Arboviral Encephalitides

Arboviral encephalitides are mosquito-transmitted viral diseases capable of causing encephalitis (brain inflammation). Varieties found in the United States include eastern equine encephalitis, western equine encephalitis, St. Louis encephalitis and La Crosse (LAC) encephalitis, and West Nile Virus encephalitis. Encephalitis is a very serious disease that can lead to coma, brain damage and death. Eastern equine encephalitis is particularly deadly, with a 30-35% fatality rate, according to the U.S. Centers for Disease Control and Prevention. However, cases are rare -- an average of four a year in the U.S., according to the CDC.

Most viral encephalitis infections either don't produce any symptoms at all or only lead to general flu-like symptoms such as fever, headache, muscle ache and malaise. Symptoms of severe encephalitis include high fever, stiff neck or back, sensitivity to light, vomiting and confusion.

West Nile Virus

What Is West Nile Virus?
West Nile virus (WNV) is a potentially serious illness. Experts believe WNV is established as a seasonal epidemic in North America that flares up in the summer and continues into the fall. This fact sheet contains important information that can help you recognize and prevent West Nile virus.

What Can I Do to Prevent WNV?
The easiest and best way to avoid WNV is to prevent mosquito bites.

When you are outdoors, use insect repellent containing an EPA-registered active ingredient. Follow the directions on the package.

Many mosquitoes are most active at dusk and dawn. Be sure to use insect repellent and wear long sleeves and pants at these times or consider staying indoors during these hours.

Make sure you have good screens on your windows and doors to keep mosquitoes out.

Get rid of mosquito breeding sites by emptying standing water from flower pots, buckets and barrels. Change the water in pet dishes and replace the water in bird baths weekly. Drill holes in tire swings so water drains out. Keep children's wading pools empty and on their sides when they aren't being used.
What Are the Symptoms of WNV?

Serious Symptoms in a Few People. About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent.
Milder Symptoms in Some People. Up to 20 percent of the people who become infected have symptoms such as fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks.
No Symptoms in Most People. Approximately 80 percent of people (about 4 out of 5) who are infected with WNV will not show any symptoms at all.
How Does West Nile Virus Spread?

Infected Mosquitoes. Most often, WNV is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite.

Transfusions, Transplants, and Mother-to-Child. In a very small number of cases, WNV also has been spread through blood transfusions, organ transplants, breastfeeding and even during pregnancy from mother to baby.

Not through touching. WNV is not spread through casual contact such as touching or kissing a person with the virus.
How Soon Do Infected People Get Sick?
People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito.

How Is WNV Infection Treated?
There is no specific treatment for WNV infection. In cases with milder symptoms, people experience symptoms such as fever and aches that pass on their own, although even healthy people have become sick for several weeks. In more severe cases, people usually need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing and nursing care.

What Should I Do if I Think I Have WNV?
Milder WNV illness improves on its own, and people do not necessarily need to seek medical attention for this infection though they may choose to do so. If you develop symptoms of severe WNV illness, such as unusually severe headaches or confusion, seek medical attention immediately. Severe WNV illness usually requires hospitalization. Pregnant women and nursing mothers are encouraged to talk to their doctor if they develop symptoms that could be WNV.