Potential Intercontinental Movement of Influenza A(H7N9) Virus into North America by Wild Birds: Application of a Rapid Assessment Framework

Abstract

A critical question surrounding emergence of novel strains of avian influenza viruses (AIV) is the ability for wild migratory birds to translocate a complete (unreassorted whole genome) AIV intercontinentally. Virus translocation via migratory birds is suspected in outbreaks of highly pathogenic strain A(H5N1) in Asia, Africa and Europe. As a result, the potential intercontinental translocation of newly emerging AIV such as A(H7N9) from Eurasia to North America via migratory movements of birds remains a concern. An estimated 2.91 million aquatic birds move annually between Eurasia and North America with an estimated AIV prevalence as high as 32.2%. Here, we present a rapid assessment to address the likelihood of whole (unreassorted)-genome translocation of Eurasian strain AIV into North America. The scope of this assessment was limited specifically to assess the weight of evidence to support the movement of an unreassorted AIV intercontinentally by migratory aquatic birds. We developed a rapid assessment framework to assess the potential for intercontinental movement of avian influenzas by aquatic birds. This framework was iteratively reviewed by a multidisciplinary panel of scientific experts until a consensus was established. Our assessment framework identified four factors that may contribute to the potential for introduction of any AIV intercontinentally into North America by wild aquatic birds. These factors, in aggregate, provide a framework for evaluating the likelihood of new forms of AIV from Eurasia to be introduced by aquatic birds into North America. Based on our assessment, we determined that the potential for introduction of A(H7N9) into North America through aquatic migratory birds is possible, but the likelihood ranges from extremely low to low.