Final RI Mosquito Report of 2023: State Confirms EEE-Positive Deer and Additional EEE-Positive Mosquito Sample; Cold Weather Minimizes Risk of Mosquito-Borne Diseases

Published on Tuesday, November 07, 2023

PROVIDENCE, RI – The Department of Environmental Management (DEM) and Rhode Island Department of Health (RIDOH) are confirming this year’s first positive detection of Eastern Equine Encephalitis (EEE) in a white-tailed deer. DEM’s Division of Law Enforcement (DLE) responded to a report of a deer with neurological symptoms in Charlestown on Oct. 23. DLE humanely dispatched the animal and its tissues were subsequently tested for rabies; the test was negative. The RIDOH State Health Laboratories then tested the deer, confirming EEE. The transmission of the EEE virus to a deer reinforces that 2023 has been a higher-than-average risk year for mosquito-borne disease in southern New England. 

DEM and RIDOH also announce that one mosquito sample collected Oct. 25 from a trap in Exeter tested positive for the EEE virus. RIDOH State Health Laboratories confirmed this finding after testing 66 mosquito samples collected from 17 traps set statewide by DEM on Oct. 25. All other samples tested negative for West Nile Virus (WNV) and the EEE virus.

Due to the first hard freeze occurring in most of Rhode Island last week, the risk of mosquito-borne disease has greatly subsided. A hard frost, which is meteorologically defined as three straight hours below 32 degrees, kills most adult mosquitoes. Its timing varies across Rhode Island. For example, much of Providence, Kent, and Washington counties experienced temperatures in the mid- to upper 20s on Nov. 1. However, the temperatures in Warwick and Bristol and Newport counties remained in the mid-30s. Until these areas experience a true hard frost, the risk of mosquito-borne disease remains. According to the National Oceanic and Atmospheric Administration (NOAA), most areas of Rhode Island, except for coastal areas of East Bay and Block Island, experienced the first hard frost on Nov. 1-2. On Nov. 2, DEM announced the reopening of state-owned recreational properties it manages in Glocester that were temporarily closed to lessen the risk of visitors and staff being bitten by mosquitoes potentially carrying EEE. The properties are now following regular operations.

EEE virus will continue to be a risk to deer, unvaccinated horses, and humans until after the first statewide hard frost, but infected deer may incubate the virus for about two weeks after exposure. Last weekend, DEM’s Division of Fish and Wildlife collected deer blood samples at state-run biological check stations for the first two days of the muzzleloader deer season. These samples will be tested for EEE and other diseases. Public health officials remind hunters to protect themselves from mosquito bites and to take the following take the following precautions while hunting this season:

  • Do not consume any harvested deer that appears unhealthy. Any harvested animal that is believed to be unhealthy should be reported to DLE at 401-222-3070.
  • Wear appropriate personal protective equipment when field dressing all game. At a minimum, this includes rubber or nitrile gloves and clothing that covers any part of the body that could be exposed to blood or other fluids.
  • According to both the US Centers for Disease Control and the United States Department of Agriculture’s Wildlife Services, there is negligible risk to hunters for contracting EEE from field dressing, handling venison, or consuming venison if proper personal protective equipment is worn while dressing, and the venison is properly cooked.
  • There is a very small risk from exposure to the brain or spinal cord of a deer infected with EEE. Anyone who is decapitating or removing the antler cap from a deer during the time where the virus may be present (2 weeks after a killing frost) should wear eye protection and a mask to avoid any contact of brain or spinal cord tissue, or spinal fluid, with their eyes or any other mucous membrane.

On Oct. 4, RIDOH announced Rhode Island’s first human case of WNV in 2023, a resident of Newport County in their 70s who developed symptoms in late August. To date, Rhode Island reports eight positive EEE virus mosquito samples: five in Glocester, two in Exeter and one on Block Island, two EEE cases in mammals (the deer in Charlestown announced today and a donkey in Glocester that was announced Sept. 7), and 14 WNV findings: six in Westerly, three in Barrington, and one each in Central Falls, Cranston, Johnston, Richmond, and Tiverton. This season, the Commonwealth of Massachusetts reported 28 EEE virus findings in mosquitoes, 164 WNV findings, and five human cases of WNV. It is notable that EEE virus has been detected in several towns in Bristol County, Massachusetts. The State of Connecticut is reporting 104 EEE virus findings, one EEE case in a mammal (a horse from New London County), one EEE case in an emu from Windham County, 188 WNV findings, and two human WNV cases.

Although extremely rare in humans, EEE is very serious and has a much higher human mortality rate than WNV. Approximately 30% of people with EEE die and many survivors have ongoing neurological problems. Unlike WNV, which is prevalent in Rhode Island every year, EEE virus risk is variable, changing from year to year. For more information on EEE and ways to prevent it, please visit WNV is the leading cause of mosquito-borne disease in the continental United States and is much more prevalent than EEE virus. Cases of WNV occur during mosquito season, which starts in the summer and continues through fall. There are no vaccines to prevent or medications to treat WNV in people. Fortunately, most people infected with WNV do not feel sick. About one in five people who are infected develop a fever and other symptoms. About one out of 150 infected people develop a serious, sometimes fatal, illness. For more information about WNV, please visit

EEE virus and WNV are typically present in wild bird populations. Birds are reservoirs of the diseases and mosquitoes transmit these viruses among birds. During an active mosquito season, the viruses are amplified in the environment with each generation of mosquitoes. At a certain point, a number of mosquito species that bite both birds and mammals serve as a bridge between infected birds and uninfected mammals. Most of the bridge species are within the Aedes, Coquillettidia, and Culex genera.

There are measures that Rhode Islanders should take to protect themselves from mosquito bites, and to help minimize mosquito breeding.

Protect yourself!

  • Put screens on windows and doors. Fix screens that are loose or have holes.
  • At sunrise and sundown (when mosquitoes that carry EEE virus are most active), consider rescheduling outdoor activities that occur during evening or early morning. If you must be outside, wear long-sleeved shirts and long pants and use bug spray.
  • Use EPA-approved bug spray with one of the following active ingredients: DEET (20-30% strength), picaridin, IR3535, and oil of lemon eucalyptus or paramenthane. Always read the label and follow all directions and precautions.
  • Do not use bug spray with DEET on infants under two months of age. Check the product label to find the concentration of DEET in a product. The American Academy of Pediatrics recommends that repellents should contain no more than 30% DEET when used on children. Children should be careful not to rub their eyes after bug spray has been applied on their skin. Wash children’s hands with soap and water to remove any bug spray when they return indoors.
  • Put mosquito netting over playpens and baby carriages.

Remove mosquito breeding grounds!

  • Remove items around your house and yard that collect water. Just one cup of water can produce hundreds of mosquitoes; an unused tire containing water can produce thousands of mosquitoes.
  • Clean your gutters and downspouts so that they can drain properly.
  • Remove any water from unused swimming pools, wading pools, boats, planters, trash and recycling bins, tires, and anything else that collects water, and cover them.
  • Remove or treat any shallow water that can accumulate on top of a pool cover. Larvicide treatments, such as Mosquito Dunks can be applied to kill immature mosquitoes. This environmentally friendly product is available at many hardware and garden stores and online.
  • Clean and change water in birdbaths at least once a week.

Best practices for horse owners!

Horses are particularly susceptible to WNV and EEE virus. Horse owners are advised to vaccinate their animals early in the season and practice the following:

  • Remove or cover areas where standing water can collect.
  • Avoid putting animals outside at dawn, dusk, or during the night when mosquitoes are most active.
  • Insect-proof facilities where possible and use approved repellents frequently.
  • Monitor animals for symptoms of fever and/or neurological signs (such as stumbling, moodiness, loss of appetite) and report all suspicious cases to a veterinarian immediately. If you are unsure if your horse is properly vaccinated, you should consult with your veterinarian.

Visit for additional mosquito prevention tips, videos, and local data. Mosquitoes are trapped weekly by DEM and tested at the RIDOH State Health Laboratories. DEM issues advisories on test results from June through September, with additional reports as necessary. Typically, positive test results trigger additional trapping to assess risk. 

For more information on DEM programs and initiatives, visit Follow DEM on Facebook, Twitter (@RhodeIslandDEM), or Instagram (@rhodeisland.dem) for timely updates.