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    Infectious Disease Prevention Section
    Mail Code: 1927
    PO BOX 149347 - Austin, TX 78714-9347
    1100 West 49th Street, Suite G401
    Austin, TX 78714

    Phone: (512) 776-7676
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FAQs - Frequently Asked Questions

West Nile Virus West Nile Virus
(West Nile Virus, WNV, WestNile)
ICD-9 066.4; ICD-10 G93.3


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West Nile Virus

Below are answers to frequently asked questions about West Nile virus (WNV) received by the Texas Department of State Health Services (DSHS).

Answers to some of the questions received by the national Centers for Disease Control and Prevention (CDC) can be found at

Q.  How many human cases have there been in the United States? How many deaths?
A.  For the latest information available on human cases in the US, please refer to the CDC website at

Q.  How many human cases have there been in Texas? How many deaths?
A.  For the latest information available on human cases in Texas, please refer to the DSHS WNV home page at

Q.  What is the risk of someone becoming ill with WNV?
A.  The risk is very low. Even in areas where the virus is circulating, very few mosquitoes are infected with the virus. Plus, even if the mosquito is infected, less than 1% of people who get bitten and become infected will get severely ill. The chances you will become severely ill from any one mosquito bite are extremely small.

Q.  What are the clinical signs and symptoms of disease in humans?
A.  In general, some of the signs and symptoms include fever, headache, weakness, muscle pain, joint pain, nausea, vomiting, diarrhea, and rash. Although uncommon, some people may have encephalitis and/or meningitis (inflammation of the brain and/or surrounding tissues) and develop neck stiffness, stupor, disorientation, coma, tremors, convulsions, and paralysis. For a more detailed overview of the variety of signs and symptoms, please refer to the Fact Sheet that is accessible at the DSHS WNV home page at and the Annual Summaries that are accessible at

Q.  Is there a vaccine for humans?
A.  No. There is no indication that a human vaccine will be available in the near future.

Q.  Can a human get the virus twice?
A.  We don't think so. It is assumed that a person would develop a natural immunity to future infection by the virus and that this immunity would be life-long. However, this immunity may fade in later years.

Q.  How can I prevent being exposed to the virus?
A.  Some quick tips include:

  • Use an approved insect repellent every time you go outside. Approved repellents include those that contain DEET, picaridin, oil of lemon eucalyptus, or IR3535. Follow the instructions on the label.
  • Regularly drain standing water, including water that collects in empty cans, tires, buckets, clogged rain gutters and saucers under potted plants. Mosquitoes breed in stagnant water.
  • Wear long sleeves and pants when outside. With the summer heat, an alternative may be to opt for longer shorts, plus socks and tennis shoes instead of sandals.
  • Avoid being outside or take extra precautions at dusk and dawn when mosquitoes are most active.
  • Use air conditioning or make sure there are screens on all doors and windows to keep mosquitoes from entering the home.

Q.  West Nile virus is considered to be an arbovirus. What is an arbovirus?
A.  Arboviruses include any of the viruses that are causative agents of diseases such as West Nile, yellow fever, dengue, and chikungunya. The range and severity of clinical signs and symptoms of these diseases vary. These viruses are transmitted chiefly by arthropods (so they are arthropod-borne), such as mosquitoes.

Q.  Where in Texas has the virus been found?
A.  West Nile Virus has been detected in most counties in Texas. For the most up-to-date information, go to

Q.  Where does the virus live?
A.  Certain types of mosquitos infect birds with the virus. The virus multiplies in the birds which then become a source of the virus for other mosquitos when they feed on infected birds. The infected mosquitoes can also transmit WNV to humans and animals while biting to take blood. The virus is located in their salivary glands and, during blood feeding, the virus can be injected into the animal or human, where it can multiply, possibly causing illness in the animal or human.

Q.  In addition to being infected by WNV, what else can cause bird "die-offs"?
A.  Chemical spills, pesticides, pollution, drought, severe weather, and other diseases can cause die-offs in birds. A die-off usually involves an event in which many otherwise healthy birds mysteriously die, usually with large numbers of deaths occurring suddenly in a short time span. To report a die-off of birds, contact the Texas Parks and Wildlife Department's Kills and Spills Team (KAST) at (512) 389-4848. For additional information, go to

Note:  The DSHS does not test birds for WNV. However, some local jurisdictions take citizen reports of dead birds and may also do testing. Please do not contact the DSHS if you find a dead bird. You may contact your city or county government to find out if they are taking reports from citizens or testing birds for WNV.

Q.  Can humans get WNV from handling dead birds?
A.  West Nile virus is spread to humans mainly through the bite from an infected mosquito. It does not appear that WNV can be readily spread from person to person or from animal to person; therefore, the risk of contracting WNV from handling dead birds is thought to be low. However, whenever you handle a dead animal, take precautions and avoid direct skin contact. For instance, if you wish to dispose of a dead bird, wear gloves and dispose of it in the garbage. As a reminder, whenever you directly handle an animal, wash your hands afterwards.

Q.  Can horses get WNV?
A.  Horses are the domesticated animals most commonly affected by WNV. Like humans, horses are considered to be dead-end hosts for the virus (i.e. the virus does not get to high enough levels in their bloodstream for it to be passed to a biting mosquito, so they do not transmit the virus to other hosts). Some of the possible clinical signs in horses include being uncoordinated, walking in circles, leaning on objects, and standing with legs spread apart or with the front legs crossed, plus features such as fever, facial paralysis (drooping lower lip), and the inability to swallow.

Q.  Is there a vaccine for horses?
A.  Yes.

Q.  Can dogs, cats, and other pets get West Nile virus?
A.  Yes. However, they rarely, if ever, get sick. No cases of West Nile disease have been confirmed in dogs and cats. The virus can infect many species of animals, but few actually get the disease. Most infections have been identified in birds, but WNV has been shown to infect dogs, cats, horses, and domestic rabbits, as well as bats, chipmunks, skunks, and squirrels.

Q.  Is there a vaccine for dogs and cats?
A.  No.

Q.  Are there laboratory tests to identify the West Nile virus?
A.  Yes, there are a variety of tests that can be done. Your health care provider would be the person to contact about any of your testing needs. Similarly, your veterinarian would handle any testing needs of your horse.

Q.  Is DSHS doing spraying around the state to kill mosquitoes?
A.  No. Vector control is up to the mosquito-control districts and local health departments. Mosquito control is best performed using the Integrated Mosquito Management (IMM) concept. The IMM develops pest-management systems that are practical and effective to protect human health and the environment.

Mosquito control can be divided into two areas of responsibility:  individual and public. Public spraying to control mosquitoes is only one of many pest-control methods used for effective long-term mosquito control. The reduction, elimination, or treatment of mosquito-breeding areas is the best and most cost-effective technique for mosquito control. The most important things you and the citizens of your community can do to reduce the risk of exposure to WNV are to eliminate mosquito-breeding areas in your environment and limit your exposure to feeding mosquitoes. Many female mosquitoes can lay 100-300 eggs on the surface of fresh or stagnant water every third night during its life span. Here are some simple things you can do to eliminate potential mosquito-breeding sites in your environment:

  • Do not allow water to accumulate in the saucers of flowerpots, cemetery urns, or in pet dishes for more than 2 days.
  • Get rid of tin cans, old tires, buckets, unused plastic swimming pools or other containers that collect and hold water.
  • Clean debris from rain gutters, remove standing water from flat roofs, and repair leaks around faucets and air conditioners.
  • Change the water in birdbaths and wading pools at least once a week.
  • Fill or drain puddles, ditches and swampy areas.
  • Check for trapped water in plastic or canvas tarps used to cover boats or pools and arrange the tarp to drain the water.
  • If ditches do not flow and contain stagnant water for a week or longer, report this problem to a mosquito-control district or public health office.

Q.  Who is responsible for draining mosquito-breeding habitat on private property in Texas?
A.  In Texas, some city and county governmental agencies have programs for mosquito control. Very often, it is the responsibility of the property owner to address these issues to prevent the creation of a nuisance or public health threat. For advice or assistance with mosquito control on or around your property, check with your local division of health officials to see if your community has a mosquito-control district or locally managed mosquito-control program.

Q.  Does the construction of purple martin houses and bat houses near homes help prevent West Nile virus because those animals eat mosquitoes?
A.  While it is true that certain types of birds and bats eat mosquitoes, putting up bird and bat houses on your property will not necessarily help prevent the transmission of WNV. Several agencies have tried to control mosquitoes by using birds, bats, dragonflies and frogs. However, according to the American Mosquito Control Association, there is no proof that bats, purple martins, or other animals that eat insects are able to eat enough adult mosquitoes to make a difference. One reason for this is because purple martins fly and eat during the day and most mosquitoes are active at night. In addition, most bats eat June bugs and moths, but do not eat mosquitoes. Also, bats can transmit the rabies virus and encouraging them to live in your yard could pose a health risk to your family and neighbors.

Q.  Are “bug zappers” effective in reducing human exposure to West Nile virus?
A.  Studies show that bug zappers actually attract mosquitoes into your yard. In addition, most insects killed by bug zappers include moths, beetles and other harmless bugs, not mosquitoes. All products should be thoroughly researched for their effectiveness before you purchase them. Your best bet would be to use a proven method for controlling mosquitoes around your home and property.

Last updated July 20, 2015