Influenza virus

Influenza virus


Morphology

  • Belong to orthomyxoviridae  → Envelope, RNA virus
  • Contain single-stranded RNA which is segmented  → 8 pieces 
Types
  • There are three viral subtypes
  • based on RNP and M protein antigens
  1. Type A       →   Causes all pandemics and most of the epidemics
  2. Type B       →    Sporadic and epidemics
  3. 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
Culture
  • 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
Hemagglutinin:
  • Cause hemagglutination.
  • 16 subtypes
  • Composed of two polypeptide
  • HA1 and HA2
  • Binds virus particle to susceptible cell
  • Major antigen against which neutralizing antibodies.
Neuraminidase
  • 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
Prevalence:
  • Data regarding the prevalence of influenza is not adequate
Cyclic trend:

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.
Exam Question
 

Morphology

  • Belong to orthomyxoviridae  → Envelope, RNA virus
  • Contain single-stranded RNA which is segmented  → 8 pieces 
Types
  • There are three viral subtypes
  • based on RNP and M protein antigens
  1. Type A       →    Causes all pandemics and most of the epidemics
  2. Type B       →    Sporadic and epidemics
  3. 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
Culture
  • 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:
Hemagglutinin:
  • Cause hemagglutination.
  •  16 subtypes 
Neuraminidase
  • 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
Prevalence:
  • Data regarding the prevalence of influenza is not adequate
Cyclic trend:

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.
Don’t Forget to Solve all the previous Year Question asked on Influenza virus

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