Pandemic Influenza. Unit 1 - Background Information. Training Kit for

Transcription

1 Training Kit for Pandemic Influenza Unit 1 - Background Information Prepared by Infectious Disease Control Training Centre, Hospital Authority Infection Control Branch, Centre for Health Protection, Department of Health

2 Objectives By the end of this unit, you will be familiar with: 1. the differences between human and avian influenza 2. emergence of H5 influenza A virus as a potential pandemic virus 3. what is a pandemic Unit 1 - Background Information Slide 1-2

3 Influenza virus Orthomyxoviridae 2 major antigenic glycoproteins: Haemagglutinin (HA) (H1-16) Neuraminidase (NA) (N1-9) Antigenic Drift Change of genetic material due to lack of proof-reading during replication Responsible for annual epidemic Haemagglutinin Neuraminidase Antigenic Shift reassortment and merging of genetic materials from different influenza strains novel viral subtype, most human lack immunity Responsible for pandemics Single-strand RNA with 8 gene segment The Influenza Virion Unit 1 - Background Information Slide 1-3

4 Influenza A H5N1 Virus H5N1 is of particular concern Mutates rapidly Acquire genes from flu strains in other species Highly pathogenic in humans Haemagglutinin Neuraminidase Birds, if surviving the infection, excrete the virus for 10 days, orally and in feces Single-strand RNA with 8 gene segment The H5N1 Virion Unit 1 - Background Information Slide 1-4

5 Human Influenza Subtypes: A(H1 - H3), B Droplet transmission Typical Incubation period: 2 4 days, with an average of 2 days Symptoms: Fever, headache, myalgia, running nose, cough, sore throat. Usually subside in 2 7 days Unit 1 - Background Information Slide 1-5

6 Emergence of H5 Influenza Human diseases caused by purely avian influenza viruses (without prior re-assortment with human virus) (from WHO website, accessed on 7 Jan 2009) Pre-1997 sporadic conjunctivitis-h7n7 1997: H5N1 ( Hong Kong) : 18 cases, 6 deaths 1998, 1999 and 2003 H9N2 ( Hong Kong ; Guangdong) 2003 H5N1: China: 1 case, 1 death Vietnam: 3 cases; 3 deaths 2003 H7N7 ( Holland) 78 conjunctivitis, 7 with flu-like illness, 4 other, 1 death 2004 H5N1 - Thailand: 17 cases; 12 deaths Vietnam: 29 cases; 20 deaths 2004 H 7 disease in Canada 2005 H5N1- Cambodia, China, Indonesia, Thailand; Vietnam: 97 cases, 42 deaths 2006 H5N1 Azerbaijan, Cambodia, China, Djibouti, Egypt, Indonesia, Iraq, Thailand, Turkey: 116 cases, 80 deaths 2007 H5N1 Cambodia, China, Egypt, Indonesia, Lao, Myanmar, Nigeria, Pakistan, Vietnam: 88 cases, 59 deaths 2008 H5N1 Bangladesh, Cambodia, China, Egypt, Indonesia, Vietnam: 42 cases, 31 death Unit 1 - Background Information Slide 1-6

7 Influenza A H5N1 Virus The Species Barrier Chicken New to H5N1 virus Invariable fatal when attacked Pigs Avian flu in pigs are particularly worrisome as they possess bird flu and human flu receptors. They act as a reservoir for genetic reassortment for flu virus Human Birds and Water Fouls: (e.g. Ducks, geese) Natural carrier of avian flu, can be symptomatic or asymptomatic Feline (Cats, Tigers and Leopards) Unit 1 - Background Information Slide 1-7

8 Influenza A H5N1 Virus How can the species barrier be broken? Method 1 H5N1 virion Mutation Mutation Affect water fouls & wild birds Affect domestic poultry like chicken Affect several mammalian species include felines, pigs, and human Unit 1 - Background Information Slide 1-8

9 Influenza A H5N1 Virus How can the species barrier be broken? Method 2 Avian Flu Human Flu Reassortment It is important to remember that H1 & H3 viral subtypes are prevalent in pigs Unit 1 - Background Information Slide 1-9

10 What is Pandemic Endemic stable pattern of occurrence of the disease. Epidemic occurrence of the disease greatly in excess of the expected rate. Pandemic worldwide spread of a disease, outbreaks or epidemics occurring in many countries & in most regions of the world Unit 1 - Background Information Slide 1-10

11 What is Pandemic Previous FLU Pandemics Year Subtype Source Result 1918 H1N1 Spanish Flu Swine & Birds million death 1957 H2N2 Asian Flu Human & Birds >2 million excess mortality 1968 H3N2 Hong Kong Flu Human & Birds 1 million excess mortality Unit 1 - Background Information Slide 1-11

12 What is Pandemic Pandemic: Health care system rapidly overburdened Social Disruption & Panic Unit 1 - Background Information Slide 1-12

13 What is Pandemic Prerequisites for the start of an influenza pandemic 1. Emergence of new Haemagglutinin subtype of influenza A virus 2. General population have no or little immunity 3. Cause human disease in a high proportion of people infected 4. Efficient human to human transmission Unit 1 - Background Information Slide 1-13

14 What is Pandemic Progression of pandemic Sporadic cases No human-to-human transmission Clusters of of cases Inefficient human-to- human transmission Pandemic On-going cluster related transmission Substantial pandemic risk Unit 1 - Background Information Slide 1-14

15 End of Unit 1 Slide 1-15