Mosquito surveillance gaps raise disease concerns as ranges shift north

Warmer and wetter conditions are helping some mosquito species expand into places such as New England, raising concern about diseases they can carry. Scientists and mosquito-control officials say better surveillance is needed because local outbreaks can be hard to stop once human cases appear.

In Connecticut, a statewide mosquito program has identified 54 species, according to the Connecticut Agricultural Experiment Station. Philip Armstrong, the station’s chief scientist, said new species are moving into the region, including the Asian tiger mosquito, an invasive species that can transmit dengue and Zika.

Armstrong said testing mosquitoes is essential for finding areas where viruses are circulating. Waiting until people are sick leaves health officials with fewer options, he said.

Patchy monitoring across the country

Connecticut has a statewide trapping and testing program, but much of the United States does not. Inside Climate News reported that more than 1,000 mosquito control agencies operate across the country, many at the local level, with varying structures and monitoring practices.

Dan Markowski of the American Mosquito Control Association said the U.S. should have a national surveillance database that gathers and shares mosquito-monitoring information. He said funding remains the central obstacle.

Connecticut officials recently reported that mosquitoes in the state had tested positive for West Nile virus this season. The virus appears each summer and has become the leading cause of mosquito-borne disease in the Northeast, according to Inside Climate News. The Centers for Disease Control and Prevention says most West Nile infections cause no symptoms, but the virus can cause flu-like illness and has been linked to more than 3,300 deaths in the U.S. since it was first detected in the country in 1999.

Connecticut began its mosquito program two years before West Nile arrived in the U.S., with a focus on Eastern equine encephalitis. The CDC describes that disease as rare but serious, with possible neurological effects and a fatality rate of about 30%.

Armstrong said New England has seen cycles of increased Eastern equine encephalitis activity that were not historically common. He said the pattern has signs of climate influence.

Climate shifts add complications

In temperate regions, warming can change mosquito-borne disease risk in several ways, according to researchers cited by Inside Climate News. It can lengthen the season for transmission, expand the territory of mosquito species that carry viruses, alter habitats and affect mosquito predators.

Brian Leydet, who studies mosquito- and tick-borne diseases at the State University of New York College of Environmental Science and Forestry, said higher temperatures can speed mosquito development. That can allow multiple mosquito generations in areas where they were previously less common.

Leydet said environmental change can also affect viruses and the animals that host them, including birds and deer. Those overlapping shifts make the risks harder to study and predict.

In 2024, Leydet helped start a mosquito-monitoring program in St. Lawrence County, New York, after an Eastern equine encephalitis outbreak. New York does not have a statewide program, and the project announcement said many counties lack the infrastructure and budget for regular mosquito monitoring.

Such programs require workers to place and collect traps, as well as specialists to identify, sort and test mosquitoes. Some traps use water containing decaying organic material to attract female mosquitoes, while others need dry ice to produce carbon dioxide. Leydet’s team had to make its own dry ice in rural New York, according to Inside Climate News.

New York bill seeks broader system

Leydet said county-run surveillance can be inconsistent and poorly coordinated, leaving some invasive species undetected. He said programs can disappear when local governments lack money or staff.

A bill introduced in the New York State Legislature this session would begin building a broader mosquito surveillance program. The bill describes the current system as sparse and disintegrated and says stronger monitoring would help public health officials act before an outbreak.

Preventive steps can include removing standing water, applying targeted larvicides in breeding areas and warning residents to use repellent and cover exposed skin outdoors. Inside Climate News reported that more widespread pesticide spraying may be used during outbreaks.

Leydet said more centralized surveillance would help, though costs can slow political support in large states. He said even limited assistance would improve the current system.

This story draws on original reporting from Ars Technica.