Dr A.J.France. Ninewells Hospital. 2010

© A.J.France 2010

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

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Replication of flu virus

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

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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

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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

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Clinical features 2

In bed for 3-4 days Then 5-6 days recovery Back to work within two weeks

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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

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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

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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

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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%

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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

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Get the full history

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Influenza vaccines

Trivalent, inactivated vaccine A: H1N1, A: H3N2, B strains Prepared in eggs Defined group of recipients

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