Influenza

1. Influenza Ieuan Davies

2. Signs and Symptoms • Influenza is an acute, viral respiratory infection. • Fever, chills, headache, aches and pains throughout the body, sore throat which may lead to bronchitis or pneumonia. • Vomiting and diarrhoea may also occur. • Many deaths have been attributed to influenza

3. Influenza Pandemics • A pandemic is a world wide spread of infection occurring in many countries simultaneously. • Flu pandemics occur approximately every thirty years. • Flu pandemics occur because a new strain of the virus emerges for which people have no immunity and there are no vaccines available.

4. Pandemics • New flu viruses occur due to mutation • Mutation occurs because different strains of influenza virus can exchange genes by infecting different animals • Avian influenza viruses can exchange genes with human influenza viruses creating hybrid strains

5. 1918 - 1919 pandemic • This killed between 20 – 40 million people • Face masks were worn but provided little protection against infection

6. Cause • The cause of influenza is the influenza virus. • Influenza A, B and C viruses are found • Influenza A viruses are associated with serious illness and pandemics

7. Influenza virus • The flu virus is an RNA virus • The genome codes for five viral proteins and is made of eight fragments. • The virus has a lipid envelope with two glycoproteins present

8. Flu virus glycoproteins • Haemagglutinin - this glycoprotein plays a part in infection and provides the “H” in the strain type. • Haemagglutinin attaches the virus to cells and allows the viral envelope to fuse with the cell membrane and enter cells. • Neuraminidase – has a mushroom shape, its role is to allow the release of viruses to infect other cells

9. HN terminolgy • H refers to Haemagglutinin types and each is given a number H1, H2 etc, • Neuraminidase is designated N and different forms are available as well e.g. H5N1 (avian) and H1N1. • Different combinations of H and N glycoproteins give rise to different strains

10. Antigenic shift and antigenic drift • Mutations which produce small changes in antigens are referred to as antigenic drift and these occur in the same strain • Mutations which result in a major change and produce new strains are referred to as antigenic shifts

11. Life cycle of the ‘flu virus

12. Transmission • The virus is spread by inhalation or by direct contact. • Reservoirs of infection are primarily humans, but birds and pigs can act as reservoirs. • The multiple host status makes for mixing of flu types.

13. Prevention • Public education campaigns are used to reduce infection rates • Isolation of infected people is desirable but not always practical • Immunisation

14. Immunisation • Vaccines are offered to people aged 65 or over (Note: Currently this group has some immunity and are not being targeted) • Clinically at risk groups – asthmatics, immuno-compromised patients, diabetics, people with chronic respiratory disease. • Health care workers • Vaccine effectiveness varies between 40 – 60%

15. Chemotherapy • Tamiflu (oseltamivir) – inhibits the neuraminidase and thus prevents the spread of the virus in the body • Tamiflu can therefore be used to reduce the length of illness and its transmission within a household • Resistance of H1N1 strain to oseltamivir has been reported at 25%

16. Conclusion • Flu can be a bit of a swine! • Prevention is better than cure! • Avoid contact with infected people. • Read how the population of Eyam avoided spreading the plague! • Eyam - Plague Village - Derbyshire

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