EEE virus: What is the mosquito-borne disease affecting the US and how deadly is it?

An outbreak of eastern equine encephalitis has already killed one person, putting health authorities on alert. Here’s what you need to know

The US is currently battling a surge in eastern equine encephalitis, a rare but extremely dangerous virus that is spread by mosquitoes.
One person has already been killed by the disease in New Hampshire, while neighbouring Massachusetts has introduced a partial curfew, shutting parks and other outdoor public spaces between dusk and dawn to reduce the risk of people being bitten by the virus-carrying mosquitoes.
Here’s everything you need to know about EEE.
Eastern equine encephalitis, commonly known as EEE or ‘Triple E’, is a virus transmitted to humans through the bite of an infected mosquito. The virus causes brain inflammation and affects the brain and nervous system’s functionality.
EEE naturally resides in certain birds and rodents in the United States – mostly on the East Coast – and has also been found in Central and Latin America, Canada, and the Caribbean.
Mosquitoes become carriers of EEE after feeding on an infected bird or rodent. These mosquitoes can then transmit the virus to humans and other animals. It cannot be spread directly between humans, and neither humans nor horses circulate enough of the virus in their bodies to pass it back to mosquitoes.
The virus is most commonly found near freshwater swamps and lakes, where mosquitoes thrive. People who work outdoors in these areas are at the highest risk.
First detected in horses in the 1830s, hence the name, EEE affects both horses and humans with acute symptoms.
The US records an average of 11 human cases of EEE each year, according to the Centers for Disease Control and Prevention (CDC).
The largest recorded outbreak occurred in 2019, with 38 cases and 12 deaths in Massachusetts.
EEE has a very high fatality rate of at least 30 per cent, meaning that around one in three people who contract the disease will die, according to the CDC.
Some people may be infected without showing any symptoms, although data is limited due to a lack of surveillance and testing.
Those most at risk include individuals over 60 and children under five, but the virus can affect people of any age. Symptoms often begin with fever, chills, body aches, vomiting, diarrhoea, and fatigue.
The infection can then progress to encephalitis, an inflammation of the brain, and meningitis, an inflammation of the membranes surrounding the brain and spinal cord.
Survivors of EEE can be left with lifelong mental and physical disabilities due to the damage caused to the brain and central nervous system. Effects can range from behavioural changes and memory loss to paralysis and permanent brain damage.
Currently, there are no medicines or vaccines available to treat EEE. 
There are clinical trials in the works for an EEE vaccine, developed by Bavarian Nordic. The jab would also protect against two other closely related diseases – western and Venezuelan equine encephalitis. 
Phase 2 of the trial is set to start later this year. If successful, it could still be several years before a safe and effective jab is ready for clinical use. Antibiotics are ineffective against EEE, as it is caused by a virus, not bacteria.
Most patients will require hospitalisation and pain management. In cases where brain inflammation leads to increased pressure within the skull, a craniotomy, a type of brain surgery, may be performed to relieve the pressure.
Due to the lack of available treatments, prevention is crucial. If a person avoids being bitten by an infected mosquito, they cannot contract the virus.
Public health authorities in several Massachusetts counties have advised citizens to avoid outdoor spaces after 6pm during peak summer months, when mosquitoes are most active. Some local health departments have also begun spraying pesticides in areas with high mosquito activity.
Wearing long sleeves and trousers during peak mosquito hours – dusk until dawn – and applying insect repellent are also effective preventive measures. Draining standing water from items like car tyres and plant pots can reduce mosquito populations around the home, as the insects thrive in stagnant water.
Five human cases of EEE have been recorded so far this year in New Hampshire, Vermont, New Jersey, Wisconsin, and Massachusetts.
So far the numbers aren’t particularly out of the ordinary – last year the US recorded seven cases.
But that might change in the coming years as a result of climate change, which is altering environmental conditions that influence the spread of mosquito-borne diseases.
Climate change is leading to generally warmer temperatures, which can extend the mosquito season.
Mosquitoes thrive in warm weather, and as temperatures rise earlier in the year and stay higher for longer, mosquitoes have more time to breed, increasing the risk of EEE transmission.
Other mosquito-borne diseases like West Nile virus, dengue, and Zika have caused significant outbreaks around the world this year and spread to new geographical areas due to the effects of climate change.
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