Influenza Social history of viruses

members of american red cross removing victim of spanish influenza house in 1918

when influenza virus undergoes genetic shift many humans have no immunity new strain, , if population of susceptible individuals high enough maintain chain of infection, pandemics occur. genetic changes happen when different strains of virus co-infect animals, particularly birds , swine. although many viruses of vertebrates restricted 1 species, influenza virus exception. last pandemic of 19th century occurred in 1899 , resulted in deaths of 250,000 people in europe. virus, originated in russia or asia, first rapidly spread people on trains , steamships.

a new strain of virus emerged in 1918, , subsequent pandemic of spanish flu 1 of worst natural disasters in history. death toll enormous; throughout world around 50 million people died infection. there 550,000 reported deaths caused disease in us, ten times country s losses during first world war, , 228,000 deaths in uk. in india there more 20 million deaths, , in western samoa 22 per cent of population died. although cases of influenza occurred every winter, there 2 other pandemics in 20th century.

in 1957 new strain of virus emerged , caused pandemic of asian flu; although virus not virulent 1918 strain, on 1 million died worldwide. next pandemic occurred when hong kong flu emerged in 1968, new strain of virus replaced 1957 strain. affecting elderly, 1968 pandemic least severe, 33,800 killed in us. new strains of influenza virus originate in east asia; in rural china concentration of ducks, pigs, , humans in close proximity highest in world.

the recent pandemic occurred in 2009, none of last 3 has caused near devastation seen in 1918. why strain of influenza emerged in 1918 devastating question still remains unanswered.