Mice are infected by mouse hepatitis virus, the rati o is 100%before cesarotomy.After having been cleaned, the mouse hepatitis viru s in closing colony mice has kept negative for 5 year.

• 剖腹产术前100%25感染小鼠肝炎病毒的小鼠种群，经无菌剖腹产术净化后，结果均为阴性，并经5年的大规模生产、繁殖，至今仍保持阴性结果。