West Michigan PRRS Area Regional Control Project Update

by 5m Editor
7 June 2011, at 12:00am

A review of the progress in PRRS Area Regional Control (ARC) project in West Michigan, which was cordinated by Michigan State University Extension by Beth Ferry, MSUE Extension Educator at Cassopolis in the latest issue of Pork Quarterly from MSU.


Porcine reproductive and respiratory syndrome (PRRS) is an economically significant disease in swine herds that has been estimated to cost the US pork industry approximately $560 million dollars a year. Farms that have been exposed to the virus have documented costs of up to $260 per sow, as result of virus presence in their herds. The estimated profit difference for farms selling pigs without the virus is $12 to $15 dollars per pig. The combinations of these economic differences, producer desire to produce high health pigs and the need to improve productivity has prompted Michigan State University Extension to coordinate a PRRS Area Regional Control (ARC) project in West Michigan, focusing on stabilising the area and eradicating the virus.


In September 2008, local veterinarians and Michigan State University Extension staff introduced the concept of area regional control for the PRRS virus in West Michigan. With the help of local producers, allied industry, veterinarians and MSU Extension, this project has continued to make progress and is making strides in the area of regional control. The West Michigan ARC project was initially awarded a USDA/NPB grant to help identify and map farms in the Allegan/Ottawa county project area, document the prevalence of the disease in this area and help support veterinary assistance for developing herd health plans.

Currently, the project has been awarded a PRRS CAP II/USDA grant to continue the work towards regional control of the disease. The project has also garnered support from Boehringer Ingelheim, Hamilton Farm Bureau and the Michigan Pork Producers Association, along with strong collaboration with local producers.

Project Milestones

As the project moved forward specific steps were accomplished by those involved with the project. A producer-led steering committee of 10 producers was formed to help guide the project and make recommendations for all producers in the area. This committee meets six times a year to help give direction to the project and make decisions concerning the methods in which regional control can be accomplished.

The continued surveillance and documentation of the PRRS status of farms in the area is also being conducted by producers and local veterinarians. Project coordinators, with the assistance of Boehringer Ingelheim are able to correlate this information with a GIS mapping system, which gives visual illustration of the disease prevalence and transmission of the virus and is beneficial to producers when deciding what disease control methods to use. With producer and veterinarian input, the steering committee has developed recommendations for the frequency of testing as producers’ complete surveillance of the disease during their herd clean-up.

The steering committee has also been working to identify areas of education that will benefit the project. It has been determined that a major emphasis will be placed on biosecurity education components for producers and swine farm employees. Efforts to provide educational opportunities for producers have been made, including a recent PRRS biosecurity and transmission presentation by Dr Scott Dee from the University Of Minnesota. Local producers also had the opportunity to complete a Production Animal Disease Risk Assessment Program (PADRAP) to gain a better understanding of the biosecurity risks present for their facilities. This information was summarised and an explanation of the regional PADRAP results was presented by Dr Laura Batista from Boehringer Ingelheim.

Individual assessments are available for each participant to review with their consulting veterinarian. Plans for a vendor training on biosecurity protocols are being made for summer 2011 by the project coordinators and efforts will be made to standardise protocols for venders servicing the area.

Additional Resources

As the West Michigan PRRS ARC project moves forward, other resources have become available to swine producers. The American Association of Swine Veterinarians (AASV) and the United States Department of Agriculture PRRS-Coordinated Agricultural Project recently released standardise terminology for the PRRS virus in an effort to enable communication between producers, veterinarians and industry members and to aid in the regional control efforts.

A combination of diagnostic results and information from production records provide the support material to classify herds. The absence of clinical signs in a herd can help characterise a status but must be combined with testing results to support a negative herd status.

For breeding herds, there are four possible classifications. These classifications are summarised in the tables below; tables are taken from Holtkamp et al., (2011) recently published in the Journal of Swine Health and Production:

Table 1. Breeding-herd classification for porcine reproductive and respiratory syndrome virus (PRRSV) according to shedding and exposure status
Herd category Shedding status Exposure status
Positive Unstable (I) Positive Positive
Positive Stable (II-A) Uncertain Positive
Positive Stable (II-B) (Undergoing Elimination) Uncertain - undergoing elimination Positive
Provisional Negative (II) Negative Positive
Negative (IV) Negative Negative

The herd classifications for the PRRS virus are determined by taking into consideration both the exposure status of the herd and instance of shedding the virus. The preferred testing method to determine shedding is by polymerase chain reaction (PCR) and exposure instance can be determined by antibody testing, enzyme-linked inmmunosorbent assay (ELISA).

The PRRS virus shedding status is classified as positive, negative or uncertain. A positive shedding status can be documented by diagnostic evidence and clinical signs in the herds. A herd in which the shedding status has yet to be determined is also labelled as positive. If a farm is considered to have a negative shedding status, the diagnostic information confirms the absence of viral shedding in the herd. If a herd is currently involved in a clean-up programme to eliminate the PRRS virus on their farm or if a negative shedding status has not been confirmed with appropriate sampling and testing instances, the herd is then classified as uncertain.

Farms that only have growing pigs follow a different classification table, which is seen below:

Table 2. Criteria for and summary of supporting evidence required for growing-pig herd classification for PRRSV
Herd category Criteria Supporting evidence required
Positive Any virus detected on the site, along with clinical signs consistent with PRRS. Herds that do not meet the criteria for Negative are Positive by default. None required. Non-tested herds are Category I by default. Detection of virus in any tissue and presence of clinical signs would confirm status.
Negative None positive by ELISA after ruling false-positives. Test serum from growing pigs by ELISA. No positive results, after ruling out false-positives, and no clinical signs consistent with PRRS observed in growing pigs.
PRRS(V) = porcine reproductive and respiratory syndrome (virus).

Herd can be defined as positive or negative. Positive herds have a positive shedding status and/or have been exposed to the virus. This also becomes the default classification if there is not enough diagnostic evidence to qualify the herd as negative. A negative growing pig herd has a negative shedding and exposure status.

Future Direction

As the West Michigan ARC PRRS project continues to gain momentum and becomes more focus on the goal of eliminating the PRRS virus in the Allegan and Ottawa county area critical steps that need to be taken have been identified by producers, allied industry, consulting veterinarians and MSU Extension.

Producers have been requested to start forming herd health clean-up plan with their veterinarians that designate short and long term goals for their herds. Emphasis on increased biosecurity education and the development of regional protocols are areas in which the project will focus on.

The project is also committed to gaining a further understanding of the trucking routes, methods and issues for the area, along with increasing the knowledge about aerial transmission of the virus.

Finally, surveillance and monitoring of the disease will have increased importance as the project progresses and producers work to stabilise and eliminate the virus in their herds.

If you have any questions about the project or would like more information about the ongoing work in Allegan and Ottawa counties, please contact Beth Ferry, Michigan State University Extension educator at [email protected] or 269-445-4438.


Holtkamp D.J., Polson D.D., Torremorell M., et al. 2011. Terminology for classifying swine herds by porcine reproductive and respiratory syndrome virus status. J Swine Health Prod. 19(1):44–56.

Further Reading

- Find out more information on PRRS by clicking here.

June 2011