Expert discusses mosquito-borne diseases and prevention measures

Rhode Island’s least favorite summer guests have arrived: mosquitos, especially those carrying eastern equine encephalitis (EEE) and West Nile Virus.

Several towns have taken measures to deal with the pests, such as spraying insecticides and rescheduling outdoor athletic events that were to be held during mosquito feeding times, particularly at dusk.

In its mosquito report released Sept. 19, the Rhode Island Department of Environmental Management and Rhode Island Department of Health urged Rhode Islanders to continue mosquito prevention measures due to the high risk of EEE and West Nile Virus.

The report also confirmed one human case and another probable case of West Nile, adding to previous findings of a confirmed and probable case of West Nile and the first human case of EEE in 2024.

The most recent mosquito samples tested by the Rhode Island State Health Laboratories confirmed one positive finding of EEE virus collected in Westerly. All other samples tested negative for EEE virus, West Nile or Jamestown Canyon Virus.

While EEE is rare, it can be fatal and individuals should take precautions to protect themselves and their families.

The University of Rhode Island’s Jannelle Couret is an associate professor of biological sciences specializing in the ecology and epidemiology of diseases transmitted by mosquitoes and ticks. In a recent conversation, she explained the disease and what can be done to reduce the risk of infection.

Is this just a bad year for mosquitos and EEE or is this a trend? Do we know what is causing the increase?

This is a slightly above average year for population sizes of mosquitoes, but more concerning is the higher than usual number of mosquitoes tested that were infected with the eastern equine virus. We know this because the Rhode Island Department of Environmental Management monitors mosquito populations throughout the summer. This information is invaluable for guiding decision making and informing the public of risk.

While there is some degree of randomness that drives mosquito populations, population sizes will fluctuate. Many studies have shown that mosquito population dynamics relate to climatic conditions such as temperature and precipitation. The impact these have depends on the species of mosquito, its biology, habitat availability, and how that interplays with local weather.

What exactly is EEE and how is it transmitted?

Eastern equine encephalitis is a disease caused by a viral pathogen transmitted through the bite of an infected mosquito. EEE is endemic to the area, meaning it is not a new or invasive pathogen.

Eastern equine encephalitis has a complex transmission cycle. Beginning in the spring and early summer, the virus builds up in the population of some mosquito species, cycling between birds and mosquitoes.

In Rhode Island, this is concentrated in white cedar swamps. Later in the summer, once you have enough of a population size of mosquitoes and a buildup of the number of infected mosquitoes, you will see spillover cases to humans, which is what we are seeing now.

It is also highly transmissible and fatal to horses. The good news is that there is a EEE vaccine for horses.

What are some of the symptoms of the virus? Can I tell the difference between a regular mosquito bite and one that transmits EEE?

Unfortunately, there is no way to tell the difference between the bite of an infected and uninfected mosquito. However, symptoms can be severe and include: headache, confusion, stiff neck, light intolerance, seizure, and coma. It is fatal in approximately 30% of cases where symptoms develop.

Of course, not everyone that is bitten by an EEE-infected mosquito will develop symptoms. The most at risk for EEE are those over 50 years of age. And some will only experience more mild symptoms of fever, chills, and joint pain. But, if you are experiencing symptoms, you should talk with your health care provider.

What steps are being taken to reduce the presence of the mosquitos?

The DEM announced recently that they would be spraying mosquito larvicide with an aerial application across 3,000 acres of Chapman Swamp in Westerly and Great Swamp in South

Kingstown. That treatment is generally effective to reduce mosquito populations and therefore reduce the risk of disease transmission.

What’s the best way to protect myself or my children?

There are many ways to protect yourself and your loved ones, including personal protection with repellants and reducing mosquito habitat in your yard. The peak activity for these mosquitoes is just after dusk and through the evening, so either avoid outdoor activities at that time or be highly vigilant with applying repellant.

I always tell people: bug spray is not like perfume. If you want protection from bites, you must have complete coverage on your clothes and exposed skin. Long clothing can help, but mosquitoes can generally bite through clothing. The Department of Health and Department of Environmental Management have a helpful guide for preventing mosquito bites.

Are there other mosquito-borne viruses I should be concerned about?

The same species that transmits EEE also carries West Nile Virus, which is also circulating in Rhode Island. Similarly for West Nile virus, the most at-risk population is over 60.