Isolation And Characterization Of An H3N2 Canine Influenza Virus

Canine influenza is a highly infectious viral disease caused by canine influenza virus belonging to subtype H3N2 and H3N8. Up to now, we don't know whether human beings and other mammals are infected with canine virus, whose natural hosts, dogs are considered as human being's closest friend. For the prevention and control of canine influenza, it is important to make clear the biological characteristics of canine influenza virus.Our studies focused on ZJH3N2, a H3N2 canine influenza virus isolated from a dead Tibetan mastiff bought from a dog exhibition in Zhejiang province, China. We compared the nucleotide sequence of all the eight gene segments of ZJH3N2 with others reference virus in Genebank. The results indicated that the sequence of all eight genes of ZJH3N2 were highly homologous to Korea H3N2 influenza viruses (Korea07) and Guangdong H3N2 influenza viruses (GD07).Dog infection studies showed that artificially infected dogs appeared same clinical symptoms as naturally infected dogs. All dogs infected showed depression, lost of appetite, high fever and cough. Two dogs were euthanized 4 days post-infection and tissues were collected for histopathological study and viral isolation. The histopathological test showed that lung had obviously inflammatory exudation and hemorrhage. Viral titers in lung tissues got to 10^4.75EID₅₀/g. The remaining infected dogs recovered without any treatment. The canine influenza virus could transmit from dog to dog by air and the dogs got fever 4 days post-contact and appeared similar symptoms as infected dogs.In order to know whether other animals were infected with ZJH3N2. We used BALB/c mice, guinea pig and duck as the animal models. The mice began to lost weight after 2 days infected with 10⁶EID₅₀ ZJH3N2 virus. ZJH3N2 virus could replicate in the nasal tissue, trachea, and lungs of mice, but did not kill mice. ZJH3N2 virus could replicate in nasal tissue of guinea pig while no virus was recovered from any tissue of ducks 4 days after the animals were infected with 10⁶EID₅₀ ZJH3N2.In summary, we isolated and identified an H3N2 canine influenza virus and its biological Characteristics were studied in detail. The result showed that ZJH3N2 virus highly homologous to Korea H3N2 influenza viruses (Korea07) and Guangdong H3N2 influenza viruses(GD07), which were originally come from avian influenza virus. This study also proved that ZJH3N2 could replicate in other mammals besides dogs, but not in ducks. The result complemented the knowledge of epidemiology of canine influenza virus, and supply material and the animal model for the studies of inter-species transmission of influenza virus.