Influenza virus
Image taken from BBC


Influenza is a highly infectious viral illness caused by influenza virus. It is a single stranded, helically shaped, RNA virus of the orthomyxovirus family. Basic antigen types A, B, and C are determined by the nuclear material. Type A influenza has subtypes that are determined by the surface antigens hemagglutinin (H) and neuraminidase (N). Three types of hemagglutinin in humans (H1, H2, and H3) have a role in virus attachment to cells. Two types of neuraminidase (N1 and N2) have a role in virus penetration into the cells.

Signs and Symptoms

  • Fever or feeling feverish/chills
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle or body aches
  • Headaches
  • Fatigue


  • It is believed that flu viruses spread mainly by droplet made when people with flu cough, sneeze or talk.
  • These droplets can land in the mouths or noses of people who are nearby.
  • Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth, eyes or possibly their nose.


  • Respiratory transmission of virus.
  • Replication in respiratory epithelium with subsequent destruction of cells.
  • Viremia rarely documented.
  • Virus shed in respiratory secretions for 5-10 days.


  • It is very difficult to distinguish the flu from other viral or bacterial causes of respiratory illnesses on the basis of symptoms alone.
  • A number of flu tests are available to detect influenza viruses. The most common are called “rapid influenza diagnostic tests.”


Prevention and Treatment

  • The first and most important step in preventing flu is to get a flu vaccination each year.
  • Antiviral drugs are prescription medicines that fight the flu in the body.
  • The FDA-approved influenza antiviral drugs are: Oseltamivir, Zanamivir, and Peramivir.




  1. CDC
  2. NCBI
  3. WHO
  4. WebMD