Of all the porcine reproductive and respiratory virus (PRRS) viruses that Paul Yeske, DVM, has seen, the PRRS strain 1-4-4 is the most dramatic.
“I think this one’s the most dramatic as far as the number of aborts and the number of sow mortalities,” Yeske said in a webinar hosted by the Swine Health Information Center (SHIC) about a new PRRS strain that has been causing high mortality in many Iowa and Minnesota pig herds. “We’ve seen anywhere from four to five weeks of production essentially aborted out and sow mortality is anywhere from 10% to 20% of the sows dying off and very rapidly within a two- to three-week period of time.”
Piglet mortality has been extremely high, too, with numbers as high as 80%, a number Yeske said he didn’t think was possible. But this strain is different.
A Distinct Footprint
Although this virus hasn’t done anything that the swine industry hasn’t seen with PRRS before, it has a pretty distinct footprint so far in what we have seen, he said.
“When you see this virus come into a herd, you almost don’t have to wait for the sequencing to come back,” said Yeske, a swine practitioner with Swine Vet Center in St. Peter, Minn. “You know what that’s going to look like before you get it back, if you’ve seen some of the clinical signs before in other herds.”
The clinical signs that present most often with this PRRS strain are pigs going off feed, abortions, increased sow mortality, increased piglet mortality, and increased mummies. Yeske said this strain tends to have a pretty high post-weaning mortality and slow growth in the finishing phase.
One of the things that’s unique to this virus from what Yeske and his colleagues at the Swine Vet Center have seen is that it tends to move very quickly through the herd. Once clinical signs are observed, it marches through the barns relatively quickly. Because of this, it’s a fairly consistent clinical picture that is easier to diagnose, he added.
“You’re probably not going to miss this one, just because of the magnitude of what you’re going to be seeing. What we’re seeing are some very low Ct (cycle threshold) values on those initial tests that we’ve run down in the teens, so lots of virus,” Yeske said.
The virus is more severe when complicated with other diseases, particularly influenza. He said some of the cases he has seen came in with the flu virus at the same time, making it even more challenging.
In addition to high sow and piglet mortality, Yeske said the virus results in slow growth in finishers. At one site, they saw pigs gaining at 2.4 lbs. a day drop down to 1 lb. a day in the period after they dropped off water consumption and broke with PRRS strain 1-4-4.
Does Previous Immunity Help?
Right now, Yeske said he’s not sure that previous immunity really made a big impact. He has seen breaks in herds that are vaccinated, breaks in herds that had previous virus exposure less than a year ago and breaks in herds that have used vaccination, previous virus exposure. In the end, he said it doesn’t really seem to change the outcome much between the various combinations or even in the negative herds.
“I always have to put the statement in there that I guess it could always be worse,” Yeske said. “But it seems hard to imagine that it would be, but never challenge ‘worse.’”
How Fast is the Virus Spreading?
This particular variant appears to produce very high levels of viremia. Yeske said this allows for easier virus spread within an area.
“I think the weather conditions have been very favorable for spread this year as we’ve had a lot of overcast days and warmer temperatures than typically normal. We’ve had more of those ice fog days – probably the perfect opportunity for the virus to move around. It appears to be moving somewhat at will in certain areas.”
From a herd stabilization standpoint, Yeske said they have managed the PRRS strain 1-4-4 like they have managed previous PRRS outbreaks.
“We’re new into these outbreaks and it’s still a little early to predict how well they’ve stabilized, but it does appear that they are stabilizing, and it appears those sow farms are returning to normal,” Yeske said. “There’s about a two-to-four-week period where it’s really tough on the farm, we get the devastating losses, then we see the sows start to recover and come back on feed and return more to normal.”
At this point, they are seeing normal pigs being born, however, Yeske said the problem is that they see very low born alive numbers due to more mummies and even some whole mummy litters.
“The stillborns tend to come down pretty quickly, but it looks like there’s going to be a fair bit of mummies on these particular farms,” he said.
They are starting to track these outbreaks on the PRRS timeline to see if they’re going to act like other viruses in the past. But we’re a little bit too early, he said, as they are just getting to the stabilization point.
“But hopefully, we can see them follow that normal track. Several of these herds are going to try and do virus elimination, get the field virus out of the herd. Hopefully, as we go forward, we’ll be able to share more later on,” Yeske said.
The Biggest Take-Home
What can producers do? Yeske urged producers on the webinar to review their biosecurity plans and try and identify the greatest areas of risk in their herd.
“I like to think of risk in two ways,” Yeske said. “How likely is something going to come into the herd? And how many times a week do you do that activity? Those two multiplied together give you the risk. Even though we have filtered farms, there’s still not really a farm in the bubble. We’ve still got to do all those biosecurity procedures properly.”
Make sure your farm’s biosecurity plan is being followed like it’s supposed to be. If it’s possible to improve any weakness in your system, Yeske recommended producers do it sooner rather than later.
“You don’t want to find out about your weaknesses when you’re doing your PRRS outbreak investigation later on,” he said.
Farm Journal’s Pork | Jennifer Shike | February 24