The disease is ripping through much of South America, where scientists say rising temperatures due to climate change have both extended the territorial range of the mosquito that carries dengue and increased its proliferation.
In the first two months of this year, Paraguay registered nearly 100,000 suspected cases — more than five times the typical rate. Peru, wracked by its own outbreak, has declared an emergency in much of the country. Argentina, too, has seen an explosion of cases.
But the disease has surged with particular virulence in Brazil, where epidemiologists expect the number of dengue cases to reach into the millions — more than doubling the previous record — and potentially kill thousands of people.
The deepening public health crisis, epidemiologists say, serves as a warning to the world. The struggle against the disease has entered an unpredictable, perilous new phase. Dengue is now creeping into places where it has never been before. And where it has long been, case numbers are soaring to unseen heights.
The disease has historically been confined to tropical climates. But in recent years, as cases have skyrocketed across much of the world — rising eightfold since the turn of the millennium — the virus has increasingly spilled over into areas once largely spared.
Local transmission is now being reported in America’s warmer, wetter states, where the disease’s vector, the Aedes aegypti mosquito, already roams. Florida last year reported a record 178 cases of local transmission. California, Arizona and Texas are also detecting local transmission. The same dynamic is also being seen in southern Europe, where dozens of cases of local transmission were recorded last year.
Epidemiologists warn this is probably only the beginning. In the coming years, as climate change broadens the reach of the A. aegypti mosquito, the disease could become increasingly prevalent, even endemic, across much of southern Europe and the southern United States.
“Cases of dengue fever are rising at an alarming rate,” said Gabriela Paz-Bailey, who specializes in dengue at the Centers for Disease Control and Prevention. “It’s becoming a public health crisis and coming to places that have never had it before.”
The risk in wealthier northern climes is attenuated by several factors, including the prevalence of screened window, widespread air conditioning and strong sanitation practices, which can shrink the number of pools of stagnant water, where the Aedes aegypti can breed.
But epidemiologists say the threat should not be dismissed, especially not this year. Brazil registered more than 1 million cases of dengue fever in January and February alone. By the end of the year, the country is expected to suffer 4.2 million — more than was registered across all of the Americas last year during its record outbreak of dengue.
“There hasn’t been extensive transmission in the U.S., but that may change,” said Albert Ko, an epidemiologist at Yale University. “We should be concerned that a large epidemic season in Brazil and the rest of South America will drive spread and transmission to places in the U.S.”
A startling rise in dengue fever
For years, cases of dengue in Brazil have steadily risen. They jumped from a few hundred thousand per year in the early aughts to more than 1.4 million in 2013, then again to nearly 1.7 million last year. But this year, several forces combined to unleash an outbreak without precedent.
An extraordinary heat wave collided with El Niño, which often coincides with wider dispersion of dengue, leading to wider proliferation of the Aedes aegypti mosquito and elongating its life span.
“It’s not just how many there are, but that they live longer,” said Kleber Luz, who coordinates research of dengue at the Brazilian Society of Epidemiology. “Even if it’s just one or two days, this will affect the number of dengue cases.”
Then came another accelerant: the simultaneous circulation of all four types of dengue fever. That reduced immunological protections people might have otherwise had in a country where dengue has long been present. “I’ve been working with dengue since 1997,” Luz said, “and I’ve never seen another year when all four are circulating at the same time.”
Felipe Naveca, an epidemiologist with the Oswaldo Cruz Foundation, a Brazilian scientific research institution, said moments such as this one, when multiple dengue variants are circulating, are particularly perilous, because people can catch the disease multiple times over a short period. Cases will probably remain high as each variant peaks in succession.
“The scenario isn’t good,” he said.
Further complicating Brazil’s struggle against dengue is a slew of chronic social ailments that the Aedes aegypti mosquito has long exploited: inequality, poverty, disorganized urban planning and a frequently faltering public health system.
Millions of Brazilians live in densely populated, irregular communities — either called favelas or “the periphery” — often beyond the reach of government services and basic utilities. With unreliable plumbing, people often resort to storing water outside, creating countless mosquito breeding sites.
“If people don’t use the water for one week, the mosquito breeds in it,” said Raman Velayudhan, an expert on dengue at the World Health Organization. “This is a disease of urban cities.”
Many of these forces are now colliding with particular force in Brazil’s Federal District, which, by the end of last month, had turned into the epicenter of the country’s dengue outbreak.
‘They didn’t have a bed for me’
With unseen velocity, the disease rushed into the district’s poorest pockets, which form a ring around the wealthy center, Brasília. By the end of February, illness was everywhere — nearly 120,000 dengue cases in a city of 2.8 million residents. The district’s hospital system, which had withstood the onslaught of the coronavirus pandemic, began to teeter. Hospital beds had run out.
“The public and private health systems in the federal district have now collapsed,” said district governor Ibaneis Rocha. “The moment is grave, and we still aren’t at the peak of the epidemic.”
When Loide Rocha dos Santos, 57, was brought to one crowded hospital last month, she said the chaos was clear. Despite the gravity of her condition — dengue fever had reduced her blood platelet count to a dangerous low — the health clinic in the region of Gama could do little to accommodate her.
“The first two days, I had to sit in a wheelchair,” she said. “They didn’t have a bed for me.”
She was one of the fortunate ones. Patients were all around her, she said, on the floor, receiving IVs. Others were yelling in anger at the lack of care, according to a video recorded by her daughter. One man screamed for pain medicine so he could go home and die.
“There wasn’t anywhere for any of us to go,” she said.
On the other end of the district, in the impoverished region of Ceilândia, another family was combing the city for a hospital bed. Mariana Torres Lima, 5, clearly had a case of dengue with a high fever, vomiting and intense pain. But when family members took her to the Regional Hospital of Ceilândia, they were turned away, they said.
So the family traveled to a field hospital built to tend to those with dengue. After seven hours of waiting, Mariana was admitted. She curled up under a coarse woolen blanket on a military cot and went to sleep.
Outside, her aunt Bruna Lira seethed with anger. “The government isn’t taking care of us,” she said. “There’s trash in the streets and no general cleaning at the schools. One thing leads to another.”
She sat back down. Around her, at the field hospital, more and more people were arriving. By midday, there were dozens. Many were slumped. Others were vomiting.
“This year is different,” said Antonia Natane Lopes de Lima, 32, accompanying her ill son. “This year is worse than ever.”