Submitted to: Pig Veterinary Society International Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/1/1998
Publication Date: N/A
Technical Abstract: In the U.S.A. during the fall and winter of 1996, a large number of unusually severe epizootics of reproductive failure in swine were reported. Affected herds experienced an abortion storm (involving 10%-60% of the herd at all stages of gestation and in all parities of sows) with a concurrent increase in stillborn and weak pigs plus sow and boar mortality (>5%). At first, diagnostic tests revealed no specific etiology and these cases became known as Sow Abortion and Mortality Syndrome (SAMS). Most of the affected herds were routinely vaccinated for porcine reproductive and respiratory syndrome (PRRS) (as are most herds in the U.S.A.) and other common pathogens. Then, PRRS virus (PRRSV) antigen was identified in tissues collected from affected swine, and eventually PRRSV was isolated from aborted fetuses and weak neonatal pigs. Because of these findings, SAMS became known as "atypical PRRS" or "acute severe PRRS" due to the fact tthese field cases were more severe than the typical PRRS cases observed in the U.S.A.; i.e., the high rates for abortion during the first half of gestation and for sow mortality were not normally associated with PRRS. We began to investigate cases of atypical PRRS to determine if the etiology was PRRSV or some other known or unknown agents that either acted in synergism with PRRSV or independently from it. Thus far, we have isolated PRRSV, but no other viruses, from cases of atypical PRRS. In general, these isolates appear more virulent than those isolated previously in that we have not only caused reproductive failure (fetal death, stillborn pigs, and weak newborn pigs) but sometimes severe illness, and in one case death, of affected pregnant gilts. In this report we will describe additional details of our in vivo investigations with one of these highly virulent strains.