Reducing PRRS outbreaks by using air filtration: What you need to know

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Jeff Feder, DVM, with Swine Vet Center (SVC), has spent 15 years fine-tuning filtration systems in client hog barns. Today, Feder has records to prove air filtration does reduce outbreaks of disease like porcine reproductive and respiratory syndrome (PRRS).

Looking back over records from 85 farms with filtration, he found these farms prior to filtration were breaking with PRRS over three times more frequently than with filtration.

“Many of the early farms were located in very pig-dense areas and, as a result, were having more breaks with PRRS and other respiratory pathogens than we would like,” reported Feder who works from SVC’s clinic in St. Peter, Minnesota.

“We looked at PRRS break rates to understand if we were moving the needle and changing the number of PRRS breaks…We were able to cut those breaks by a third.”

Explaining filters

Air filtration systems are expensive. Feder said the early ones cost $150 per sow space, but today are at least three times that amount. They can be installed on new and existing facilities.

The filters are key to keeping pathogens out of hog buildings, and Feder has learned which ones are best. Fiberglass filters retain efficiency much longer than synthetic filters. He took used filters of both types out of hog buildings to be tested for filtering efficiency at certified labs.

“Often clients budgeted for those filters to last 2 to 3 years,” he said. “What we found was…the fiberglass filters will maintain their efficiency for a long time.”

Feder also recommends using fiberglass filters with a minimum efficiency reporting value (MERV) of 15 or 16. This means 92% to 95% of the very smallest particles will be removed by the filter.

“Typically, in a filtration system in a pig barn, you have what I call the main filter or end filter, and most commonly those have MERV 14, MERV 15 or MERV 16,” he explained. “Then they have a type of prefilter like the furnace filter in your home. The goal of the prefilter is to take out the large dust particles so those particles don’t plug up our expensive end filters.”

Impact on existing ventilation

Most of the filtration systems used by SVC clients are retrofits put on existing ventilation systems in hog barns.

“One common scenario in the top-down ventilation system is to simply install the filters over the top of the ceiling inlets, and that is your point of filtration,” Feder explained. “In tunnel-ventilated barns, you build filter banks in front of the cool cells before air enters through the end of the barn.”

Other modifications may be needed to accommodate air filtration. Often existing fans don’t move as much air as before the filters were added due to higher static pressure. Keeping fan shutters and blades clean may be enough to increase their efficiency. Otherwise extra fans can be installed to boost airflow.

When cool cells are involved, Feder recommends making sure they work correctly and are on a timer. Airflow filtration is reduced when water is running through the cell pads.

Negative versus positive pressure

Most existing hog facilities are negative-pressure ventilation systems, according to Feder. Some new buildings with filtration use positive-pressure systems.

“The benefit of the positive-pressure system, at least in a filtration scenario, would be if there are any leaks in the barn, those leaks are getting pushed out so it’s filtered air being pushed out,” he explained. “On the flipside in negative-pressure systems, if there are leaks, it’s unfiltered air leaking into the barn and that’s not a good thing.”

While the positive-pressure system sounds better, he cautions that ventilation rates run higher which can lead to higher LP usage rates in colder climates. In addition, there’s more potentially contaminated air being pushed into the barn, which could be a problem.

“Negative-pressure systems run at much lower ventilation rates in the winter, but we do have to worry about leaks,” Feder said. “We’ve spent a lot of time over the years figuring out how to build them tighter with different construction ideas using foam and caulk…to get these barns very tight.”

Air filtration works

“I completely believe in filtration and think that it’s a good tool to use, especially if you’re in a pig-dense area,” Feder said. “I would just caution, though, that it’s like any other tool that has to be managed.

“Along with filtration come some additional things that need to happen. Make sure we’re monitoring the performance of the filters, looking for air leaks on farms and we do all the other things for biosecurity correctly as well.”



Is reducing inflammation key to improving PRRS control?

By JoAnn Alumbaugh
Farm Journal’s Pork

Porcine reproductive and respiratory syndrome (PRRS) continues to be a critical concern to the U.S. pork industry. The combined production losses associated with PRRS in breeding and growing-pig herds are estimated at more than $663 million, and that doesn’t include secondary infections.

There is usually a high degree of interaction between pathogens, and it has been shown in previous studies that a reduction in PRRS also causes a reduction in the impact of co-infections like Streptococcus suis, Haemophilus parasuis, Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae and Salmonella spp.

PRRS is a viral disease, yet it is known to cause considerable inflammation in the respiratory system. In PRRS-infected gilts, endometrial inflammation and vasculitis increased progressively from 2 to 14 days post-inoculation.

Inflammation may be one of the factors associated with abortions in the presence of PRRS as well. Inflammation at the point of attachment of the uterus with the placenta may disrupt the fetus, resulting in loss of the fetus or the formation of the mummy, says Paul Yeske, DVM, with the Swine Vet Center in St. Peter, MN.

“There are certainly some things we don’t understand, and we have changed our thought processes on how we can manage these things,” Yeske says, adding that PRRS-infected pigs are more vulnerable to secondary bacterial infections requiring an antibiotic therapy, so having an antibiotic and an anti-inflammatory can be a good combination.

“The inflammatory response is a call to action of the whole pig,” says John Deen, DVM, PhD, professor at the University of Minnesota. “It affects behavior, reproduction, metabolism and even the pig’s ability to survive. It has to be taken seriously, especially in the face of a disease like PRRS. We need to provide extra care for animals to recognize when they cannot cope with the insults they have in front of them.”

Inflammation is usually associated with bacterial infections; in which case an antibiotic would be used to help reduce the inflammation that accompanies an infection. Now, researchers are learning more about the role of inflammation in viral infections like PRRS.

Research findings

Andre Buret, PhD, a professor in the department of biological sciences at the University of Calgary, Canada, has done extensive research on the immunomodulation properties of an injectable antibiotic on pigs infected with PRRS. Immunomodulation refers to a change in the body’s immune system, caused by agents that activate or suppress its function.

While no vaccine against PRRS provides 100% protection, some injectable antibiotics have been shown to exhibit potent immune-modulating effects — that is, they activate, boost or restore normal immune function once it’s damaged. That in turn can help better withstand the inflammatory responses associated with PRRS.

“Treatment options to control PRRS outbreaks are limited, and the efficacy of vaccines is thwarted by the antigenic variability of PRRSV,” Buret says.

He explains that PRRS can create immune dysregulation — a breakdown of the immune system, in other words — that makes the host more susceptible to opportunistic pathogens. Disease severity is closely related to the ability of the virus to disrupt the functions of the macrophage — a large white blood cell that is an important part of the immune system — and induce inflammation, he adds. For those reasons, he theorizes that targeting inflammation with an antibiotic used for bacterial co-infections might be a critical element in managing the costly PRRS virus.

In laboratory experiments conducted by Buret and his team, using an injectable macrolide antibiotic did not change intracellular or extracellular viral titers, nor did it alter expression of the viral receptors (CD163 and CD169) on porcine macrophages. It did yield other benefits, however.

“In contrast, [the antibiotic] exhibited potent immunomodulating properties, which therefore occurred in the absence of any direct antiviral effects against PRRSV,” Buret says. “These data demonstrate that [the injectable antibiotic used in the study] inhibits PRRSV-induced inflammatory responses in porcine macrophages and protects against the phagocytic impairment caused by the virus.”

The antibiotic was also shown to inhibit the production of pro-inflammatory mediators (CXCL-8, LTB4) and promote the production of pro-resolving mediators (LXA4), Buret explains.

Research evolution

Buret’s work with pigs and PRRS marked an evolution in the battle against the PRRS virus.

“We spent two and a half years of research…and we were able to demonstrate [the antibiotic] may very well have benefits in the context of PRRS viral infections based on what we discovered,” he says. “It seems to disarm the ability of the virus to prevent host immunity to clean up bacteria in the lungs.”

If a producer has the background of a viral infection like PRRS on the farm, the engulfment of foreign particles by the macrophages is compromised. As a result, the lung cannot clean itself anymore and the pigs are more prone to secondary infections, Buret says.

“The virus alone triggers an inflammatory response and impairs phagocytic clearance by macrophages. We observed that this type of antibiotic protects against both effects. It’s really one discovery leading to the next,” he adds.

“As it turns out, our discoveries have established for the first time that controlling inflammation at the same time as you control the microbe is the best way to deal with these diseases clinically,” Buret says.

Anecdotal evidence

Swine Vet Center’s Yeske recalls working with a client who had a PRRS break in a herd that was being treated with an antibiotic as part of a Mycoplasma hyopneumoniae (M. hyo) elimination program.

“We were treating the herd with an antibiotic [for M. hyo] and [it] broke with PRRS in the middle of the M. hyo elimination,” Yeske says. “You never know if an outbreak is going to be as severe from herd to herd as other similar outbreaks, even if the virus is similar, but we saw much less of an impact in this particular case as we went through and treated the animals for the M. hyo elimination. We had fewer clinical signs than we would have expected to see, based on other very similar farms that had essentially the same virus. It does make us think about some of the mechanisms that may be going on [associated with inflammation].”

Because PRRS is often a co-infection with bacterial infections that also cause inflammation, antibiotic treatments for M. hyo might yield secondary benefits that make the effects of PRRS less severe.

This is a new approach for veterinarians to consider when PRRS is present in herds infected with swine respiratory disease, Buret says. The antibiotic controlled the bacterial infection, which in turn helped to not only reduce inflammation but also the host’s response to it — a process that, if left unchecked, ultimately causes pulmonary failure and death.

“Research in live pigs is warranted to assess the potential clinical benefits of this antibiotic in the context of virally induced inflammation and tissue injury,” Buret says.

(Read the article at Farm Journal’s PORK.)