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 are so severe, and that they have occurred in well-vaccinated herds is reason for serious concern. The unique hepatitis lesions in some of the cases suggest that there could be additional pathogens involved in this syndrome or that strains of PRRSV have developed tissue tropism for the liver.
Iowa State University
Halbur, Patrick G.; Sorden, S. D.; Royer, R.; and Bruna, J., "Investigation into the Severe Acute PRRS Outbreaks" (1998). Swine Research Report, 1997. 42.