Efficacy of the International Embryo Transfer Society (IETS) washing procedure for rendering oocytes matured in vitro free of bovine viral diarrhea virus (BVDV)

To ensure the freedom of embryos from pathogenic agents prior to embryo transfer (ET), a specific sanitary washing procedure has been recommended by the International Embryo Transfer Society (IETS). In the present study, the efficacy of removing the bovine viral diarrhea virus (BVDV) from cumulus-free matured oocytes at the stage of extruded first polar body (N = 240) was evaluated, using the IETS-recommended 10 sequential wash procedure, after exposure in vitro to BVDV type 2 (strain PA-131, 1 × 105.2 TCID50/mL for 1 h). In general, the percentage of contaminated oocytes was reduced (P < 0.03) after the first two washes. Nevertheless, after 10 washes, approximately 20% of oocytes still remained infectious or contaminated with virus, as detected by the virus isolation test (VI) and quantitative reverse transcription PCR (qRT-PCR) of viral RNA (on average 13 copies/oocyte). Similarly, a higher percentage of positive washing fluid samples were detected in the first three washes (50-100%). The six subsequent washes had lower but variable proportions of fluid samples contaminated with infectious virus. We concluded that the standard washing procedure may not render all oocytes free from the infectious virus adhered to the zona pellucida (ZP), and application of an additional method of oocyte disinfection was warranted to ensure nontransmission of BVDV to recipients by embryos derived from infected oocytes.