In the summer of 1975, fear gripped the United States as hundreds began dying of a mysterious illness. Sudden onset of fever, headache, delirium and brain inflammation was killing one out of eight victims.
It was not the first time the virus had caused an epidemic in America. A similar outbreak forty-two years earlier that had been dubbed "St. Louis Encephalitis" after thousands of cases suddenly appeared in Missouri. Like the Japanese Encephalitis and West Nile arboviruses, the virus remains dormant in bird populations until transmitted to humans through the bite of an infected Culex mosquito. The majority of infected people show few symptoms, but elderly victims can experience up to 20% mortality. There is no known treatment or vaccine, although lucky survivors develop antibodies that give lifelong immunity.
Every year, hundreds of cases of St. Louis Encephalitis are reported in the central United State, but there is no simple explanation as to what causes severe 50-fold epidemics. Dry conditions may force birds to interact more closely with mosquitoes, and transmission could be modulated by immunity among the house sparrows that offer a major reservoir to the virus.
If you are nervous about catching St. Louis Encephalitis, you might want to adopt a strategy recommended by the Center for Disease Control, and place a "Sentinel Chicken" in your front yard to monitor virus activity. When blood tests show these heroic birds have turned positive for St. Louis Encephalitis, it's time to leave town -- or at lease notify your county health department to increase mosquito spraying and pond clean-up. However, when the disease was detected among Sentinel Chickens in Florida in 2011, no major epidemic followed.
One thing is certain -- more cycles of widespread infection with St. Louis Encephalitis will occur in the future, perhaps when a new generation of humans lacking immunity reaches a high enough concentration to kindle a new epidemic.
Keep your eye on the year 2017.
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