Project 4 - Molecular Determinants of Adaptation of Influenza Viruses to Domestic Birds and their Effect on Interspecies Transmission

Principal Investigator: Daniel Perez, Ph.D.
Associate Professor, Department of Veterinary Medicine
University of Maryland, College Park, MD

Avian reservoirs. Influenza pandemics occur when influenza A viruses from the animal reservoir establish sustained transmission in an immunologically naïve human population. Although aquatic birds are the primary reservoir of influenza A viruses, the adaptation of viral gene segments in intermediate hosts is considered necessary for the emergence of a pandemic strain. The recent H5N1, H7N7 and H9N2 avian influenza viruses, that have acquired the ability to transmit from bird to humans, highlight the need for a better understanding of the molecular factors, both of viral and host origin, that lead to their emergence. These viruses contain genes that circulated and adapted in domestic birds prior to their transmission to humans. Thus, domestic birds: quail, mallard duck, guinea fowl, turkeys, and geese, may serve as intermediate hosts in which influenza viruses acquire the genetic changes necessary to cause human infection and provide an environment where avian and human influenza can replicate and spread leading to potential pandemic strains.

A molecular basis for transmission between species. Our goal is to determine the molecular basis of transmissibility of influenza viruses in avian intermediate hosts. The viral hemagglutinin (HA) has a major role in the host range and pathogenicity of each influenza virus subtype and strain. The receptor-specificity of influenza HA depends on the host species from which they evolved. Influenza infections are dependent on interactions between the HA and cell surface oligosaccharides displaying sialic acid residues. Avian viruses preferentially bind to sialyloligosaccharides terminated by SAa2,3Gal-linkage, whereas human viruses prefer SAa2,6Gal-linkage conformation. It is generally accepted that to change host range, influenza viruses need to override the selective binding. A possible route is by going through an intermediate host carrying both receptors, thus creating a new virus through reassortment. We are mapping the distribution of receptors in the intestinal and respiratory tract to determine the type and frequency, particularly of SAa2,6Gal receptors, in domestic avian species, including quail, mallard duck, guinea fowl, turkeys, and geese; and studying the biological significance of subtle changes on the influenza A virus HA surface protein for binding sialic acids, including for H5N1 viruses, and HA attached to different sugar moieties using a glycan array. This research specifically will provide clues to whether domestic poultry can generate influenza viruses with sugar binding patterns similar to those observed for human viruses.

Virulence. A major goal of CRIP is to define the molecular mechanisms that result in differences in virulence and pathogenicity of highly pathogenic influenza viruses. By a "checkerboard" approach, reassortant viruses are being engineered containing one or more genes from one transmissible avian strain and the rest from a non-transmissible avian strain. Host response to these viruses in the chicken will be measured by using cDNA microarrays. Furthermore, the contributions of PB1-F2 and NS1 to the virulence of avian influenza viruses for avian species will be correlated to those observed in mammals.