The summary
- Nearly 12 million cases of dengue fever have been recorded in America this year, almost triple last year’s total.
- New research suggests climate change is responsible for almost a fifth of the world’s dengue infections.
- According to the findings, that share is likely to increase significantly in the future.
It’s been an exceptionally bad year for dengue, with nearly 12 million cases recorded in America through October, nearly triple last year’s total of 4.6 million.
Research presented Saturday at the annual meeting of the American Society of Tropical Medicine and Hygiene quantifies the role climate change has played in the trend, with nearly a fifth of the existing dengue burden attributed to rising temperatures.
The research predicts that by 2050, climate change could be responsible for a 60% increase in the incidence of dengue if emissions continue at the same rate, with some places – such as parts of Peru, Mexico, Bolivia and Brazil – reaching peaks of up to will be visible at 200%. .
Public health experts have long warned that global warming could allow mosquito-borne diseases to spread to new places because it expands the geographic range where the insects that serve as vectors live and thrive . Mallory Harris, co-author of the new study and postdoctoral associate in the biology department at the University of Maryland, said her team’s findings provide evidence of the important role climate change has played in the spread of dengue. More broadly, the study highlights the link between greenhouse gas emissions and specific health impacts.
“Dengue is a growing health threat that can have very serious consequences. It’s something we have to prepare for,” Harris said. “We should expect these kinds of major epidemics in the future and think about ways to respond to them.”
The United States and its territories have seen more than 7,200 cases of dengue so far this year – more than double last year’s total and the highest since 2013.
In June, the Centers for Disease Control and Prevention issued a health warning about an increased risk of dengue infections. After two locally acquired cases were discovered in the Florida Keys, the Monroe County Department of Health issued its own alert the following month. To date, 53 locally acquired cases — meaning they were not associated with travel to a country where dengue is common — have been recorded in Florida, according to the CDC. California has recorded 15 such cases.
But the vast majority of U.S. cases this year have been in Puerto Rico, which declared a public health emergency in March amid an alarming rise in dengue infections. More than 4,500 locally acquired cases of dengue have been reported in Puerto Rico, compared with fewer than 1,300 last year and even fewer the year before.
The new study, which has not yet been published or peer-reviewed, analyzed temperature records and dengue incidence data in 21 countries in Asia and the Americas over an average of 11 years. The researchers compared the data with a simulation of what would have happened during that period without human-induced climate change.
The resulting estimates are likely at the lower end of the spectrum, according to a press release about the findings, due to a lack of dengue data from some areas, such as sub-Saharan Africa and South Asia. Furthermore, predictions for the southern US are difficult to make as the virus has only recently emerged as a local threat.
The researchers found that the mosquitoes that carry dengue — called Aedes aegypti — transmit the virus most efficiently when temperatures are between 68 and 82 degrees Fahrenheit. They concluded that even if global greenhouse gas emissions were significantly reduced, the majority of countries analyzed would still see a climate-driven increase in dengue.
“The risks of this are going to increase anyway, so we need to think about mitigation,” Harris said, suggesting a focus on vaccines and efforts to curb mosquito populations.
The maker of the only Food and Drug Administration-approved dengue vaccine discontinued it earlier this year, according to the CDC.
More than half of people who contract dengue, a viral fever, are asymptomatic. Most others experience mild cases, with symptoms including fever, headache, joint pain, nausea and vomiting. Serious infections — about 2% of cases in U.S. areas between 2010 and 2020, according to the CDC — can cause bleeding under the skin, in the nose or in the urine or stool, as well as a sudden drop in blood pressure or even death.
The disease is most common in places with humid, tropical climates in Latin America.
Derek Cummings, professor of epidemiology at Johns Hopkins Bloomberg School of Public Health who was not involved in the new research, said it “takes something that we all knew – that temperature is important – but quantifies how much and how important it is to the changes we see.”
Cummings, who has published his own research on dengue, added that on a global scale he sees a need to prioritize vaccinations, better manage mosquito populations and ensure hospitals and healthcare providers prepare for an increase in numbers cases of dengue.
Harris emphasized that the new research shows how the impacts of climate change are affecting different parts of the world in different ways.
“The greatest impact of historical climate change on dengue burden has been in places like Peru, Bolivia and Mexico, which are not necessarily the places that are generally the warmest. They are not necessarily the places where the number of heat deaths is highest,” she says. “There are effects that you might experience in places that are slightly cooler and that you should also take into account.”