Mosquitoes and Disease - Frequently Asked Questions

1. What do I need to know about mosquitoes?

While mosquitoes usually are considered a nuisance pest, occasionally they can transmit infections that can cause illness and even death in people and some animals. Mosquitoes are small flying insects that feed on human and animal blood or plant juices. There are about 70 species of mosquitoes in New York State. Only female mosquitoes bite to get a blood meal for their growing eggs. Mosquitoes usually become infected from feeding on infected birds.

2. Do all mosquitoes spread disease?

No. Most mosquitoes do not spread disease. While there are about 70 different species of mosquitoes in New York State, only certain species transmit disease.

3. Where do mosquitoes live and breed?

Mosquitoes lay their eggs in moist areas, such as standing water. The eggs become larvae that remain in the water until they mature into adults and fly off. Weeds, tall grass and shrubbery provide an outdoor home for adult mosquitoes. They also can enter houses, apartments and buildings through unscreened windows and doors. Many mosquitoes will breed in any container that holds water, such as flowerpots, wading pools or discarded tires.

4. When are mosquitoes most active?

Some mosquitoes are active between dusk and dawn, when the air is calm. However, others will feed at any time of day. Mosquitoes prefer a warm, moist environment. They are active from early summer until late fall in New York State. In southern states that have a warm year-round climate, mosquitoes that can transmit diseases are active year round. New Yorkers should take measures to protect themselves from mosquito bites whenever mosquitoes are active.

5. What diseases can mosquitoes transmit to people?

Mosquitoes can spread a number of diseases to people, but two viruses that some mosquito species in New York State can transmit are eastern equine encephalitis (EEE, "triple E") and West Nile virus (WNV).

EEE is spread only from infected mosquitoes. Infected mosquitoes also are the primary way people become infected with WNV, although a few cases of WNV have been transmitted by blood transfusion, organ transplantation, from a pregnant woman to her infant and through breastfeeding. Neither virus is spread from person-to-person, from humans to animals or from animals other than infected mosquitoes to people.

6. What animals can be infected with eastern equine encephalitis (EEE) or West Nile Virus (WNV)?

A number of animals can be infected with these mosquito-borne infections, but horses are the most susceptible to serious illness and death from EEE and WNV. EEE occasionally occurs in livestock, deer, dogs, reptiles, amphibians and captive birds such as the ring-necked pheasant, emu, ostriches, quail and ducks. WNV has been identified in at least 326 bird species and in horses, dogs and cows.

7. Are there vaccines for EEE or WNV for people?

No, there are no human vaccines for EEE or WNV. The best way to prevent eastern equine encephalitis is to limit your exposure to mosquitoes and mosquito bites.

8. Are there vaccines for EEE or WNV for my pets?

There are no EEE or WNV vaccines for dogs or cats. There are vaccines for EEE and WNV for horses and other equines (donkeys and mules). These vaccines should never be given to humans or other animals.

9. What is the treatment for EEE and WNV infections?

There is no specific treatment for EEE or WNV. Antibiotics are not effective against viruses. Patients' symptoms are treated and those with severe illnesses receive supportive therapy, which may include hospitalization, respiratory support, IV fluids and prevention of other infections.

10. How common is eastern equine encephalitis (EEE) in people?

About 5-10 EEE cases of EEE are reported in the U.S. each year. New York State has reported five human cases: one each in 1971, 1983, 2009, 2010 and 2011. All were fatal. The risk of getting EEE is highest from late July through September.

11. Who is at risk of becoming infected with EEE?

People of all ages are at risk for infection with EEE virus (EEEV). However, people 50 of age and younger than 15 years of age are at greatest risk for developing serious disease.

12. When do symptoms of EEE infection appear?

Most people bitten by an infected mosquito will not develop any symptoms. Of those who do, symptoms usually appear 4-10 days after the bite of an infected mosquito.

13. What are the symptoms of EEE?

Cases of EEE begin with the sudden onset of headache, high fever, chills and vomiting. The illness may then progress into disorientation, seizures, inflammation of the brain (encephalitis) or coma. Many people (about 3 out of 10) who develop EEE die, and many of those who survive have mild to severe brain damage for life.

14. How common is West Nile virus (WNV) in people?

Since 2000, 490 cases of West Nile virus have been reported in New York State. Of these 37 people died (less than 1% of reported cases).

15. Who is at risk of being infected with WNV?

Anyone who is exposed to infected mosquitoes and is bitten is at risk of WNV. However, people over 50 years of age are at the greatest risk of developing severe WNV disease (called neuroinvasive disease).

16. When do symptoms of WNV infection appear?

Most people bitten by an infected mosquito will not develop any symptoms. People who become ill from WNV usually develop symptoms within 3-14 days after exposure, although people with weakened immune systems may take up to 3 weeks to develop symptoms.

17. What are the symptoms of WNV?

Most people (about 8 out of 10) infected with the West Nile virus do not have any signs or symptoms.

About 20% of the people who become infected with WNV develop West Nile fever (WNF), also called non-neuroinvasive disease. People with WNF typically have mild symptoms, including a sudden onset of fever, headache, stomachache, body aches and occasionally a skin rash and swollen lymph glands. Symptoms usually improve after several days, but people may feel tired, weak and generally unwell for weeks.

About 1 in 150 people infected with WNV (less than 1%) develop severe neuroinvasive disease that affects the central nervous system. Symptoms of neuroinvasive disease can include sudden onset of headache, high fever, neck stiffness, muscle weakness, altered mental status, tremors, convulsions, paralysis, inflammation of the brain (encephalitis) or of the membranes of the brain and spinal cord (meningitis) or coma. Death from WNV is very rare, but can occur. Most people recover completely from even severe WNV neuroinvasive disease.

18. How can I protect my family and myself from mosquito-borne infections?

Although your chances of being infected with a disease through a mosquito bite are small, there are simple steps you can take to reduce your risk of being bitten. Reduce the mosquito population around your home and property, reduce or eliminate all standing water:

  • Dispose of tin cans, plastic containers, ceramic pots or similar water-holding containers.
  • Dispose of used tires, which are a significant mosquito-breeding site. Call your local landfill or Department of Public Works to find out how to dispose of used tires properly.
  • Drill holes in the bottoms of outdoor recycling bins so they can drain freely.
  • Clean clogged roof gutters and make sure they drain properly.
  • Remove leaf debris from yards and gardens.
  • Drain temporary pools of water or fill with dirt.
  • Turn over wading pools and wheelbarrows when not in use.
  • Change the water in birdbaths twice weekly.
  • Clean vegetation and debris from edges of ponds.
  • Clean and chlorinate swimming pools, outdoor saunas, hot tubs and other water features, such as fountains and garden ponds.
  • Drain water from pool covers.
  • Use landscaping to eliminate standing water that collects on your property.

19. Should we stay indoors when mosquitoes are out?

It is not necessary to stay indoors. However, try to reduce your risk of being bitten by mosquitoes. In addition to reducing standing water in your yard, take the following steps:

  • Make sure all windows and doors have screens, and that screens are free of rips, tears and holes.
  • Cover your skin as completely as possible. Wear shoes and socks, long pants and a long-sleeved shirt when outdoors for long periods or when mosquitoes are most active.
  • Use mosquito repellent. Always apply according to label directions. Information on choosing and safely using insect repellents is on the U.S. Environmental Protection Agency (EPA) website at
  • Cover baby carriers and beds with mosquito netting when outdoors.
  • Stay indoors at sunrise, sunset and early in the evening when mosquitoes are most active.

20. What is my community doing to control mosquitoes?

Local communities, in consultation with the NYSDOH, may implement various control measures, for example, spraying, based on geographic location and assessed level of risk. However, the risks and benefits of control methods must be carefully considered prior to taking such measures.