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Title: Pathobiology of triple reassortant H3N2 influenza viruses in breeder turkeys and its potential implication for vaccine studies in turkeys

Author
item PILLAI, S P - OHIO STATE UNIV/OARDC
item Pantin Jackwood, Mary
item JADHAO, S - USDA-FAS-OICD-RSED
item Suarez, David
item WANG, L - OHIO STATE UNIV/OARDC
item YASSINE, Y - OHIO STATE UNIV/OARDC
item SAIF, Y - OHIO STATE UNIV/OARDC
item LEE, C-W - OHIO STATE UNIV/OARDC

Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2008
Publication Date: 2/1/2009
Citation: Pillai, S.S., Pantin Jackwood, M.J., Jadhao, S.J., Suarez, D.L., Wang, L., Yassine, Y., Saif, Y., Lee, C. 2009. Pathobiology of triple reassortant H3N2 influenza viruses in breeder turkeys and its potential implication for vaccine studies in turkeys. Vaccine. 27:819-824.

Interpretive Summary: The genome of influenza viruses consist of eight RNA gene segments. The segmented nature of the virus genome permits genetic reassortments to occur during co-infection of a host with different influenza viruses. Triple reassortant (H3N2) influenza viruses containing gene segments derived from human, swine, and avian influenza viruses, have become endemic in the U.S. turkey population. The H3N2 infections do not usually cause mortality in turkeys, but produce disease leading to reduced egg production and poor body weight gain, accounting for huge economic losses. In this study, we performed genetic, antigenic and pathobiological characterization of selected H3N2 virus isolates. Phylogenetically, the TR H3N2 viruses shared high genetic similarity (98-99%). Antigenically, all isolates were similar. These viruses replicated efficiently in 3-week-old turkeys, although poorly in 4-week-old chickens and 2-week-old ducks, indicating the possible species specific preferences of these viruses. In 26-week-old layer turkeys, one of the TR H3N2 strains completely stopped egg production after infection. The virus replicated to high titers in the oviduct of these turkeys. Because the TR H3N2 viruses in turkeys are endemic and of economic importance, there is the need for continuos monitoring and improvement of vaccination to provide better protection and lower economic losses in turkey production.

Technical Abstract: Triple reassortant (TR) H3N2 avian influenza viruses have become endemic in the United States turkey population. The H3N2 infections do not usually cause mortality in turkeys, but result in clinical disease of varying severities leading to reduced egg production and poor body weight gain, accounting for huge economic losses. In this study, we performed genetic, antigenic and pathobiological characterization of selected H3N2 virus isolates. Phylogenetically, the TR H3N2 viruses isolated from domestic turkeys in the United States during 2003-2005 clustered together and shared high genetic similarity (98-99%). Antigenically, all turkey isolates were similar, showed lesser cross-reactivity to swine origin viruses and did not react with avian origin H3N2 viruses that were not triple reassortants. These viruses replicated efficiently in 3-week-old turkeys and transmitted to the contact control cage mates. The TR H3N2 viruses exhibited poor replication and transmissibility in 4-week-old chickens and 2-week-old ducks, indicating their possible species specific preferences in replication and transmission. In 26-week-old layer turkeys, one of the TR H3N2 strains tested caused complete cessation of egg production within 13 days post infection. We confirmed high levels of virus replication and abundant distribution of avian specific alpha2,3 sialic acid-galactose receptors in the oviduct of these turkeys. The endemicity of the TR H3N2 viruses in turkeys and associated economic importance underscore the need for their enhanced monitoring and surveillance. In addition, H3N2 vaccine strains should be updated to offer a better antigenic match with endemic turkey TR H3N2 avian influenza viruses to provide better protection and lower economic losses in turkey production.