Risk of mosquito-borne diseases remains low in NYC, but that could change

New York City is leading the Northeast in cases of dengue, a viral disease transmitted through mosquito bites, according to data from the Centers for Disease Control and Prevention. All reported cases came from travel abroad, suggesting that the virus isn’t circulating locally, health experts say. But they warn that could change in coming years as temperatures continue to rise due to climate change.

So far this year, the city has reported 95 cases of travel-related dengue, with cases across every borough except Staten Island. With two months left in mosquito season, it’s on track to beat last year’s total of 152, according to the CDC data.

Dengue infection may cause fever, muscle aches, nausea and rash. A slim fraction of infections progress to severe dengue, which can be deadly.

A smattering of cases have also been reported in New Jersey and the rest of New York state. All told, the two states have reported just under 200 new infections in 2024. Each reported case was traced back to travel out of the country, health officials said.

The virus is surging across the Americas, with cases more than double last year’s count across the region. It is primarily carried by Aedes aegypti, a mosquito species that doesn’t tend to thrive in temperate climates . Experts say it’s unlikely that our local dengue-transmitting mosquito, Aedes albopticus, could drink enough blood from infected travelers to start circulating it locally.

“[Aedes] albopictus is less efficient at transmitting the virus and feeds on both animals and humans, making it less likely to transmit dengue virus,” NYC health officials wrote in an email bulletin to doctors late last month. “As such, an outbreak of locally acquired dengue in NYC is unlikely, though isolated cases may occur.”

But mosquitos multiply rapidly in the kind of warm, wet conditions that are becoming more common in our region due to climate change, increasing transmission of mosquito-borne diseases and raising dengue’s odds of becoming endemic, explained Stephen Morse, a professor of epidemiology at Columbia University’s Mailman School of Public Health.

“Within your lifetime, we may very well be thinking about some of these once-tropical infections being transmitted by Aedes albopictus,” Morse said.

Even now, rising temperatures and persistent humidity in New York City are driving the risk of mosquito-borne diseases higher than ever. City health officials detected West Nile virus in the mosquito population on June 5 this year – the earliest in the year that it’s ever been found, the health department said in a July 17 email advisory to healthcare providers.

Since then, West Nile has been found in mosquitoes across the city, particularly in broad swaths of Queens and Staten Island, health department data shows.

The city hasn’t yet reported any cases of illness from West Nile virus this year. Most people with the virus don’t show many symptoms, so it’s difficult to track infections. But documented cases have risen slightly in recent years, after a dip during the pandemic, the data shows.

“Human infections are being detected earlier and later into the season and with more frequency,” city health officials wrote in the July 17 email.

Like dengue, West Nile virus can cause fever and rash, according to city health officials. In rare cases, it can also cause inflammation of the brain and spinal cord. Older adults and immunosuppressed people are at greater risk of severe disease from the virus.

The NYC health department sprays pesticides around the city dozens of times each summer to cut down on mosquito populations and, by extension, keep mosquito-borne diseases at bay.

Morse praised these efforts, adding that mosquito-wary New Yorkers should do their best to remove standing water from outdoor areas, wear long sleeves and pants when possible and apply insect repellent when going outside.

“We need both,” Morse said. “We need to be careful, and we need to have public health really be on the watch — as they are — to protect us.”