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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.
- Enveloped virus
- Has helical nucleocapsid
- sense segmented single-stranded RNA
- Viruses are spherical in shape
- Their size varies from 80-180 nm
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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
- 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
- Sore throat
- Runny or stuffy nose
- 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.
- 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.
- Increase liquid intake, warm shower.
- Warm compresses, especially in the nasal area can reduce nasal congestion.
- 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.
Influenza virus- Structure, Types, Life Cycle