Introduction to Avian InfluenzaDavid L. Suarez D.V.M., Ph.D.Research Leader Exotic and Emerging Avian Viral Disease Research UnitAgricultural Research ServiceUnited States Department of AgricultureHAPB1PB2PANPNAMANSM2 HemagglutininNeuraminidaseM1Influenza A VirusNegative sense RNA Single strandedSegmented16 Hemagglutinin subtypes9 Neuraminidase SubtypesInfluenza NomenclatureA/Chicken/Pennsylvania/1370/83 (H5N2)1 2 3 4 5 6 71) Antigenic type 2) Isolate host of origin3) Geographic location 4) Isolate reference5) Year of isolation 6) Hemagglutinin subtype7) Neuraminidase subtypeInfluenza Subtypes• 16 Hemagglutinin subtypes• 9 Neuraminidase subtypes• 2 Nonstructural subtypes• Can occur in any combination• Useful for epidemiologyWhat Defines a Subtype?• Neutralizing antibody produced against one virus will neutralize all other viruses of the same subtype• A different subtype is defined when neutralizing antibody produced for one subtype will not neutralize viruses from other subtypes• Subtypes are defined by antigenic characteristics of the virus• Virus isolates will occasionally cross react with more than one reference antibodies• Hemagglutination inhibition tests provide a simple way to measure subtype differencesNatural Ecology of Avian InfluenzaMallardsBlue Wing Teal Herring Gulls• Avian Influenza is naturally found in wild birds • Virus infection is not normally thought to cause disease in itsnatural host (Viruses are low pathogenic)• Wild bird surveys have shown certain duck, gull, and shorebirdsspecies are commonly infected at different times of the year• All type A influenza viruses are thought to originate from wildbirdsIsolation of Avian Influenza from Different Bird Species•Most isolations from Anseriformes (ducks, geese, and swans) and Charadriiformes (gulls, terns, plovers, surfbirds, sandpipers, puffins)•Within Anseriformes highest isolation rates from Mallards and other dabbling ducks•Isolations of virus from many other Orders of birds (ex. loons, grebes, shearwaters, pelicans, herons, and coots)•The complete host range is not knownGeographic Range of Avian Influenza•Most reported isolations have been from North America, Europe and Asia•A few isolations from Australia Africa, and South America•No reported isolations AntarcticaWaterfowl Surveys•Most hemagglutinin and all neuraminidase subtypes have been found in wild waterfowl•The distribution of subtypes is not uniform-H6, H3, and H4 tend to predominate in North America•Some important influenza hemagglutinin subtypes are found uncommonly in birds, including H5 and H7•The distribution of hemagglutinin subtypes differ from year to year at the same locationAvian Influenza in Poultry• AIV is not normally found in domestic ducks, chickens and turkeys• Transmission of AIV from wild birds to domestic poultry species occurs commonly (ducks>turkeys> chickens)• AIV on rare occasions may become established in chickens and turkeys and result in serious disease outbreaks• AIV once adapted to chickens and turkeys can be difficult to eradicateAvian Influenza: Infection and Disease• Infection may cause a wide range of clinical signs from no disease (asymptomatic), respiratory disease, to severe disease with high mortality• Localized Infection-mild to moderate disease– Intestinal-wild ducks and shorebirds, poultry – Respiratory-humans, swine, horses, poultry, domestic ducks, seal, mink• Systemic Infection-high mortality– chickens, turkeys, other gallinaceous birdsHighly Pathogenic Avian Influenza• Systemic, rapidly fatal disease of poultry• Only H5 and H7 subtypes are recognized to cause HPAI• OIE List A Disease-outbreaks are reportable• HA cleavage site critical virulence factor• Low pathogenic H5 and H7 AI viruses can mutate into the highly pathogenic form of the virusEmergence of HPAILPAI H5 or H7 virus transmitted to poultryLPAI virus circulates in poultry with mild diseaseLPAI Virus Mutates to HPAI with severe diseaseHistory of HPAI in the Americas in the last 30 years• HPAI is considered a foreign animal disease in the Americas• Five HPAI outbreaks have occurred in the Americas in the 1990s– Pennsylvania 1983-84 (17 million birds)– Mexico 1994-95 (Millions of birds)– Chile 2002 (2 million birds)– Canada 2004 (17 million birds)– Texas 2004-Molecular definition of HPAI only (5,000 birds)Hemagglutinin (HA) Protein• Protein is cleaved into HA1 and HA2 subunits by host proteases• Cleavage of HA is necessary for virus to be infectious (necessary to release fusion domain)• HA has receptor binding site (receptor = sialic acid)• Fusion domain becomes active when pH is lowered in endosomeStandards for Highly Pathogenic Avian Influenza• 1) If influenza isolate kills 6 or more, out of 8, infected chickens in standard pathotyping test• 2) Any H5 or H7 influenza virus that has multiple basic amino acids at the hemagglutinin cleavage site compatible with highly pathogenic AI• Low Pathogenic H5 or H7 Avian Influenza H5 is notifiable to O.I.E.Cleavage of Hemagglutinin Protein by Host Proteases• In LPAI viruses, only trypsin-like proteases found in the enteric and respiratory tracts can cleave the HA protein-virus replication and disease is restricted• In HPAI viruses, the HA protein can be cleaved by ubiquitous proteases found in most cells-virus can replicate systemicallyH5 Hemagglutinin Cleavage Site• For H5 LPAI waterfowl viruses, the consensus cleavage site sequence is Arg Glu Thr Arg/ Gly• Most H5 HPAI viruses have additional basic amino acids at cleavage site – Mexico 1995 Arg Lys Arg Lys Thr Arg/ Gly– Hong Kong 1997 Arg Glu Arg Arg Arg Lys Lys Arg/Gly• The loss of a glycosylation site was also important in the emergence of HPAI in Pennsylvania in 1983 – LPAI PA/83 Lys Lys Lys Arg/ Gly + glycosylation at 11-13– HPAI PA/83 Lys Lys Lys Arg/ Gly - glycosylation at 11-13H7 Hemagglutinin Cleavage Site• For H7 NA LPAI waterfowl viruses, the consensus cleavage site sequence is Asp Pro Lys Thr Arg/Gly• H7 HPAI viruses have additional basic amino acids at cleavage site – Australia 1992 Pro Lys Lys Lys Lys Arg/ Gly– Australia 1994 Pro Arg Lys Arg Lys Arg/ Gly– Pakistan Pro Lys Arg Lys Arg Lys Arg/ Gly– Australia 1997 Pro Arg Lys Arg Lys Arg/ Gly– Italy 1999 Pro Lys Gly Ser Arg Val Arg Arg/ GlyReassortment of Gene Segments• Influenza has 8 separate gene