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 H5 or H7 Low pathogenicity avian influenza (LPAI) Causes mild disease in poultry Contains other H subtypes Includes non-hpai H5 and H7 LPAI H5 or H7 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 Domestic and wild birds Waterfowl and shorebirds Natural reservoirs for influenza A Carry all known H and N antigens Usually in the LPAI form Predominant subtypes change periodically Pigs 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 H5N1 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 H5N1 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 H5N1 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/h1n1flu/updates/us/
http://www.cdc.gov/h1n1flu/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/0601fauci/0601fauci.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 H5N1 viruses may be resistant to amantadine, rimantadine Center for Food Security and Public Health, Iowa State University, 2013
The H1N1 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