Arboviral diseases, Western equine encephalitis virus disease in Washington

• Most infections are asymptomatic or mild (fever, headache, malaise, muscle aches).
• *Severe disease (encephalitis)*: Sudden onset of high fever, severe headache, stiff neck, confusion, tremors, and light sensitivity.
• In severe cases, seizures, paralysis, and coma can occur, with infants and young children being particularly vulnerable to long-term neurological damage.

WEEV is transmitted to humans and horses primarily through the bite of infected mosquitoes, particularly *Culex tarsalis*. Wild birds serve as the primary reservoir hosts, maintaining the virus in nature. Humans and horses are considered 'dead-end hosts,' meaning they do not develop high enough viral loads to transmit the virus further to mosquitoes.

• Use insect repellent containing DEET, picaridin, or oil of lemon eucalyptus when outdoors.
• Wear long-sleeved shirts and long pants, especially during dawn and dusk when mosquitoes are most active.
• Eliminate standing water around homes (e.g., in planters, gutters, old tires) to reduce mosquito breeding sites.
• Ensure windows and doors have intact screens to prevent mosquitoes from entering living spaces.
• *Vaccines are available for horses*, but currently *none are approved or available for human use*.