Influenza

1. Influenza What is it?

2. Influenza Virus

3. Understanding Terminology • Epidemic: serious outbreak in a single community, population or region • • Pandemic: epidemic spreading around the world affecting hundreds of thousands of people, across many countries

4. More on pandemics • Usually a novel strain, the majority of the population has not been exposed to it before (no immunity) • highly contagious • old flu vaccines are not effective

5. Influenza • Family orthomyxoviridae • Enveloped viruses – 80-120 nm, negative stranded RNA with 8 different segments. Allows for genetic re-assortment when >1 virus infects a single cell • Types A, B, and C: Significant differences in structure, genetics, organization, host range, epidemiologic and clinical characteristics • Covered with surface projections or spikes – Hemagglutinin and neuraminidase—used to subtype influenza A virus types.

6. Influenza Types Influenza Types Hosts Type A Humans, birds, pigs and horses Type B Humans only Type C Humans only

7. Naming of influenza viruses • Named by type / place isolated / culture # / year of isolation For example: • – A/Fujian/411/2002 (H3N2) • – B/Shanghai/361/2002-like

8. Spread • direct transmission (infected person sneezes mucus into the eyes, nose or mouth of another person) • through people inhaling the aerozolized droplets produced by infected people coughing, sneezing and spitting • hand-to-mouth transmission from either contaminated surfaces or direct personal contact, such as a hand-shake (doorknobs, light switches, bank notes…)

9. Symptoms of the cold and flu

11. Influenza – Epidemiology (study of health and illness at the population level) • Incubation period 1-4 days • Virus first detected just before onset of illness. • Virus usually not detected after 5 - 10 days. • More prolonged shedding in children, • immunosuppressed hosts • Transmission: via respiratory droplets – person to person, – direct contact,

12. Epidemiology continued • Attack rates 10-20% general population, selected populations 40-50% • • Typical Season: 200,000 hospitalizations and 36,000 deaths

13. How Does Influenza Change? • Particular characteristic that enables influenza A viruses to cause annual epidemics, even pandemics • Type A viruses undergo frequent changes in their surface antigens or proteins • Minor changes - antigenic drift • Major changes - antigenic shift

14. Antigenic Drift • Occurs among influenza A viruses resulting in emergence of new variants of prevailing strains every year • New variants result in seasonal flu each winter • Some years are worse than others – partly related to degree of ‘drift’

15. Antigenic Shift Occurs in two ways: • Sudden ‘adaptive’ change during replication of a normal virus OR • From an exchange of genes between human strain of an influenza A virus and an animal strain (e.g. avian flu)

16. Influenza Diagnosis • Most often a clinical diagnosis • Laboratory tests – molecular detection of virus in clinical specimens – culture of virus – serology • Rapid ‘near patient’ tests – detect the presence of flu within 30 minutes – cannot determine the specific virus

17. Treatment options • Let the immune system deal with it • If symptoms severe – antiviral drugs

18. Antiviral drugs • Prevent the flu virus from reproducing • Treatment can shorten the illness by a day and reduce hospitalisations by an estimated 50% (based on seasonal flu) • To be effective, must be taken within 48 hours of the onset of flu symptoms • Some common anti-virals for the flu are zanamivir and oseltamivir (Tamiflu)

19. Prevention 1) Basic measures to reduce the spread of infection • Hand washing: washing hands frequently with soap and water reduces the spread of the virus from the hands to the face, or to others • Respiratory hygiene: covering the mouth and nose when coughing or sneezing; using a tissue when possible; disposing of dirty tissue promptly and carefully – bag and bin • Avoiding non essential travel: non attendance at large gatherings such as concerts, theatres, cinemas, sports arenas etc

20. Prevention 2) Vaccines • Vaccines can prevent influenza infection, particularly important for the elderly and infants • Vaccine coverage is generally poor for infants – less than 10 percent; for the elderly, it can be above 60 percent

21. Influenza Vaccine • Vaccine takes 6-8 months to produce following the emergence of a new virus • •Supplies will be limited, if available at all – Priority groups are usually established for use of limited vaccine (like who?) – 2nd dose after 30 days will likely be required – Need to monitor vaccine safety and efficacy

22. Priority groups for vaccinations • Children 6-23 months of age • Adults >65 years • Persons 2-64 years of age with underlying chronic medical conditions • Women who will be pregnant during influenza season

23. Examples of influenza outbreaks

24. Bird and human influenza

25. Birds to humans or birds to animals to humans • Hong Kong 1997, H5N1 • HK, China 1999, H9N2 • Netherlands 2003, H7N7 • Hong Kong 2003, H5N1 •Viet Nam and Thailand, 2004 H5N1 Bottom shows bird to animal to human influenza

26. H1N1/09 virus • thought to have originated in Asia • mix of swine, avian, and human flu, with pigs as the “mixing vessel”

27. H1N1 Viral Structure • an enveloped RNA virus • has Hemagluttinin and Neuraminidase glycoproteins on its surface • RNPs: ribonucleoproteins, transcribe viral RNA into cellular RNA

28. Life Cycle • influenza attaches itself to cell’s surface using hemagluttinin (H) • it is brought into the cells entire and disassembles in it • once the virus has made copies of itself it uses nueraminidase (N) to leave the cell