Influenza or flu is an acute respiratory illness caused by two types of influenza viruses A and B. Influenza A viruses are not restricted to humans, but infect many species of mammals and birds, unlike the stable virus type B. Influenza A viruses keep mutating and evolving each year in course of shifting between animal and human hosts. This occurs due to changes in surface glycoproteins of virus envelope, which leads to differing antigenicity (recognized as a foreign substance by the immune system to produce antibodies) of viruses. This “antigenic drift” gives Influenza A viruses the best chances to escape the body’s immune response, even in the people who got the flu last year. As a result, influenza outbreaks occur every year. Influenza viruses known to infect animals (e.g. Pigs and horses) and birds, when occasionally infect humans turn into serious disease outbreaks with potential to turn into a pandemic disease affecting wide regions of the world. Avian flu or bird flu (H5N1 influenza) discovered in 1997 in Asia caused the major poultry epidemic and some fatal human cases. Swine flu (H1N1 influenza) caused pandemic in 2009 is known to mainly infect pigs, but poses a serious threat to humans each year during the flu season.
Influenza spreads easily through the school going children in the age group 5-9. Higher death rates and serious illness occur mostly in children <2 years, senior citizens, pregnant women (after first trimester) and persons with certain medical conditions (lung or heart disorders; metabolic disorders e.g. Diabetes, kidney ailments, etc.; and immunosuppression).
How is Influenza (flu) contagious?
Influenza viruses are mainly spread by flu viruses, trapped in large droplets or aerosol sprays, produced by infected people when they cough, sneeze or talk. They can also be transmitted by touching the viral infected surfaces followed by touching the mouth or nose. It is a highly infectious disease which is transmitted by the infected persons, even before their own symptoms appear till 5-7 days after they become sick. Young children and people with weak immunity are able to spread the virus for a longer time than a week.
Symptoms of flu:
Persons with flu may or may not have abrupt rise in temperature/fever with chills, suffer from sore throat, cough, runny nose, congestion, chest pain, body aches, headaches, fatigue, nausea, diarrhea (more common in children than adults).
Complications of flu:
Elderly people and patients having chronic diseases fell prey to influenza complications caused by secondary bacterial pneumonia by Streptococcus pneumonia, Haemophilus influenzae or Staphylococcus aureus. Ear infections and sinus infections can also occur. Flu can be prevented by yearly Influenza shots.