LF303:Medical Virology
,LECTURE 1: INFLUENZA VIRUS
Influenza signs and symptoms
• Very sudden onset, 1-4 days post-infection
• Severe respiratory disease with URT and LRT involved
• Headache, chills, dry cough, bodyaches
• High temperature (fever)
• Followed by sore throat / congestion
• Can develop pneumonia
• Exhaustion which can last 1-2 weeks
• Susceptible to secondary respiratory infections during recovery phase
• High mortality in elderly, very young and those with chronic heart, lung or kidney
problems, diabetes etc
Influenza disease in humans
- There are 2 important patterns of epidemiological spread of influenza:
1. Annual epidemics: Timing depends on location (temperature and tropical) and the scale can vary
2. Sporadic global pandemics: Scale and timing is unpredictable
- Issue of differential diagnosis: influenza like illness (symptoms may be similar to another disease)
Geographic variation in influenza epidemic months
- Annual epidemics occur at different times, depending on
the location.
- The maximum incidence of influenza infection, occurs in
the winter for the norther temporal latitude. The peak is in
January and is down to very low levels in spring and summer
and starts to re-appear in the autumn.
- That corresponds perfectly for the southern temporal
latitude as the peak for influenza is in July, which is the
metered-logical equivalent of our January.
- In the tropical latitudes, we see a much more even
distribution of flu incidents but with some tendency towards
a peak in the months of winter.
, Annual epidemic of influenza in the UK Pandemic of influenza
In the UK the annual epidemics are recorded - The most recent influenza pandemic was in
based on number of GP consultations for a 2009 and the peak was in summer for the UK.
certain set of symptoms. Evenrey year there is a - Pandemics can occur unpredictable and
peak during winter time and some years the peak spread along time.
is much higher with much more infections. More
recently the number of infections have been
declining, with small variations. It could have
declined but to the effect of the influenza vaccine
Viruses causing influenza
- Influenza viruses A, B and C:
• All from the Orthomyxovirus family
• All have segmented, negative sense RNA genomes
• Only flu A causes pandemics
- Flu A is found in many other species:
• Including wild and farmed birds, pigs and horses
• Subclinical gut / RT infection in wild aquatic birds
• Potentially a lethal disease in poultry
• Flu B and C have much more restricted host ranges
• Flu D is not known to infect humans
Influenza A particle
- The surface of the virus has HA and NA proteins.
- These two are the major antigens of the virus which our
immune system responds to against to make antibodies.
, Flu A replication cycle
- It is an enveloped virus.
- After it attaches to the cell surface
receptor, you get internalisation in an
endosome. The fusion with the endosome
triggered by low pH to release the genome
in the cytoplasm of the cell (-ve sense RNA).
- It gets imported in the nucleus replication
and transcription occurs. The mRNA comes
to the cytoplasm to be translated and
processes of replication and translation give
rise to the components required to
reassemble a progeny virus.
- That progeny then is formed through
budding to release intact virus particles.
Influenza A subtypes
- Haemagglutinin and Neuraminidase these represent structural classes of
the proteins of HA and NA.
- HA: H1-H16
- NA: N1-N9
- The structural architecture of these proteins can be described through the
numbering systems and they make up the names of the viruses, such as:
!
1. H1N1
2. H2N2 Human pandemics
3. H3N2
4. H3N8 (maybe)
- This allows genome reassortment where there is a mix and mach of viral
parts and combinations
Influenza A virus circulation
- All subtypes circulate in wild birds with reassortment
of these viruses within the host species
- Restricted sets of subtypes to other species, such as
farm animals that can also support a range of viral
subtypes, horses, dogs etc.
- This flow is responsible for the emergence of influenza
virus pandemics.
,LECTURE 1: INFLUENZA VIRUS
Influenza signs and symptoms
• Very sudden onset, 1-4 days post-infection
• Severe respiratory disease with URT and LRT involved
• Headache, chills, dry cough, bodyaches
• High temperature (fever)
• Followed by sore throat / congestion
• Can develop pneumonia
• Exhaustion which can last 1-2 weeks
• Susceptible to secondary respiratory infections during recovery phase
• High mortality in elderly, very young and those with chronic heart, lung or kidney
problems, diabetes etc
Influenza disease in humans
- There are 2 important patterns of epidemiological spread of influenza:
1. Annual epidemics: Timing depends on location (temperature and tropical) and the scale can vary
2. Sporadic global pandemics: Scale and timing is unpredictable
- Issue of differential diagnosis: influenza like illness (symptoms may be similar to another disease)
Geographic variation in influenza epidemic months
- Annual epidemics occur at different times, depending on
the location.
- The maximum incidence of influenza infection, occurs in
the winter for the norther temporal latitude. The peak is in
January and is down to very low levels in spring and summer
and starts to re-appear in the autumn.
- That corresponds perfectly for the southern temporal
latitude as the peak for influenza is in July, which is the
metered-logical equivalent of our January.
- In the tropical latitudes, we see a much more even
distribution of flu incidents but with some tendency towards
a peak in the months of winter.
, Annual epidemic of influenza in the UK Pandemic of influenza
In the UK the annual epidemics are recorded - The most recent influenza pandemic was in
based on number of GP consultations for a 2009 and the peak was in summer for the UK.
certain set of symptoms. Evenrey year there is a - Pandemics can occur unpredictable and
peak during winter time and some years the peak spread along time.
is much higher with much more infections. More
recently the number of infections have been
declining, with small variations. It could have
declined but to the effect of the influenza vaccine
Viruses causing influenza
- Influenza viruses A, B and C:
• All from the Orthomyxovirus family
• All have segmented, negative sense RNA genomes
• Only flu A causes pandemics
- Flu A is found in many other species:
• Including wild and farmed birds, pigs and horses
• Subclinical gut / RT infection in wild aquatic birds
• Potentially a lethal disease in poultry
• Flu B and C have much more restricted host ranges
• Flu D is not known to infect humans
Influenza A particle
- The surface of the virus has HA and NA proteins.
- These two are the major antigens of the virus which our
immune system responds to against to make antibodies.
, Flu A replication cycle
- It is an enveloped virus.
- After it attaches to the cell surface
receptor, you get internalisation in an
endosome. The fusion with the endosome
triggered by low pH to release the genome
in the cytoplasm of the cell (-ve sense RNA).
- It gets imported in the nucleus replication
and transcription occurs. The mRNA comes
to the cytoplasm to be translated and
processes of replication and translation give
rise to the components required to
reassemble a progeny virus.
- That progeny then is formed through
budding to release intact virus particles.
Influenza A subtypes
- Haemagglutinin and Neuraminidase these represent structural classes of
the proteins of HA and NA.
- HA: H1-H16
- NA: N1-N9
- The structural architecture of these proteins can be described through the
numbering systems and they make up the names of the viruses, such as:
!
1. H1N1
2. H2N2 Human pandemics
3. H3N2
4. H3N8 (maybe)
- This allows genome reassortment where there is a mix and mach of viral
parts and combinations
Influenza A virus circulation
- All subtypes circulate in wild birds with reassortment
of these viruses within the host species
- Restricted sets of subtypes to other species, such as
farm animals that can also support a range of viral
subtypes, horses, dogs etc.
- This flow is responsible for the emergence of influenza
virus pandemics.
