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Answers to the New Pig Virus Start Here . . . Maybe

06/09/2014 @ 7:07am

If anybody can figure out a way to slow the spread of porcine epidemic diarrhea virus, it might be Hank Harris and his cutting-edge vaccine technology at Harrisvaccines in Ames, Iowa.

The PED bug has proven a tough nut. About the only approach that has been effective is an old, crude system of feeding dead baby pigs or infected sow manure back to gestating sows that haven’t farrowed yet. Farmers have done this for years to fight TGE, a virus in the same category as PED. This intentional infection of gestating sows with live virus temporarily makes them sick, and triggers an immune response that is expressed in the colostrum of their milk. It takes a sow herd from what they call “naïve” category to infected, and when they farrow, most of their babies will live.

There are problems with this. One, it perpetuates and expands the prevalence of a live, deadly virus on a farm. And second, for two to four weeks – and sometimes longer – following a PED outbreak, it’s a grim task in the farrowing house day after day of disposing of dead pigs. PED causes so much damage to the lining of the small pigs’ intestines, and such a rapid and severe case of acute diarrhea, that they simply dehydrate to death within a day or two. Pigs that are older at the onset of a PED outbreak may have a fighting chance at survival, due to their greater energy and fluid reserves.

“We started working on a PED vaccine immediately when it showed up in herds of 2013,” says Harris. “We have some vaccine technology that we licensed from a company in the human-health field. With this technology, you don’t actually have to grow the virus, all you need is to know the particular gene that is impacted. It lets us get a vaccine out there much more quickly.”

With PED, Harris scientists identified from Chinese sources what they call the Spike gene sequence of the virus, and manufactured a vaccine that they felt would neutralize it. They released the first (and still the only) vaccine in August of 2013. But because it was only a partial copy of the gene sequence, and didn’t include the second variant PED strain that has since been identified, it wasn’t effective in showing immunity in suckling pigs and was only partly effective with growing pigs.

So they went back to the drawing board using the full Spike gene. When that product was tested in the fall of 2013, it showed full immune response. That version of Harris’s iPED+ Vaccine was released (it requires a veterinary prescription) in January, and it includes protection against the original strain. Experiments are ongoing to show if there is cross protection against the variant strain of PED. However, Harrisvaccines has already produced a vaccine that 100% matches the variant strain and has had some limited sales. Hank Harris admits that it, too, is not exactly perfect. Various reports have circulated around the industry that the vaccine does or doesn’t work. “We have just reported all the results, good and bad. Overall, it is effective,” says Harris.

After vaccination with iPED+, sow milk in Harris trials was found to be about 50% higher in anti-PED components compared to unvaccinated sows that were previously exposed to the virus. While that’s not perfect, it is significant and will save more pigs, says Harris. In a limited study with gilts that were given two doses of the vaccine before they farrowed, piglet mortality was 42% in the non-vaccinated control group and 15% in the vaccinated group. Harris says that study is being repeated with more sows and more intense challenges of the virus.

But where the vaccine has been more effective, Harris says, has been as a booster shot to sows a few weeks after the initial outbreak. In typical farm situations, the disease strikes and within a few days, all newborn pigs are dying. At that point, most producers intentionally expose sows in gestation to the live virus. It takes two to four weeks for those sows to develop immunity. For those four weeks, newborn pig loss lingers at 80% to 100%. When exposed sows start showing up in the farrowing house, losses will typically drop, but may still linger for weeks at 20% to 40% pig death loss (around 12% is typical before PED outbreaks).

Often on outbreak farms, there may be a second spike in PED virulence about 9 or 10 weeks after the initial break, for unknown reasons. Some of these farms tend to stay chronic for PED, with ongoing losses of 30% or more in the farrowing house.

That is where the Harris vaccine is showing some of its best success, says Harris. On eight chronic farms they have monitored, when the iPED+ vaccine was given at eight to 13 weeks after the outbreak, pigs losses dropped from over 40% to under 15% by week 25. The exposure to live virus right at the point of outbreak is like an initial vaccination, and the iPED+ is a booster that takes them to a higher level of protection.

Joel Harris is Hank Harris’s son, and the director of sales for the company. He says they want to get to the point that the vaccine can be used to vaccinate gilts before they farrow the first time, and avoid those big losses of the first few weeks of a PED outbreak. “And we will further shorten the time we get back to normal production,” he says. “We hope to have a conditional license for the vaccine soon, so you can buy it off the shelf without prescription. It’s in government regulators' hands now.”

Harrisvaccines makes many herd-specific vaccines, built specifically for a farm using genes from the actual disease bug for a more targeted attack. They think they will be able to do that with PED to get even better at controlling PED on individual farms. But, says Hank Harris, with PED we may never get to the point of such good immune response that we never have outbreaks. “Maybe we’ll have to accept mitigating the losses so we don’t have these complete 100% episodes,” he says. It’s too early in the disease history to know all of the answers, he concludes.

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