PATHOGENESIS OF IN-UTERO INFECTION IN PORCINE FETUSES WITH PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS

Porcine fetuses were exposed in utero to porcine reproductive and resp iratory syndrome virus (PRRSV) at stages of gestation ranging from 34 to 85 days and examined 17 to 31 days later to determine the effect of gestational age on fetal susceptibility, For each of the 8 litters te sted during the study, ail of the fetuses of 1 horn of the uterus were exposed to virus by intraamniotic injection; those of the other horn were exposed similarly to a sham inoculum that consisted of sterile ce ll culture medium. Viral infectivity titers associated with fetal tiss ues collected at necropsy indicated that, regardless of gestational ag e, the virus had replicated in fetuses exposed intraamniotically, In a ddition, virus had also spread and replicated in sham-inoculated litte rmates in 3 litters, On the basis of these findings it appears that th ere may be little or no temporal difference in fetal susceptibility to infection with PRRSV, If so, the lack of early fetal death as a commo nly recognized feature of naturally occurring cases of PRRS may be due to a greater resistance of early gestational fetuses to the lethal ef fects of PRRSV, as suggested by this study, and/or a greater likelihoo d of transplacental infection during late gestation.