Influenza virus

• Antigenic drift: refers to minor antigenic changes either in hemagglutinin or neuraminidase or both.
• Antigenic shift: It is an abrupt, drastic discontinuous variation in the antigenic structure resulting in a novel virus strain unrelated antigenically to predecessor strains.

There are 16 subtypes of hemagglutinins.

Rest of the statements given are true.

Antigenic changes occurs only to a lesser degree in group B influenza virus.

Influenza C virus appears to be antigenically stable.

Note: Almost all of the pandemic which has ever occurred is due to Type A influenza virus.

Ref: Park, Edition 21, Page – 143,144

Human infections with avian influenza H5N1 was first reported in Hong Kong in 1997.

Ref: Epidemiology of communicable diseases

Park’s textbook of Preventive and Social Medicine, 21stedition, page-330.

Ans. is b i.e., Allantoic cavity

In embryonated egg cultivation for influenza virus site of inoculation are :- Allontoic cavity or amniotic cavity

Inoculation sites in embryonated eggs

• Chorioallantoic membrane          -4 HSV, Poxvirus, Rous-sarcoma virus
• Amniotic cavity                          -4 Influenza virus, mumps virus
• Allantoic cavity                           –  Influenza virus, mumps virus, avian adenovirus, newcastle disease virus
• Yolk sac                                   –> HSV, chlamydia, rickettisia    

Ans. is ‘c’ i.e., H₅N,

• At present three types of influenza viruses are circulating in the world: A(H_/N₁), A (H₃N₂) and B viruses.
• WHO global surveillance activities have identified human infection with a new influenza virus called A ) in Hong Kong in mid1997. However, the possibility that the outbreak heralded a global influenza pandemic did not materialize.

Ans. is ‘d’ i.e., Hemagglutinin and Neuraminidase is strain specific

Ans. is ‘a’ i.e., Epidemic is due to antigenic drift

Ans. is ‘a’ i.e., Small mutation in neuraminidase and hemagglutinin

Ans. is ‘a’ i.e., 18 – 72 hrs

Ans. is `D’ i.e., All ages sex are equally affected 

• Influenza affects all ages and both sexes.

About other options

o Most infections are subclinical.

o Incubation period is 18-72 hours.

o Influenza causes pandemic every 10-15 years.

o Major reservoir of influenza virus exists in animal and birds.

Ans. is ‘d’ i.e., H₇N₉ 

• In china, there was an outbreak of influenza caused by Avian influenza H₇N₉, in 2013.
• It started in china and spread to Hong Kong.
• Most common age group affected was older male (> 50 years).

Ans. B: Cyclical

These viruses are only distantly related to the human parainfluenza viruses, which are RNA viruses belonging to the paramyxovirus family that are a common cause of respiratory infections in children such as croup.

Sore throat, fever and coughs are the most frequent symptoms.

In more serious cases, influenza causes pneumonia, which can be fatal, particularly for the young and the elderly. Typically, influenza is transmitted through the air by coughs or sneezes, creating aerosols containing the virus.

Influenza can also be transmitted by direct contact with bird droppings or nasal secretions, or through contact with contaminated surfaces.

Influenza viruses can be inactivated by sunlight, disinfectants and detergents. As the virus can be inactivated by soap, frequent hand washing reduces the risk of infection.

Influenza pandemics show cyclical trend and are known to occur at intervals of 740 years, due to antigenic variations.

Ans. is ‘a’ i.e., Influenza

Some viruses have segmented nucleic acid (genome).

These are (Mnemonic BORA) :‑

1) Bunyaviridae : 3 segments of single stranded RNA.

2) Orthomyxoviridae (influenza) : 8 segments of single stranded RNA.

3) Reoviridae (rotavirus, reovirus) : 10-12 segments of double stranded RNA.

4) Arenaviridae : 2 segments of single stranded RNA.

Ans. is ‘d’ i.e., Influenza

Influenza virus is an enveloped RNA virus containing 8 pieces (8 segments) of single stranded RNA.

There are three viral subtypes : (i) Type A (causes all pandemics and most epidemics); (ii) Type B; and (iii) Type C (not circulating currently).

Ans. is ‘c’ i.e., Orthomyxoviridae

Ans. is ‘b^‘ i.e., Cyclic trend

Ans. is ‘d’ i.e., Data regarding prevalence of influenza is not adequate

Ans. is ‘b’ i.e., Most infections are subclinical

Influenza

• Influenza virus a RNA virus, belongs to orthomyxovirus.
• There are three viral subtypes : i) Type A (causes all pandemics and most epidemics); type B; and type C (not circulating currently).
• Currently the influenza viruses circulating in the world are : 11₁ N, of type A (causes swine flu); H2 N2 of type A; H₃ N₂ of type A ; H₅ N_I of type A (causes birdflu or avian influenza); H₇ N₉ of type A (caused epidemic of avian influenza in China in 2013); and type B.
• Influenza shows cyclic trend with epidemic occuring every 2-3 years in case of influenza – A and every 4-7 years in case of influenza-B. Pandemics are caused by only influenza – A every 10-15 years.
• Influenza affects all ages and both sexes.
• Source of infection of influenza is a clinical case or subclinical case.
• Major reservoir of influenza virus exists in animal and birds.
• Incubation period is 18-72 hours. Most of the infections are subclinical. Clinical cases present with cough, fever, myalgia and headache.

Ans:D.)(a) (b) & (c) True.

The virus shown in the picture above represents influenza virus.

INFLUENZA VIRUS

IClassified into A, B and C – based on RNP and M protein antigens

• • Antigenic variation is highest in type A, less in type B and not seen in type C
    • Type A – pandemics(an epidemic of world-wide proportions).
    • Type B – sporadic and epidemics
    • Type C – endemic throughout the world

Antigenic Shift and Drift

• Antigenic drift occurs in both influenza A and influenza B viruses.
  Antigenic shift, however, occurs only in influenzavirus A because it infects more than just humans and Causes major epidemics and pandemic

Ans. c. Influenza

Ans. is ‘d’ i.e., 8 segments of ssRNA 

Influenza virus

• Belong to orthomyxoviridae  → Envelope, RNA virus
• Contain single stranded RNA which is segmented  → 8 pieces