Influenza: Types, Causes, Symptoms, Transmission & Prevention

Influenza: Index

What is Influenza?

Influenza, more commonly known as flu is a medical condition that results from infection of influenza viruses (RNA virus of an orthomyxoviridae family).Influenza mainly affects respiratory tract, nose and the throat, which may spread to the lungs and bronchi.

It is a contagious and infectious condition which often manifests itself as major pandemics, which may occur in any season interspersed with seasonal epidemics of varying severity.

Influenza is more prominent during the winter season. In winter, the immune system of the body is weak. As people usually stay indoors and are in close proximity to each other, it spreads quickly during winter.

Prognosis of Influenza

The prognosis of Influenza is more severe and lasts longer than ‘common cold’. Recovery period of flu is about one to two weeks. The person remains contagious for about six days from the date of infection.

Influenza leaves the respiratory epithelium weak and prone to several other infections and attack by other pathogens. Influenza can be life threatening when it develops into pneumonia. It may affect people of any age.

Types of Influenza

There are three types of influenza viruses, they are:

1) Type A influenza virus which generally affects the mammals and birds like ducks, chicken and in some cases human beings. There are three variants of Type A influenza viruses namely H1N1 (e.g swine flu), H1N2 (e.g Asian flu and Hongkong flu), and H1N3 viruses.

2) Type B flu virus that infects only humans. This causes mild fever and is less harmful than type A flu.

3) Type C flu which causes mild respiratory infections. virus C. The symptoms of Type C influenza infection resembles the symptoms of common cold and is not pandemic.This flu infects only humans.

Causes of influenza

Influenza is usually caused due to faulty eating habits (dietetic errors) and unhygienic living conditions, like stuffy rooms. Anxiety, overwork, Lack of exercise and faulty lifestyle also provide grounds for influenza infection. The flu virus spreads easily through the saliva droplets released in the air due to sneezing and coughing of the person infected by flu and can infect and weak person quickly.

The birth of influenza virus is closely associated with birds(Avian flu) and other animals (e.g swine flu). Thus Influenza pandemics often originate in places where human beings live in close proximity of animals.

Symptoms of Influenza
The symptoms of influenza are:

  • High fever (upto 40 ° C)
  • Chills and headache
  • Sore throat
  • Dry cough
  • Irritated eyes
  • Nasal congestion and Congestion of the lungs
  • Body aches including Muscle and joint pain
  • Wheezing
  • Fatigue
  • Pharyngitis

Transmission of influenza virus

Influenza is transmitted to a healthy person from an infected person through tiny droplets expelled from a runny nose or during sneezing, breathing or coughing.

People with weak immune systems are more prone to getting infected. Once the virus attaches itself to cell receptors, it replicates in large quantities and invades the entire body.

Influenza: phases of viral replication

The first signs of influenza are felt after round 48 hours (incubation period) of the viral infection. The influenza virus originates and infects the human body in 4 phases. They are:

a) Attachment: The virus binds to a respiratory epithelial cell membrane.

b) Endocytosis: The virus wraps in an endocytic vesicle and releases mucleocapsides into the cytoplasm of the cell.

c) Replication: Genome of influenza virus serves as a template using which each infected cell produces virus in large number

d) Protein synthesis: The virus starts using the energy released from cellular metabolism to synthesize its own proteins.


Vaccination for Influenza

Vaccination is perhaps the best guard against influenza infection. Prophylaxis is the most commonly administered vaccination for influenza. However the kind of vaccination administered depends on the epidemiological context.
The effectiveness of Influenza vaccination lasts for around a year, after which fresh vaccination is required. The body develops immunity after round two weeks of vaccination. In addition, the vaccination is effective only against certain strains of influenza and may fail as new strains originate.

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