INFLUENZA VIROLOGY OF INFLUENZA Subtypes A Causes outbreak

INFLUENZA

VIROLOGY OF INFLUENZA Subtypes: A - Causes outbreak B - Causes outbreaks C - Does not cause outbreaks

PATHOGENICITY • High pathogenicity avian influenza (HPAI) – Causes severe disease in poultry – Contains subtypes H 5 or H 7 • Low pathogenicity avian influenza (LPAI) – Causes mild disease in poultry – Contains other H subtypes • Includes non-HPAI H 5 and H 7 • LPAI H 5 or H 7 subtypes can mutate into HPAI Center for Food Security and Public Health, Iowa State University, 2013

Immunogenic Components of the Influenza Virus • Surface glycoproteins, 15 hemagglutinin (H 1 -H 15), nine neurominidases (N 1 -N 9) • H 1 -H 3 and N 1 N 2 established in humans • Influenza characterized by combination of H and N glycoproteins § 1917 pandemic - H 1 N 1 § 2004 avian influenza - H 5 N 1 § 2009 H 1 N 1 • Antigenic mix determines severity of disease • Human response specific to hemagglutinin and neurominidase glycoproteins

Antigenic Drift and Shift • Antigenic drift – Small changes in influenza virus due to point mutations accumulated during virus replication • Antigenic shift – Abrupt change in virus subtype • Genetic reassortment between subtypes • Direct transfer of virus • Re-emergence of virus Center for Food Security and Public Health, Iowa State University, 2013

RESERVOIRS v. Domestic and wild birds v. Waterfowl and shorebirds ØNatural reservoirs for influenza A ØCarry all known H and N antigens – Usually in the LPAI form ØPredominant subtypes change periodically v Pigs v Wet markets (live animals) Center for Food Security and Public Health, Iowa State University, 2013

Figure 1. Natural hosts of influenza viruses Nicholson et al. Influenza. Lancet 362: 1734, 2003

Nicholson et al. Influenza. Lancet 362: 1735, 2003 Figure 2. Origin of antigenic shift and pandemic influenza. The segmented nature of the influenza A genome, which has eight genes, facilitates reassortment; up to 256 gene combinations are possible during coinfection with human and non-human viruses. Antigenic shift can arise when genes encoding at least the haemagglutinin surface glycoprotein are introduced into people, by direct transmission of an avian virus from birds, as occurred with H 5 N 1 virus, or after genetic reassortment in pigs, which support the growth of both avian and human viruses.

Morbidity and Mortality: Birds • Domesticated poultry – HPAI morbidity and mortality rates approach 90 -100% • Wild birds – Typically asymptomatic • Some H 5 N 1 viruses may cause death Center for Food Security and Public Health, Iowa State University, 2013

Influenza Epidemics • Epidemic requirements 1. New influenza subtype must emerge in species with little to no immunity 2. Virus must produce disease in that species 3. Sustainable transmission must occur in new species • Note: Asian lineage H 5 N 1 has NOT met third criteria in humans Center for Food Security and Public Health, Iowa State University, 2013

Transmission in Poultry • In an infected flock, virus can spread in multiple ways – Fecal-oral – Aerosol – Fomites – Mechanical vectors • Virus introduction – Migratory birds – Infected poultry, pet birds Center for Food Security and Public Health, Iowa State University, 2013

Influenza Virus Survival • Virus persistence in aquatic environments – Weeks to months – Preferred conditions • Low temperatures, brackish water – May survive indefinitely when frozen • Virus persistence in feces – Weeks to months Center for Food Security and Public Health, Iowa State University, 2013

SURVEILLANCE FOR FLU

http: //www. cdc. gov/h 1 n 1 flu/updates/us/

http: //www. cdc. gov/h 1 n 1 flu/updates/us/ - real-time

Update: influenza activity – U. S. , Sept 29 -Dec 7, 2013. MMWR 62(50): 1034, 2013.

The figure shows peak influenza activity for the United States by month for the 1976 -77 through 2008 -09 influenza seasons. The month with the highest percentage of cases (nearly 50%) was February, followed by January with 20% and March and December, with approximately 15% of all cases. Prevention and control of seasonal influenza with vaccines. MMWR 58(RR-8): 5, 2009

http: //www. milbank. org/reports/0601 fauci/0601 Fauci. pdf

CLINICAL OUTCOMES OF INFLUENZA INFECTION • Asymptomatic • Symptomatic § Respiratory syndrome - mild to severe § Gastrointestinal symptoms § Involvement of major organs - brain, heart, etc. § Death

Factors Influencing the Response to Influenza • Age • Pre-existing immunity (some crossover) • Smoking • Concurrent other health conditions • Immunosuppression • Pregnancy

Treatment in Humans • Antiviral drugs – Amantadine – Rimantadine – Zanamivir – Oseltamivir • Currently circulating H 5 N 1 viruses may be resistant to amantadine, rimantadine Center for Food Security and Public Health, Iowa State University, 2013

The H 1 N 1 Epidemic

Kaplan K. How the new virus came to be. LA Times, 14 Sept, 2009; latimes. com/health

RECOMMENDATIONS TO PREVENT FLU

STRATEGIES TO PREVENT FLU (1) • COVER MOUTH AND NOSE WHEN SNEEZING • WASH HANDS FREQUENTLY WITH SOAP AND WATER OR ALCOHOL • AVOID TOUCHING EYES, NOSE AND MOUTH • AVOID CONTACT WITH SICK PEOPLE • AVOID CROWDED CONGESTED ENVIRONMENTS

STRATEGIES TO PREVENT FLU (2) • IF SICK STAY HOME, DON’T EXPOSE OTHERS • FOLLOW PUBLIC HEALTH ADVICE; e. g. school closures etc. • GET FLU SHOT(S) • TAKE ANTIVIRAL DRUGS IF PHYSICIAN RECOMMENDS