RI Mosquito Report: State Announces First Positive Finding of WNV in RI this Year; Reminds Public to use Personal Precautions

Published on Friday, July 26, 2024

PROVIDENCE, RI – 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) have confirmed the first detection of West Nile Virus (WNV) in the state in 2024. The mosquito sample testing positive for WNV was collected in Pawtucket on July 15. All other samples tested negative for Eastern Equine Encephalitis (EEE) virus or Jamestown Canyon Virus (JCV). These results are from 190 samples collected from 28 traps set statewide by DEM on July 15. This season, Rhode Island previously announced two EEE findings, the State of Connecticut has announced four EEE virus findings and 48 WNV findings, and the Commonwealth of Massachusetts has announced 27 WNV findings and 14 EEE findings. This WNV finding is expected because mosquito-borne diseases become more prevalent in Southern New England as the summer progresses. WNV has become firmly established throughout North America and the first detection of WNV in Rhode Island each year typically occurs in early August. 

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.

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. With continued trapping and testing, DEM and RIDOH will be able to assess the EEE virus risk level this mosquito season. For more information on EEE virus and ways to prevent it, please visit www.health.ri.gov/eee.

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.

The testing of mosquito samples for JCV is new for Rhode Island due to a new Polymerase Chain Reaction (PCR) testing method, but the virus is not new to the region. JCV is a mosquito-borne pathogen that circulates widely in North America, primarily between deer and mosquitoes, but can also infect humans. Human cases can occur from late spring through mid-fall and is most common early and late in the mosquito season with cooler weather. Four human JCV cases have been reported in Rhode Island residents since 2013. People can be infected and not develop any symptoms, or only develop very mild symptoms. Early symptoms can include fever, muscle aches, headaches, and fatigue. Rarely, more serious central nervous system disease, including meningitis or encephalitis, can occur. There are no vaccines to prevent or medicines to treat JCV.

Local communities voluntarily participate with mosquito control through DEM’s larvicide distribution program, which provides municipalities with a limited free supply of mosquito larvicide briquettes that release environmentally-benign bacteria over a 90-day period in underground stormwater catchment basins that are prime breeding areas of mosquitoes, requiring only one application per season. In April, the Town of Westerly conducted an aerial application of mosquito larvicide across 500 acres of Chapman Swamp and nearby swamplands by helicopter recommended as part of the state's action plan to reduce mosquito populations and related disease risk.

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 it is expected to be 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.

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.
• At sunrise and sundown (when mosquitoes carrying 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 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, 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. Sign up here to receive the latest press releases, news, and events from DEM's Public Affairs Office to your inbox.