Mosquito Report: State Announces First Case of EEE in a Mammal in 2023

Published on Thursday, September 07, 2023

PROVIDENCE, RI – The Department of Environmental Management (DEM) and Rhode Island Department of Health (RIDOH) are announcing that a donkey in Glocester tested presumptive positive for Eastern Equine Encephalitis (EEE). It is the first case of a mammal contracting the EEE virus in the state in 2023. A University of Connecticut lab conducted the test on Sept. 5. The lab’s positive finding is expected to be confirmed by the national reference lab by the end of the week. EEE cannot be transmitted from a mammal to a human. Humans can only contract the disease through a bite from an infected mosquito.

DEM and RIDOH also announce that two mosquito samples collected Aug. 28 from a trap in Glocester tested positive for EEE and a sample taken from a trap in Westerly tested positive for WNV. One of the two samples in Glocester contained a species of mosquito known to bite mammals. This is in addition to the first EEE detection in mosquitoes that the state announced last week. On Aug. 28 DEM collected 149 samples of mosquitoes from 31 traps set statewide.

To date, the Commonwealth of Massachusetts reports five EEE findings in mosquitoes, 99 WNV findings, and two human cases of WNV. The State of Connecticut reports one EEE-positive mosquito sample, in nearby Thompson, along with 105 WNV findings in mosquitoes and one human case of WNV. Year to date, Rhode Island reports three positive EEE mosquito samples, one mammal case of EEE, and six WNV findings in mosquitoes. WNV and EEE findings in mosquitoes are expected because mosquito-borne diseases become more prevalent in Southern New England as the season progresses.

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 risk is variable, changing from year to year. For more information on EEE and ways to prevent it, please visit www.health.ri.gov/eee.

Although EEE has now been detected in a mammal and in three mosquito samples in Glocester, and from multiple samples in nearby areas of Connecticut and Massachusetts, state health and environmental officials stress that at this stage of mosquito season, it is likely present in mosquitoes statewide and not confined to a geographic clustering in northwestern Rhode Island.

With these findings, Rhode Island’s EEE risk level is now considered high. DEM and RIDOH are urging Rhode Islanders to continue protecting themselves and their loved ones from mosquito bites until the first hard frost of autumn. A hard frost, which is meteorologically defined as three straight hours below 32 degrees, kills adult mosquitoes. Its timing varies widely across Rhode Island. It often occurs in northern communities such as Burrillville in early October and in southern, ocean-facing communities later.

The two state agencies, which along with experts from the University of Rhode Island, form the Mosquito-Borne Disease Advisory Group, are recommending that schools and communities consider “smart scheduling” — namely, that games, practices, and other outdoor activities scheduled to occur during early morning or dusk hours be rescheduled to earlier in the afternoon or relocated to an indoor venue. The “smart scheduling” of events is intended to help minimize the risk of mosquito bites for players, coaches, and spectators. The agencies also recommend that officials consider keeping smart scheduling measures in effect for the remainder of the mosquito season (which may end variably per above).

Also, RIDOH and DEM are intensifying public awareness of protection measures using all channels of communication, displaying EEE signage at central locations at DEM-managed parks, campgrounds, and wildlife management areas; and will be reaching out to municipal and school leaders in Glocester and Foster, Rhode Island veterinarians, and the Rhode Island Interscholastic League, the organization that supervises and regulates interscholastic high school athletic programs in the state. 

EEE 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. The EEE-positive samples taken Aug. 28 in Glocester and Aug. 30 in nearby Southbridge, MA, all came from these cross-biting species.

Along with smart scheduling, there are other 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 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. 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 health.ri.gov/mosquito 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 www.dem.ri.gov. Follow DEM on Facebook, Twitter (@RhodeIslandDEM), or Instagram (@rhodeisland.dem) for timely updates.