PROVIDENCE – The Department of Environmental Management (DEM) today announced that the most recent round of testing by RIDOH State Health Laboratories has confirmed no new positive isolations (findings) of West Nile Virus (WNV). DEM collected 365 pools (samples) of mosquitoes from 85 traps set statewide Aug. 31-Sept. 15. Results from mosquitoes collected during the Sept. 16-23 period are pending. To date, the state has confirmed five positive WNV findings, but no mosquito samples have tested positive for Eastern Equine Encephalitis (EEE).
WNV is much more prevalent than EEE. It has become established in North America following its introduction in 1999. To date this summer, 190 pools of mosquitoes trapped in Connecticut and 133 mosquito pools in Massachusetts have tested positive for WNV. Connecticut has confirmed three WNV cases in humans and Massachusetts has confirmed seven human cases and one alpaca case. The positive findings in Connecticut, Massachusetts, and Rhode Island indicate that WNV has established seasonal activity in our area. WNV will become more prevalent as the season progresses, so DEM and the Rhode Island Department of Health (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.) There have not been any findings of EEE in mosquito pools in Connecticut, Massachusetts, or Rhode Island.
As the warm season wanes, mosquito numbers are naturally diminishing. However, populations of one species, the Asian Tiger Mosquito, remain particularly high this year. It is notable as a day-time biter encountered in shaded backyards in urban settings in RI. This species is established throughout much of the southern and eastern United States and has recently become common in some urban zones in southern New England. It has a striking black and white pattern evident to the naked eye.
This species develops from eggs laid in artificial containers (see accompanying photo), so residents are urged to remove standing water from containers such as buckets, pots, wheelbarrows, boats, and pools. (Eggs can be scrubbed from the sides of containers to prevent hatching next spring.) Clogged rain gutters and puddles formed on tarps also can support the larvae of the Asian Tiger. It is also known to transmit several mosquito-borne diseases including West Nile Virus.
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 o Put screens on windows and doors. Fix screens that are loose or have holes. o 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. o 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. o 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. o Put mosquito netting over playpens and baby carriages.
Remove mosquito breeding grounds o 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. o Clean your gutters and downspouts so that they can drain properly. o 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. o 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. o 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:
o Remove or cover areas where standing water can collect. o Avoid putting animals outside at dawn, dusk, or during the night when mosquitoes are most active. o Insect-proof facilities where possible and use approved repellents frequently. o 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. DEM and RIDOH also remind Rhode Islanders to take precautions to avoid mosquito bites when traveling to Zika-affected countries. Pregnant women and women who are considering becoming pregnant should not travel to countries with active transmission of Zika. Mosquitoes are trapped weekly by DEM and tested at the RIDOH State Health Laboratories. DEM issues advisories on test results from July through September, with additional reports as necessary. Typically, positive test results trigger additional trapping to assess risk.