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New PRRS research shows a need for a united shield

Porcine Reproductive and Respiratory Syndrome (PRRS) cost hog farmers $1.8 million daily in veterinary treatments. With the unpredictable nature of the virus, researchers are continuously searching for an effective solution beyond a vaccine.

"The virus we see today is not the same one we had 31 years ago. It keeps evolving," says Daniel Linhares, a veterinary diagnostic and production animal medicine professor at Iowa State University.
Since 1992, several variants of PRRS have swept through swine barns in many states, including Iowa, Missouri, and Illinois. Current strains, C-124 and C-144, are more pathogenic than past strains. 

"We have to keep learning, and we can't stop because the virus doesn't," says Linhares. 

Currently, Linhares and his team at Iowa State University (ISU) are studying the frequency of the virus's whole genome. The hope is to develop a method to predict the evolution of the genome and prevent the spread of a new strain in a swine herd, Linhares adds. 

How farmers and veterinarians handle PRRS 

PRRS spreads quickly by air or direct contact with other pigs, and indirectly from equipment, year-round. The virus infects pigs' lungs and reproductive organs. PRRS also makes pigs more susceptible to several other viral and bacterial pathogens. 

In addition, the virus can mimic the symptoms of other diseases, such as poor growth performance, feed efficiency, and livability, which can make diagnosis challenging and costly. This copy-cat like behavior of the virus has led to various response and recovery plans from veterinarians across hog barns. 

"If you ask 10 different veterinarians how they control PRRS, you will get 15 different responses," he says.

For Linhares and other ISU researchers, the first step to a better-united front against PRRS started with the PRRS Outbreak Management Program (POMP) in 2019, collecting data from veterinarians across the Midwest and learning how they recommend a response to an outbreak on a farm. 

By putting the program’s data into benchmark, POMP’s results showed how divided the industry is in combating PRRS. 

Some veterinarians choose to eliminate it, while others prefer to control it at a low frequency depending on the type of operation and the location. For example, POMP's research found that most breeding swine farms prefer to keep PRRS at a low frequency because the chances of re-exposure are higher, particularly if the farms are near other swine operations. 

"However, keeping the virus at low prevalence in breeding herds helps it leak down to grow-finish pigs, where the virus replicates the most," Linhares says. 

Today, most producers and veterinarians have vaccination programs to reduce significant production losses such as weight loss or sudden death, according to the report. 

But the vaccine is not a silver bullet to prevent the circulation of new strains.

"Immunization works to mitigate the losses. It's not the only thing needed, but it's a crucial piece to the equation," Linhares says. 

Eventually, the industry will need a product or practice that will eradicate the virus permanently in swine herds, according to Linhares. But that has yet to happen. 

The fight continues 

There are no plans to stop POMP. The bigger POMP's database gets, the better analysis Linhares and his team of researchers will have at their fingertips to develop the next steps or forecasting trends of the evolving virus. 

Linhares also expects farmers and veterinarians will turn to the database when they are creating a plan for a speedy recovery for infected pigs.

But, Linhares believes the POMP results will force farmers and veterinarians to find a singular, permanent cure for the virus. 

"Farmers will soon realize they can't live with PRRS anymore," he says. 


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