Quantity and infectivity of embryo-associated bovine viral diarrhea virus and antiviral influence of a blastocyst impede in vitro infection of uterine tubal cells

In previous studies, bovine viral diarrhea virus (BVDV) remained associated with IVF embryos after viral exposure and washing. However, uterine tubal cells (UTC) were not infected when exposed embryos were washed and individu ally co-cultured with them. The objective of this study was to evaluate qua ntity and infectivity of embryo-associated virus and antiviral influence of a blastocyst as possible explanations for failure to infect the UTC in vit ro. Morulae and blastocysts were produced in vitro and washed. A portion of the embryos were incubated for 2 h in medium containing 10(6) to 10(8) cel l culture infective doses (50%, CCID50) of a genotype I, noncytopathic BVDV per milliliter and then washed again. Virus isolation was attempted on son icated negative (virus unexposed) and positive (virus exposed) control embr yo groups after washing. The influence of quantity and infectivity of embry o-associated virus was evaluated by transferring exposed, washed embryo gro ups (2, 5, and 10 embryos/group) or sonicate fluid of exposed, washed, soni cated embryo groups (2, 5, and 10 embryos/group) to cultures containing bov ine UTC in NC medium that was free of BVDV neutralizing activity. The antiv iral influence of an embryo was evaluated by adding 1 to 10(5) CCID50 of BV DV to UTC in the presence or absence of a single unexposed blastocyst in IV C medium. After 2 d in co-culture, the UTC, IVC medium and washed embryos ( when present) were tested separately for the presence of BVDV using virus i solation. Virus was isolated from sonicate fluids of all positive but no ne gative controls. Virus was not isolated from any UTC following 2 d of cultu re with virally exposed groups of intact embryos. However, virus was isolat ed from UTC cultured with sonicate fluids from some groups of 5 (60%) and 1 0 (40%) embryos. Infective virus also remained associated with some groups of 2 (20%), 5 (40%) and 10 (60%) intact embryos after 48 h of post-exposure culture. Finally, primary cultures of UTC were more susceptible to infecti on with BVDV in the absence of a blastocyst (P=0.01). Results indicate that insufficient quantity and reduced infectivity of embryo-associated virus a s well as an antiviral influence of intact IVF blastocysts may all contribu te to failure of embryo-associated virus to infect UTC in vitro. (C) 1999 b y Elsevier Science Inc.