In 2019, cases of the mosquito-borne virus Eastern equine encephalitis (EEE) hit a record high in the United States. 38 people were diagnosed and 15 died, a steep increase from the decade’s last record in 2012, with only 15 confirmed cases and 5 deaths. As mosquito season approaches its peak, the number of people at risk of the deadly disease rises once more. The disease is vectored by Coquillettidia perturbans, Aedes sollicitans, and Ochlerotatus canadensis mosquitoes.
EEE is rare, affecting only five percent of those bitten by an infected mosquito, but of those five percent, 30 to 40 percent will develop fatal complications. While some patients only suffer from fevers and mild flu-like symptoms, others face severe, lasting brain damage, leading to seizures, paralysis, and nerve dysfunction. Symptoms show up within a week of a mosquito bite, but for many, EEE will dominate their lives for years.
2019 cases were disproportionately focused in the Northeastern states, particularly Massachusetts, with 12 cases, followed by Connecticut and New Jersey, each with four. Many states enforced precautions to prevent further spread: campsites were closed, concerts were rescheduled, and Friday night football games were played on Saturday mornings.
But because the virus travels through birds and mosquitos, with no human-to-human transmission, EEE outbreaks are sporadic and often understudied. There’s no EEE vaccine or confirmed treatment. The number of cases fluctuates from year to year, depending on weather and the growth of local mosquito and bird populations, so a spike in 2019 doesn’t necessarily mean an upward trend in EEE infections.
However, some researchers caution that the sudden increase could be correlated to warmer winters and hotter summers in the Northeast. With a longer mosquito season leading to larger insect populations and increased transmission rates, vector-borne diseases like EEE, West Nile virus, and Lyme disease may all see climbing rates in the coming years.
EEE’s low infection rate means its control and prevention methods are administered by state-level public health departments. Through proper mosquito control practices, EEE can be better contained before it reaches humans, helping to prevent a resurgence of the deadly disease.