Eastern equine encephalitis
Eastern equine encephalitis (EEE) is a rare but serious viral infection primarily affecting the brain and central nervous system, mostly transmitted by infected mosquitoes that have bitten wild birds. While EEE poses a greater threat to horses, humans can also be infected, leading to severe illness in some cases. The onset of symptoms typically occurs four to ten days after exposure and can range from mild systemic issues, like fever and muscle pain, to severe neurological disturbances, including confusion or seizures. Unfortunately, the mortality rate for encephalitic EEE is about 30%, and many survivors may experience long-term neurological complications.
EEE is most prevalent in the Eastern United States, particularly in temperate woodland and wetland areas during the warmer months. Individuals at higher risk include children, the elderly, and those with weakened immune systems. Currently, there is no specific antiviral treatment for EEE in humans; care is primarily supportive, focusing on symptom management. Preventive measures include avoiding mosquito-prone areas, using insect repellents, and eliminating potential mosquito breeding sites. Despite the low incidence of EEE, it remains a significant public health concern, particularly following outbreaks reported in recent years.
Eastern equine encephalitis
- ANATOMY OR SYSTEM AFFECTED: Brain, central nervous system
Definition
Eastern equine encephalitis (EEE) is a zoonotic virus affecting wild birds. It is carried by certain mosquitoes and is occasionally transmitted to horses and, rarely, to humans. EEE affects the brain and central nervous system.
Although EEE is more dangerous to horses than to humans (many people infected with the EEE virus do not have any apparent health problems), people infected can become suddenly and seriously ill and may experience severe injury to the nervous system. Death followed infection in 30 percent of cases, and continuing neurological problems were evident in many survivors. The Centers for Disease Control and Prevention reported an average of eleven cases of EEE annually in the United States.
In areas where EEE is known to be present, people should take extra precautions to avoid mosquitoes and protect themselves against mosquito bites.
Causes
EEE, an arbovirus, is spread by infected invertebrate animals, mostly blood-sucking (hematophagous) insects. Arboviruses are usually spread by infected mosquitoes. Mosquitoes most often get the EEE virus by biting infected birds and then spreading the virus to horses and other mammals, including humans.
Risk Factors
Because the only known way for humans to contract EEE is by being bitten by an infected mosquito, the risk factor most commonly associated with EEE is exposure to mosquito bites, which increases for those living or working outdoors near or visiting a temperate woodland area, a wetland area, or an area known to have incidents of EEE between late spring and early autumn in the Eastern United States. People aged fifteen years and younger and aged fifty years and older seem to be more susceptible to the infection. Individuals with a weakened immune system, people who work outside, and specific genetic factors may also increase the risk of contracting EEE.
Symptoms
The onset of symptoms typically occurs between four and ten days after exposure. EEE infections tend to present as systemic or encephalitic disease. If a person experiences any of the symptoms of EEE, they should not assume EEE causes it. Other, less serious health conditions may cause these symptoms; however, one should consult a doctor for a proper diagnosis. In systemic EEE, symptoms include chills, fever, joint pain, muscle pain, and weakness. Encephalitic EEE may produce fatigue or drowsiness; fever; headache; lack of appetite; vomiting; diarrhea; restlessness or irritability; bluish skin; confusion, impaired judgment, or an altered mental state; or seizures. Sometimes, EEE infections produce no symptoms.
Screening and Diagnosis
A doctor will ask about symptoms and medical history, will perform a physical exam, and may order the following tests: blood tests to check if the virus is present; a spinal tap to remove a small amount of spinal fluid to check for signs of infection; an electroencephalogram (EEG) to measure the brain’s activity; a neurological exam to access reflexes, memory, and other brain function; a magnetic resonance imaging (MRI) scan (a scan that uses radio waves and a powerful magnet to produce detailed computer images); and a computed tomography (CT) scan (a detailed X-ray picture that identifies abnormalities of fine tissue structure). Chemical analyses are performed at a few specialized laboratories and require a few weeks to return results.
Treatment and Therapy
There are no drug options to treat the EEE virus in humans, so medical treatment focuses on the symptoms of the infection. Such treatments may include antibiotics for secondary infections; anticonvulsants to treat seizures; a respirator to help with breathing; pain relievers to treat headache, fever, and body aches; corticosteroids to reduce swelling in the brain; and sedatives for restlessness or irritability. In cases of severe EEE, doctors may administer intravenous immunoglobulin therapy. This process involves injecting antibodies from a healthy individual into the patient with EEE to help boost their immune system response.
Prevention and Outcomes
Those who contract systemic EEE generally recover within one to two weeks. Nearly one-third of those who develop encephalitic EEE die of it, usually within two to ten days after symptoms begin. Survivors tend to have ongoing neurological impairments, which can include cognitive impairment, cranial nerve dysfunction, paralysis, personality disorders, and seizures. These may worsen over time.
There is no EEE vaccine available to consumers. Because of the rarity of the disease and the costs of drug development, one is unlikely to be developed for widespread use. There is, however, a vaccine available for horses.
To help reduce the chance of getting EEE, one should avoid areas of mosquito activity, if possible, and stay inside when mosquitoes are most active (at dawn and dusk). When inside, rely on intact screened windows and doors and air conditioners for cooling. When outside, one should wear insect repellent, insecticide-treated clothing and gear, closed-toe shoes, and long pants and long-sleeved shirts of tightly woven fabric to limit exposure to bites.
To help limit mosquito populations in and around the home, one should eliminate insect breeding areas, such as standing water in ponds and pools, pet bowls, gutters, planters, and other containers. States and local communities experiencing EEE outbreaks often spray Environmental Protection Agency-registered insecticides for mosquito control, distributed through truck-mounted or aerial sprayers. EEE remained a significant public health concern in the twenty-first century. The mid-2020s saw one major outbreak of the disease in the northeastern United States, and cases appeared to be on the rise as the decade progressed.
Bibliography
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