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Mosquito Sample Tests Positive for Eastern Equine Encephalitis Virus

Eight Additional Mosquito Samples Test Positive for West Nile Virus

The New York State Department of Health informed Suffolk County health officials today that a mosquito sample tested positive for Eastern Equine Encephalitis (EEE) virus, also referred to as EEE or Triple E.  The mosquito sample, Culiseta melanura, was collected on July 31 in the Manorville area.

The presence of EEE in a mosquito sample poses a potential health risk. For this reason, Suffolk County Commissioner of Health Services Dr. James Tomarken has requested the Health Commissioner of the New York State Department of Health to confirm a declaration of an Imminent Threat to Public Health for Suffolk County. Such designation will permit the county to take additional steps to control mosquito populations.

Eastern equine encephalitis is a rare but potentially deadly illness for humans. The disease is also a concern for horses, though a vaccine is available and recommended for horses. Both EEE and West Nile virus are transmitted by the bite of an infected mosquito.

“The reason EEE is less common in humans is that the primary mosquito vector, Culiseta melanura, does not typically feed on humans,” said Dr. Tomarken. “However, the virus may be transmitted to humans and horses by bridge vectors, which are other kinds of mosquitoes that have contracted the virus by feeding on infected birds.”

In the United States, an average of seven human cases of EEE is reported annually. New York State reported eight cases of EEE from 2009 through 2018. To date, there have been no human cases of EEE in Suffolk County.  Four EEE positive mosquitoes were reported in Suffolk County in 2017.

In severe cases of EEE, a person may experience encephalitis, or swelling of the brain, that may result in death. The mortality rate of those that develop EEE is about 33 percent, the highest among human arboviruses (a virus transmitted by arthropod vectors) cases reported in the U.S. Currently, there is no human vaccine for EEE and patients are treated with supportive care.

Horses are particularly vulnerable if they contract EEE. The equine mortality rate due to EEE ranges from 75 to 90 percent.  In 2018, the USDA reported 107 cases of EEE in horses from 13 states, including three from upstate New York. Suffolk County reported three cases of EEE in horses in 2003.  Owners of equines have an essential role in preventing EEE from spreading. Horse owners are encouraged to vaccinate their animals and put safeguards in place that prevent animal exposure to mosquitoes as well as report any suspicious signs of EEE in animals to a veterinarian.

An additional eight mosquito samples have tested positive for West Nile virus. The samples, all Culex pipiens-restuans, were collected on July 30 and July 31from Cold Spring Harbor (1), Melville (1), Northport (3), Smithtown (1), Holtsville (1) and Jamesport (1).

To date this year, Suffolk County has reported 13 mosquito samples confirmed positive for West Nile virus and three birds confirmed positive for West Nile virus.  No humans or horses have tested positive for West Nile virus in Suffolk this year.

West Nile virus may cause a range of symptoms, from mild to severe. Symptoms may include fever, headache, vomiting, muscle aches, joint pain, and fatigue. There is no specific treatment for West Nile virus. Patients are treated with supportive therapy as needed.

The Suffolk County Department of Health Services continues to ask residents to assist in controlling the mosquito population by eliminating standing water on their property.  With the finding of Eastern Equine Encephalitis virus in the county, Dr. Tomarken is asking the public to take steps to be even more vigilant, especially those who live in or visit the Manorville area.

Individuals, especially those aged 50 or over, or those with compromised immune systems, are urged to take precautions to avoid being bitten by mosquitoes.  To avoid mosquito bites, residents are advised to:

  • Minimize outdoor activities between dusk and dawn.
  • Wear shoes and socks, long pants and long-sleeved shirts when mosquitoes are active.
  • Use mosquito repellent, following label directions carefully.
  • Make sure all windows and doors have screens, and that all screens are in good repair.
  • Keep mosquitoes from laying eggs inside and outside of your home. Once a week, empty and scrub, turn over, cover, or throw out containers that hold water, such as vases, pet water bowls, flowerpot saucers, discarded tires, buckets, pool covers, birdbaths, trash cans and rain barrels.
  • Download a copy of Suffolk County’s informational brochure “Get the Buzz on Mosquito Protection,” available in English and Spanish, and share it with your community.

According to Dr. Tomarken, information regarding measures Suffolk County will take to control mosquito populations will be forthcoming.

Dead birds may indicate the presence of West Nile virus in the area. To report dead birds, call the Public Health Information Line in Suffolk County at 631-787-2200 from 9 a.m. to 4:30 p.m., Monday through Friday.  Residents are encouraged to take a photograph of any bird in question.

To report mosquito problems or stagnant pools of water, call the Department of Public Works’ Vector Control Division at 631-852-4270.

For further information on mosquito-borne illnesses, visit the Department of Health Services’ website at

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