Risks associated with bovine embryo transfer and their containment.

Abstract

Abstract Virus-embryo interactions have been widely studied in cattle. This review examines possible routes of viral infection, sources of contamination and protective measures that can be taken when performing embryo transfer in cattle, and when appropriate, in other domestic species. Fertilized embryos are protected by the zona pellucida, but recent evidence in cow, pig and mouse embryos has shown that the pores in the zona pellucida are sufficiently large to mechanically entrap certain viruses, although penetration through the zona with infection of embryonic cells is considered unlikely. Whether this assumption holds true for very small viruses, and for embryos of other species remains to be determined. Viral transmission may not always be related to infection of the gametes or embryos, but may originate from infection of the genital tract of the donor, or from contamination of the media or of equipment used to manipulate the embryos. Recent technologies involving vitrification and subsequent storage of the embryos or semen in liquid nitrogen in open containers represent an increased contamination risk during long-term cryobanking. Sanitary measures to guard against the risk of viral infection need to be taken, especially when working with embryos from infected donors or with techniques that may compromise the embryo's defence mechanisms. In cattle, sanitary guidelines have been developed and accepted worldwide that can ensure that the risks of transmission via reproductive technology is very low when sanitary guidelines are being followed rigorously. For other species, such guidelines are in the process of development.