The 2009 Influenza Pandemic

Influenza A virus, subtype H1N1

“pandemic” novel strain, the majority of the population

has not been exposed to it before (no immunity)

flu pandemic highly contagious

can infect cells deep in the lungs

old flu vaccines are not effective

Flu vs. cold

there is no “stomach flu” – if it lasts 24 h and makes you vomit and have diarrhea it’s viral gastroenteritis!

both are caused by viruses and antibiotics, herbal remedies and homeopathic medicines are useless ...

Cold• usually comes on gradually — over the

course of a day or two

• leaves you feeling tired, sneezing, coughing and with a runny nose

• fever is rare and not very high

• usually last three to four days, but can hang around for 10 days to two weeks

Flu• comes on suddenly

• feel weak and tired and you could run a fever as high as 40 C

• muscles and joints will probably ache, you will feel chilled and could have a severe headache and sore throat

• fever may last three to five days, but you could feel weak and tired for two to three weeks

Signs & symptoms Cold Flu

Fever Occasional Often above 38.5 C for 2-4 days

Headache Frequent, but not severe Prominent and often severe

Aches/pains Slight Often severe

Fatigue/weakness Mild Can last 2-3 weeks

Extreme exhaustion

Never Early and prominent

Stuffy nose Common Occasional

Sore throat Common Occasional

Cough Hacking Can be severe

Chest discomfort Mild to moderate Common, can become severe

Onset Gradual (develops over a day or two) Sudden (within a few hours)

Cause 200 strains of cold virus 3 strains of influenza virus

The Flu

Influenza is mainly a disease of water fowl

H1-16\N1-9

Influenza Types

Influenza Types Hosts

Type A Humans, birds,

pigs and horses

Type B Humans only

Type C Humans only

Influenza Viral Structure

an enveloped RNA virus

has Hemagluttinin and Neuraminidase glycoproteins on its surface

RNPs: ribonucleoproteins, transcribe viral RNA into cellular RNA

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

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, and immunosuppressed hosts

...a sneeze

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…)

Attack rates: 10-20% general population, selected populations 40-50%

• Typical Season: 200,000 hospitalizations and 36,000 deaths

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

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’

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)

BIG change, can cause pandemics

PANDEMICS OF INFLUENZA

20

H7

H5

H9*

1980

1997

Recorded new avian influenzas

1996 2002

1999

2003

1955 1965 1975 1985 1995 2005

H1N1

H2N2

1889RussianinfluenzaH2N2

H2N2

1957AsianinfluenzaH2N2

H3N2

1968Hong KonginfluenzaH3N2

H3N8

1900Old Hong Kong influenzaH3N8

1918SpanishinfluenzaH1N1

1915 1925 1955 1965 1975 1985 1995 20051895 1905 2010 2015

2009PandemicinfluenzaH1N1

Recorded human pandemic influenza(early sub-types inferred)

Reproduced and adapted (2009) with permission of Dr Masato Tashiro, Director, Center for Influenza Virus Research, National Institute of Infectious Diseases (NIID), Japan. Animated slide: Press space bar

H1N1Pandemic

H1N1

GENETIC ORIGINS OF THE PANDEMIC (H1N1) 2009 VIRUS: VIRAL REASSORTMENT

21

PB2PB1PAHANPNAMPNS

PB2PB1PAHANPNAMPNS

PB2PB1PAHANPNAMPNS

Classical swine, N. American lineageAvian, N. American lineageHuman seasonal H3N2Eurasian swine lineage

Eurasian swine H1N1

N. American H1N1(swine/avian/human)

Pandemic (H1N1) 2009, combining swine, avian and human viral components

H1N1 Antigenic ShiftH1N1 Antigenic Shift

Human and avian flu viruses infect same host cell (eg. swine); exchange of segments occurs

New subtype of influenza with potential to cause a pandemic may be produced

RNA

Haemagglutinin

Neuraminidase

Antibodies bind to haemagglutinin; inhibit infection

Antigenic Drift

Mutation in haemagglutinin

Antibodies can no longer bind to haemagglutinin; infection and disease results

THE “SWINE FLU”: H1N1 (APRIL 2009 - 2010)

Caused by a strain of influenza A, H1N1

Originated as a mixture of swine, avian, and human influenzas

The genetic change that allows a virus to “jump species” is called antigenic shift

SEASONAL INFLUENZA COMPARED TO PANDEMIC — PROPORTIONS OF TYPES OF CASES

26

Asymptomatic

Clinicalsymptoms

Deaths

Requiring hospitalisation

Seasonal influenza Pandemic

Asymptomatic

ClinicalsymptomsDeaths

Requiring hospitalisation

WHAT WE KNOW ABOUT 2009 H1N1

Infection rate for probable and confirmed cases highest in 5−24 year age group.

Hospitalization rate highest in 0−4 year age group, followed by 5−24 year age group. • Pregnant women seem particularly at risk

Most deaths in 25−64 year age group in people with chronic underlying disease. (total about 300 000 world-wide, most in Africa and Southeastern Asia)

Adults, especially 60 years and old, may have some degree of preexisting protection

There are some predictions that up to 1/3 of the population could have become infected…

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H1N1/09 virus

thought to have originated in Asia

mix of swine, avian, and human flu, with pigs as the “mixing vessel”

a new vaccine did arrive mid-October

was not mutating quickly

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

Treatment options Let the immune system deal with it

If symptoms severe – antiviral drugs

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)

Prevention

1) Basic measures to reduce the spread of infection Hand washing

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.

Prevention2) 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

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

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

Examples of influenza outbreaks

Canada Flu Video

http://www.cbc.ca/news/health/story/2012/11/22/flu-deaths-crowe.html

What can we do to prepare ourselves for a pandemic?