Influenza, commonly called "the flu" in caused by Influenza A, B and C genera of the retroviruses family Orthomyxoviridae. Common sypmtoms include chills, fever, runny nose, sore throat, muscle pains, headache, coughing, fatigue etc., and can occasionally lead to pneumonia. Influenza results in flu pandamics which could kill 250,000 to 500,000 people in yearly deaths. In 2009 WHO declared flu pandemic dubbed "swine flu" caused by a novel Influenza strain evolved from combined genes from human, pig and bird flu strains. However this pandemic was more agressive in its infectivity and had lower rate of mortality than common flu outbreaks.
Treatment is largely symptomatic. Neuraminidase inhibitors (oseltamivir and zanamivir) and M2 protein inhibitors (adamantane derivatives) are some of the preferred options available for antiviral treatment.