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Why do summer PRRS breaks last longer than winter breaks?

Summer outbreaks of porcine reproductive and respiratory syndrome (PRRS) take 15 weeks longer to stabilize than PRRS outbreaks beginning in the winter, according to data from the Morrison Swine Health Monitoring Project (MSHMP).

“We had around 35 weeks for the time to stabilize [PRRS] with winter and autumn breaks, and around 50 weeks for summer breaks,” Juan Sanhueza, DVM, PhD, post-doctoral associate, University of Minnesota, told Pig Health Today

“It’s a large difference.”

This trend primarily occurred in the hog-dense areas of Minnesota and Iowa.

Change in weather?

The MSHMP data also holds a possible answer to why summer PRRS breaks take longer to eliminate than winter PRRS breaks.

“We’re seeing in the data that summer breaks [at first] are achieving stability at a similar rate with winter breaks in time,” Sanhueza said. But then progress toward stability stalls. This time period coincides with the arrival of winter.

“We don’t know if it is the temperature that drops, the ventilation that drops, or what factors are involved,” he said. “But it seems that during winter, this PRRS virus is able to linger in the sow farm until the next season — spring or summer — when the farm can perhaps finally get rid of it.”

The MSHMP data also shows the type of PRRS virus is associated with increased time to stability. Outbreaks caused by PRRS virus 174 took longer to reach stability, Sanhueza reported.

Filtered farm connection?

The data on PRRS outbreaks exposed other questions. For example, the data showed more summer outbreaks of PRRS in areas with a higher density of filtered farms.

“Something may be happening during the summer in filtered farms that makes them more prone to have a PRRS outbreak,” Sanhueza said. “Could be they are replacing filters at that time or they stop filtering in the summer.”

Another observation was the high rate of outbreaks in some swine-dense areas but not all of the high-dense areas. Something other than pig density is driving the higher rate of PRRS outbeaks, he theorized.

The next step for Sanhueza is identifying all the factors to help growers get rid of the PRRS virus in a shorter time, especially for the summer outbreaks. 

Posted on April 24, 2019

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Challenges associated with controlling porcine reproductive and respiratory syndrome virus (PRRSV) have resulted in the increased use of molecular diagnostic tests and sequencing, according to Phillip Gauger, DVM, PhD, Iowa State University.

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