Caused by influenza viruses, ‘fluĀ is a short-term (acute) infectious respiratory disease. When inhaled, the virus attacks the lining of the respiratory (breathing) system and the resulting inflammation results in the production of a lot of catarrh. There is a sudden onset of chills, fever of short duration (3-4 days), severe fatigue, headache, muscle aches, and a dry cough that may make the individual prone to further bacterial infection.