|Halbur, Pat - IOWA STATE UNIVERSITY|
|Sorden, S - IOWA STATE UNIVERSITY|
Submitted to: Swine Disease Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 30, 1997
Publication Date: N/A
Technical Abstract: Management practices such as replacement stock acclimatization, nursery depopulation, all-in-all-out pig flow, and vaccination have generally been successful in minimizing losses associated with porcine reproductive and respiratory syndrome (PRRS). In the last quarter of 1996 and the first quarter of 1997, unusually severe disease outbreaks described as "atypical PRRS," "severe acute PRRS," or "Swine Abortion and Mortality Syndrome" (SAMS) were reported and investigated by practitioners, diagnosticians, and researchers. Although these cases were relatively few in number, several aspects called particular attention to the episodes: incidence of abortions reached 10-50% in a 1-5 week period; abortions occurred at all stages of gestation; incidence of sow mortality reached 5-10% of the breeding herd inventory during the episode; most of the herds involved were vaccinated multiple times with PRRS virus (PRRSV) vaccine; and most of the herds also experienced markedly increased preweaning mortality and decreased nursery pig performance primarily due to respiratory disease. The clinical, diagnostic, and preliminary experimental evidence that we have to date suggests that severe acute PRRS/SAMS/atypical PRRS is due to a severe manifestation of PRRSV. The fact that the outbreaks were so severe and that they occurred in well-vaccinated herds is reason for serious concern. The unique hepatitis lesions in some cases suggested that there could have been additional pathogens involved in this syndrome or that strains of PRRSV developed tissue tropism for the liver. The good news is that reports of new cases since June of 1997 have been few and far between.