First, a little more than half of the US sow herd had been exposed to PEDv and developed herd immunity in 2015.

“We know from research that the immunity was very protective, not only for the sow but then also for the piglets through the sow's milk. Once you get that large percentage of the population that is carrying immunity, you expect the impact and spread of the disease to slow because the virus doesn't have a host,” said Tom Dr. Burkgren, DVM and Executive Director of the American Association of Swine Veterinarians (AASV).

Next, Dr. Burkgren said the industry learned a lot about the virus - how it spread, its infectivity and its pathogenicity.

“Containment of PEDv is all about biosecurity aimed at keeping the virus out,” he said. “The virus survived very well under the circumstances that we used to transport pigs in trailers and trucks while slaughter plants spread the infection back out to farms.”

Then, PEDV’s connection to feed was made - the entrance of the virus into the feed mills, going back out on trucks and then in feed.

“Producers and veterinarians started paying much more attention to what was coming on the farm, making sure that they maintained a clean side and a dirty side and all employees were trained,” he said. “A heightened sense of keeping the virus out and being aware of all possible risks for entrance of the virus into the farm was critical.”

Last, the process of clearing the virus from the herd and reducing the length of time it was in the herd has greatly improved versus 2013-2014. The pork industry has advanced its ability to get a farm back to normal production when it has an outbreak of PEDv, noted Dr. Burkgren.

“We continue to see virus pop up here and there at some sow farms, and there is a fair amount of virus still circulating in some of the finishers, but I think that knowledge serves us very well in maintaining separation between finishers and the rest of the pig flow, the sow farms and the nurseries,” Dr. Burkgren said.

Containing PEDv On-farm

Within a herd, the first sign a farmer will see is scouring pigs.

“Wherever the virus enters, if that is through the nursery or if it's in the gestation or farrowing, you're going to see the pigs scour and have diarrhea,” he said. “The big impact is when it enters the farrowing rooms, but it can enter any place on the farm - from gestation through farrowing into the nursery and certainly out into the finishers.”

Diagnostics, which are significantly better now than at the initial disease outbreak, are used to determine which of the viruses you have and then the clean-up process begins.

Cleaning up the farm is focused on a few steps. First, avoiding a very large viral load.

“Those infected baby pigs that are scouring are virus factories, and they kick out an enormous amount of virus in a very short period of time,” he said. “Once we confirm the diagnosis, then the focus moves to decreasing the viral load, which might mean euthanizing baby pigs on first recognition, so they can't increase your virus load.”

The next step is increasing PEDv exposure to the entire farm usually through backfeeding of manure or intestines from infected pigs to develop uniform and stable immunity throughout the farm so all the pigs go through the disease pretty much at the same time.

The third step is cleaning and sanitation of all areas to decrease the environmental load of the virus and get your farm back to normal production.

“It's a big effort. Nobody likes to clean, disinfect and dry those farrowing rooms, and then you need to take environmental swabs looking for the virus,” he said. “It's a real effort, but it's needed to decrease the environmental load, and then producers must continue to monitor pigs, looking for clinical disease but also doing diagnostic swabs in pigs to see if they're shedding virus.”

Dr. Burkgren said it takes about six to seven weeks to get the virus under control and get the viral load down and stabilized, uniform immunity throughout that herd.

PEDv Best Management Practices

Basically, farmers need to know what's clean and what's dirty, which begins with knowing everything that comes on the farm - vehicles, people, feed, supplies, new animals, etc.

“You have to change your mindset to think of your farm with a dirty side and a clean side, and everything on the dirty side should stay on the dirty side and must not enter the clean side until you are certain it's clean,” Dr. Burkgren said.

Consider anything to be dirty that would have a potential to transmit the PED virus into or throughout the farm. First and foremost, be sure new animals coming onto your farm are not shedding PEDv, and that can be done through diagnostics.

“If you bring a live pig that's shedding PEDv onto your farm, that's the dirtiest you can get,” he said.

Everything has to be suspect. On sow farms, people don't enter without showering in and leaving their dirty clothes on the dirty side and then changing into clean clothes on the clean side and being clean themselves.

“The same goes for trailers; there shouldn't be a dirty trailer entering your farm,” Dr. Burkgren said.

“Those trailers should be washed, disinfected, and dried before they come back onto a sow farm. We know that slaughter plants are sources of virus coming back to the farm both from the finishing side and also the cull sow side.”

If the trailer is backed up to a packing plant to unload pigs and personnel for the packing plant come on your trailer to move the pigs off or if a pig runs off and then runs back on, that trailer is now dirty. Any time there's a potential transfer of virus - manure from the loading dock back into your trailer by animals or people - you're bringing potentially PED-infected manure back to your farm.
Dr. Burkgren said it takes is a suspicious mind that looks at every input coming onto your farm with a jaded eye, including supplies.

“If a box of supplies comes in - maybe a box of medication - where's that box been before? Who's delivering it? You want to make sure that person stays on the dirty side. If you're suspect about the box, you may want to do a gas sterilization,” he said. “Wood pallets are often overlooked as well.”

Transmission of PEDv

Transfer of PEDv is through fecal oral transmission, but a very, very small amount of manure can transfer the virus. It's not just the manure, but it's anything that may have touched the manure certainly can carry the virus, including your pant leg or your boots.

Pig saliva can also contain the virus. Pigs explore their environment with their mouth, so if the virus is present, pigs will pick it up with their mouth by chewing on something. It's an efficient way of transmitting the disease.

“The virus likes cool weather but is heartier than first thought. It survived the trip all the way from China to the US, so it isn’t hard to imagine the transfer of it from a packing plant to a sow farm,” he said.

As for seasonality of the virus, Dr. Burkgren said it’s not an absolute that it lessens in the summer.
“In the summer of 2013, Oklahoma saw the virus move pretty rapidly through sow farms during the summer when it was hot and dry,” he said. “We continue to see the virus circulate in the summer time as well, but it does seem to circulate more efficiently and more widely with the advent of cooler, moister weather.”

Expectations for 2016

What happens in 2016 is still the big question, but Dr. Burkgren expects the US will continue to see cases of PED pop up.

“We know there's still virus circulating out there and the same risk factors are present,” he said.

“And herds may not be as immune as they were going into 2015, which is a concern. As sow herd immunity declines because they're not exposed to the virus that leaves a naïve or vulnerable population. We could see PED rear its ugly head again, but certainly not with the impact we saw with the initial entry of PED in the winter of 2013/2014.”

The rules of biosecurity must be heeded, and anyone handling pigs needs to pay attention to the detail.

“You always worry when we're not seeing a lot of PED that people will get a little lax - cut some corners, maybe don't wash that trailer as good as they should - and the next thing you know, then we start seeing the virus pop up again. Biosecurity compliance is critical.”

This article first appeared in the January 2016 IPPE Digital.