197 SUSCEPTIBILITY OF PORCINE MORULAE AND BLASTOCYST STAGE EMBRYOS TO PSEUDORABIES VIRUS AND PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS

Abstract

Porcine preimplantation embryos are refractory to infection with pseudorabies virus (PRV) and porcine reproductive and respiratory syndrome virus (PRRSV) during the 2–4 to 16-cell stage as described by Bolin et al. (1981 Am. J. Vet. Res. 42: 1711–1712) and Prieto et al. (1996 Theriogenology 46: 687–693), respectively. Research on the effects of PRV and PRRSV on embryonic cells of morulae, blastocysts and hatched blastocysts is limited. Therefore, the objectives of the present study were (i) to assess the effects of PRV and PRRSV exposure on further embryonic development, and (ii) to determine whether PRV and PRRSV are able to replicate in embryonic cells of porcine morulae and blastocysts. In vivo produced ZP-intact and ZP-free morulae (6 days post-insemination), early blastocysts (7 days post-insemination), and hatched blastocysts (8 days post-insemination) derived from 22 superovulated sows were exposed to 10⁵ TCID₅₀ PRV (strain 89v87, second passage in swine testicle cells) or to 10⁵ TCID₅₀ PRRSV (Lelystad virus strain, 13^th passage in swine alveolar macrophages) for 1 h at 39°C. Control embryos were incubated under the same circumstances without viruses. Each group of morulae and blastocysts consisted of approximately 20 embryos. Embryonic development was assessed every 12 h and differences in rates of development were analyzed using Chi-square analysis or Fisher’s exact test. At 48 h post-incubation, embryos were collected and examined for viral antigen by indirect immunofluorescence. Further embryo development of ZP-intact and ZP-free morulae and blastocysts was not affected by exposure to PRV or PRRSV compared to controls (P < 0.05). Moreover, using indirect immunofluorescence, no PRV or PRRSV antigen-positive cells were detected. Exposure of hatched blastocysts to PRV inhibited further embryo development as 100% (n = 5) of the embryos degenerated 24 h after viral exposure. This was significantly different (P < 0.05) from the controls and the PRRSV-incubated hatched blastocysts that did not experience any negative influence on embryo development. Based on these results it can be concluded that embryonic cells are not susceptible to a PRRSV infection up to the hatched blastocyst stage. Embryonic cells of morulae and blastocysts are refractory to PRV, but the virus has a detrimental effect on further embryo development of hatched blastocysts. More experiments are necessary to confirm these results and to investigate whether, or at which preimplantation stage, embryos are susceptible to a PRRSV infection.