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FAQs - "B" Agents

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Western Equine Encephalitis (WEE)

What is Western Equine Encephalitis?

Western Equine Encephalitis (WEE) is a mosquito-borne viral disease that can affect the central nervous system and cause severe complications and death.

How do people become infected with WEE virus?

WEE virus is transmitted to humans through the bite of an infected mosquito. The main WEE transmission cycle is between birds and mosquitoes. Horses can also become infected with, and die from, WEE virus infection.

What causes WEE?z

WEE is caused by a virus that is a member of the family Togaviridae, genus Alphavirus. It is closely related to Eastern and Venezuelan equine encephalitis viruses.

Where is WEE found?

WEE is found in North, Central, and South America, but most cases have been reported from the plains regions of the western and central United States.

What are the signs and symptoms of WEE?

Infection can cause a range of illnesses, from no symptoms to fatal disease. People with mild illness often have only a headache and sometimes fever. People with more severe disease can have sudden high fever, headache, drowsiness, irritability, nausea, and vomiting, followed by confusion, weakness, and coma. Young infants often suffer seizures.

How soon after exposure do symptoms appear?

Symptoms usually appear in 2 to 10 days after the bite of an infected mosquito.

How common is WEE?

Human cases occur relatively infrequently and can occur in isolated cases or in epidemics. Human cases in the US are usually first seen in June or July.

Who is at risk for developing WEE?

Anyone can get WEE, but those at increased risk include people who engage in outdoor work and recreational activities and people living in or visiting areas where the disease is common. WEE occurs in all age groups.

How can people avoid infection with WEE virus?

Though a vaccine is available to protect horses, there is no licensed vaccine for human use.

To avoid infection people should avoid mosquito bites by employing personal and household protection measures, such as using insect repellent containing DEET, wearing protective clothing, taking precautions from dusk to dawn when mosquitoes are most likely to bite, and controlling standing water that can provide mosquito breeding sites.

Find the PDF version of this FAQ in the Zebra Manual.