Brazil’s dengue fever crisis is a warning to the world

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.

Climate change and demographic growth could put more than 5 billion people at risk for malaria

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…