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Page last reviewed: July 14, 2023
West Nile Virus
West Nile virus (WNV) is the leading cause of mosquito-borne disease in the continental United States. It is most commonly spread to people by the bite of an infected mosquito. Cases of WNV occur during mosquito season, which starts in the summer and continues through fall.
There are no vaccines to prevent or medications to treat WNV in people. Fortunately, most people infected with WNV do not feel sick. About 1 in 5 people who are infected develop a fever and other symptoms. About 1 out of 150 infected people develop a serious, sometimes fatal, illness. You can reduce your risk of WNV by using insect repellent and wearing long-sleeved shirts and long pants to prevent mosquito bites.
West Nile virus (WNV) is spread to people through the bite of an infected mosquito. Mosquitoes bite during the day and night. There is no vaccine to prevent WNV infection. The best way to prevent West Nile is to protect yourself from mosquito bites. Use insect repellent, wear long-sleeved shirts and pants, treat clothing and gear, and take steps to control mosquitoes indoors and outdoors.
No symptoms in most people. Most people (8 out of 10) infected with West Nile virus do not develop any symptoms.
Febrile illness (fever) in some people. About 1 in 5 people who are infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with febrile illness due to West Nile virus recover completely, but fatigue and weakness can last for weeks or months.
Serious symptoms in a few people. About 1 in 150 people who are infected develop a severe illness affecting the central nervous system such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord).
- Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.
- Severe illness can occur in people of any age; however, people over 60 years of age are at greater risk for severe illness if they are infected (1 in 50 people). People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk.
- Recovery from severe illness might take several weeks or months. Some effects to the central nervous system might be permanent.
- About 1 out of 10 people who develop severe illness affecting the central nervous system die.
Diagnosis
- See your healthcare provider if you develop the symptoms described above.
- Your healthcare provider can order tests to look for West Nile virus infection.
- To learn more about testing, visit the CDC Healthcare Providers page.
Treatment
- No vaccine or specific medicines are 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.
- If you think you or a family member might have West Nile virus disease, talk with your health care provider.
- To learn more about treatment, visit the CDC Healthcare Providers page.
West Nile virus is most commonly spread to people by the bite of an infected mosquito.
Mosquitoes become infected when they feed on infected birds. Infected mosquitoes then spread West Nile virus to people and other animals by biting them.
In a very small number of cases, West Nile virus has been spread through:
- Exposure in a laboratory setting
- Blood transfusion and organ transplant
- Mother to baby, during pregnancy, delivery, or breast feeding
West Nile virus is not spread:
- Through coughing, sneezing, or touching
- By touching live animals
- From handling live or dead infected birds. Avoid bare-handed contact when handling any dead animal. If you are disposing of a dead bird, use gloves or double plastic bags to place the carcass in a garbage can.
- Through eating infected animals, including birds. Always follow instructions for fully cooking meat.
Mosquito control is something anyone can do, ranging from individuals to mosquito control professionals.
- You, your neighbors, and the community can also take steps to reduce mosquitoes in and around your home and in your neighborhood.
- Professionals from local government departments or mosquito control districts develop mosquito control plans, perform tasks to control mosquito larvae and adult mosquitoes, and evaluate the effectiveness of actions taken.
The Houston Health Department conducts surveillance of WNV in Houston while Harris County Public Health conducts surveillance in Harris County. Mosquito control services for the city of Houston and Harris County are provided by Harris County Public Health.
| Gender | Age Range | Date Reported | Area | Case Number |
| Male | 45-54 | 09/25/2018 | Southwest Houston | 4 |
| Male | 35-44 | 09/25/2018 | Southwest Houston | 3 |
| Female | 45-54 | 09/05/2018 | Southwest Houston | 2 |
| Male | 45-54 | 07/16/2018 | Northwest Houston | 1 |
| Male | 45-54 | 03/06/2017 | Northwest Houston | 5 |
| Male | 45-54 | 09/13/2017 | Northwest Houston | 4 |
| Male | 85-94 | 09/09/2017 | Southwest Houston | 3 |
| Male | 45-54 | 08/03/2017 | Northwest Houston | 2 |
| Female | 5-14 | 08/11/2017 | Southwest Houston | 1 |
| Male | 75-84 | 08/02/2016 | Northeast Houston | 2 |
| Female | 55-74 | 08/02/2016 | Northwest Houston | 1 |
Statistics
- Map of zip codes where mosquitoes have tested positive for viruses that infect humans. The yellow shading are zip codes where mosquitoes have tested positive for West Nile Virus. | Harris County Public Health
- West Nile Virus statistics and maps | CDC
- West Nile Virus in Texas | Texas Department of Health and Human Services
3D Defense
The Houston Health Department encourages people to use the “3D Defense” to prevent mosquito bites and reduce the risk of infection:
- Drain: Drain standing water around your home so mosquitos don’t have a place to breed.
- DEET: Apply EPA-approved insect repellent with the ingredient DEET.
- Dress: Dress in long sleeves and pants while outdoors to limit exposed skin.