RI Mosquito Report: State Announces Additional WNV Positive Sample; Urges Rhode Islanders To Use Personal Precautions To Reduce Risk

Published on Friday, September 29, 2023

PROVIDENCE, RI – The Department of Environmental Management (DEM) and Rhode Island Department of Health (RIDOH) are announcing that one mosquito sample collected Sept. 19 from a trap set in Central Falls has tested positive for West Nile Virus (WNV). RIDOH State Health Laboratories confirmed the finding after testing 167 mosquito samples collected from 40 traps set statewide by DEM on Sept. 17 and Sept. 19. All other samples tested negative for WNV and Eastern Equine Encephalitis (EEE) virus, including the remaining 97 samples pending testing at the time of last week’s report from traps set on Sept. 12 and Sept. 14.

To date, Rhode Island reports six positive EEE virus mosquito samples: five in Glocester and one on Block Island, one EEE case in a mammal (a donkey in Glocester that was announced Sept. 7), and 13 WNV findings: six in Westerly, two in Barrington, and one each in Central Falls, Cranston, Johnston, Richmond, and Tiverton. The Commonwealth of Massachusetts reports 23 EEE virus findings in mosquitoes, 159 WNV findings, and three human cases of WNV. It is notable that EEE virus has now been detected in several towns in Bristol County, Massachusetts, which border Rhode Island’s East Bay communities. The State of Connecticut is reporting 49 EEE virus findings, 180 WNV findings, and two human WNV cases. The significant EEE virus activity on the borders of Massachusetts and Connecticut indicates a higher risk in Rhode Island. Earlier this month, DEM announced that it has temporarily closed state-owned recreational areas in Glocester, including the George Washington State Campground, Durfee Hill and George Washington Management Areas, and Pulaski State Park until further notice to protect the health and safety of visitors and staff.

With the state’s EEE virus and WNV risk levels 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. Humans can only contract these diseases through a bite from an infected mosquito. RIDOH and DEM are issuing a heightened public health warning that it is a particularly active mosquito season and that both EEE virus and WNV are likely present in mosquitoes statewide.

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 www.health.ri.gov/eee. 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 www.health.ri.gov/wnv.

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).

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.

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 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 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.

Map of mosquito disease detections as of 9/29/23