A review of the risk of contamination of semen and embryos during cryopreservation and measures to limit cross-contamination during banking to prevent disease transmission in ET practices

This review summarizes pertinent data and opinions regarding the potential hazard of disease transmission through cryopreserved and banked embryos in liquid nitrogen (LN). Special attention is given to the survival of pathogens in LN, new vitrification methods, sterility of LN, risks associated with the use of straws and cryovials, and LN dewars including dry shippers. It was experimentally demonstrated that cross-contamination between LN and embryos may occur, when infectious agents are present in LN and embryos are not protected by a sealed container. It is important, therefore, to prevent direct contact of embryos with LN during cryopreservation and their banking. This includes the usage of hermetically sealed, high-quality, shatter-proof freezing containers and/or the application of a secondary enclosure such as “double bagging or straw in straw.” A periodic disinfection of cryo-dewars should be considered as an additional precaution to diminish the potential for inadvertent cross-contamination. It might be advisable to use separate LN dewars to quarantine embryos derived from infected donors of valuable genotype or from unknown health status, extinction-threatened species. Nevertheless, in summary, it has been concluded that over 25 yr with no direct evidence of disease transmission by transferred cryopreserved human and animal embryos, that the present cryopreservation technology is sanitary sound, with the stipulation that biocontainment measures recommended by the International Embryo Transfer Society (IETS) and the World Organization for Animal Health - Office International des Epizooties (OIE), are strictly followed.