West Nile Virus

Older Adults

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.

Are older adults at greater risk for severe West Nile virus disease?

Yes. 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, and they should take the greatest care to prevent exposure to mosquitoes.

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, nausea and vomiting, 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, nausea and vomiting, confusion, muscle weakness, or your eyes become sensitive to light, you should consult your doctor.

How is West Nile Virus 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.

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. A West Nile virus vaccine has been approved for use in horses.

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 or oil of lemon eucalyptus to help reduce exposure to mosquitoes. Always read the repellents label. For more information, see DOHMH's Insect Repellent Use and Safety Fact Sheet.

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. Weeds, tall grass, and bushes can also 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.

What is the City doing to address the possible return 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 and birds 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. The City is hopeful that with an early and aggressive campaign to reduce mosquito-breeding areas, the need for spraying of pesticides will be reduced.

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

How 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.

If the City sprays pesticides in an area where I am what should I do during the spraying?

If spraying is necessary, DOHMH recommends that all individuals take the following precautions to avoid direct exposure to pesticides and reduce the risk of any reactions to pesticides:

• • Whenever possible, stay indoors during the 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 indoors 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. If toys are left outside, wash them 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).

For more information on West Nile virus, call 311 or visit nyc.gov/health/wnv.