West Nile Virus

What is West Nile virus?

West Nile virus is spread by mosquitoes and can cause illness in people and animals. West Nile virus and St. Louis Encephalitis virus come from the same family of viruses, called flaviviruses, and cause diseases that are similar to one another.

Have there been any human cases of West Nile virus infections in Louisiana?

West Nile virus was found in the United States  in New York City in 1999. Since then, it has spread across the continental United States. Residents of Louisiana have reported infections with WNV since 2001, and the virus has been active in the state since 2002, the outbreak year when the state saw 328 cases and 24 deaths from the disease. DHH issues weekly reports on the number of human West Nile cases detected here.

How do people get West Nile virus?

Infected Mosquitoes

Humans primarily get West Nile virus through mosquito bites. WNV is spread to humans by the bite of an infected mosquito. A mosquito gets infected by biting a bird that is infected with the virus. An uninfected mosquito cannot bite an infected human and become infected. Mosquitoes also do not transmit the virus between people.

Transfusions, Transplants, Mother-to-Child

Less often, the virus has been spread by blood transfusion, organ transplant, breastfeeding, and from mother to child during pregnancy. Donated blood is check for WNV before being used.

West Nile virus is NOT spread by casual contact such as touching, kissing, or caring for someone who is infected.

Can you get West Nile virus from another person?

West Nile virus is spread to humans commonly by the bite of infected mosquitoes. In rare instances, the virus has been spread by blood transfusion, organ transplant, breastfeeding, and from mother to child during pregnancy. West Nile virus is NOT spread by casual contact such as touching, kissing, or caring for someone who is infected.

What are the symptoms of West Nile virus infection?

Symptoms generally occur 3-14 days following the bite of an infected mosquito.

 Asymptomatic West Nile (most people)
Most people - 80 percent- of the people who are infected with West Nile have no symptoms or may experience mild illness, then recover fully. Often, these people only know they have West Nile because the virus is detected when they have blood work done for an unrelated reason, such as blood donation or routine lab work.

West Nile Fever (some people)
Up to 20 percent of people who are infected with West Nile contract West Nile Fever, a flu-like illness that causes symptoms such as fever, headache, body aches, nausea, and, less frequently, skin rash on chest, stomach and back, or sometimes swollen lymph glands or eye pain.

West Nile Neuroinvasive Disease (few people)
Fewer than 1 percent of individuals infected with West Nile can develop West Nile neuroinvasive disease, a serious form of the virus that affects the nervous system. Symptoms include severe headache, high fever, stiff neck, disorientation, muscle weakness, numbness, tremors, vision loss, coma, or paralysis. These symptoms last several weeks, and can cause death or permanent brain damage. The elderly are most at risk for this form of West Nile, but anyone who contracts West Nile has a chance of developing this most severe form.

Who is at risk of West Nile virus infection?

If you can get bitten by a mosquito, you are at risk for West Nile virus. People older than 50 are more likely to become ill and develop serious symptoms when infected because as we age, our bodies have a harder time fighting off disease. Being outside increases your risk of being bitten by a mosquito, which increases your risk for getting West Nile virus. The best ways to avoid West Nile are to take precautions against mosquito bites, and to stay generally healthy so that your body is better able to fight off infection so that if you do get West Nile, you'll be less likely to get the more severe form of the virus.

The risk of West Nile transmission from medical procedures is very low – donated blood is tested before being used.

How soon do signs of West Nile virus infection appear?

Signs for West Nile virus infection begin to appear 2 to 15 days after infection (being bitten by an infected mosquito that transmits the virus). Most people who are infected with West Nile virus have no symptoms or experience only mild illness.

How is West Nile diagnosed?

West Nile virus infection can only be diagnosed by a doctor. If you think you have any of the signs or symptoms, you should make an appointment to see your doctor. If your doctor suspects that you may have West Nile virus infection, he or she will take your blood sample or draw spinal cord fluid. Your doctor will then send these samples to a testing laboratory for specific tests to be done to see if you have West Nile virus.


Is there a treatment for West Nile virus infection?

There is no specific treatment, medication or cure. Most people who get this illness recover from it on their own. In more severe cases, people may need to go to the hospital where they can receive supportive care to treat their symptoms.

Are there long-term consequences of getting West Nile Virus?

Most people who get West Nile virus contract either the asymptomatic form of the virus or the milder West Nile Fever. But, West Nile can develop into neuroinvasive disease, which affects the brain and spinal cord and can cause brain damage or death. Of the people who get West Nile neuroinvasive disease, 10 percent will die, and another 10 percent will have permanent neurological damage (paralysis, brain damage).

The best way to prevent getting West Nile and its related complications is to take precautions against mosquito bites.




Is there a vaccine for humans for West Nile virus?

No vaccine for West Nile virus for humans is currently available. People should protect themselves from West Nile by avoiding mosquito bites.

Can a human get West Nile virus twice?

Medical professionals don't believe so. Like many other viruses, medical tests indicate that once a person has been infected with West Nile, he/she develops a natural immunity to future infection by the virus for life. However, this immunity may decrease over time or with further health conditions that compromise the immune system. Because West Nile has not been active in the United States for many years, future tests may tell us more about the long-term health implications of West Nile.

How can I reduce mosquitoes around my home?

The following are measures that can help reduce mosquitoes in and around your home:

  • Install or repair window screens
  • Elimination of standing water, which mosquities require for breeding. Dispose of water-holding containers, such as tin cans, plastic containers, ceramic pots, used tires, and tire swings.
  • Pay special attention to discarded tires that may have collected on your property. Stagnant water in tires is a common place for mosquitoes to breed.
  • Drill holes in the bottom of containers such as those used for recycling.
  • Clean clogged roof gutters.
  • Turn over objects that may trap water when not in use, such as wading pools and wheelbarrows.
  • Change water in bird baths on a weekly basis. Do not allow water to stagnate in birdbaths; aerate ornamental ponds or stock them with fish.
  • Clean and chlorinate swimming pools. When pools are not in use, use pool covers and drain when necessary. Be aware that mosquitoes may even breed in the water that collects on swimming pool covers.
  • Use landscaping to eliminate standing water that collects on your property. Mosquitoes will develop in any puddle that lasts for more than four days.

How can I avoid mosquito bites when outdoors?

Mosquitoes feed on blood from humans and other animals, which is why they bite.

The following are measures that can help reduce bites from mosquitoes that feed on people and can cause West Nile:

  • Be particularly careful at dusk and dawn, when mosquitoes are most active.
  • Wear shoes, socks, long pants and long-sleeved shirts. Clothing material should be tightly woven.
  • Use mosquito netting when sleeping outdoors or for baby strollers.
  • Use mosquito repellent when you will be outdoors. Always use according to label instructions. The most effective repellents contain DEET, Picaridin, oil of lemon eucalyptus or IR3535.
  • Always wash treated skin when returning indoors.  Do not apply repellant under clothing, to wounds or irritated skin, the hands of children, or to infants younger than two months old.
  • Be sure your home's door and window screens are tight fitting and in good repair to avoid mosquitoes entering indoors.

Can dogs, cats and other pets get the West Nile virus?

Pets are exposed to West Nile virus through mosquito bites the same way humans are. But, animals rarely get sick or show symptoms of West Nile. Concerned pet owners should consult with a veterinarian about mosquito prevention for animals. Most West Nile animal infections have been identified in birds, but West Nile virus has also been shown to infect dogs, cats, horses and domestic rabbits, as well as bats, chipmunks, skunks and squirrels.

Is there a West Nile virus vaccine for dogs and cats?

No. But, there is a very effective vaccine against encephalitis in horses. Horse owners should consult their veterinarians for vaccine information.

Is Louisiana's Department of Health and Hospitals doing spraying around the state to kill mosquitoes?

No. Local mosquito abatement districts handle mosquito spraying at the local, parish and community level. But, as part of its annual West Nile surveillance, DHH corresponds regularly with mosquito abatement districts statewide to assess West Nile virus activity in mosquitoes. DHH also works with local health officials to remind people that they have a personal responsibility to protect themselves from West Nile by avoiding mosquito bites.