Highly infectious PRRS variant causes high mortalities on sow farms

A variant of the porcine reproductive and respiratory syndrome (PRRS) virus is taking a heavy toll on hog farms in southern Minnesota and northern Iowa. The variant, identified as PRRS 1-4-4, hits sow farms especially hard, causing 10% to 20% sow mortality and high mortalities in the nursery of 50% and even as high as 80%. In grow-finish units, mortalities are less but still can be significant, and growth rates drop dramatically.

“This PRRS virus hasn’t done anything we haven’t seen with PRRS; it’s just way more dramatic,” reported Paul Yeske, DVM, Swine Vet Center, St. Peter, Minnesota. Yeske talked about PRRS 1-4-4 as part of a webinar presented by the Swine Health Information Center and American Association of Swine Veterinarians.

Clinical signs

“From what we’ve seen on sow farms, this virus has a pretty distinct footprint,” Yeske explained. “You almost don’t have to wait for sequencing because you know what it looks like from the clinical signs.”

Symptoms include sows going off feed, abortions, increased sow mortality, increased piglet mortality, increased mummies and high post-weaning mortality.

“One thing that’s unique to this virus is it tends to move quickly through the herds once you see clinical signs,” he added. “You’ll start with four to five animals off feed and then 200 the next day and 300 the next. It marches through the herd quickly.

“The abortions start about the same time the animals go off feed. We’ve seen upwards of 3 to 5 weeks of production aborted and 10% to 20% of the sows dying in 2 to 3 weeks.

“Also, there’s high piglet mortality in the farrowing house…50% up to 80%, which I didn’t think was possible.”

In addition, neither vaccination nor prior exposure to the virus appears to reduce the outbreaks, he added, but it’s difficult to tell with the limited number of herds experiencing an outbreak.

High viremia

The PRRS 1-4-4 variant produces high levels of viremia, allowing it to spread easily in an area, Yeske explained. In addition, a milder winter with overcast, warm weather has helped the virus move around.

An increased number of diagnoses started in October 2020 in the two-state area, beginning with outbreaks in grow-finish sites and moving into sow farms.

“Certainly, the worst breaks have been, like we always see with PRRS, when you have viremic pigs leaving the sow farms,” he added. “But with this virus, we have lateral outbreaks even at the end of nursery with significant mortality.”

Yeske indicated some of the farms that broke were filtered, while others stayed negative even when located next to positive finishing sites and lots of positive pigs.

“Filters continue to show us they help but are not perfect,” he added. “The PRRS viral load is very high. There are lots of opportunities for this virus to get in, and if there’s a weakness, it’s likely going to find it.”

Stabilizing herds

After a 2- to 4-week period where herds experience the devastating losses, farms start to stabilize.

“We see sows start to return to normal,” Yeske said. “We see normal pigs born again but with very low, live born due to mummies, even though total born are still in the 16 to 17 pigs range. There are a lot of mummies on these farms but not necessarily all farms.”

As the herds continue to stabilize, Yeske said they will track them on the PRRS timeline to see if it runs similar to other strains they have dealt with in the past.

Review biosecurity

The big lesson Yeske hopes producers will learn from these outbreaks is the importance of a biosecurity plan that is strictly followed. He urges everyone to review their biosecurity.

“Identify the greatest area of risk in your herd,” he explained. “Risk is how likely something is to come into the herd and then how many times a week do you do that activity. Multiply those two to give you the risk.

“Then improve any weakness in your biosecurity system, and do it sooner rather than later,” he added. “Don’t wait to identify it in your outbreak investigation.”

 

 

Virulent PRRS outbreaks in grow-finish require fast action to cut losses

A particularly difficult variant of the porcine reproductive and respiratory syndrome (PRRS) virus recently hit hog farms in south-central Minnesota. Henry Johnson, DVM, with Swine Vet Center in St. Peter, Minnesota, was called to diagnose and treat the PRRS outbreaks on client farms.

The virus has been identified as PRRS 1-4-4 and, to date, is the most virulent PRRS variant to infect hogs in the US.

“More herds have gotten infected, and this PRRS strain seems to be extremely pathogenic and more prone to airborne transmission,” Johnson said.

When it affects grow-finish units, he recommends immediate and aggressive treatment to reduce mortalities.

First symptoms

“When you walk into a PRRS 1-4-4 outbreak, you see a lot of pigs with varying degrees of respiratory challenge,” Johnson explained. Often, he sees pigs “thumping,” where the animals labor to breathe through airways blocked by bacterial and viral pneumonias.

“Other times, pigs are very, very lethargic because PRRS attacks and disables the whole immune system in pigs,” he said.

An outbreak can be identified early if grow-finish units are tracking water consumption. Pigs will quit drinking first, causing a dramatic drop-off in water usage. This should signal the need to start intensive pig care immediately, Johnson noted.

These symptoms may affect 5% to 25% of the pigs, depending on where they are in the disease challenge.

Diagnose, separate sick pigs

Johnson’s first action is to gather samples and send them to a diagnostic lab. The PRRS virus strain needs to be verified, and secondary bacterial infections identified.

“Get good bacteriology and susceptibility information from the lab, so you can make better microbial decisions and have confidence that you are putting the right medication for the right bug and utilize it appropriately,” he said. “It’s also good, judicious antibiotic use.”

At the same time, he wants to be aggressive and get help started for ailing pigs. He recommends moving critically ill pigs to sick pens for individual care.

“The best thing to do is provide a warm, dry, comfortable area with less pressure and competition for feed, water and space,” Johnson said. “Pigs can recover and subsequently move back to the general population where they are mixed in with other pigs. Then you can cycle other pigs through that sick pen.”

Another immediate action should be to increase barn temperatures, especially for young pigs. Pigs rarely die from being too warm in the winter during the nursery phase but can die of complications from being too cold.

Suppress secondary bugs

“A lot of times with these nasty PRRS [outbreaks], you are already behind the eight ball when you start,” he said. “You will never cure viral disease with an antibiotic. You are just trying to suppress secondary bacterial infections and control them when the immune system is devastated and rebooting after going through the PRRS infection.”

Depending on the herd and challenge, Johnson said they will use different antibiotics and delivery methods. He recommends starting water medication right away to address common secondary bugs like Streptococcus Suis, Glasser’s disease, Mycoplasma hyopneumoniae and Pasteurella.

When pigs are unable to get up to drink, Johnson recommends a mass injection followed by oral antibiotics or water medications.

“A lot of focus for me is to make sure we use the right antibiotics and follow up with caregivers to make sure the pigs that need help are moved and getting the necessary care,” he said.

Even with these care regimens, mortalities can still be high. He estimates as much as 15% mortality can occur.

Biosecurity alert

“When you get a virus that is really severe like this and spreads quickly across multiple production systems and geographies, it is a wake-up call to biosecurity practices in grow-finish,” Johnson said.

If any labor or equipment is shared, make sure all parties involved know what is going on. It’s also good to keep the feed mill in the loop as well.

“It’s a hard culture to establish, but if you are able to reduce a break like this, it demonstrates the importance of keeping our barns clean,” he said.