Mosquitos carrying disease are still out until first hard frost

More EEE Virus and West Nile Virus Mosquito Findings

Hard frost ends mosquito season

The Rhode Island Department of Environmental Management (DEM) and Rhode Island Department of Health (RIDOH) are announcing that the most recent mosquito samples tested by the Rhode Island State Health Laboratories (RISHL) has confirmed one positive finding of Eastern Equine Encephalitis (EEE) virus and one positive finding of West Nile Virus (WNV). 

The mosquito sample testing positive for EEE virus was collected in Westerly and the mosquito sample testing positive for WNV was collected in Exeter. 

These results are from 84 samples collected from 35 traps set statewide by DEM on September 19, 30, and October 2. All other samples tested negative for EEE virus, WNV, or Jamestown Canyon Virus (JCV). RIDOH and DEM are reminding the public that it remains a particularly active mosquito season in Southern New England and that recent human cases of both EEE virus and WNV and mosquito testing indicate that a high risk level remains statewide. 

Due to the high risk level statewide, RIDOH and DEM are urging schools and organizations that have not yet implemented “smart-scheduling” to consider rescheduling outdoor activities scheduled to occur during early morning or dusk hours to earlier in the afternoon or relocating them to an indoor venue. 

Although adult mosquitoes are not killed until a hard frost (defined as three consecutive hours below 32 degrees), mosquitoes become less active at temperatures below 58 degrees and they become largely inactive when temperatures fall below 50 degrees. 

It is important for all Rhode Islanders to take precautions to limit exposure to mosquitoes and prevent mosquito bites, including using an EPA-approved insect repellent and wearing long sleeves and pants when outdoors.  

Previously this season, Rhode Island has announced 18 EEE virus findings in mosquito samples, 14 WNV findings, one confirmed human case off EEE virus, three confirmed human cases of WNV, and three probable human cases of WNV. The State of Connecticut has announced 70 EEE virus findings, 309 WNV findings, two JCV findings, nine human cases of WNV, and two animal cases of EEE, and the Commonwealth of Massachusetts has announced 333 WNV findings, 97 EEE findings, four human cases of EEE virus, three animal cases of EEE virus, and 15 human cases of WNV. It is notable that EEE virus and WNV have been detected in several Massachusetts and Connecticut towns bordering Rhode Island, indicating a higher risk in bordering Rhode Island communities. 

On Aug. 29-30, DEM conducted an aerial application of mosquito larvicide across 3,000 acres of Chapman Swamp in Westerly and Great Swamp in South Kingstown to reduce mosquito populations and related disease risk. As mosquito season continues, the Mosquito Borne Disease Advisory Group (MDAG), which DEM and RIDOH convene, will continue to evaluate the risk level statewide and will provide updates if any further mosquito control measures are planned. DEM and RIDOH continue to urge Rhode Islanders to protect themselves and their loved ones from mosquito bites and the diseases they carry, including EEE virus and WNV. Weekly mosquito trap density and mosquito testing results are available on RIDOH’s arboviral surveillance data webpage.

Although extremely rare in humans, EEE virus is very serious and has a much higher human mortality rate than WNV. Approximately 30% of people with EEE virus 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 virus 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. 

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, several mosquito species that bite both birds and mammals serve as a bridge between infected birds and uninfected mammals. Most bridge species are within the Aedes, Coquillettidia, and Culex genera.

Mosquito Control:

Residents can help control mosquitoes by removing backyard mosquito breeding grounds. The Asian Tiger Mosquito has become prevalent in Rhode Island urban environments, and has been common again this season. It is notable as a daytime biter encountered in shaded backyards. It has a striking black and white pattern evident to the naked eye. It develops from eggs laid in artificial containers, so residents are urged to remove standing water from containers such as buckets, pots, wheelbarrows, boats, and pools. Clogged rain gutters and puddles formed on tarps also can support the larvae of this species. The Asian tiger mosquito is known to transmit several diseases, including WNV.

In addition to considering smart-scheduling, Rhode Islanders should take the following measures 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.
• Consider rescheduling outdoor activities that occur during the evening or early morning at sunrise and sundown (when mosquitoes carrying the EEE virus are most active). If you must be outside, wear long-sleeved shirts and 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 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 signs 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, consult your veterinarian.

Visit health.ri.gov/mosquito for additional mosquito prevention tips, videos, and local data. DEM traps mosquitoes weekly and tests them at the RIDOH State Health Laboratories. From June through to the first hard frost of the season, which usually occurs in mid-October, DEM issues advisories on test results, 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. Sign up here to receive the latest press releases, news, and events from DEM's Public Affairs Office to your inbox.