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Saturday, September 11, 2021

Bad bugs: DEM finds West Nile Virus in mosquito samples

No EEE or human cases of either WNV or EEE - yet

The Department of Environmental Management (DEM) today announced that the most recent round of testing by RIDOH State Health Laboratories has confirmed one new positive isolation (finding) of West Nile Virus (WNV) collected Aug. 30 from a trap in Johnston. 

DEM collected 82 pools (samples) of mosquitoes from 23 traps set statewide Aug. 26-30. Results are pending for mosquitoes trapped Aug. 31- Sept. 9. 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, 154 pools of mosquitoes trapped in Connecticut and 108 mosquito pools in Massachusetts have tested positive for WNV.

Connecticut has confirmed three WNV cases in humans and Massachusetts has confirmed four 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. There have not been any findings of EEE in mosquito pools in Connecticut, Massachusetts, or Rhode Island.

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:

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 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. Test results are pending for the traps set statewide Aug. 31-Sept. 9 and will be included in future announcements. Typically, positive test results trigger additional trapping to assess risk.

Related links

DEET Fact Sheet

Mosquito Dunks

Mosquito Bite Prevention Tips