Mosquito-borne diseases in New York State

What diseases can mosquitoes spread to people in New York State?

Mosquitoes can spread several diseases to people, but two viruses that some mosquito species in New York State can transmit are:

Neither virus is spread from person-to-person, from humans to animals, or from animals other than infected mosquitoes to people.

There are no human vaccines for EEE or WNV.

People who travel to tropical and subtropical regions outside the U.S. can get diseases from mosquitoes that are common to those areas, such as dengue fever and malaria. The CDC has guidance about preventing mosquito bites while traveling. Rarely, people that come back from other countries with mosquito-borne diseases can transmit those diseases to other people in NYS.

  • EEE is a very rare but serious disease. Mosquitoes infected with EEE virus (EEEV) can infect people, horses and other mammals, some birds, reptiles, and amphibians.
  • An average of 10 EEE human cases are reported each year in the U.S.
  • There have been 12 people diagnosed with EEE in New York State between 1971 and 2024. Seven of these 12 people died. Before 2024, the last cases were in 2015.
  • The risk of getting EEE is highest from late July through September. People who are more likely to develop severe disease are those over 50 years of age and younger than 15 years of age.

West Nile virus is a mosquito-borne illness first found in New York State in 1999. It is more common than EEE, but less likely to cause severe disease for those who have symptoms.

Getting bitten by infected mosquitoes is the most common way people get infected with WNV, but a few cases of WNV have been transmitted by:

  • Having a blood transfusion
  • Having an organ transplant
  • A pregnant woman spreading it to her infant
  • Breastfeeding
  • There is no specific treatment for EEE or WNV. Antibiotics do not treat viral infections.
  • Treatment focuses on managing symptoms. People with mild cases of EEE and WNV usually recover completely.
  • In cases of severe illness, patients are cared for in the hospital where they get help breathing, IV fluids, and treatment of other infections that develop.

If you think you might have EEE or WNV, talk with your health care provider.

  • About one third of patients who develop EEE die and many of those who survive have long term complications.
  • Of the less than 1 in 150 people infected with WNV who develop severe disease, death is very rare and almost all patients recover completely.
  • Horses are the most susceptible animal to getting serious illness and death from EEE and WNV.
  • Sometimes livestock, deer, dogs, reptiles, amphibians, and captive birds such as the pheasant, emu, ostriches, quail, and ducks also get EEE.
  • No, there are no human vaccines for EEE or WNV.
  • The best way to prevent EEE or WNV is to avoid mosquitoes and mosquito bites as much as possible.
  • 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.
  • Anyone who comes into contact with infected mosquitoes and is bitten is at risk of WNV and EEE.
  • However, people over 50 years of age and younger than 15 years of age are at greatest risk for developing serious disease.

Eastern Equine Encephalitis (EEE, "triple E")

  • Symptoms of people who get EEE begin suddenly and include headache, high fever, chills, and vomiting.
  • People may then become disoriented, have seizures, swelling of the brain (encephalitis), become unconscious (comatose).
  • Some people (about 3 out of 10) who develop EEE die, and many of those who survive have long term complications.

West Nile Virus (WNV)

  • About 20% of the people who become infected with WNV develop West Nile fever (WNF).
  • People with WNF usually have mild symptoms, including suddenly having a fever, headache, stomachache, body aches, and sometimes 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 disease that affects the brain and spine.
  • People with severe disease have symptoms that can include sudden onset of headache, high fever, neck stiffness, muscle weakness, confusion, tremors, convulsions, paralysis, swelling of the brain (encephalitis), or swelling 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 disease.
  • Most people bitten by an infected mosquito will not develop any symptoms.
  • Of those who do, EEE symptoms usually appear 4-10 days after the bite of an infected mosquito.
  • 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.