The Viral Distribution and Pathological Characteristics of BALB/c Mice Infected With Highly Pathogenic Influenza H7N9 Virus

Background: The highly pathogenic Influenza H7N9 virus is believed to cause multiple organ infections. However, there have been few systematic animal experiments demonstrating the virus distribution after H7N9 virus infection. The present study was carried out to investigate the viral distribution and pathological changes in the main organs of mice after experimental infection with highly pathogenic H7N9 virus.Methods: The mice were infected with A/Guangdong/GZ8H002/2017(H7N9) virus via nasal inoculation. Some mice were killed at 2, 3, and 7 days after infection. The other mice were used to observe their illness status and weight changes. The characteristics of viral invasion were analysed using reverse transcription polymerase chain reaction and viral isolation. The pathological changes of the main organs were observed using haematoxylin and eosin staining and immunohistochemistry.Results: The weight of mice infected with A/Guangdong/GZ8H002/2017(H7N9) virus increased slightly in the first two days. However, the weight of the mice decreased sharply in the following days by up to 20%. All the mice had died by the 8th day after infection and showed multiple organ injury. The emergence of viremia in mice was synchronous with lung infection. On the third day after infection, except in the brain, the virus could be isolated from all organs (lung, heart, kidney, liver, and spleen). On the seventh day after infection, the virus could be detected in all six organs. Brain infection was detected in all mice, and the viral titre in the heart, kidney, and spleen infection was high.Conclusion: Acute diffuse lung injury was the initial pathogenesis in highly pathogenic H7N9 virus infection. In addition to lung infection and viremia, the highly pathogenic H7N9 virus could cause multiple organ infection and injury.