Definition

Western equine encephalitis (WEE) is a virus spread by a bite from an infected mosquito. While WEE is rare, an infection can be serious or fatal.

Causes

WEE is caused by a virus. The virus is passed through the bite of an infected mosquito.

Risk Factors

Factors that may increase your chance of WEE include:

• Living in or visiting the plains regions of western and central US
• Doing activities outdoors and not using insect repellent

Symptoms

Most people with WEE do not have any symptoms.

If symptoms do occur, they appear within 5-10 days after infection and include:

• Headache
• Fever
• Nausea and vomiting
• Neck stiffness
• Chills
• Fatigue
• Joint and muscle pain

WEE can lead to more serious, life-threatening symptoms like inflammation of the brain (encephalitis), seizures, and coma. These serious symptoms are more common in infants and older adults.

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Diagnosis

In addition to taking your medical history and doing a physical exam, your doctor will ask you:

• What kind of symptoms you are experiencing
• Where you have been living or traveling
• Whether you have been exposed to mosquitoes

Your doctor may need to test your bodily fluids. This can be done with:

• Blood tests
• Lumbar puncture to evaluate the fluid that surrounds the brain and spinal cord

Imaging tests to evaluate the brain can be done with:

• MRI scan
• CT scan

Treatment

Because the infection is viral, there is no specific treatment for WEE. Treatment will focus on managing your symptoms and related complications through:

• IV fluids
• Antiseizure medications
• Medications to decrease brain swelling
• Mechanical ventilation

Prevention

There is no vaccine for humans. There is a vaccine for horses. Prevention of WEE focuses on controlling mosquitoes and avoiding mosquito bites. Steps you can take to avoid mosquito bites:

• Stay inside between dusk and dark, when mosquitoes are most active.
• Wear long pants and long-sleeved shirts when outside.
• Use an insect repellent with DEET.
• Repair screens to prevent mosquitoes from entering the house.
• Use proper mosquito netting at night. Look for netting treated with insecticide.
• Remove standing water (such as birdbaths, clogged gutters) to prevent mosquito breeding.