According to the National Pork Producers Council (NPPC), PRRS is among the most costly diseases facing the swine industry today. Economic costs of PRRS virus infection include increases in infertility, abortions, secondary infections, and mortality. There are decreases in feed conversion and growth rate, production flow is disrupted and diagnosis, treatment, control and prevention costs are increased (Table 1).

PRRS virus also has emotional and political effects on the industry worldwide. Movement of animals, semen and meat is affected, adversely impacting international commerce. Also, PRRS virus infection increases financial risk, thereby contributing to the economic uncertainty of swine producers. For the aforementioned reasons, PRRS has gained considerable attention and notoriety throughout the swine industry and research community.

PRRS virus is an arterivirus tentatively classified in the family Arteriviridae. The virus closely resembles other arteriviruses including equine viral arteritis virus, lactate dehydrogenase elevating virus, and simian hemorrhagic fever virus. There are two strains of PRRS virus worldwide, the European (prototype strain - Lelystad) and the North American (prototype strain - VR-2332) strains. Although these virus strains share a common group antigen and cause similar reproductive and respiratory diseases, they have considerable genetic and antigenic differences. To date, there is no evidence of a Lelystad-like strain in the United States (Eric Nelson, South Dakota State University).

We have made considerable progress understanding the pathogenesis of PRRS virus (Figure 1). However, the biology of this virus is complex, consequently, much remains to be learned.

The American Association of Swine Practitioners (AASP) in 1995 established a PRRS subcommittee to help disseminate PRRS information and assist the National Pork Producers in establishing research priorities. Committee membership includes swine practitioners and researchers from throughout the United States and Canada (Table 2). Reports on the Laboratory Diagnosis of PRRS and on the Control of Porcine Reproductive and Respiratory Syndrome (PRRS) Virus have been published in the January and March issues of Swine Health and Production, the Journal of the AASP. The committee plans to rapidly disseminate recent PRRS research and continuing education information.

The National Pork Producers Council sponsored a PRRS Research Summit on April 4, 1996. Researchers from throughout the United States exchanged results and helped establish future research priorities. It was announced that the NPPC has allocated $240,000 for PRRS research during 1996-97. Approximately eight PRRS research projects of $30,000 each will be funded. A call for proposals will be made in the near future, proposals will be peer-reviewed, and funds will be awarded by late summer or early fall of 1996.

The following list provides a brief summary of research needs as defined during the NPPC PRRS Research summit.

• A need to standardize PRRS testing methods among diagnostic laboratories.

• A need to establish a central repository for PRRS virus isolates and reagents to be shared among PRRS researchers.

• A need to expand the number of field based research projects.

A need to...

• establish the duration of protective immunity after vaccination;

• determine the effects of inoculum dose and administration route on the immune response;

• determine if immunotolerance occurs;

• determine the effects of PRRS vaccination on field PRRS outbreaks;

• develop techniques to measure protective immunity;

• understand the maternal influences on vaccination response.

Pathogenesis:

A need to...

• understand the persistence of PRRS virus... How long does PRRS virus persist and in what cells? Is there reactivation of PRRS virus shedding? How stable are PRRS viruses in persistently infected animals?

• understand concurrent infection of PRRS virus with other agents...Does PRRS virus predispose pigs to secondary infections? Are co-infections more severe?

• determine the effects of PRRS virus on farrowing rate, especially during early gestation.

A need to ...

• establish a differential serological test so vaccinated animals can be distinguished from unvaccinated animals;

• develop rapid/low cost virus detection methods;

• determine PRRS risk factors;

• better understand PRRS virus transmission - How to keep PRRS from entering a herd (persistency & environmental stability of PRRS virus);

• establish the stability of PRRS virus in raw and extended semen.

Figure 1

Table 2