Influenza. Paul K. S. Chan Department of Microbiology The Chinese University of Hong Kong

Transcription

1 Influenza Paul K. S. Chan Department of Microbiology The Chinese University of Hong Kong

2 Classification & Nomenclature Influenza virus A, B & C Influenza A : Haemagglutinin (H 1-16), neuraminidase (N1-9) A H3N2, A H1N1 A/Beijing/262/1995 (H1N1) A/Fujian/411/2002 (H3N2) A/Brisbane/59/2007 (H1N1) A/swine/Guangxi/13/2006 (H1N2) A/duck/Italy/69238/2007 (H1N1) A/goose/Guangdong/1/1996 (H5N1) A/quail/Hong Kong/G1/1997 (H9N2) A/Hong Kong/483/1997 (H5N1) A/California/04/2009 (H1N1) A/Texas/04/2009 (H1N1) A/Mexico/4482/2009 (H1N1)

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4 Seasonal Vs. Pandemic Influenza Seasonal Usual types A H3N2, A H1N1, B Severe disease for high-risk group Generally mild for healthy adults No. of Cases Jan Apr Jul Oct 1997-Jan Apr Jul Oct 1998-Jan Apr Jul Oct 1999-Jan Apr Jul Oct 2000-Jan Apr Jul Oct 2001-Jan Apr Jul Oct Pandemic Novel type in human Global involvement High-mortality in general population H1N1 H2N2 H3N2 H1N

5 Species Barrier of Influenza Strains Haemagglutinin H Neuraminidase N Genetic Reassortment Direct Transmission

6 Distribution of Influenza subtypes Human Swine Equine Avian HA subtype H1 H2 +/- H3 H4 H5 H6 H7 H8 H9 H10-H16 NA subtype N1 N2 N3 N4 N5 N6 N7 N8 N9

7 Gene Reassortment Avian Cell cytoplasm Progeny reassortants 256 different combinations H5N1 Co-infection of 2 subtypes in the same cell H5N2 H5N1 H3N2 Human Intermediate Host Pig Human H3N1 H3N2

8 Human Swine H1N1

9 Swine Influenza Highly contagious respiratory disease of pigs caused by several Flu A viruses H1N1, H1N2, H3N1, H3N2 H1N1 is the most common High morbidity but low mortality (1-4%) in pigs Pigs can be infected by avian influenza and human influenza virus Simultaneous infection can allow mixing of gene from different viruses to form a reassortant virus

10 Previous Swine Influenza in Humans United States 1976, Fort Dix 1 death, ~500 infected ~500 Guillian-Barre syndrome, 30 death after 40 million doses of vaccine 1988, Wisconsin 1 death Feb 2009, 12 cases in US Hong Kong Hong Kong 1999: 10 mth old girl, mild, recovered 2001: 4 mth old girl, mild, recovered

11 Incubation Period & Infectious Period Incubation period: 7 days (usually 1-3 days) Infectious Period: Starting: 1 day before symptom onbset Ending: 1 days after symptom subsided Usually 7 days for adults Longer for young children

12 Signs & Symptoms Incubation period: 7 days Abrupt onset of fever & chills + headache, sore throat, myalgia, malaise, anorexia, dry cough Young children: Non-specific febrile illness, GI complaints, otitis media, seizures, croup, conjunctivitis Adults: Hoarseness, dizziness, arthralgia, chest pain, insomnia Elderly: Sputum production, dyspnoea

13 Transmission Droplet 1 m New Flu Airborne???

14 Transmission Fomite Contact with respiration contaminated items survival in environment ~ 8-12 hr. (up to 48 hr) easily to disinfect ~ >56 o C, hypo6, hibiscrub, alcohol, soap + water

15 Transmission Faecal shedding Human H5N1: Seasonal influenza: Human (swine) H1N1: some cases rare NO information yet

16 Prevention High risk situations Face mask Most situations Hand washing Environmental cleansing

17 Prevention Social Distancing

18 Influenza Vaccine

19 Properties of Influenza Vaccines Tri-valent inactivated vaccine Flu A H1N1 Flu A H3N2 Flu B Repeat each year Short duration of protection 9-12 months Efficacy Matching between vaccine strains and circulating strains

20 Vaccine Efficacy Healthy adults: 70-90% preventing illness High-risk group: 50% reduction in severe disease and death Matching of Strains

21 Seasonal vaccine & Human (swine) H1N1 No data on cross-protection against the new human (swine) H1N1 Prevent seasonal flu Avoid false-alarm

22 Anti-viral agents Amandatine / Rimantidine Oseltamivir (Tamiflu) Zanamivir (Relenza) Seasonal A H1N1 Sensitive Resistant Sensitive New Human Swine A H1N1 Resistant Sensitive Sensitive

23 How serious is influenza pandemic? 1918 : ~20-50 million deaths 1957 : ~1 million deaths 1968 : 0.75 million deaths

24 Human swine flu situation update

25 Human swine flu situation update 5 May 2009 Worldwide: 21 countries 1124 cases Mexico: 590 cases 25 deaths US: HK: 286 cases 1 death 1 case 0 death

26 Will this be a severe or mild pandemic? 1918 Spanish Flu: 1 st wave ~ Spring 1918, Kansa Mild, contagious, a few deaths, received limited attention Spread to Europe 2 nd wave~ Late Aug 1918, A virulent form emerged in Western France, Spread around the world Sept Nov 1918 Death rate >2.5% 3 rd wave~ Spring 1919 Similar impact as 2 nd wave

27 Let s s try every means to keep human swine flu away