Pigs are expected to head to the World Pork Expo at the Iowa State Fairgrounds this week in record numbers, despite a deadly disease that's killed millions of animals nationally, reports Des Moines Register.

Experts say they expect the disease – almost always fatal to piglets – will do little to disrupt county and state fairs in Iowa, the top US pig producer with $7.6 billion in sales.

Pig producers and breeders can expect tough biosecurity measures to get tougher at the World Pork Expo and fairs to avoid spreading the highly contagious virus, officials say.

The porcine epidemic diarrhoea virus, called PEDv, is believed to have killed an estimated seven million animals nationally in a little over a year. It has swept through more than 30 states nationally.

The virus poses no threat to other animals or humans. And pork products remain safe for consumers, officials say.

The decision might have been different a few months earlier, "during the heat of the outbreaks," said Harold Hill, a Cambridge veterinarian. He's also president of the National Pork Producers Council, the group behind the expo.

Then, producers were struggling to contain the disease. Now, "producers understand if they take proper biosecurity measures, they can attend the show and not risk their livestock," Dr Hill said.

The disease prompted the New York State Fair last month to cancel all pig competitions and exhibits.

"Animals come to the fair from all over the state. With a disease like PED circulating, it's in the best interests of the animals that we take this action," said New York State Veterinarian David Smith.

And it has sparked discussions across Iowa. For example, a producer in Buena Vista County decided against providing pigs for kids who do not raise their animals to show because of PEDv concerns. Other county producers, however, decided to proceed with the show, with farmers who own and raise pigs competing, the Associated Press reported.

Dr Hill said part of the work at the Expo begins before animals come to the fairgrounds.

Animal exhibitors are required to prove that a pig has been examined by a veterinarian before coming to Des Moines and is healthy. A vet will inspect it again on arrival for PED and other diseases, Dr Hill said.

Workers also are disinfecting about 326,000 square feet of fairground pig barns, and they will be cleaned again after the animals leave.

Producers watching the shows will be asked to take special precautions as well: making sure the clothes and boots they wear to the expo have not been worn at home in pig barns. And they will have places at the Expo where they can disinfect their boots "before they drive back home", Dr Hill said.

The reasons for the caution is clear, according to Des Moines Register.

"It takes only microscopic amounts" of the virus to infect a herd, said Rodney "Butch" Baker, an Iowa State University veterinarian.

Vets have speculated that a thimble-full of the virus could effectively infect all of the state's nearly 20 million pigs, which is about one-third of the US pig population.

Three PED strains entered the country about a year ago, Dr Baker said. "We have to assume that they may still be coming in," he said, adding that "it's a weakness" in the nation's biosecurity effort.

"Most of the larger production systems have been affected," he said. "And a lot of the smaller family farms have been affected."

Low pig supplies have driven market prices for producers to record highs, and they are expected to boost prices for consumers by 15 per cent this year.

Producers had hoped the worst of the disease was behind them, since herds can develop an immunity to the disease and reduce its prevalence.

An Ames-based company, Harrisvaccines, has developed a vaccine that can be given to a sow to boost its immunity, which is passed on to her piglets. Other animal pharmaceutical and university researchers are working on a vaccine as well.

Last week, Reuters reported that a farm in Indiana has experienced a second outbreak, giving rise to concerns that new strains are developing and sparking fear that the disease might be harder to contain than initially believed.

Dr Baker, director of the Iowa Pork Industry Center at Iowa State University, said his group recommends animals remain at state fairs before they are taken to market. And animals that return to farms typically are isolated to prevent the spread of disease.

Some state fairs have decided against having pigs as part of their birthing centres, he said. "If sows do get PED, the baby pigs are the ones that die. ... That's not going to be a good experience" for fairgoers.

An Iowa State Fair official said its birthing centre will have piglets.

Bruce Leuschen, the Iowa State Fair veterinarian, and his team of veterinarians and senior vet students will be walking the State Fair barns, looking at all the animals for disease. In six years at the fair, he said it is not uncommon to isolate an animal or send it home because it is ill.

"Biosecurity is a big part of the State Fair," Dr Leuschen said.

And it has a big part of what students learn in preparing and going to county and state fairs, Dr Baker said.

"Fairs are for kids. It's a training, teaching, learning process. And it's a lot of fun, and a good way to attract people to livestock farming," he told Des Moines Register.