Influenza pandemic shows which type of trend: September 2009, March 2013 (d, f)

Ans. B: Cyclical Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Ohomyxoviridae (the influenza viruses), that affects birds and mammals. These viruses are only distantly related to the human parainfluenza viruses, which are RNA viruses belonging to the paramyxovirus family that are a common cause of respiratory infections in children such as croup. Sore throat, fever and coughs are the most frequent symptoms. In more serious cases, influenza causes pneumonia, which can be fatal, paicularly for the young and the elderly. Typically, influenza is transmitted through the air by coughs or sneezes, creating aerosols containing the virus. Influenza can also be transmitted by direct contact with bird droppings or nasal secretions, or through contact with contaminated surfaces. Influenza viruses can be inactivated by sunlight, disinfectants and detergents. As the virus can be inactivated by soap, frequent hand washing reduces the risk of infection. Influenza pandemics show cyclical trend and are known to occur at intervals of 740 years, due to antigenic variations.