West Nile Virus (WNV)

Preguntas generales sobre el virus del Nilo Occidental en Espanol: http://www.cdc.gov/westnile/esp/preguntas/genQuestions_en_espanol.html

What is West Nile virus?

WNV is an arboviral (arthropod-borne virus) disease that was first discovered in the West Nile Region of Africa and is transmitted by mosquitoes. WNV became established in the U.S.A. in 1999. In Virginia, WNV is the most common mosquito-borne infection and occurs during the summer months when mosquitoes are most active. Other mosquito-borne arboviruses in Virginia include La Crosse encephalitis virus, St. Louis encephalitis virus, and eastern equine encephalitis virus.

Who get WNV infections?

Anyone can become infected with WNV and suffer a severe illness, but persons older than 50 years of age are far more susceptible to illness and account for most of the serious illness cases. In areas where WNV has been detected, only a small proportion of mosquitoes are likely to be infected. Most people bitten by an infected mosquito do not become sick.

What are the symptoms of arboviral infections?

  • No symptoms in most people. Most people (70-80%) who become infected with West Nile virus do not develop any symptoms.
  • Febrile illness in some people. About 1 in 5 people who are infected will develop a fever with other symptoms such as 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.
  • Severe symptoms in a few people. Less than 1% of people who are infected will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues). The symptoms of neurologic illness can include headache, high fever, neck stiffness, disorientation, coma, tremors, seizures, or paralysis.

Recovery from severe disease may take several weeks or months. Some of the neurologic effects may be permanent. About 10 percent of people who develop neurologic infection due to West Nile virus will die.

How soon after exposure do symptoms occur?

Symptoms may occur 3 to 14 days after exposure to infective mosquitoes.

How are WNV infections spread?

WNV is mostly spread from birds to people by the bites of infected mosquitoes. Among the 57 species of mosquitoes that occur in Virginia, there are only five species that potentially transmit WNV. The most important species is the northern house mosquito, and based on extensive mosquito testing data, Asian tiger mosquitoes are also an important WNV vector. Northern house mosquito populations may sometimes develop infection rates of as high as 5%, but these mosquitoes primarily bite birds. Asian tiger mosquito populations typically have very low infection rates (less than 0.01%) but they frequently bite people. Migrating birds may carry WNV from one region to another, but people are unlikely to become infected with WNV from contact with infected birds. Transmission between people does not occur.

Does past infection with WNV make a person immune?

Yes, infection with WNV is thought to provide lasting immunity to the virus.

What is the treatment for a WNV infection?

There is no specific treatment available for WNV infections other than care and support of patients during severe illness.

How can WNV infections be prevented?

Avoid mosquito bites by using insect repellents when outdoors in mosquito-infested areas. Home doors and windows should be well screened to prevent entry of mosquitoes. Eliminate mosquito breeding sites from yards by removing old tires, buckets, toys and other items that hold water. Dump ornamental containers (e.g., bird baths) on a weekly basis, or use mosquito larvicide pellets or dunks periodically to treat larger containers (e.g., ornamental ponds, stagnant swimming pools). Communities or municipalities may establish mosquito surveillance and control programs to reduce mosquito populations by spraying insecticides, treating storm sewers and puddles with larvicides, and draining stagnant water from ditches.

Standing Water Left Alone...Keeps Mosquitoes Close to Home

For more information about how to eliminate standing water:


How can I learn more about WNV?

  1. If you have concerns about WNV, contact your healthcare provider.
  2. Look at the resource available on the Virginia Department of Health’s Website located at: https://www.vdh.virginia.gov/epidemiology/epidemiology-fact-sheets/west-nile-virus-wnv/
  3. Call your local health department. A directory of local health departments is located at: https://www.vdh.virginia.gov/local-health-districts/
  4. Visit the Centers for Disease Control and Prevention website at: http://www.cdc.gov/ncidod/dvbid/westnile/index.htm.

If you are a provider, here is some guidance about specimen collection and when to test:
Arbovirus Specimen Collection Info
Arbovirus Testing Guidelines


You can also contact Henrico County about a particular question at these phone numbers.

Topic Name Department Phone/E-mail
Public Health Questions Laura Young Health 501-5216
[email protected]
Media Inquiries Public Relations & Media Services 501-4257
Report dead birds or horses West Nile Virus Hotline Public Works 226-6453
Request a speaker or West Nile video Public Works 226-6453
Field Staff Training General Services 501-5667
Mosquito Control Advice West Nile Virus Hotline Public Works 226-6453
Standing Water Complaints Public Works/
Environmental Division

Contact Us


Henrico Health Dept.
West Clinic

8600 Dixon Powers Dr.
Henrico, VA 23228

Henrico Health Dept.
East Clinic

1400 N. Laburnum Ave.
Richmond, VA 23223

(804) 205-3501
West End Main
(804) 501-4522
West End Clinic
(804) 501-4651
East End Clinic
(804) 652-3190

Shrader Rd WIC
(804) 501-1610
East End WIC
(804) 652-3180


Mailing Address
P. O. Box 90775
Henrico, VA 23273-0775


Shrader Road WIC
7740 Shrader Rd, Suite B
Henrico, VA 23228

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