On Sept. 24, Michigan's Department of Health and Human Services announced a suspected second human case of EEE in Montcalm County, leading to another night of aerial mosquito treatments.
According to some experts, the frequency and intensity of the recent EEE outbreaks in Michigan and northern Indiana could be related to climate change.
The first EEE outbreak in the area occured from 1942-1943. The next was from 1973-1975, and since then, outbreaks have become more and more frequent.
“We have shorter and shorter time intervals between outbreaks, and then since 1980, we’ve seen more and more human cases," said Michigan State University Professor of Entomology Ned Walker. "And so, there has been some kind of a change.”
Walker recently completed a data review of EEE trends and he said that the increase in cases was "more complex" than just climate change. For example, the region has experienced rapid population growth, which could lead to more cases, and has a historically high water table, which fosters mosquito communities.
However, he said the increase can also be tied to warming temperatures.
"We are, in fact, having warmer summer conditions. That trend is just true," Walker said. "Virus transmission increases with warmer temperatures."
Milder winter temperatures could also increase the likelihood of a summer EEE oubreak.
“This mosquito species over winters in our area actually has a larva in water," Walker said. "If the water gets not so cold and doesn’t freeze so much, then they’ll have a better survival through the winter.”
He said that in order to mitigate future outbreaks, public health agencies should promote regional surveillance and begin treatments earlier in the mosquito season.
"We ought to find a way to intervene much, much earlier in this virus transmission cycle, say, in June, before the virus amplifies in the mosquito population and before the transmission to humans and horses can begin," Walker said.
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