Orthomyxoviruses September 15,16, 2010

The big pandemic of 1918

John Hopkins Hospital Bulletin April 1919

Nature Jan 18, 2007

The 1918 virus Loo and Gale Nature Jan 18, 2007

Orthomyxoviridae -ve stranded RNA, segmented Haemagglutinin (HA) and neuraminidase (N) on surface

Viruses with -ve RNA genomes Paramyxoviridae Rhabdoviridae Orthomyxoviridae Filoviridae Bunyaviridae parainfluenza virus canine distemper virus respiratory syncytial virus rabies virus vesicular stomatitis virus influenzaviruses Ebola virus Haantan virus

Orthomyxoviridae Influenzavirus A Influenzavirus B Influenzavirus C humans horses pigs birds marine mammals humans pigs dogs cats

Influenza virions nucleocapsid (RNA fragments wrapped in protein) envelope haemagglutinin and neuraminidase “spikes” In envelope 100 nm

Haemagglutinin and Neuraminidase receptor binding site active site variable loops variable loops HAN sialic acid on receptor

Distribution of HA serotypes in nature HA serotypeBirdsHorsesPigsHumans HA1 HA2 HA3 HA4 HA5 HA6 HA7 HA8-16 yes

Distribution of N serotypes in nature BirdsHorsesPigs N1 N2 N3 N4 N5 N6 N7 N8 yes N9yes Humans yes

Nomenclature A/equine/Saskatoon/1/90(H3N8) group species location Isolate number year Serotype of HA and N A/equine/Prague/1/56(H7N7) A/fowl/Hong Kong/1/98(H5N1) A/swine/Lincoln/1/86(H1N1)

Influenzavirus replication HA cleaved by proteases HA binds to receptor virus in phagolysosome lowered pH, HA fuses membranes RNA released virus buds N releases virus

Cleavage of HA Clara (mucus), extracellular, serum, bacterial proteases HA0 HA1 HA2 binds receptor binds receptor penetrates cell

Chemotherapy Prevent membrane fusion –Amantidine (Symmetrel) –Remantidine (Flumadine) Neuraminidase inhibitors –Zanamivir (Relenza) –Oseltamivir (Tamiflu)

Epidemiology of influenza ?

How do flu viruses change? virus polymerase makes mistakes selection of antigenic and host variants viruses re-assort

How changes have led to human pandemics avian H1N1 virus adapts to humans reassortment H2, N2, PB1 from duck rest from human H1N1 H3, PB1 from duck rest from human H2N2 H2N2 H3N2 swine human avian H1N1

Factors that sustain epizootics/epidemics Antigenic drift Reassortment and antigenic shift Short term immunity Cross species transfer

Introduction of influenza to horses Before 1950s –A/eq/Prague/1/56(H7N7) from birds? –A/eq/Miami/1/63(H3N8) persists today (“Eurasian” “American strains”) from birds –A/eq/Jilin/1/89(H3N8) –epizootoics in 1989,90 –none since Extinguished World-wide, except New Zealand, Iceland Extinguished, central Asia ? dogs 2004

Pathogenesis inhalation (infected animal or fomites) replication in epithelial cells upper RT

Clinical signs Sudden onset Fever (39-42), biphasic Dry cough Nasal discharge (serous ->mucopurulent)

Risk factors Current specific antibody levels Time since last vaccination Age Sex

Other pathogens that cause similar signs influenza equine herpesvirus 1, 4 S. equi equine viral arteritis

Diagnosis Clinical signs Virus isolation Directagen Flu-A Serological tests –HAI –Single radial haemolysis

Vaccines Inactivated, H7N7 and H3N8 isolates –Adjuvant –Most -> short lived protection Revaccinate at 6 week intervals Intranasal, cold-adapted Vectored (Recombitek)

Swine influenza H1N1 - two variants H3N2 Ontario ( ) –53% H1N1 –17% H3N2 (similar to human virus) –4% H1N2 (similar to human virus)

WHO update ml

Avian influenza Highly Pathogenic Avian Influenza (to date H5, H7) –Pennsylvania $65,000,000 –Mexico $$? –B.C –Saskatchewan 2007 (H7N3) flu/2007sask/repsaske.shtml Asymptomatic to fatal (HPAI)

HA cleavage and virulence May ‘94 -> June ‘94 Dec ‘94 -> Jan ‘95 P Q - - R E T R low cleavability low virulence P Q R K R K T R high cleavability high virulence systemic infection respiratory infection ?

Cleavage of HA Clara (mucus), extracellular, serum, bacterial proteases HA0 HA1 HA2 binds receptor binds receptor penetrates cell

The 2004 BC outbreak 17 million birds destroyed 1128 claims, 56 million dollars dispensed August 18, 2004 –surveillance indicates highly pathogenic influenza eliminated from BC flocks –all control measured eliminated

Avian H5N1 disease in cats intra tracheal inoculation in-contact feeding infected chick control or H3N2 virus excretion by cats Kuiken et al. Oct 2004 Science 306:241

HA and host specificity 2,3 2,6 2,3 2,6 avian gutpig resp. tracthuman resp. tract avian H1-H15 pig H1, H3 H1(1918)H2, H3 human Stevens. Science, March 19, 2004

Why does avian H5N1spread inefficiently between humans Shinya et al. Nature March 22, 2006 nasal mucosa paranasal sinus bronchus resp. bronchiole alveolus

Process for human influenza vaccines February meeting –Commonwealth Serum Labs (Australia) –CDC (USA) –Natl. Inst. For Medical Research (UK) –European Inst. For Biological Standardization (EU) –Food and Drug Admin. (USA)

Process for human influenza vaccines March-April –Genetic and antigenic characterization of approved strains –Distribution by WHO to manufacturers –Production of seed stock –Tests for contaminants (bacteria, mycoplasma, viruses)

Process for human influenza vaccines April-August –Vaccine production –License application made –Clinical trials (to be submitted before vaccination season)

Process for human influenza vaccines August-September –Distribution begins

Human flu vaccine composition for 2008 A/Brisbane/59/2007 (H1N1) A/Brisbane/2007 (H3N2) B/Florida/4/2006