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School of Veterinary Science (SS, NP, MRM) and Department of Microbiology & Parasitology (HBO), University of Queensland, Brisbane, Queensland, Australia; Virology Laboratory, Elizabeth MacArthur Agricultural Institute, Camden, New South Wales, Australia (PDK); and Department of Farm Animal & Equine Medicine & Surgery, Royal Veterinary College, North Mymms, Hatfield, UK (MRM)
Despite the importance of congenital viral infections in both veterinary and human medicine, only limited experimental work has been carried out to elucidate the mechanisms involved in transplacental virus infections. To further an understanding of fetal infection with pestiviruses, the distribution of bovine pestivirus in the uterine and fetal tissues of ewes in early pregnancy, following a natural route of infection, was investigated. On the 18th day of pregnancy, nine ewes were inoculated by the intranasal route with 1 x 105 50% tissue culture infective doses of an Australian isolate of noncytopathic bovine pestivirus (bovine viral diarrhea virus genotype 1). All ewes were ovariohysterectomized at approximately 100 hours postinfection. Samples from the reproductive tract and conceptus were examined histologically and tested for bovine pestivirus by nested reverse transcriptionpolymerase chain reaction (RT-PCR) and immunohistochemistry and for interferon-tau mRNA expression by nonnested RT-PCR. Although no histopathologic changes were observed in the maternal or fetal tissues, virus was detected in the reproductive tract of all nine ewes and in all of the conceptuses examined. At the time of surgery, only two of the nine ewes were demonstrably viremic. This study demonstrates that bovine pestivirus can spread from a natural site of infection to the ovine fetus within 4 days in the absence of maternal immunity and despite the presence of interferon expression in the reproductive tract.
Key words: Bovine pestivirus; immunohistochemistry; interferons; polymerase chain reaction; sheep; transplacental infection.
Request reprints from Dr. M. McGowan, Department of Farm Animal Medicine & Surgery, The Royal Veterinary College, Hawkeshead Lane, North Mymms, Hatfield, Hertfordshire AL9 7TA (UK).
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