Amid the challenging times of the COVID-19 pandemic, another serious viral threat had also just emerged, raising serious concerns among the public. In 2019, the Centers for Disease Control and Prevention (CDC) announced the largest outbreak of Eastern Equine Encephalitis (EEE) seen in over fifty years. This outbreak lasted until 2020 and spread to new areas that are not usually affected by the virus.^1,2 Unfortunately, many people who fell ill lost their lives, and over half of those who survived suffer from long-term brain and nerve complications.^3,4 Despite these risks, there is still no human vaccine for EEE,³ which raises many important questions: what caused the sudden increase in EEE cases in 2019 and 2020, and what can we do to protect ourselves?

What is eastern equine encephalitis (EEE)?

• EEE has several names, including Triple E, Sleeping Sickness, EEE, and EEEV, but they all refer to the same viral infection.
• Eastern Equine Encephalitis (EEE) is a viral infection that can lead to brain inflammation (encephalitis) in humans, horses, and other animals. This infection spreads through the bite of a mosquito carrying the EEE virus.^1,2 The EEE virus belongs to the genus Alphavirus. These types of viruses attack the brain of  humans and animals, causing fevers and encephalitis.^5,6 Among the Alphaviruses, the EEE virus is considered the most dangerous.⁷ According to the CDC, one in three people infected with the EEE virus die, and even those who survive are likely to suffer from long-term brain and nerve complications.³ 

Where is the EEE virus found? 

The EEE virus is normally found in:^7,9

• North America
• The Caribbean Islands
• Parts of Central and South America. 

 EEE outbreaks affecting humans and horses occur in North America.¹⁰ The areas of higher EEE incidence in the United States (US) include:^2,7

• Gulf Coast region near the Gulf of Mexico (e.g., Florida, Louisiana, and Texas)
• Coastal areas along the Atlantic Ocean (e.g., Massachusetts, Connecticut, and Delaware)
• States bordering the Great Lakes (e.g., Michigan and Wisconsin)

How is the EEE virus spread?

The EEE virus primarily spreads through a natural cycle between mosquitoes and birds. This cycle is most active from spring to fall, and usually happens in swampy areas. A specific type of mosquito known as Culiseta melanura, or black-tailed mosquito, carries the EEE virus and infects birds by biting them. Since this mosquito species cannot feed on humans or animals, the virus remains limited to the bird population. Sometimes, other mosquitoes that can feed on humans and animals may transmit the infection from the infected birds to humans and animals.^11,12 These mosquitoes act as a vector, and some species include:

• Coquillettidia perturbans
• Aedes sollicitans
• Ochlerotatus canadensis

 After biting an infected bird, these mosquitoes become carriers of EEE. When an infected mosquito bites a person, it injects its saliva and the virus into their skin. Once inside the body, the virus targets specific cells and starts to multiply, eventually spreading throughout the body.^11,12 

How common are EEE outbreaks?

EEE has been a significant public health concern since its discovery in 1933 in Delaware, USA.¹³ Since then, periodic outbreaks have occurred every 10-20 years, each lasting 2-3 years.¹⁴ 

The first recognized outbreak of EEE took place in eastern Massachusetts in 1938, where 25 out of 38 infected people died.¹⁴ Another significant outbreak occurred in 1959 in New Jersey, with 32 reported cases of encephalitis.² Despite no significant outbreaks since 1959, reported cases of EEE have been increasing in recent years.

According to the CDC, an average of 6-8 cases of EEE are reported each year.² However, in 2019, there was a significant increase in cases, with 38 reported cases and 19 deaths.^4,15 This outbreak also spread to new areas. Although EEE usually affects 20 states, such as Massachusetts, Florida, and New Hampshire, recent outbreaks have also included areas such as Arkansas, Connecticut, Maine, Tennessee, North Carolina, and Vermont.² However, it appears the frequency of EEE cases has returned to its typical annual rate after 2020. Based on data from the CDC,¹ five cases were reported  in 2021. One was reported in 2022, followed by seven cases in 2023.

Why has there been so many EEE cases recently?

Researchers are still uncertain about the cause behind the increase in EEE cases. However, several experts have identified factors contributing to the rise in EEE cases in 2019. Catherine Brown, a state epidemiologist and state public health veterinarian at the Massachusetts Department of Public Health, suggests that a decrease in immunity among bird populations, coupled with a presence of mosquito species, likely facilitated the spread of the virus. Additionally, changes in the strain of the EEE virus might have also played a role in its prevalence, across the Northeastern and Midwestern regions.^16,17

What are the symptoms of EEE?

Not everyone infected with EEE shows symptoms. For those that do, they often start with feelings similar to the flu, including:¹¹

• Fever
• Headache
• Fatigue
• Chills
• Joint pain
• Muscle pain
• Nausea and vomiting

Symptoms usually show 4 to 10 days after an infected mosquito bite. Approximately 5% of people who experience EEE symptoms develop encephalitis, which can lead to coma if not treated early enough.^4,11,17 As such, early diagnosis can greatly increase the chances of successful treatment and even save lives.

How is EEE diagnosed? 

Your doctor will examine you and ask about your health history. That includes events like recent insect bites. There is no specific test for EEE, but a blood test can help rule out other diseases. A healthcare professional may also analyze your cerebrospinal fluid to find antibodies in your body in response to the virus. They might also do scans and run other tests. These can show signs of encephalitis, like brain damage, nerve cell death, and inflammation of blood vessels in the brain.¹⁸

How is EEE treated?

• While there is no treatment for EEE, healthcare providers may recommend some suggestions to help manage mild symptoms. These can include getting plenty of rest, staying hydrated, and over-the-counter pain relievers¹⁹ 
• If someone is experiencing severe symptoms, they should be admitted to the hospital, so a doctor can closely monitor their condition. If the brain inflammation creates too much pressure inside the head, doctors might have to do a surgery called a craniotomy to lessen the pressure
• Although antibiotics are not effective against EEE, doctors may suggest immunoglobulin therapy for severe cases. This is a treatment where antibodies are administered to your body through a needle to help fight the virus¹⁹ 

What can you do to protect yourself from EEE?

Avoiding mosquito bites is important if you wish to protect your family and yourself against the EEE virus. The CDC and CT.gov. recommend the following guidelines to avoid mosquito bites:

• Plan indoor tasks for evening hours as this is the time when mosquitoes are most active.
• Use screens on windows and doors for a mosquito-free home. 
• When outside, keep your skin covered. Wear trousers, long-sleeved tops, socks, and shoes. This helps make sure mosquitoes stay away from your skin.
• Make sure to use mosquito nets when sleeping outside, especially for babies.
• Fight off mosquitoes with EPA-sanctioned repellents, DEET, Picaridin, IR3535, or lemon eucalyptus oil.
• Be careful during camping, especially near freshwater swamps. Always use netted tents and apply repellent.
• Permethrin can be used to treat your clothes and gear. You can buy permethrin-treated items for added protection.
• Keeping your house cool via air conditioning helps keep mosquitoes at bay.
• Remove standing water from your surroundings to stop mosquitos from multiplying. Keep an eye out for tires, buckets, birdbaths, etc.
• Regularly empty, disinfect, secure, and get rid of items collecting water to stop mosquitoes from reproducing.

In addition, communities can also prevent EEE's spread by embracing programs such as Integrated Mosquito Management (IMM). It informs people, tracks mosquitoes, and manages their population at different life phases. This work cuts down mosquito numbers and stops the transmission of EEE and other mosquito-borne diseases.

FAQs

Is EEE contagious?

No. The EEE virus only spreads to humans through mosquito bites. It can't pass straight from one person to another or from a horse to a person.¹²

Is there a vaccine for EEE?

There is no vaccine for humans to protect them from EEE virus yet. There is only a vaccine for horses which is not safe for humans to use.³

Are there any risk factors for EEE?

There are several risk factors for EEE including:¹⁹

• The summer months
• People who live and work near wetland and swamp areas 
• People below 15 or over 50 years old
• Weakened immune system due to factors such as cancer treatment, organ transplants, diabetes, hypertension, and kidney disease.

How long will it take to start feeling better after treatment?

• A mild case of EEE can last from one to two weeks. However, it's possible to still feel weak or tired for several weeks to even months. 
• If the symptoms were severe, a full recovery might take several months.¹⁹ 

Summary

In recent years, there has been a sudden increase in the number of Eastern Equine Encephalitis (EEE) cases across the United States, which left many concerned. EEE is a viral infection that spreads through mosquito bites, targeting the brain and causing severe neurological complications and fatalities. 

Since we don't have a vaccine yet, it's important to learn about EEE's characteristics, how it spreads, its signs, how it's diagnosed, and how to protect ourselves. Several factors, including climate change, contribute to the higher number of EEE outbreaks. 

Early detection, supportive care, and preventive strategies, such as mosquito avoidance and community-based interventions, can help stop the spread of EEE virus and keep the public safe.