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Title: Genetic and antigenic relatedness of H3 subtype influenza A viruses isolated from avian and mammalian species

item Suarez, David

Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2007
Publication Date: 1/1/2008
Citation: Yassine, H.M., Lee, C.W., Suarez, D.L., Saif, Y.M. 2008. Genetic and antigenic relatedness of H3 subtype influenza A viruses isolated from avian and mammalian species. Vaccine. 26:966-977.

Interpretive Summary: Swine influenza is commonly isolated from pigs in the U.S. and vaccination is routinely practiced. Turkeys are also susceptible to being infected with swine influenza viruses, and the most common clinical disease sign is a drop in egg production in turkeys used for egg production (turkey breeders) as a source of turkeys used for meat production. Vaccination is often used in turkey breeders. Recently an outbreak of swine influenza was seen in a turkey breeder flock that had been vaccinated. This observation of lack of protection from vaccination prompted a study of the turkeys viruses and two other viruses that are used for vaccine production. The study showed that the turkey viruses were different in the areas of the virus related to protection from vaccination. The data suggests that a new vaccine is needed to provide optimal protection from disease.

Technical Abstract: Turkeys are susceptible to some swine influenza viruses based on natural and experimental transmissions of H1 and H3 subtype viruses from swine to turkeys. In 2004, we isolated triple reassortant H3N2 viruses from turkey breeder hens in Ohio and Illinois. These H3N2 viruses are currently the dominant cause of influenza in both swine and turkey populations in the United States. The Illinois flock was vaccinated twice with an inactivated H3N2 vaccine containing a swine origin virus before the outbreak. Additionally, a commercial inactivated vaccine containing an H3N4 virus of duck origin is being used in some turkey breeders. This prompted us to initiate a comparative study on the antigenic and genetic relatedness of various H3 subtype influenza viruses isolated from turkeys, ducks, pigs, and humans. The antigenic relatedness between the different viruses was evaluated with the Archetti and Horsfall formula, while genetic similarities were calculated using pairwise alignments. Results obtained indicated a high degree of antigenic (>90%) and genetic (>99%) similarities among the turkey-origin H3N2 viruses. However, the turkey viruses were antigenically distantly related to the swine-origin vaccine virus (<30%), although they had approximately 95% genetic similarity in the HA1 gene. Additionally, major genetic and antigenic changes were observed between the turkey viruses and the H3N4 duck vaccine virus as well as the H3N2 human virus. Such genetic and antigenic differences between the turkey-origin viruses and other H3 subtype viruses including vaccine strains could be the reason for the failure in protection in the Illinois turkey breeders vaccinated with swine origin virus. This also emphasizes the importance of using viruses for vaccines that are antigenically similar to the field strains.