1. Dr A.J.France. Ninewells Hospital. 2010 © A.J.France 2010

2. Influenza virology  RNA enveloped particles  Three genera: A B C  Haemagglutinin H1 – H15  Neuraminidase N1 – N9  H1 H2 H3 N1 N2 in man since 1900  Spread by fine droplets and by fomites © A.J.France 2010

3. Replication of flu virus

4. Influenza virology  Antigenic drift  Natural selection  A feature of seasonal flu  Antigenic shift  Reassortment in other species  Pigs, ducks, chickens  A feature of pandemic flu © A.J.France 2010

5. Influenza nomenclature  Seasonal flu – every year  Small numbers of cases amongst a population with background immunity  Pandemic flu – not very often  Large number of cases with rapid spread in a population with minimal immunity  Bird flu - rare  Migration of avian flu to poultry workers. Very high mortality but little man to man transmission  General public flu  Not flu at all © A.J.France 2010

6. Clinical features 1  Incubation 1-4 days  Abrupt onset fever, chills, headache, sore throat, myalgia, malaise, anorexia, dry cough  Clear nasal discharge  Signs of complications © A.J.France 2010

7. Clinical features 2  In bed for 3-4 days  Then 5-6 days recovery  Back to work within two weeks © A.J.France 2010

8. Complications of influenza  Death 0.37%  Primary viral pneumonia  Dry cough, bloody sputum and respiratory failure within 24 hours of onset of initial fever  Secondary bacterial pneumonia  A new fever on day 7  Myositis (Skeletal and cardiac)  Encephalitis  Depression © A.J.France 2010

9. Anti-viral drugs  Neuraminidase inhibitors  Zanamavir (Relenza) disc haler  Oseltamivir (Tamiflu) oral  Benefits of oseltamivir  Reduced duration of symptoms by one day  Reduced use of antibiotics  Might reduce infectivity  No data on mortality © A.J.France 2010

10. Influenza pandemics  1918 more than 6 million deaths worldwide  1957 H2N2 Asian flu  1968 H3N2 Hong Kong flu  1997 H5N1 a close call  2009 H1N1 Mexico - mild © A.J.France 2010

11. Pandemic flu calculations for 16 weeks  In a population of 100,000  500-800 new cases per week. Max 1300  25,000 people taken ill  5,000 extra GP consultations  150 extra hospital admissions  100 excess deaths if attack rate is 25% and death rate 0.37% © A.J.France 2010

12. Pandemic influenza time course  International spread  First wave in UK within 3 months of initial case  First wave duration 3 – 5 months  Second wave, months later © A.J.France 2010

13. Get the full history © A.J.France 2010

14. Influenza vaccines  Trivalent, inactivated vaccine  A: H1N1, A: H3N2, B strains  Prepared in eggs  Defined group of recipients © A.J.France 2010