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 Influenza Virus Nomenclature Influenza virus A, B & C Influenza A : Haemagglutinin (H), neuraminidase (N) A H3N2, A H1N1 A/New Caledonia/20/99 (H1N1) A/Beijing/262/95 (H1N1) A/Fujian/411/2002 (H3N2) A/Moscow/10/99 (H3N2)

3 Signs & Symptoms 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

4 Influenza Transmission & Infection Control Droplet 1 m Avian Flu Airborne?? Faecal shedding

5 Influenza Transmission & Infection Control Direct contact with respiration secretion / excretion-contaminated items survival in environment ~ 8-12 hr. (up to 48 hr) easily to disinfect ~ >56 o C, hypo6, hibiscrub, alcohol, soap gowns, masks, gloves & careful handwashing

6 Influenza Transmission & Infection Control Two most important defenses

7 Influenza Vaccine

8 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

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

10 Vaccination Priority Groups Persons living or working in personal care institutes Elderly persons aged >= 65 yr living in community Persons with chronic illness Health care workers Poultry workers Children aged 6-23 months Pregnant women 2 nd or 3 rd trimester # All other individuals not included above also benefit from vaccination

11 Anti-flu agents: Neuraminidase inhibitor Zanamivir : Relenza TM Dry powder, inhalation Targeted delivery Dosage adjustment not required Bronchospasm Oseltamivir : Tamiflu TM Capsule, oral suspension Systemic administration Cr ml/min, BD to QD Mild GI symptoms

12 What is Influenza Pandemic?

13 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

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

15 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

16 Concept of Reassortment of Influenza Viruses 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

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18 How close is the next Influenza Pandemic? Emergence of a potential strain in avian species Wide-spread transmission in avian species Occasional transmission to human / mixing vessels 1996 > H5N1 evolved 1997 > 2004, 2005 HK > Asia > Europe Efficient human-to-human transmission Pandemic > 380 human influenza H5N1 > 240 human deaths

19 Spread of H5N1 Influenza in Asia Japan 100s of millions of birds culled (As at 10 Jun 2008) China Laos Vietnam Cambodia Thailand Indonesia South Korea Human Cases: 383 Human Deaths: 241 Vietnam: 52 deaths Thailand: 17 deaths Cambodia: 7 deaths Indonesia 108 death China: 20 deaths

20 How serious is influenza pandemic? 1918 : million deaths 1957 : 1 million deaths 1968 : 0.75 million deaths Present estimates : >15% of population infected Death rate > 50%

21 Time-frame of Pandemic Alert Response Serious Response Emergence response Pandemic 1 st phase Pandemic 2 nd phase Human avian flu is occurring as isolated cases outside HK Poultry outbreaks in HK Human case in HK No efficient human-tohuman transmission Efficient human-tohuman transmission Focal / regional 100s-1000s cases No vaccine Antiviral prophylaxis Antiviral treatment Last for wks - months Regional / global few % of population Vaccine may be availa Antiviral: resistant? Last for months

22 Influenza Pandemic Preparedness Government Level Education & awareness Healthcare facilities Minimize spread of infection Maintain order of society Vaccine production & delivery Antiviral stockpiling Department / Unit Level Individual Level

23 Updates on April 2008 In early 2008, three children died of acute febrile illness and had influenza detected from their respiratory samples. An ad hoc committee was set up to investigate the cause of death and the possibility of emergence of a new influenza strain in Hong Kong. The investigation report concludes that the causes death of the 3 cases were different and were not linked with each other. There was no evidence to suspect that a new strain of higher pathogenicity was circulating in Hong Kong.

24 Updates on June 2008 In early June 2008, 4 retail life-poultry markets in Hong Kong had environmental samples found positive for influenza AH5N1. The Government raised the Alert Response Level to Serious Response Level All life chicken in retail markets in Hong Kong are culled. Importation of life chicken to Hong Kong was suspended for 21 days. As at 12 th June, no human H5N1 infection was suspected or confirmed.

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