U.S. Hit Hard by Mosquito-Borne EEE this Fall

Features - /// Pests of Public Health

Rare disease responsible for 13 deaths; New England heavily impacted.

November 7, 2019

The important role pest management professionals play in protecting public health was underscored in October when the thirteenth person in the U.S. died as a result of having contracted the mosquito-borne Eastern equine encephalitis (EEE) virus.

The thirteenth death was a Baldwin County (Ala.) resident, the Alabama Department of Health reported on Oct. 25. The person, who became ill in September, was the first human EEE case in an Alabama resident since 2014.

As of Oct. 22, the Centers for Disease Control and Prevention (CDC) said the U.S. has had 35 confirmed cases of EEE with 13 deaths. Cases have been reported in Connecticut (4), Indiana (1), Massachusetts (12), Michigan (10), North Carolina (1), New Jersey (3), Rhode Island (3), and Tennessee (1). The Alabama information was not included in the updated numbers.

According to CDC, anyone can be infected with EEE, with people who spend a great deal of time outdoors at higher risk. People over age 50 or younger than 15 are at greatest risk of developing serious infections from the virus. EEE is not spread person to person or from animals to people.

“Eastern equine encephalitis is a relatively rare mosquito-borne illness, but can be life-threatening for those who contract it,” Dr. Jorge Parada, medical advisor for the National Pest Management Association, stated in a press release. “EEE can result in one of two types of illness, systemic or encephalitic, with encephalitic being the deadlier of the two.”

According to Parada, once bitten by an infected mosquito, those who contract the virus may start to experience flu-like symptoms such as chills, fever and joint pain, which usually last for one to two weeks. Most people make a full recovery, but about four to five percent of those infected develop the encephalitic form of EEE which affects the brain and causes symptoms including vomiting and convulsions.

CDC reports that approximately 30 percent of people with EEE die as a result of the infection and many survivors have ongoing neurologic problems. “Unfortunately, many who recover from the illness are left with disabling mental disorders and brain dysfunction,” Parada added.


OUTBREAK FACTORS. According to CDC, in an average year the U.S. sees only seven human cases of eastern equine encephalitis. In 2019, the U.S. had already seen 35 cases (at press time).

Jim Fredericks, vice president of technical and regulatory affairs, NPMA, told PCT that a “perfect storm” of factors have led to the increased numbers this year.

“It’s been a bad mosquito season and the more mosquitoes out there increases the likelihood of receiving a bite from a mosquito that is infected with the pathogen,” Fredericks said.

The other part of the equation is the reservoir, which are birds typically found in swampy areas. “The disease is typically just transmitted from bird to bird by one particular mosquito (Culiseta melanura). And that mosquito doesn’t typically bite us. But it’s when some of the other different mosquitoes (various Culex and Aedes species) bite an infected bird and then bite a human — then it ends up being transmitted to humans,” Fredericks said. “With any of these mosquito-borne illnesses you need two things: you need the mosquito and you need the pathogen. So, when these pathogen loads are higher in the reservoir of the bird population, that’s when that perfect storm happens, and you see these outbreaks.”

As to why the outbreaks seem to be worse in New England and Michigan, Fredericks speculates it’s related to the habitat of the aforementioned mosquito species and birds. “Typically, these mosquitoes are going to be associated with swampy and humid forests. So, I suspect that where we’ve seen these kinds of outbreaks they may very well be associated with these types of conditions where that virus is going to amplify in the bird population. “

While Eastern equine encephalitis certainly is a concern, particularly because of its high mortality rate, it’s important to remember that mosquitoes are transmitting disease every single day, Fredericks said. For example, in 2018 there were more than 2,500 cases of West Nile virus. “From a messaging standpoint for PMPs it’s important to make sure that the public knows that this is part of the work that we’re doing to protect public health,” Fredericks said.

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The author is Internet/managing editor of PCT and can be contacted at bharbison@gie.net.