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Puerto Rico declared a public health emergency this week as cases of dengue fever, a potentially deadly mosquito-borne infection, rise precipitously across the United States territory. In the emergency order, the commonwealth’s department of health said it had recorded 549 cases of the disease this year so far, a 140 percent increase over the same period a year ago.

The numbers have “surpassed historical records,” health secretary Carlos Mellado López said.

Puerto Rico’s health department is the latest government agency to mobilize its public health resources in service of controlling and treating large outbreaks of dengue. Bangladesh and Sri Lanka tried to tamp down unprecedented rates of dengue infections in the last year with varying degrees of success. Vast portions of Central and South America are battling months-long, record-breaking dengue crises. Some 5 million cases of the infection were reported worldwide in 2023, and the disease continues to spread. Already, an estimated 3.5 million cases of the infection and 1,000 deaths have been reported across the Americas in 2024 thus far — a rate of infection health officials predict will lead to a record-breaking number of dengue cases this year.

Epidemiologists and climate change researchers warn that warmer temperatures, intensifying storms, and more erratic and frequent rainfall events are contributing to outbreaks of mosquito-borne illnesses around the world. Research shows that over the past two decades, the........

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