It has been an exceptionally bad year regarding dengue: as of October, almost 12 million cases were recorded in the Americas, almost triple last year’s total, when there were 4.6 million.
Research to be presented at the American Society of Tropical Medicine and Hygiene’s annual meeting on Saturday quantifies the role the climate emergency has played in the trend, attributing nearly a fifth of the current dengue burden to rising temperatures.
By 2050, research predicts that the climate crisis could be responsible for a 60% increase in dengue incidence if emissions continue at the same rate, and some places, such as parts of Peru, Mexico, Bolivia and Brazil, will see peaks of up to 200%.
Public health experts have long warned that global warming allows mosquito-borne diseases to spread to new places because it expands the geographic range where insects that serve as vectors live and thrive. Mallory Harris, co-author of the new research and a postdoctoral associate in the biology department at the University of Maryland, said her team’s findings provide evidence of the significant role the climate crisis has played in the spread of dengue. More broadly, he said, the research highlights the connection between greenhouse gas emissions and specific health consequences.
“Dengue is a growing health threat that can cause really serious consequences. It is something we must prepare for,” Harris said. “We should be expecting these kinds of large epidemics in the future and thinking about ways to respond to them.”
In the United States and its territories, more than 7,200 cases of dengue have been recorded 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 (CDC) issued a health warning about an increased risk of dengue infections. After two locally acquired cases were detected in the Florida Keys, the Monroe County Health Department issued its own alert the following month. To date, 53 locally transmitted cases (that is, 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 cases in the United States this year have occurred in Puerto Rico, which declared a public health emergency in March amid an alarming rise in dengue infections. More than 4,500 cases of local transmission have been reported in Puerto Rico, compared to fewer than 1,300 last year and even fewer the year before.
The new research, 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 to a simulation of what would have happened during that time period without the man-made climate crisis.
According to a press release about the results, the resulting estimates are likely on the lower end of the spectrum, due to a lack of data on dengue in some areas, such as sub-Saharan Africa and South Asia. Additionally, it is difficult to make predictions for the southern United States, given that the virus has recently emerged as a local threat.
Researchers found that the mosquitoes that transmit 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 are significantly reduced, most countries analyzed would still see climate-driven increases 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 manufacturer of the only Food and Drug Administration-approved vaccine for dengue suspended it earlier this year, according to the CDC.
More than half of people who contract dengue, a viral fever, are asymptomatic. Most of the rest experience mild cases, with symptoms that can include fever, headache, joint pain, nausea and vomiting. Severe infections (about 2% of cases in U.S. territories between 2010 and 2020, according to the CDC) can cause bleeding under the skin, in the nose, or in urine or stool, as well as a sudden drop in blood pressure. blood pressure or even death.
The disease is more common in places with humid tropical climates in Latin America.
Derek Cummings, a professor of epidemiology at the 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 it quantifies how much and how important it is to the changes we are seeing.”
Cummings, who has published his own research on dengue, added that, on a global scale, he sees a need to prioritize vaccines, better manage mosquito populations and ensure hospitals and healthcare providers are prepared for an increase in dengue cases.
Harris highlighted that the new research shows how the consequences of the climate crisis affect different parts of the world differently.
“The greatest impacts of the historic climate crisis on the burden of dengue were in places like Peru, Bolivia and Mexico, which are not necessarily the hottest places overall, nor where they are experiencing the largest increases in heat deaths,” he counted. “There are effects that can be experienced in places that are slightly colder that also need to be taken into account.”
