Influenza virus- Structure, Types, Life Cycle

Last edited and updated on: January 3, 2020 by Sagar Aryal

Influenza commonly called a flue is a highly contagious viral infection of the respiratory tract mainly infects humans and animals.

• Influenza virus belongs to the family: Orthomyxoviridae
• The annual attack rate of influenza virus is 5-10% in adults and 20-30% in children.

Virus Structure

• Enveloped virus
• Has helical nucleocapsid
•  sense segmented single-stranded RNA
• Viruses are spherical in shape
• Their size varies from 80-180 nm

Image Source: News-Medical.net

Types of influenza virus

There are three main types of influenza virus :

1. Influenza A

• Most virulent human pathogen.
• Capable of infecting humans, chickens, and pigs.
• Type A viruses are divided on the basis of the difference in a viral surface protein called Haemagglutinin and Neuraminidase.
• Influenza virus undergoes two kinds of changes :
  • antigenic drift
  • antigenic shift

• There are two subtypes of influenza A virus :
  • H5N1, H1N1.

2. Influenza B

• Influenza B viruses change only by the more gradual process of antigenic drift.
• Mainly infects humans.
• Causes epidemic disease similar to type A.

3. Influenza C

• Influenza C virus usually causes mild disease in children.
• This type of virus lack NA and contain esterase.
• Type C viruses are less common than other types.

Life Cycle Of Influenza Virus

Steps

• The entry of vRNPs into the nucleus
• Transcription and replication of the viral genome
• Export of vRNP from the nucleus
• Assembly and budding at the host cell plasma membrane

Signs And Symptoms

• Fever
• Cough
• Sore throat
• Runny or stuffy nose
• Headache
• Muscle aches
• Extreme fatigue

Mode of Transmission

• Spread from person to person by droplet infection created by sneezing, coughing and talking.
• The portal of entry is the respiratory tract.

Pathophysiology

• The virus infects both upper and lower respiratory tracts.
• Sialic acid on epithelial cells are their receptors.
• The typical incubation period is 24 hrs to 4 days.

Treatment

• Increase liquid intake, warm shower.
• Warm compresses, especially in the nasal area can reduce nasal congestion.

Prevention

¨Vaccines”

• 1: flu shot – an inactivated vaccine that is given with needle in the arm
• 2: nasal spray – a vaccine made with live weakened flu viruses that are given as nasal spray.

References

1. https://www.mayoclinic.org/diseases-conditions/flu/symptoms-causes/syc-20351719
2. https://en.wikipedia.org/wiki/Influenza
3. https://www.cdc.gov/flu/about/viruses/index.htm

Influenza virus- Structure, Types, Life Cycle