead and those are the ones that must be tested to determine cause.

“The only thing we can do is be very fast in detecting the first case. We are not dreamers. We know preventing introduction is something very difficult.… If we detect it early we might have a chance to do the proper measures to fight it.”

There is no vaccine for ASF, although researchers are working to develop one. For now, biosecurity is the only protection, and Depner quoted three basic rules:

  • No swill feeding.
  • No barn contact by strangers.
  • Change boots before entering hog barns.

“Everybody is waiting for a vaccine,” said Depner, but that is considered to be years away and even the best vaccine won’t work without a good management strategy.

“Biosecurity is the only potent tool to control ASF. Believe me. There is where we should spend the money.”

He noted ASF cases have appeared in Europe because workers unfamiliar with protocols have been on duty when regular staff is on vacation. In other cases, less profitable operations feed kitchen waste to save on feed costs. If that waste contains contaminated meat and is eaten by the swine, the virus is spread.

Swill feeding as well as providing blood plasma and abattoir waste to hogs is common in China, Depner said, and that has worsened the problem in that country.

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