Do we need better Influenza vaccine for Ohio turkeys?

Abstract

Since 2003, triple reassortant (TR) swine H3N2 virus have been detected in the U.S turkey population including Ohio flock. The virus has been isolated even from birds that were vaccinated with the currently available swine- and avian- origin vaccines. To better understand this newly emerged TR H3N2 virus that contains gene segments from human, avian and swine origins, we undertook genetic, biologic and antigenic characterization of selected H3N2 viruses isolated from different species in different years. Phylogenetically, all turkey isolates were closely related and grouped together with the TR swine isolates including the vaccine strain. However, the avian-origin vaccine strain shared less than 80% sequence homology with the turkey isolates for the HA1 protein which is directly related to humoral protective immunity.Critical amino acid changes were also detected in the HA1 protein between turkey isolates and swine or avian origin vaccine strains. Our in vivo study demonstrated the successful establishment and replication of H3N2 viruses in turkeys, both in upper respiratory and intestinal tracts. These viruses also transmitted efficiently to the contact control cage mates. Antigenically, all turkey isolates were closely related to each other. However, the turkey isolates showed little or no cross-reactivity with the avian origin or swine origin vaccine strains. These results call for the re-evaluation of currently available vaccines being used in turkey flocks. Our research is currently focused on developing an effective vaccine that can also be used to differentiate vaccinated and infected flocks using an H3N2 virus isolated from Ohio turkeys