With the discovery of Rhode Island’s first human case of eastern equine encephalitis (EEE) since 2019, the Department of Environmental Management is warning that it is a particularly active mosquito season in southern New England.

Mosquito testing and recent human cases of both EEE and West Nile virus (WNV) in Rhode Island indicate a high risk level for the viruses statewide, according to DEM. The person with EEE is from Providence County and is in their 70s. The state’s second human case of WNV has been reported in a Newport County resident in their 60s, and the first human case was discovered Aug. 16, in a Providence County person also in their 60s, according to the Centers for Disease Control and Prevention (CDC).

“This year’s clearly a higher-than-normal risk for eastern equine encephalitis,” said Alan Gettman, DEM’s mosquito abatement coordinator. “Based on evidence for other states in southern New England, it’s more prevalent out there now than it normally is for this time of year.”

The DEM said the most recent mosquito samples tested by the Rhode Island State Health Laboratories (RISHL) has confirmed five positive findings of WNV in Westerly and East Providence. The results are from 114 samples collected from 26 traps set statewide by DEM on Aug. 27 and Sept. 3. All other samples tested negative for EEE, WNV, and Jamestown Canyon virus (JCV).

The state recommends that members of the public, schools, and communities consider “smart scheduling” of outdoor activities during peak mosquito activity hours to help minimize the risk of mosquito bites and limit exposure to mosquitoes by wearing long sleeves and pants when outdoors.

Due to the high risk level statewide, DEM and the Department of Health are urging schools and organizations that have not yet implemented smart scheduling to consider rescheduling outdoor activities that occur during early morning or dusk hours 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.

“We are seeing more human cases of mosquito-borne disease in Rhode Island and in bordering communities in Massachusetts and Connecticut,” said Jerome Larkin, the state’s director of health. “This underscores how important it is that all Rhode Islanders need to continue protecting themselves from getting mosquito bites. Avoid outdoor activity at sunrise and sunset because that’s when mosquitoes are most active. If you have to be outside, wear long-sleeved shirts, pants, and bug spray.”

WNV is the most common mosquito-borne disease in the continental United States and is much more prevalent than EEE. There are no vaccines to prevent or medications to treat WNV in people. Most people infected with WNV don’t feel sick. About one in five people who are infected develop a fever and other symptoms, and about one out of 150 develop a serious, sometimes fatal, illness — a New Hampshire man died from the virus in late August.

Although extremely rare in humans, EEE has a much higher human mortality rate than WNV. About 30% of people with EEE die, and many survivors have ongoing neurological problems. Unlike WNV, which is prevalent in Rhode Island every year, EEE risk is variable, changing from year to year.

Mosquito control

The Asian tiger mosquito, which can transmit WNV and other diseases, has become prevalent in Rhode Island urban environments, and is expected to be common again this season. It is a daytime biter encountered in shaded backyards with 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 buckets, pots, wheelbarrows, boats, and kiddie pools. Clogged gutters and puddles formed on tarps also can support the larvae of this species.

Residents can protect against mosquito bites by putting screens on windows and doors and fixing screens that are loose or have holes; consider rescheduling outdoor activities that occur at sunrise and sundown; 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; and putting mosquito netting over playpens and baby carriages.

To remove mosquito breeding grounds, residents should:

Remove items around the house and yard that collect water. Just one cup of water can produce hundreds of mosquitoes.

Clean gutters and downspouts so they 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, according to DEM.

Clean and change water in birdbaths at least once a week.

Horses are particularly susceptible to WNV and EEE. Horse owners are advised to vaccinate their animals early in the season and 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; and monitor animals for signs of fever and/or neurological signs (such as stumbling, moodiness, loss of appetite). Report all suspicious cases to a veterinarian immediately.