The evolution of influenza viruses

Influenza virus infection, one of the most com-mon infectious diseases is a highly contagious airborne disease that causes an acute febrile ill-ness and results invariable degrees of syste-mic symptoms, ranging from mild fatigue to re-spiratory failure and death. In addition to humans, influenza also infects a variety of animal species. Influenza A viruses also can infect domestic ani-mals (pigs, horses, dogs, chickens and ducks) and some wild birds. Some of these influenza strains are species specific, but new strains of influenza may spread from other animal species to humans. These deadly strains produced 3 global pandemics in the last century, the worst of which occurred in 1918. Three pandemics of influenza have swept the world since the “Spa-nish ” flu of 1918, the “Asian ” flu pandemic of 1957, the “Hong Kong ” flu pandemic of 1968, the “Swine ” flu pandemic that began in April of 2009. The pandemic of 1957 probably made more peo-ple sick than the one of 1918, but the availability of antibiotics to treat the secondary infections that are the usual cause of death resulted in a much lower death rate. An influenza pandemic occurs only when the influenza virus mutates into something dangerously unfamiliar to our immune systems and yet is able to jump from human to human through a sneeze, cough or touch. Asia is the source of many outbreaks be-cause swines, birds and humans live under the same roof, providing opportunity for viral mixing. The best way to prevent the sickness is to get yearly injections of a vaccine that prevents in-fluenza