Congenital abnormalities in newborn lambs following Akabane virus infection in pregnant ewes.

To clarify the pathogenicity of Akabane virus for ovine embryos, pregnant ewes were inoculated intravenously with the virus. As a result, all of them were affected with viremia and showed an increase in neutralizing antibody 2 weeks after inoculation. The virus was recovered from many organs of embryos which were inoculated with it at 29--45 days of pregnancy and sacrificed 9--30 days later. In particular, some of these embryos which were sacrificed 15 days after inoculation were found suffering from systemic infection. A large quantity of virus was recovered from the organs all over the body of them. No virus, however was recovered from any organ of embryos which were inoculated with the virus at 81 days of pregnancy and sacrificed 30 days later. Abnormal changes were observed in neonatal lambs born from ewes inoculated with the virus at 30--50 days of pregnancy. They were especially severe when the virus was inoculated at 30 days of pregnancy. They consisted of ankylosis of the limbs, scoliosis, hydranencephaly, porencephaly, stillbirth with dwarfism, and death after birth with dwarfism and weakness. Nothing abnormal was found in any neonatal lambs born from ewes inoculated with the virus at 91--101 days of pregnancy. When embryos exceeded 64 days of intra-uterine life more than 29 days after virus inoculation, it was possible to detect immunoglobulin, IgM or IgG or both, and antibody from the serum. Attempts failed to detect either immunoglobulin from embryos less than 59 days of intrauterine life. No IgA was detected from the serum of any embryo. In almost all the neonatal lambs born from ewes inoculated with the virus at 28--101 days of pregnancy, neutralizing antibody was detected from the serum at the time of birth.