NC_OLD229: Porcine Reproductive And Respiratory Syndrome (PRRS): Mechanisms Of Disease And Methods For The Detection, Protection And Elimination of the PRRS Virus
Statement of Issues and Justification
The United States swine industry is at a crucial economic crossroads. Increased production costs and declining prices have severely impacted many swine operations in recent months. In addition to market and price factors, pork producers are continually hampered with infectious disease problems that continue to increase production costs due to morbidity, mortality and treatment. Viral diseases of swine (transmissible gastroenteritis virus, pseudorabies, rotavirus, swine influenza, porcine reproductive and respiratory syndrome virus and the emerging circovirus) represent the greatest challenges in the control and prevention of infectious diseases in this species. When pseudorabies eradication programs were implemented in the 1980s, it was thought that one of the most devastating diseases in the U.S. swine industry would shortly be eradicated. Although the process has taken longer than expected, the U.S. is on a timetable to eradicate this disease in the next few years. However, our confidence in reducing losses in swine due to viral diseases was shaken with the appearance in 1987 of porcine reproductive and respiratory syndrome (PRRS), which is now the most important viral disease of swine in North America.
Twelve years have elapsed since the first report of PRRS in 1987 (Keffaber, 1989) and more than seven years since the discovery of the virus that causes PRRS (Wensvoort et al, 1991; Collins et al, 1992; Benfield et al, 1992). Despite the resolution of the etiology of PRRS, many aspects of the basic mechanisms of pathogenesis, immunity and protection against this virus remain unknown. Research on PRRSV in the U.S. has also been uncoordinated, isolated and influenced by aggressive industry interests that succeed in dividing and isolating efforts of individual research and academic groups through implementation of exclusive confidentiality agreements, proprietary and patent rights between individuals and institutions. Hopefully, this regional project proposal represents an alternative to this trend. This project involves scientists from eleven AES (IL, IA, KS, MI, MN, MO, NC, ND, NE, OH and SD) conducting collaborative and prioritized research on various aspects of PRRSV.
JUSTIFICATION: Since the initial description of "mystery swine disease", now known as porcine reproductive and respiratory syndrome (Keffaber, 1989), this viral disease has become the most economically devastating disease in the U.S. and other swine- producing countries in the world. Reproductive failure and respiratory disease are the principal outcomes following PRRSV infection (reviewed in Benfield et al, 1999; Rossow, 1998; Zimmerman et al, 1998). PRRS appears prior to breeding and continues to exert its negative economic impact through farrowing, nursery, and finishing units. Respiratory disease in infected neonates is severe, frequently resulting in acute respiratory distress and death. The reproductive form of PRRS appears following the infection of pregnant gilts or sows and results in abortions, stillbirths and weak, live-born pigs. Mortality in weak, live-born pigs and pre-weaned pigs can reach 100% within 3 weeks after infection. PRRSV can also retard growth and lengthen the time to market weight in grow/finishing pigs. Estimated monetary losses due to PRRSV outbreaks range from $100 to $510 per inventoried female (Hoefling, 1992; Poison et al, 1994) or $25,000-$127,500 and $100,000-$510,000 in a 250 and 1,000 sow herd, respectively. Dee and Joo (1993) estimated that PRRSV infection delayed marketability for 14-30 days at an additional cost of $7.50 to $15.00/pig marketed. Since PRRSV is a worldwide problem its overall economic impact is considerable.
Even after 12 years of study the name "Mystery Disease" is still an appropriate description of PRRS. Once the viral etiology was initially established in 1991 by investigators in Europe (Wensvoort et al, 1991) and later in the United States (Collins et al, 1992; Benfield et al, 1992) research progressed significantly towards finding a resolution to this problem. The release of the first live-attenuated commercial vaccine in June 1994 was hailed as a significant achievement and a hoped for solution for an industry that was experiencing acute and chronic infections of PRRSV in breeding, weaned and finishing pigs. However, the recent outbreak of severe "abortion storms" in southeastern Iowa in 1996-1997 were also believed to be caused by a "new and perhaps different strain of PRRS virus" (Epperson and Holler, 1997; Halbur and Bush, 1997). This new outbreak of PRRS and the continuing endemic persistence of PRRSV in some herds frustrated producers and veterinarians and sent many looking for alternative but untested methods to control this disease.
There is a renewed demand within the swine industry for the development of management practices that will prevent, control or eliminate PRRSV, including improved methods of prophylaxis and immunoprophylaxis, as well as, methods to detect acute and persistently infected swine within large herds. Meeting these producer demands requires us to increase our knowledge of the PRRSV including: 1) molecular characterization of translated and untranslated regions of the genome, 2) understanding interactions between host and virus that lead to pathogenesis, persistence, and immunity, 3) understanding of the epidemiology of PRRS and 4) development of better methods to diagnose and detect the disease and the virus.
PRRS is a complicated disease and a difficult virus to characterize and understand. We realize the best hope for the control, and elimination of PRRS is collaborative, multidisciplinary research on various aspects of the disease. Thus, there is a need to formalize cooperation and collaboration between AES sites to maximize these research efforts. The accelerated elimination of pseudorabies in most North Central and other states offers an opportunity to shift resources and personnel from a disease that is controlled and almost eliminated to one that has emerged as the most economically important viral disease of swine. The Regional Project format is the prototype for the organization of cooperative projects between AESs. The eleven stations in this proposal have a history of collaboration or are planning future collaborative efforts to answer questions related to basic mechanisms of the pathogenesis and control of PRRS. The investigators from each participating AES stations have many years of experience in PRRS research and have published widely on the topic.
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