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West Nile Virus


West Nile Virus is caused by - and referred to as - an arbovirus (arthropod-borne virus). West Nile fever and West Nile neuroinvasive disease (sometimes called West Nile encephalitis) is enzootic throughout Texas, and the virus may infect humans, birds, horses and some other animals.

West Nile Virus Overview

About West Nile Virus (WNV)

In addition to being major pests, mosquitoes may also transmit serious (sometimes fatal) pathogens. West Nile fever and West Nile neuroinvasive disease are currently of particular public health concern in Texas. West Nile virus was introduced into the eastern seaboard of the U.S. in 1999.

Transmission of West Nile Virus

West Nile virus is maintained in a complex lifecycle involving various species of birds and mosquitoes. This virus maintenance cycle usually remains undetected until human disease cases begin to be reported. Only about 15-20% of people infected with the West Nile virus will develop symptoms.

Symptoms of West Nile Virus

Typical symptoms include fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with this type of West Nile virus disease recover completely, but fatigue and weakness can last for weeks or months.

Less than 1% of people who are infected with the virus will develop a serious neurologic illness such as encephalitis or meningitis, and about 10% of people who develop neurologic infection due to West Nile virus will die.

Prevention of West Nile Virus Transmission

These infections generally occur during warm weather months when mosquitoes are active. The easiest and best way to avoid all arboviruses is by preventing mosquito bites by following these guidelines:

  • Use insect repellent containing DEET, picaridin, IR3535, some oil of lemon eucalyptus or paramenthane-diol.
  • Wear long sleeves and pants.
  • Stay in places with air conditioning or that use window and door screens.
  • Use a bed net if your sleeping area is exposed to the outdoors.
  • Consider using permethrin-treated clothing and gear.


There is no vaccine or specific antiviral treatments available for West Nile virus infection. Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms. In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.


Risk to travelers is highest in areas experiencing ongoing epidemics of the disease. The CDC presently recommends that travelers use standard precautions when traveling to areas that have confirmed cases of West Nile virus.