Evolving PRRS Maintains Challenge for Producers

US - A new strain of Porcine Reproductive and Respiratory Syndrome (PRRS), under observation by the University of Minnesota Veterinary Diagnostic Lab since the Spring of last year, is likely to keep the virus bubbling on US pig units well into 2008.
calendar icon 22 January 2008
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"The difficulty with PRRS is it's always changing, so you really have to - from a standpoint of vaccinating or treating - consult with your local veterinarian, because each herd might have just a slightly different isolate," said Mark Whitney, University of Minnesota Extension swine specialist.

And Dr. Bob Morrison, a veterinarian and professor at the University of Minnesota College of Veterinary Medicine, agrees. In a recent article in Minnesota's Farm Guide, he says that there are always new strains of PRRS emerging and this is where the difficulties in controlling the disease lies.

The PRRS virus is constantly mutating. The changes in the characteristics can be enough to warrant using a vaccine, but the challenge comes when another new strain develops.

"Basically it can act like a completely different organism," said Whitney. "There are some commonalities or similarities, but the new strain can be genetically different enough."

Clinically Severe

The new strain, referred to as "1?2", is slightly different from previous strains, because it is identifiable and clinically very severe, said Dr. Bob Morrison, a veterinarian and professor at the University of Minnesota College of Veterinary Medicine.

The PRRS virus can cause stillbirths, mummified piglets, third trimester abortions and elevated pre-weaning mortality. It can also produce a respiratory form in growing pigs that weakens immunity and allows a number of pathogens to emerge in the nursery and grow-out phases.

"It's not unique that this is a new strain of PRRS that has come about and that it is spreading. There may be some producers that are seeing the "1?2" strain, but also other strains of PRRS as well," said Whitney.

However, what is unusual is that veterinarians and producers are following the course of the disease and communicating about this particular strain of PRRS.

"Very similar to most viruses, they like colder temperatures and also they need moisture. We get into late fall and winter and that's an ideal time for those viruses to stick around in the environment longer and cause problems," said Morrison.

Morrison says that members of the hog industry are learning how to work together to keep out PRRS. In two regions of Minnesota - Stevens County and the eastern portion of Rice County - producers and veterinarians are working together to communicate when PRRS shows up.

This is important because a hog farmer may eliminate the PRRS virus in their breeding herd, and although they have very good biosecurity, the herd sometimes becomes infected again.

"Producers are learning to work together and are making good progress," said Morrison. "We want every producer to do as much biosecurity as they can to keep PRRS out."

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