In August 2024, a man from Worcester County was infected with the Eastern equine encephalitis virus, the first human case in Massachusetts since 2020. The virus, also known as Triple E, can severely impair the human nervous system and cause illness, potentially proving fatal.
Triple E was first discovered in Massachusetts in 1831 when 75 horses unexpectedly died from brain inflammation. Over the past two centuries, the virus has rarely infected humans, but two recent outbreaks in 2012 and 2019 raised notable concern. The 2019 outbreak, the largest in 50 years, saw 38 confirmed cases of human infection across the country. Twelve of those infected died from the virus, with half of those deaths being in Massachusetts. In 2024, the Northeast is again in the midst of an EEE outbreak. As of Oct. 15, 16 people in the US have contracted EEE. All cases have become neuroinvasive, meaning the disease impacts the brain.
EEE is a single-stranded RNA virus commonly transmitted by arthropods such as mosquitoes. The infection often spreads through birds that reside in marshy areas together with mosquitoes of the species Culiseta melanura, which typically do not prey on mammals. Mosquitoes of other species then contract the virus and go on to spread it to horses, other livestock and — rarely — humans. Humans and horses are considered dead-end hosts as the viral load carried in the bloodstream during infection is too low to transmit to other potential hosts. In this process, mosquitoes act as a vector, spreading EEE across different species. There are currently no specific treatments or vaccines against the virus for humans, making its current uptick concerning.
However, the majority of people who get the virus do not develop symptoms. In fact, according to the CDC, only 4%–5% of the infections actually result in Eastern equine encephalitis. However, for those who do, the symptoms can be serious or even fatal. The incubation period, the period it takes for symptoms to present, of EEE is 4–10 days after a bite from an infected mosquito.
Those who contract the virus may present with symptoms like fever, joint pain and body aches. Assuming there is no damage to the nervous system, they should recover without permanent damage of any kind. However, the EEE virus can also cause the neurological disease encephalitis, which refers to inflammation of the brain. The virus invades the host organism’s cells, using them to replicate its own genetic information and multiply. EEE also produces proteins that inhibit the host organism’s interferons, signaling proteins that activate the immune system in the presence of viruses. While the blood-brain barrier generally prevents harmful substances from entering the brain, EEE can infect cells lining blood vessels in the brain and inflame the vessels, making the barrier more permeable. Once the virus infects neurons, these brain cells die from both the infection and the immune system releasing inflammation-causing cytokines, proteins that signal for infection-fighting cells to come to the site of infection. This impact on the nervous system can result in serious or fatal brain damage. Some symptoms include those of fever-induced illness, with the addition of vomiting, seizures and even an encephalitis-induced coma.
The most concerning part of EEE is that 30% of cases where individuals develop severe disease result in death. Moreover, a large portion of people who survive develop long term neurological problems, including paralysis. The extreme nature of EEE means preventing people from contracting it in the first place is essential.
Two cases of Triple E have been confirmed over the past two months in Middlesex County, where Tufts is located. While not a cause for immediate concern, it is important for members of the Tufts community to take appropriate precautions against the virus. Mosquitoes can still be active in October, especially around still water and swampy areas; an EEE death was reported on Oct. 10 in Vermont. Since there are no preventative treatments or vaccines, the CDC recommends wearing long sleeves and long pants, particularly in the morning and evenings. Additionally, using mosquito repellent on skin and clothes can aid in preventing bites.
Whether studying on President’s Lawn or enjoying a burrito bowl at Hodgdon Food-on-the-Run, it is important to take preventative measures against mosquito bites to decrease the current risk of EEE.
