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Influenza, commonly known as flu is caused by RNA viruses that affect birds and animals. It has three types of influenza A, B, C. Influenza A viruses (IAV), together with influenza B viruses are the common cause of respiratory illness in humans. About 95% of influenza cases are caused by influenza virus type A .Wild aquatic birds are the natural reservoir of influenza A virus. Influenza pandemics occur when humans are introduced to IAV’s which they have not been exposed to before. We have experienced four pandemics since the beginning of the 20th century: Spanish influenza (H1N1) in 1918/1919, Asian influenza (H2N2) in 1957, Hong Kong influenza (H3N2) in 1968, and H1N1 influenza in 2009. Among these pandemic viruses, the 1918 virus was the most devastating, causing massive acute pulmonary hemorrhage and edema. As antibiotics were not available then, secondary bacterial pneumonia was a major cause of death among those infected with the virus.

The influenza viral proteins play a role in the lung pathology of humans targeting the epithelial cells of the upper respiratory tract in humans. The symptoms of influenza have a sudden onset one to two days after infection. The first symptoms that appear are chills with fever approximately 100-103 °F. Other symptoms include cough, nasal congestion, body aches, headache, reddened eyes with watering, sore throat, muscle aches and generalized discomfort, fatigue; influenza may produce nausea and vomiting in children. Many people feel so ill, weak, and tired that they remain in bed for days.  The most common complication of influenza is pneumonia, which can be viral, bacterial, or both.  The main treatment for influenza is to rest adequately, drink plenty of fluids, and avoid exertion. Drugs like acetaminophen and NSAIDS are used to prevent muscle aches and fever but aspirin should be avoided in children as it may lead to acute liver failure. The course of disease can be shortened by giving anti viral drugs like oseltamivir and zanamivir within 48 hours of the onset of the symptoms.

A good way to reduce the transmission of influenza is maintain good health and hygiene habits frequent hand washing, covering while coughing and sneezing, and avoiding close contact with sick people and staying home yourself if you are sick. One should also avoid spitting. Face masks might help while caring for the sick. Since influenza spreads through both aerosols and contact with contaminated surfaces, surface sanitizing may help prevent some infections. Annual vaccination is the good way to protect against influenza. Influenza vaccines contain killed influenza virus and are given by injection. A newer vaccine, inhaled as a nasal spray, and contains weakened live virus. This vaccine is used only in healthy people aged 5 to 49 years. Different vaccines may be given every year to keep up with changes in the virus. Vaccination is particularly important for people who are likely to become very ill if infected. These people include the young (particularly those younger than 24 months), those older than 65, and people with decreased immunity and chronic diseases like diabetes, heart or lung diseases.