Potential vertical transmission: The case of Norovirus

Mouse Norovirus was !rst described in 2003 and it is now one of the most prevalent viral pathogen in rodent animal facilities. We report a natural infection of murine Norovirus in immunocompetent C57BL/6N and immunode!cient athymic Nude-nu (nu/nu) mice. Virus was detected by molecular methods (RT-PCR) and the study was carried on for the duration of 1 year in which tissues (feces, mesenteric lymph nodes, intestine, spleen, liver, lung, brain, ovary and testis) from 3 males and 3 females of each strain were collected and analysed at 2, 4, 8, 12, 24, 52 weeks. Tissue distribution shows that all the organs tested were infected at various time and in particular that reproductive organs were positive at speci!c dates. Sperm derived from positive testis was tested and showed positivity after several washes, indicating that the virus strictly associates with spermatozoa. These spermatozoa were used to perform In Vitro Fertilization (IVF) and produce two-cells embryos. Em- bryos produced this way after a minimum of ten washes were infected but failed to transmit the infection to the foster mother after embryo reimplantation. Positive ovaries were used for ovarian transplantation without vertical transmission. Potential vertical transmission of mouse Norovirus through assisted reproductive technologies, especially the ones that soften or break the integrity of the zona pellucida, is under investigation.