Dengue fever cases in Mass. are on pace to break local records

Experts say this could be a preview of things to come as climate change transforms local ecosystems. Here’s what you need to know.

What is dengue fever?

Dengue fever is a mosquito-borne viral disease that is endemic in tropical and subtropical climates. Symptoms include sudden high fever, severe headaches, joint and muscle pain, nausea and pain behind the eyes, swollen glands, and rash. Severe cases can cause shock and internal bleeding. Fatalities, though, are rare, said Dr. David Hamer, a professor of global health and medicine at the Boston University School of Public Health who also directs a travel clinic at Boston Medical Center.

There is no medication for dengue; treatment usually consists of bed rest, fluids, and, in severe cases, hospital care.

How do you know if you have it?

The disease can only be diagnosed through a blood test.

If you have recently traveled to an area where the disease is endemic, such as Brazil or Cuba, and suspect you have it, you should consider seeking medical care, said Hamer.

“Because physicians in Massachusetts on average may not be aware of dengue, it may be useful to say, ‘I think I might have dengue,’” Hamer says.

What is the risk of contracting it in New England?

There has never been a local case of dengue transmission in Massachusetts, said Hamer, who runs a surveillance network that tracks outbreaks of imported infectious diseases at 70 international sites, including 12 in the United States.

But dengue cases in Massachusetts have been steadily rising. There were a record 60 cases in the state in 2023, more than double the number seen in 2022 and almost a third of the 185 total cases reported in the state since 2010.

Ominously, recent years have seen the introduction to New England of a new breed of invasive mosquito capable of carrying the disease. The species, Aedes albopictus, also known as the tiger mosquito, has been identified in northeast Massachusetts and a couple of other parts of the state in recent years, and some local authorities have started conducting surveillance on the mosquitos. The mosquito, explains Hamer, has “been marching north” for several decades, as global temperatures have risen, and has made it as far north as Ontario.

“Wherever you have the tiger mosquito, you have a potential risk for introduction and spread of certain kinds of viruses like dengue,” Hamer says. The same mosquitoes can transmit other diseases, like Zika and chikungunya, he said.

Where are travelers with dengue coming from?

Hamer said cases have “exploded” in Latin America and the Caribbean. Brazil, in particular, has seen a massive surge and is most likely to be feeding local numbers, he said.

“Because we have a lot of people that either go back and forth between the places or go there for vacations, the potential, with having lots of the right kind of vector in the United States, for introduction and local transmission increases,” he said.

What is the likelihood dengue will become endemic to our region?

In order for the disease to become endemic, the virus would have to take up residence in a local species of mosquito. That has not happened yet. Tiger mosquitos can only pick up the disease from an infected human if they bite an infected individual during the acute phase of the illness, which usually only lasts for a week.

Warmer temperatures, due to climate change, make it easier for dengue to spread among mosquitoes and accelerate how quickly they can transmit the virus. Weather patterns that lead to increased rainfall create more standing water, which is where dengue-carrying mosquitoes lay their eggs.

A closely related species of tiger mosquito, known as Aedes aegypti, is a far more common carrier of dengue. It has been found in many Southern states and California. But it is not yet considered endemic in any US states and has not yet arrived in Massachusetts.

What can be done to minimize the spread of dengue?

The state of Massachusetts has a surveillance and response plan known as ARBOVIRUS. If outbreaks are detected early enough, it is possible to control them through spraying and other techniques designed to limit mosquito populations. The best way to identify the presence is through testing mosquitos to see if they are infected and increasing reporting for human cases.

“The challenge is if physicians [are] not aware that there might be a risk of seeing dengue in somebody who has not traveled, they won’t test for it,” said Hamer. “So you need to have raised awareness so that people are actually doing testing for it.”

The best way to minimize individual risk is to avoid mosquito bites. Unlike malaria, which is transmitted by mosquitoes that are active at night, dengue is transmitted by mosquitoes that are active during the day, said Dr. Vandana Madhavan, clinical director of pediatric infectious disease at Mass General for Children.

“So it’s really important to think about wearing insect repellent with an appropriate level of DEET, wearing treated clothing, wearing longer light-colored clothing, and staying away from standing water,” she said.

---

Adam Piore can be reached at [email protected].