What is West Nile virus?
West Nile virus is a mosquito-borne virus that can infect humans, birds, horses and other mammals. In most humans, West Nile virus infection causes a mild or moderate, short-lived flu-like illness, or causes no symptoms at all. However in some cases, particularly among persons 50 years of age and older, it can cause serious neurological diseases such as encephalitis, meningitis, or acute flaccid paralysis. West Nile virus first appeared in North America in New York City in 1999. Since then, the virus has spread across the continental United States. Visit www.cdc.gov for more information on West Nile virus nationally.
What are the symptoms of West Nile virus?
Most people who are infected with West Nile virus either have no symptoms or experience a mild or moderate illness with symptoms such as fever, headache, fatigue, or body aches before fully recovering. Some persons may also develop a rash or swollen lymph glands.
In some individuals, particularly persons 50 years of age and older, West Nile virus can cause serious disease that affects the brain and spinal tissue. Severe illness may include encephalitis (inflammation of the brain), meningitis (inflammation of the membrane around the brain and spinal cord), or acute flaccid paralysis (a polio-like syndrome in which muscles become very weak or paralyzed). Symptoms of more severe disease may include headache, high fever, stiff neck, nausea and vomiting, confusion, coma, tremors, convulsions, muscle weakness and/or paralysis.
At its most serious, West Nile virus can cause permanent neurological damage and death. Among those people who need to be hospitalized for West Nile virus, 10-15% die of their illness. People who do develop symptoms normally become ill 3-15 days following the bite of an infected mosquito.
How is West Nile virus spread?
West Nile virus is predominantly spread to humans by the bite of an infected mosquito. In 2002 other methods of human transmission were discovered but appear to be rare. It has now been shown that West Nile virus can be transmitted to humans who receive transfusions of infected blood or blood products, or who receive infected organs through transplantation. Also, in 2002 there was one case of transmission from a pregnant woman to her fetus, and one probable case of mother-to-baby transmission through breast milk. Additionally, two laboratory workers were accidentally infected following injuries while handling infected birds. West Nile virus is NOT spread by casual contact such as touching, kissing, or caring for someone who is infected.
How is West Nile Virus encephalitis treated?
There is no specific treatment for West Nile virus. Most people who become infected will get better on their own. In more severe cases, intensive supportive therapy is indicated, i.e., hospitalization, intravenous (IV) fluids and nutrition, airway management, ventilatory support (ventilator) if needed, prevention of secondary infections and proper nursing care.
Recently, some experimental treatments for West Nile virus have become available for people with severe disease. In New York City, two hospitals are participating in clinical trials of these experimental therapies. Not every patient with West Nile infection is eligible for these treatments. Patients or their families who want more information about these experimental treatments should ask their medical providers about them. Medical providers may contact the Bureau of Communicable Disease at the New York City Department of Health and Mental Hygiene for more information.
Where did West Nile virus come from?
Outbreaks of West Nile virus have occurred in Africa, Egypt, Israel, Asia, Romania, Russia and France. Before 1999, West Nile virus had never before been found in the Western Hemisphere. The virus was most likely introduced by an infected bird or mosquito that was imported from a country where the virus is common.
Who is most at risk for getting severe West Nile virus disease from being bitten by an infected mosquito?
Anyone who is infected can potentially develop severe West Nile virus disease (e.g. encephalitis, meningitis, or acute flaccid paralysis). However, persons older than 50 have the highest risk of becoming severely ill. There is also increasing evidence that immunocompromised persons (e.g., people who are taking immunosuppressive medications such as prednisone, or people who have received organ transplants) are at higher risk for severe West Nile virus disease.
How long does it take to get sick if bitten by an infected mosquito?
Most people who are infected with West Nile virus have no symptoms or experience only mild illness. If illness does occur, symptoms generally appear between 3 to 15 days of being bitten by an infected mosquito.
Can you get West Nile virus directly from birds?
In 2002, CDC reported two human cases of West Nile virus in laboratory workers who became infected after injuries while handling infected dead birds. It is extremely unlikely that members of the general public would be exposed to West Nile virus in this manner. However, as always, when handling a dead bird or animal for disposal, use gloves to carefully place the bird in double-plastic bags and then place in the outdoor trash.
Besides mosquitoes, can you get West Nile virus directly from other insects or ticks?
Infected mosquitoes are the primary source of West Nile virus and caused the recent outbreaks in the United States. Although several types of ticks in Africa and Europe have been found to be infected with West Nile virus, there is no evidence that ticks or other insects in this country are able to transmit the virus.
Are children and infants at greater risk for severe West Nile virus disease?
Although anyone who is infected can potentially develop severe West Nile virus disease (e.g. encephalitis, meningitis, or acute flaccid paralysis), persons older than 50 have the highest risk of becoming severely ill. Children and infants, however, can develop serious disease from West Nile virus. In 2002 and 2003, more than 200 children under age 19 years in the US were reported with West Nile encephalitis or meningitis.
Recent evidence suggests that babies born to mothers with West Nile virus infection during pregnancy may be infected with West Nile virus themselves. However, it is unknown how often this occurs, and what the effects of West Nile virus infection may be on the fetus and newborn infant. Also, there is one case of probable transmission of West Nile virus to a newborn via breast milk; in this one case, which occurred in 2002, the baby has remained completely healthy.
If a pregnant woman gets infected with West Nile virus, can it affect her fetus?
Maybe. In 2002 there was one case of transmission of West Nile virus from mother to fetus during pregnancy. The newborn was infected with West Nile virus at birth and had severe neurological problems, including abnormalities of the brain and retinas. It is possible that West Nile virus caused these abnormalities in the baby; however, it is not proven.
More information is now being gathered about other babies born to mothers infected with West Nile virus during pregnancy in order to improve our understanding of the effects of West Nile virus on the fetus and newborn. Three other instances of maternal infection were investigated in 2002; babies born to these mothers appeared normal and had negative laboratory tests for West Nile virus. The Centers for Disease Control and Prevention (CDC) is currently investigating outcomes of about 70 pregnant women who were infected with West Nile virus in 2003.
Can West Nile Virus be transmitted through breast milk?
Possibly. It appears that West Nile virus may be transmitted to infants through breast milk. In 2002, a woman developed encephalitis due to West Nile virus acquired through a blood transfusion she received shortly after giving birth. Laboratory analysis showed evidence of West Nile virus in breast milk collected from the mother soon after she became ill. She had been breastfeeding her infant and approximately 3-4 weeks after birth the infant tested positive for the West Nile virus. Because of the infant's minimal outdoor exposure, it is unlikely that the infection was transmitted by a mosquito. The infant had no symptoms of West Nile virus and remained healthy.
Is there a vaccine for West Nile virus?
There is currently no human vaccine for West Nile virus, but several companies are working towards developing one. There is a West Nile virus vaccine that has been approved for use in horses.
What should I do if I think I have West Nile virus?
People with mild or moderate symptoms should recover completely, and do not usually require any specific medication or laboratory testing. However, if you develop symptoms such as fever, headaches, stiff neck, confusion, muscle weakness, or your eyes become sensitive to light, you should consult your doctor and be tested for West Nile virus..
If I am bitten by a mosquito, should I be tested for West Nile virus?
Most mosquitoes are not infected with West Nile virus and illnesses related to mosquito bites are uncommon. There is no need to be tested for West Nile virus unless you are ill and your symptoms suggest possible West Nile virus infection. As mentioned, if you develop symptoms such as fever, headaches, stiff neck, confusion, muscle weakness, or your eyes become sensitive to light, you should consult your doctor.
What can I do to prevent infection with West Nile virus?
From June through October, when mosquitoes are most active, take the following precautions:
- Wear protective clothing such as long pants and long-sleeved shirts, particularly at dusk and dawn when most mosquitoes are searching for a blood meal.
- Avoid shaded, bushy areas where mosquitoes like to rest.
- Limit outdoor evening activity, especially at dusk and dawn when mosquitoes are most active.
- Use an insect repellent containing DEET, picaridin, oil of lemon eucalyptus, or IR3535 to help reduce exposure to mosquitoes. Always read the repellents label. For more information, see DOHMH's Insect Repellent Use & Safety Fact Sheet.
There have been no reported adverse reactions following the use of repellents containing DEET in pregnant or breastfeeding women. As a precaution, prior to handling infants, nursing mothers should wash repellents off their hands and areas of the breast that an infant may contact. (Please see the DOHMH fact sheet on Insect Repellent Use & Safety).
If I travel outside New York City, do I need to worry about West Nile virus?
Yes. West Nile virus has spread throughout the United States and is present in other parts of the world as well. In some areas of the country, particularly the south and the west, the West Nile virus transmission season lasts longer. People can become infected with West Nile virus early in the spring or as late in the year as November or December. So when you travel, especially during the spring, summer and fall, you should check with the local health department wherever you go to see if West Nile virus is present. If it is, then you should take precautions to avoid mosquito bites, as described in the previous question.
What can I do around my home to help reduce exposure to mosquitoes?
Mosquitoes lay their eggs in standing or slow moving water. Also weeds, tall grass, and bushes provide an outdoor resting place for mosquitoes. In residential areas, standing water can accumulate in unused tires, cans, unused pools and pool covers, and other receptacles that collect water. Mosquitoes can enter homes through unscreened windows or doors, or broken screens. Follow these general guidelines to help reduce mosquito populations in your area:
- Eliminate any standing water that collects on
your property by:
- Removing all discarded tires from your property.
- Disposing of tin cans, plastic containers, ceramic pots, or similar water-collecting containers.
- Making sure roof gutters drain properly and cleaning clogged gutters in the spring and fall.
- Cleaning and chlorinating swimming pools, outdoor saunas and hot tubs. If not in use, keep empty and covered.
- Draining water from pool covers.
- Changing the water in bird baths at least every 3 or 4 days.
- Turning over plastic wading pools and wheelbarrows when not in use.
- Repair or replace all screens in your home that have tears or holes.
- Remind or help neighbors to eliminate mosquito-breeding sites on their properties.
Some local hardware stores may carry a product called Mosquito Dunk® that contains a larvicide - Bacillus thuringiensis israelensis (BTI) - for use in areas of standing water around the home. The New York City Department of Health and Mental Hygiene recommends eliminating standing water around the home to reduce breeding sites for mosquitoes and warns that direct handling of larvicides may cause skin and eye irritation. Use these products only as directed by the manufacturer. If these products are purchased for home use, we recommend careful reading of the hazards label, directions, and details regarding storage and handling.
Should I report dead birds to the Department of Health and Mental Hygiene?
No, unless you are reporting a group of 10 or more dead
birds of any species, or a group of 3 or more dead waterbirds. The Health Department will no longer take reports of individual dead birds to monitor for West Nile virus. These tests had limited value as an early warning system for the virus. The Department will continue to take reports of groups of dead birds (10 or more of any species or 3 or more waterbirds). To report these clusters, call 311. If you need to dispose of a dead bird, use disposable rubber gloves to carefully place it in a double plastic bag, then put the bag in the outdoor trash. Wash your hands with warm soapy water afterwards.
What is the City doing to address the problem of West Nile virus?
New York City is working to reduce the risk of West Nile virus infection. The main goal is to decrease the number of adult mosquitoes by eliminating breeding sites wherever possible and applying larvicides (to kill the immature larval form of the mosquito) to areas of standing water that cannot be drained completely. The City also regularly tests mosquitoes for West Nile virus throughout the spring and summer.
Is the City planning to spray pesticides?
New York City may spray pesticides to target adult mosquitoes if there is a risk to human health from West Nile virus. Spraying will be concentrated in areas most at risk for disease occurrence and will be conducted by experienced and licensed applicators who are required to follow New York State Department of Environmental Conservation (NYSDEC) and EPA requirements. The City is hopeful that with an early and aggressive campaign against mosquito breeding areas, the need for the spraying of pesticides will be reduced.
Will the public be notified in advance about spraying activities?
Residents can learn about adulticiding schedules in advance through public service announcements, the media, the City's website (nyc.gov/health/wnv), or by calling 311, the City's Information Line. DOHMH will provide notification at least 24 hours prior to a spray event.
What health risks are posed to people and pets from pesticides for adult mosquitoes?
In the amounts used, risks to people and pets are relatively low. However, some people may be more sensitive to pesticides and may want to reduce their chance of exposure by following the suggestions below. Anyone experiencing adverse reactions to pesticides should seek medical care or call 311 or the NYC Poison Control Center at (212) POISONS (764-7667).
If the City sprays pesticides in an area where I am, what should I do during the spraying?
If pesticide spraying occurs, DOH recommends that all individuals take the following precautions to avoid direct exposure to pesticides and reduce the risk of reactions:
- Whenever possible, stay indoors during spraying.
- Some individuals are sensitive to pesticides. Persons with asthma or other respiratory conditions are encouraged to stay inside during spraying since there is a possibility that spraying could worsen these conditions.
- Air conditioners may remain on. But if you wish to reduce the possibility of indoor exposure to pesticides, set the air conditioner vent to the closed position, or choose the recirculate function.
- Remove children's toys, outdoor equipment and clothes from outdoor areas during spraying. If outdoor equipment and toys are exposed to pesticides, wash with soap and water before using again.
- Wash skin and clothing exposed to pesticides with soap and water.
- Always wash your produce thoroughly with water before cooking or eating.
Anyone experiencing adverse reactions to pesticides should seek medical care or call 311 or the NYC Poison Control Center at (212) POISONS (764-7667).
Last Updated: August 31, 2012