Q+A: AS TEMPERATURES CLIMB, IS THE UNITED STATES PREPARED FOR A DENGUE FEVER OUTBREAK?

Known as “breakbone fever” due to the joint pain and sometimes week-long high fevers that can accompany the disease, dengue fever is on the rise. There have been more than a million cases in Brazil so far this year. Mosquitos carrying the dengue virus are also causing major outbreaks in Paraguay, Argentina and Peru, and infecting millions — particularly in the Caribbean and in Latin America, where the 2024 case count is roughly triple the number reported in 2023.

While many of those infected with dengue show no symptoms, others may experience high fever, headaches, rash and other symptoms that are typically treated with acetaminophen. Rare cases can be serious or deadly. More than 1,800 people have died in the Americas in just the first four months of this year from this mosquito-borne disease.

The Pan American Health Organization says environment plays a critical role in surging dengue cases. As climate change brings warmer global temperatures, more rainfall and more extreme weather, the habitat for dengue-carrying mosquitoes continues to expand. Combined with housing, public utility and mosquito control programs that have not yet adapted to accommodate the population shifts caused by climate change in many regions, leaving many people outside and exposed — it’s a formula for dengue to spread in new areas.

The World Health Organization suggests roughly half of the world’s population is at risk. Areas that don’t typically experience major outbreaks, such as Bangladesh where there were 300,000 cases in 2023, are preparing hospitals for severe cases. 

The Drexel News Blog checked in with Esther Chernak, MD, a clinical professor at the Dornsife School of Public Health and College of Medicine and Director of the Center for Public Health Readiness and Communication, to explain the current global situation for dengue, how to minimize the disease’s spread, and what the United States needs to do to ensure dengue doesn’t spread throughout the country.

As dengue surges in Peru, Brazil, Bangladesh, Vietnam, Puerto Rico, and other warm climates around the globe, we’re also witnessing new cases in places that aren’t used to seeing dengue, such as Niger, and cases in Texas, Florida and California. Why are we seeing this spread into new areas that aren’t used to dengue? 

The surge in dengue in South America and the Caribbean is due to many factors: climate factors with increasing temperatures that foster mosquito activity and heavy rains that lead to standing water, particularly in urban areas, that become mosquito breeding sites. The mosquito that transmits dengue, Aedes aegypti, thrives in urban areas and breeds well in small containers. Increasing numbers of people living in urban areas and global travel all facilitate the transmission and circulation of the virus.

Travelers who have recently been to endemic areas account for many of the cases of dengue that are reported in places like Florida and Texas. However, we have seen local (“autochthonous”) transmission occur in those places, where the Aedes mosquito is established and there are sufficient cases to support human to human transmission, via the bite of the mosquito. Again, increasing temperatures, urbanization, coupled with cutbacks in mosquito control programs, allow local transmission to occur. 

Beyond anti-mosquito public health messages (encouraging bug spray, long clothing to cover skin where possible, emptying out stagnant water, etc.), have you seen any other creative ways that countries are combatting dengue? What role do you expect vaccines to play in helping to stem the spread of dengue?

Mosquito control programs are key. They include surveillance for mosquitoes, species identification, testing for dengue (and other mosquito-borne viruses), in addition to control measures like killing mosquito larvae in standing water, and killing adult mosquitoes through spraying. Of course, eliminating breeding sites in the first place by getting rid of standing water wherever possible, is important for control.

There are several dengue vaccines, only one approved in the United States. Dengvaxia, produced by Sanofi Pasteur, is indicated for children between the ages of 6 to16 years old who have already had dengue at least once (blood tests can determine this), and is used to prevent severe disease or hospitalization if a second infection occurs. Three shots are needed for full protection. 

A vaccine made in Japan, Qdenga, is approved in the European Union for the prevention of dengue in anyone, regardless of prior exposure. But this vaccine is expensive, is in limited supply, and requires two doses for full protection. Brazil has purchased the entire global stock and is planning to give it to children between the ages of 6 to 16 — an important and vulnerable age group — but a small percentage of Brazil’s population. The New York Timeshas reported that this investment will cover only 3.3 million of the country’s 220 million people.

A new one-shot vaccine that covers all four types of dengue viruses has recently been studied in both children and adults by the Instituto Butantan, a public research institute in Brazil. In a recent study, it was 89% effective in people who have had dengue and 80% effective in people who have not. This is great news, but this vaccine won’t be available in sufficient supply to help us now. 

Unfortunately, vaccination is not likely to stop this epidemic. The countries that can access the limited supplies of available vaccine right now are hoping to limit disease severity among the highest risk populations. They’re not likely to reduce overall viral transmission.

We need to ask this with almost any public health emergency: are we ready for a rise in dengue cases in the United States? Are public health surveillance measures warning people in time, clinicians prepared to treat patients that need care in areas expected to have a surge in cases, etc.?

To prepare for dengue cases in the United States, we need to improve mosquito control programs, and identify dengue activity in mosquitoes before human cases occur, so that we can prevent them. The outbreaks of Zika virus, transmitted by the same mosquito, that occurred in 2016-2017 demonstrated what we need to do. There is no specific antiviral treatment for dengue: therapy is supportive care for severe cases, including intravenous fluids, blood transfusions, and careful medical monitoring. 

And as in other public health emergencies, we will need to make sure that front-line clinicians can recognize the symptoms of dengue and have access to the appropriate tests to confirm the diagnosis. We’ve had plenty of practice ramping those up in recent years. And we need to make sure that everyone has access to health care. This is a critical issue in general, and even more important during epidemics.

What can individuals and communities focus on to inhibit the spread of mosquitos and dengue? Any advice for travelers going to tropical places that may also be home to outbreaks?

Travelers to countries where dengue outbreaks are occurring should prepare to protect themselves against mosquito exposure: use mosquito repellants, cover arms and legs with long-sleeved shirts and pants, treat clothing and gear with insecticides like permethrin and, if possible, spend time indoors in dwellings with screened doors and windows or air conditioning.

Based on reports in other countries, are you concerned about a dengue outbreak here in Philadelphia?

The likelihood of a dengue outbreak in Philadelphia is low, as we currently do not have many Aedes Aegyptimosquitoes in this region. But that can change, especially with warmer temperatures and more frequent severe weather events. We certainly have other mosquitoes that can spread serious diseases like West Nile virus. Mosquito control is an important part of our public health programs here.

Media interested in speaking with Chernak should contact Assistant Director of News & Media Relations, Greg Richter at gdr33@drexel.edu or 215.895.2614.