RI Mosquito Report: No West Nile Virus (WNV) Or EEE Findings; The Asian Tiger Mosquito Will Re-Emerge With Recent Rain

Published on Tuesday, August 30, 2022

PROVIDENCE, RI – The Department of Environmental Management (DEM) today announced that the most recent round of mosquito testing by Rhode Island Department of Health (RIDOH) State Health Laboratories has confirmed no new positive findings of West Nile Virus (WNV) or Eastern Equine Encephalitis (EEE). DEM collected 87 samples of mosquitoes from 37 traps set statewide during the week of Aug. 14. Results from mosquitoes collected during the week of Aug. 22 are pending. The state confirmed its first EEE and WNV findings of 2022 on Aug. 17.

To date, Connecticut has reported 114 positive WNV samples but no WNV human or animal cases, and no EEE in mosquitoes, humans, or animals. Massachusetts reports 54 positive WNV samples and one human case and no EEE in mosquitoes, humans, or animals. Positive detections are expected at this time because mosquito-borne diseases become more prevalent as the summer season progresses. WNV is much more prevalent than EEE. It became established in North America following its introduction in 1999 and will become more prevalent as the season progresses, so DEM and the RIDOH advise residents to reduce their exposure to mosquitoes until the first hard frost. (A hard frost is when the air and the ground freeze below 32°F for three hours or below 28°F for two hours.)

DEM and RIDOH advise that the rainfall experienced in many parts of Rhode Island last week will likely have caused dormant mosquito eggs to hatch, so numbers of the Asian tiger mosquito will rise. This species became prevalent in Rhode Island urban environments in 2021. 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.

Personal protection is the first line of defense against mosquitoes that may carry WNV, EEE, or other diseases – and the most effective way to avoid infection. With WNV established in the state, residents are reminded to eliminate mosquito breeding grounds and prevent being bitten, whenever possible. The following precautions are advised.

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. 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.