PRRS Regional Elimination Project – Michigan

Barbara Straw, DVM (extension swine veterinarian) Jerry May (pork educator in Ithaca, Gratiot County) and Beth Ferry (pork educator in Cassopolis, Cass County) explain how a project to eliminate Porcine Reproductive and Respiratory Syndrome (PRRS) is progressing in Michigan in MSU Quarterly Pork Quarterly.
calendar icon 14 July 2010
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Allegan and Ottawa counties are one of the intensive swine raising areas of Michigan. Given the intense production in a relatively small geographical area, similar to other areas of intensive swine production, these farms have had to deal with recurrent PRRS infections. Yet this area, because of a unique combination of regional barriers – both natural and man-made – and a history of producer cooperation holds promise for the elimination of the disease.

MSU Extension and veterinary practitioners in the area were awarded a grant to undertake a PRRS Regional Elimination Project in this region. This USDA/NPB grant covers initial testing to determine herd status and also provides support for veterinary assistance in developing herd stabilization and elimination plans.

A unique feature of this area is the existence of substantial natural and man-made barriers. To the west (the direction of the prevailing wind) is Lake Michigan. To the south is the Allegan State Forest and to the east is a large urban area (Grand Rapids). These barriers serve to isolate the area from outside infection. Also, the bulk of the pigs that are finished in this area are derived from nearby sow farms, rather than being shipped in from outside sources.

Goals of the Project

  • Phase 1
    • Identify all the sites in the area containing pigs
    • Document the prevalence and severity (reflecting any on-going outbreaks) of PRRS infection in the area
  • Phase 2
    • Involve producers and generate interest and cooperation among them to address the challenge
    • Facilitate communications among participants and provide a forum for sharing current program progress.
    • Compare strains of PRRSV to detail the source of infection for herds – whether from the sow herd supplying pigs or regional spread
  • Phase 3 – Assist producers to stabilize and then eradicate PRRS from breeding herds.

Update - Year One - June 2009 to May 2010

Identification of farms in the Allegan-Ottawa area

Participating veterinarians supplied address of clients’ farms in the area which was followed up with GPS satellite imaging to identify all farm buildings in the region and then collaborated with a knowledgeable local person to verify the identity of all locations in respect to the kind of animals housed. Swine and poultry facilities were given project ID numbers. A four-foot by eight-foot aerial map of the area has been constructed along with one in a GPS mapping programme (below).


The veterinarians serving herds in the area have all joined in carrying out the project. Hamilton Feed Co has graciously provided the project group with a facility for holding meetings. Boehringer Ingelheim has made available two of its veterinarians who have experience with other regional eradication projects in Chile and Mexico, and also provided a GPS mapping system. The USDA Wildlife Service has shared samples from feral hogs collected for the pseudorabies control programme.

PRRS status

Veterinarians provided results of diagnostic testing done either as a survey procedure or part of a control program. Positive farms through history or ELISA testing were followed up with PCR testing to determine strain genotype. Farms and status are shown here.

Additional surveillance

In conjunction with David Marks of the USDA Wildlife Service, 19 feral pigs that were captured or shot in Michigan were tested for PRRS. Samples were tested for PRRS antibody using an ELISA test. Results are shown below.

While the ELISA test analyzes for antibodies against PRRS virus, not the virus itself, these results indicate that these feral pigs have never been exposed to the virus and therefore currently are not a threat for spread of virus. Three of these samples tested positive for pseudorabies.

Participant education

Several producer meetings have been held to promote the concept of regional eradication and report preliminary results. Programme concepts regarding the nature of the disease, pertinent animal movement strategies and factors influencing the survival and spread of the virus have been covered. Producer concerns have been incorporated into the program. Producers have specifically requested veterinarians to develop truck sanitary procedure protocols for the region.

PRRS has been determined to cost the US swine industry $5 billion per year, or $1.5 million per day due to decreases in litter size and reduced growth rates. Previous control programs (such as hog cholera, brucellosis, pseudorabies) have relied on regulatory and legal support. The PRRS Eradication Program is voluntary and does not rely on regulatory mandates and penalties. For this to be program to be successful, individuals involved have to appreciate that they are the decision makers and enforce the critical policies necessary to complete eradication themselves. Producers and veterinarians involved in this pilot project do appreciate that they are the decision-makers and enforcers.

Genome dendogram

PRRS is caused by an RNA virus that is able to frequently mutate. The mutations can be documented through an analysis which identifies the sequence of RNA material in a specified segment of the virus. On an individual farm, the virus can mutate enough that the earlier immunity is no longer effective and a 'new' outbreak occurs. Also whether, on two different farms, if the virus originated from the same source it can be determined by examining the virus genome. Farms in the project area that were positive for virus were sampled to recover virus for genome sequencing.

Future Directions

Experience with managing the project in the first year has identified some strategy/approach/policy that would assist in making the programme advance.

  • The primary item needed is a close-by/neighbouring regional coordinator. A person who is familiar with, trusted and well-accepted by the community who would be responsible for reminders and updates documenting the cost of infection and strategies for control, as well as promoting continuing efforts at herd as well as regional control.
  • A web site
  • Strategies for data handling
    • Premise ID
    • Automatic release of diagnostic lab reports to the system
  • Continued surveillance
  • Estimation of aerial infection pressure by monitoring negative pigs moved into the area.

Further Reading

- Find out more information on porcine reproductive respiratory syndrome (PRRS) by clicking here.

July 2010
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