The Pathogenesis Of H5N1Virus Infection In Pregnant Mice And Risk Survey Of Avian Influenza Virus Infection Among Poultry Workers

H5N1avian influenza virus spreads widely in Eurasia. The pandemic potential of H5N1virus is a great threat to public health security. It would be helpful for the prevention of H5N1outbreak if we try to explore the pathogenesis of the virus. This study focused on the pathogenesis of H5N1virus infection during pregnancy. Pregnancy is a risk factor for some diseases. The pathogenicity of H5N1virus in pregnant women is not known yet. In this study,We used mouse as a model to research the effect of H5N1on pregnancy.The replication ability of H5N1virus, and body’s innate immune response, organs pathological damage of pregnant and nonpregnant BALB/c mices were studied. The results showed that the virus titers in the lungs of pregnant mice were significantly higher than that of nonpregnant mice at3day post inoculation (dpi). And virus positive type II alveolar epithelial cells in the pregnant mice lungs were more than that of nonpregnant mice. In the early infection, antiviral cytokines IFN-y, TNF-a levels in pregnant mice lungs were significantly higher than that of nonpregnant ones. In the late infection, chemokine MCP-1, MIP-la and IL-6in pregnant mices were significantly increased, and caused lots of inflammatory cells infiltration, with lung diffuse alveolar damage. Oxygen saturation of pregnant mice significantly decreased in the middle and late periods of the infection, with severe symptoms of respiratory distress. H5N1virus infection did not affect the concentration of estradiol and progesterone in serum. The results showed that H5N1virus on pathogenicity in mice during pregnancy was higher than normal female and pregnancy was a risk factor to aggravate infection.To study the vertical transmission ability of H5N1virus, pregnant mice with day13gestation were infected H5N1virus. The viremia appeared at3dpi, viruses were isolated from placenta at4dpi, and fetuses could be infected since5dpi. Immunohistochemical staining showed that the viruses were mainly distributed in the labyrinthine trophoblast. The H5N1virus was found in the placental villus epithelial cells and macrophages in the interface of maternal blood-syncytiotrophoblast interface and a small amount of virus scattered at the decidual layer. Viral antigen was also detected in alveolar epithelial cells and liver cells of fetuses, suggesting that H5N1avian influenza virus transmited vertically through placenta and infected fetuses. Focal necrosis and inflammatory cell infiltration appeared in the placenta of the infected mice. Inflammatory cytokines IFN-y, TNF-a and IL-6in placenta were significantly increased in late virus infection. Pregnancy failure such as miscarriage and necrosis was observed. To explore the mechanism of the vertical transmission of the H5N1virus, we detected the virus in blood cells, receptors distribution in placenta, and virus infection ability in trophoblast cell. Mononuclear cells and multinucleated cells could both be infected by virus, indicating that blood cells could serve as carriers that transport virus to placental tissue. Both the SA-a2,6-Gal and SA-a2,3-Gal receptors were expressed in placental vascular endothelial cells, trophoblast cell, and epithelial cell in chorionic plate. The virus could infect and replicate in trophoblast cell cultured in vitro. The results proved that the H5N1virus could reach the placenta by infecting blood cells as carriers and infect placental cells. The damage induced directly by virus and inflammation caused placental tissue necrosis and structural integrity broken, which facilitated virus breaking through placental barrier and infected fetuses, leading to pregnancy failure.To evaluate the risk of avian influenza infection of poultry workers, we conducted an H5, H7, H9serological study and questionnaire survey in Beijing poultry farms.14persons in305(4.49%) were positive for H9. Questionnaire survey suggested that most of workers had not recognized the threat of bird flu.In summary, this study provides evidence for the transmissibility of the H5N1virus in mammal animal. Studies on the mechanism of the pathogenesis of H5N1virus is significant for avian influenza prevention and control.