Influenza virus
Morphology
- Belong to orthomyxoviridae → Envelope, RNA virus
- Contain single-stranded RNA which is segmented → 8 pieces
- There are three viral subtypes
- based on RNP and M protein antigens
- Type A → Causes all pandemics and most of the epidemics
- Type B → Sporadic and epidemics
- Type C → Causes endemic infection
- Types of influenza viruses are circulating in the world –
- A (H1N 1)-causes swine flu
- A (H3 N2)
- B
- H7 N9 of type A (caused an epidemic of avian influenza in China in 2013)
- A(H5 N 1)-
- causes bird flu or avian influenza
- 1997 bird flu pandemic
- In embryonated egg cultivation for influenza virus site of inoculation are:-
- Allontoic cavity or amniotic cavity
Antigenic structure
- It has two types of antigens:
a.Internal Antigen:
- Type-specific, i.e. (A, B, C) and stable.
- Consists of RNP or soluble (S) antigen and M protein antigen.
- It also includes envelope lipid antigen which is host specific.
b.Surface Viral or V antigen:
- Strain specific
- Show antigenic variations (A>B).
- Antigenic variation is highest in type A, less in type B and not seen in type C
- Two types:
|
Antigenic drift |
Antigenic shift |
|
Gradual and sequential change in genome occurring at regularly at frequent intervals |
Abrupt, drastic and discontinuous variation resulting in a novel virus |
|
New antigen related to previous antigen |
New surface antigen not related to previous |
|
Inaccurate viral RNA polymerase frequently produces point mutations in certain error-prone regions in the genes. |
Due to genetic reassortment between 2 strains, presumably during coinfection of a single host. |
|
Cause periodic epidemics |
Causes major epidemics and pandemic |
- V antigen composed of at least 2 virus-coded protein:
- hemagglutinin (H) and neuraminidase (N) which are critical for virulence.
- Strain-specific
- Cause hemagglutination.
- 16 subtypes
- Composed of two polypeptide
- HA1 and HA2
- Binds virus particle to susceptible cell
- Major antigen against which neutralizing antibodies.
- Receptor destroying enzyme (RDE)
- Cause elution.
- 9 subtypes
- Not as effective in protection as that of hemagglutinin.
- During budding release of virus particle from infected cell.
Source of infection:
- Case or subclinical case
Mode of transmission:
- Droplet infection by respiratory route
- Influenza affects all ages and both sexes.
Incubation period:
- 18-72 hour
- Data regarding the prevalence of influenza is not adequate
Influenza shows cyclic trend :
- With epidemic occurring every 2-3 years in case of influenza – A
- Every 4-7 years in case of influenza-B.
- Pandemics are caused by only influenza – A every 10-15 years.
Morphology
- Belong to orthomyxoviridae → Envelope, RNA virus
- Contain single-stranded RNA which is segmented → 8 pieces
- There are three viral subtypes
- based on RNP and M protein antigens
- Type A → Causes all pandemics and most of the epidemics
- Type B → Sporadic and epidemics
- Type C → Causes endemic infection
- Types of influenza viruses are circulating in the world –
- A (H1N 1)-causes swine flu
- A (H3 N2)
- B
- H7 N9 of type A (caused an epidemic of avian influenza in China in 2013)
- A(H5 N 1)-
- causes bird flu or avian influenza
- 1997 bird flu pandemic
- In embryonated egg cultivation for influenza virus site of inoculation are:-
- Allontoic cavity or amniotic cavity
Antigenic structure
a.Internal Antigen:
b.Surface Viral or V antigen:
- Antigenic variation is highest in type A, less in type B and not seen in type C
- Two types:
|
Antigenic drift |
Antigenic shift |
|
Gradual and sequential change in genome occurring at regularly at frequent intervals |
Abrupt, drastic and discontinuous variation resulting in a novel virus |
|
New antigen related to previous antigen |
New surface antigen not related to previous |
|
Inaccurate viral RNA polymerase frequently produces point mutations in certain error-prone regions in the genes. |
Due to genetic reassortment between 2 strains, presumably during coinfection of a single host. |
|
Cause periodic epidemics |
Causes major epidemics and pandemic |
- V antigen composed of at least 2 virus-coded protein:
- Cause hemagglutination.
- 16 subtypes
- Receptor destroying enzyme (RDE)
- Cause elution.
- 9 subtypes
Source of infection:
- Case or subclinical case
Mode of transmission:
- Droplet infection by respiratory route
- Influenza affects all ages and both sexes.
Incubation period:
- 18-72 hour
- Data regarding the prevalence of influenza is not adequate
Influenza shows cyclic trend :
- With epidemic occurring every 2-3 years in case of influenza – A
- Every 4-7 years in case of influenza-B.
- Pandemics are caused by only influenza – A every 10-15 years.
