Tuesday 15 October 2019

Outbreak of Eastern Equine Encephalitis kills at least thirteen people in the United States.

At least thirteen people have died in an outbreak of Eastern Equine Encephalitis in the United States since August 2019. Outbreaks of the disease are expected in the US at this time of year, but this year's epidemic is exceptional both in terms of the number of cases reported and the number of fatalities. Five people have died in Michigan alone, out of a total of ten cases reported in the state, with three fatalities each in Massachusetts and Connecticut, and one each in Rhode Island and Indiana.  Only a single fatality was reported from the disease in 2018, out of 23 cases reported across the US, with 2 deaths in 2017 out of a total of 45 cases.

Eastern Equine Encephalitis is caused by the Eastern Equine Encephalitis Alphavirus, a form of Togavirus closely related to the Venezuelan Equine Encephalitis Alphavirus, and the Western Equine Encephalitis Alphavirus. These are single stranded positive-sense RNA Viruses. 

Colourised TEM micrograph of a mosquito salivary gland: The virus particles (virions) are coloured red. Fred Murphy and Sylvia Whitfield/Centers for Disease Control and Prevention/Public Health Image Library/Wikimedia Commons.

Eastern Equine Encephalitis is a Mosquito-born disease which primarily infects Birds, but is occasionally passed to Mammals through Mosquito bites. It gets the name 'Equine Encephalitis' because it is much more virulent in Horses than Humans, having first been discovered after an outbreak in Massachusetts killed 75 Horses in 1831. 

About 95% of people infected by the disease develop no symptoms, and are only detected if screening programs are introduced during an epidemic. Those who do develop symptoms suffer chills, fever, malaise, arthralgia, and myalgia for about two weeks, with about a quarter developing encephalitis (swelling of the brain), which can cause symptoms such as fever, headache, irritability, restlessness, drowsiness, anorexia, vomiting, diarrhea, cyanosis, convulsions, and coma. Around a third of patients that develop encephalitis die of the illness, with many others suffering permanent brain damage.

A vaccine against Eastern Equine Encephalitis is available for Horses, but none has been developed for Human use, nor is any specific treatment available, though fluid replacement, plus treatment with anticonvulsants (drugs to reduce convulsions) and antipyretics (drugs to reduce fever) have been shown to help.

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