Eastern equine encephalitis, also called EEE or triple E, is a virus that spreads from infected mosquitoes to horses and people. These mosquitoes generally live in freshwater swamps.
The virus is found in North America, South America, Central America, and the Caribbean.
EEE is rare – only a few cases are reported each year in the U.S., but it can be very serious. About 30% of people with the virus die, and survivors can have lasting health problems.
Eastern Equine Encephalitis Causes
EEE is caused by an arbovirus that's a member of the genus alphavirus. An arbovirus is a virus that’s spread by insects, like mosquitoes. Other arboviruses include West Nile, Zika, dengue, and chikungunya.
How does eastern equine encephalitis spread?
The eastern equine encephalitis virus is found in several types of animals, including birds, mammals, and amphibians. If a mosquito bites an infected animal, usually a bird, the mosquito itself becomes infected.
Then, when the mosquito bites a person, they pass the virus on to that person. People can’t spread the virus to each other, either through direct contact or through body fluids. Horses and people are the two species that are most commonly affected by the virus. Most other species may have the infection but not get sick or show any signs of illness.
Researchers know of one case where the infection was spread through organ transplants. An organ donor, infected with EEE, gave organs to three people. They became infected, too.
Who gets eastern equine encephalitis?
Anyone can get eastern equine encephalitis, but some people are at higher risk of becoming infected with the virus than others. These are people who live near, visit, or work in areas where the virus is, especially from May through October. This is when the virus is the most active. The Atlantic and Gulf Coast states, as well as the Great Lakes region, are the likeliest places to get the infection in the U.S.
Other risk factors for contracting eastern equine encephalitis include:
- Spending time outdoors in high-risk areas at dawn or dusk
- Being younger than 15 or older than 50
- Having a weakened immune system, either from illness or medications that suppress the immune system
Eastern Equine Encephalitis Symptoms
If you’ve been infected with the eastern equine encephalitis virus, you might not have any symptoms. If you do, they often show up about 4 to 10 days after you’ve been bitten by an infected mosquito. You might have:
- Chills
- Fever
- Joint pain
- Muscle pain
These symptoms generally last about 1 or 2 weeks. But if you get a severe infection that worsens to encephalitis (inflammation of the brain), you could have more severe symptoms that make it seem like you have the flu. If you’ve been in an area that is known to have EEE and you’ve been bitten by a mosquito, having these symptoms could mean you have the virus. Symptoms of more severe eastern equine encephalitis include:
- Confusion
- Diarrhea
- Drowsiness
- Headache
- High fever (over 104 F or 38 C)
- Loss of appetite
- Vomiting
Among older children and adults, typically the symptoms appear several days after being infected, but they can appear much faster in infants.
Eastern Equine Encephalitis Diagnosis
It’s important that EEE be diagnosed as soon as possible so you can watch for complications.
Your doctor will ask you about your signs and symptoms and if you’ve been where the virus is present. Also mention if any family members have recently gone to high-risk areas with you and have been diagnosed.
Your doctor may do some blood tests to rule out other possible causes of infection. To diagnose EEE specifically, you would need eastern equine encephalitis virus IgM testing. This isn’t available everywhere, but the CDC offers it, as do some state health departments. If this test is positive, the diagnosis needs to be confirmed by another type of test called neutralizing antibody testing. This looks at specific antibodies in the blood.
Your doctor might want to test your cerebrospinal fluid to check for signs of infection. This test is called a lumbar puncture or spinal tap. The doctor numbs the skin in your lower back, in the center. A needle is then inserted between two vertebrae (bones in your backbone). Using a syringe, the doctor removes some fluid to send to a lab for testing.
Eastern Equine Encephalitis Treatment
Currently, there aren’t any antiviral medications that can treat eastern equine encephalitis. Since it is a virus, antibiotics can’t treat the infection either. So for now, treatment for EEE involves treating the symptoms and making you feel as comfortable as possible as your body fights the infection. This means:
- Resting
- Drinking fluids so you stay hydrated
- Taking over-the-counter medications, like acetaminophen or ibuprofen, to help relieve pain and fever. Please note: Don’t give a child or teen aspirin if they have a virus. It can cause a rare but serious condition called Reye’s syndrome.
If your symptoms don’t go away or become severe, seek medical help right away. You may need to be in a hospital to be monitored for brain inflammation. If this does happen, you might need surgery, called a craniotomy, to help relieve pressure and reduce the risk of brain damage.
Eastern Equine Encephalitis Complications
Eastern equine encephalitis is a serious infection that can cause complications in some people. These complications could be:
- Seizures
- Paralysis
- Psychosis
- Intellectual disability
The infection can lead to brain damage and death.
Eastern Equine Encephalitis Prevention
Until we have a vaccine that can prevent the eastern equine encephalitis infection, the only way you can prevent getting EEE is by avoiding mosquito bites, especially if you’re in an area known to have the virus.
Be sure to use insect repellents registered with the Environmental Protection Agency (EPA). It’s important to use approved repellents because they have been proven to be safe and effective in preventing mosquito bites. They are also safe for people who are pregnant or nursing. If the insect repellent is for a young child, check the label because some repellents shouldn’t be used on children ages 3 years and younger. Be sure to reapply the product regularly, according to the instructions. If you are using sunscreen, apply the sunscreen first and the repellent after.
Recommended repellents include:
- DEET
- Picaridin
- IR3535
- Oil of lemon eucalyptus (OLE)
- Para-menthane-diol (PMD)
- 2-undecanone
Here are some more tips:
- Wear long sleeves and pants.
- Wear insect-repellent clothing and gear.
- Avoid being outside when mosquitoes are the busiest, at dawn and dusk.
- Get rid of things nearby that encourage mosquitoes, like standing water.
- Make sure you have screens in your windows, and patch any holes that might appear.
Takeaways
Eastern equine encephalitis is a rare but potentially serious infection. It’s spread to humans and to horses from the bite of an infected mosquito. People can’t give it to each other, though. Most people will recover from the infection in a week or two, but some people do have serious complications, including inflammation of the brain, called encephalitis. If your symptoms don’t go away or they get worse, contact your doctor as soon as possible.
Eastern Equine Encephalitis FAQs
What is the survival rate for eastern equine encephalitis?
About 70% of people who contract eastern equine encephalitis survive the infection. But many survivors can have long-lasting issues, such as seizures, paralysis, psychosis, and intellectual disability.
How do birds get EEE?
Birds can get EEE the same way humans do: through the bite of an infected mosquito.
Where is eastern equine encephalitis most common?
Eastern equine encephalitis is found in North America, Central America, South America, and the Caribbean. In the U.S., you’re more likely to come across it in Atlantic and Gulf Coast states, as well as in the Great Lakes region.