Influenza is an infectious disease that infects lungs, respiratory system. It is commonly called as Flu. Influenza is caused by three types of influenza virus A, B and C. Flu belongs to family Myxovirus. Flu particles are highly pleomorphic. The most common shape of virus is icosahedral and capsid ranges from 80-120 nm in diameter. All influenza viruses have lipid envelops that contain two types of spikes, haemagglutinin (HA) and neuraminidase (NA). Strains that are easily transmitted between people have haemagglutinin proteins that bind to receptors in the upper part of the respiratory tract, such as in the nose, throat and mouth.

Influenza can be spread by direct transmission when person infected with virus sneezes mucus into eyes, nose or mouth of another person, by inhaling aerosols produced by infected people because of  sneezing, through hand to mouth by shaking hands or by personal contact.

Influenza is seen in both mammals and birds. It usually affects millions of people world wide both males and females including adults and children.

Types: There are three types of Influenza virus include,

Influenza virus A - it is the most virulent human pathogen of three types of virus. Wild aquatic birds are natural hosts for this virus. Occasionally these viruses are transmitted and cause outbreaks in domestic poultry, give rise to human influenza pandemics.

It also infects animals, including birds, pigs and horses. Infection by birds is known as Avian Flu.

Influenza virus B - it is less common than type A. It mutates 2-3 times lower than type A. It is acquired usually at an early age. It exclusively infects human.

Influenza virus c - it is less common than the above 2 types. Usually it causes mild disease in children. It infects humans, dogs, pigs.