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
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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?
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