Puerto Rico declared a public health emergency this week as cases of dengue fever, a potentially deadly mosquito-borne infection, rise rapidly across the United States territory. In the emergency orderThe Commonwealth Department of Health said it had recorded 549 cases of the disease so far this year, a 140 per cent increase over the same period a year ago.
The numbers “surpassed historical records,” Health Secretary Carlos Mellado López said.
Puerto Rico’s Department of Health is the latest government agency to mobilize its public health resources in the service of controlling and treating large outbreaks of dengue. Bangladesh and Sri Lanka have tried to combat unprecedented rates of dengue infections in recent years with varying degrees of success. Large portions of Central and South America struggling with months-long, record-breaking dengue crises. Some 5 million cases of the infection was 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 so far in 2024 — a rate of infection that health officials predict will lead to a record number of dengue cases this year.
Epidemiologists and climate change researchers warn that warmer temperatures, increasing storms and more erratic and frequent rainfall events contribute to outbreaks of mosquito-borne diseases around the world. Research shows that the environment in many regions of the world has changed over the past two decades more hospitable to the Aedes genus of mosquito, the insect whose bite spreads dengue to humans. Warmer winters, warmer summers and especially milder spring and fall allow these mosquitoes to move to new areas and higher elevations that have historically been too harsh for their survival.
“It’s a complex problem, but climate change, and most importantly consistently increasing temperatures, even at higher elevations,” said Manisha Bhinge, vice president of the Rockefeller Foundation’s health initiative, is creating “fertile ground for an outbreak.”
Climate change is not solely responsible for the millions of dengue cases that have occurred since the beginning of 2023. The natural weather phenomenon El Niño, which brings warmer-than-average global temperatures and erratic changes in rainfall patterns across Latin America and other parts of the world, may play a role. Rotting and broken infrastructure, deforestation and urban sprawl, and underinvestment in sewage, water and sanitation systems all contribute to the rise of disease by exposing more people to mosquitoes and creating pockets of stagnant water for the insects to breed in.
Warmer temperatures and extreme weather on top of these existing issues compound and exacerbate the community’s vulnerability to dengue and other diseases spread by blood-sucking bugs.
Three out of every 4 people who get dengue — also known as broken bone fever — show no symptoms, meaning the true extent of the virus infection in Puerto Rico and other places is likely much higher than official reports indicate. Those who develop symptoms often report fever of 104 degrees Fahrenheit or higher, muscle aches and vomiting. Severe symptoms, such as intense stomach pain; bloody vomit, stools, or gums; and extreme fatigue, usually develop after the fever has passed. Individuals who contract the disease twice, from two different strains, are at a much higher risk of developing severe dengue or dying. The disease cannot be passed directly between peoplebut a person with dengue in their blood can transmit the infection to a mosquito, which can infect other people.
About 340 people have been hospitalized with severe dengue symptoms in Puerto Rico so far this year. More than half of the island’s dengue cases occurred in San Juan, the territory’s capital, and surrounding municipalities. The Puerto Rican government has not restricted travel to or from the island, but the health department has said the infection has reached epidemic levels. The emergency order, which will remain in effect for three months, allows the health department to tap government resources more quickly as it works to detect and control mosquitoes.
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Last year, a small but unusual number of locally acquired cases of dengue surfaced California, Texasand Florida. The risk to people living in the contiguous United States still comes largely from travel to countries where disease rates are much higher, although it can change in the coming years as temperatures continue to rise.
The Centers for Disease Control and Prevention is currently Advising Americans to take precautions against dengue when traveling to many countries in Central and South America, the Caribbean, sub-Saharan Africa, the Middle East, South and Southeast Asia, and the Pacific Islands. In Brazil, which registered 1.5 million cases of dengue so far this year and recently became the first country in the world to have a public vaccination campaign against the virus infection17 cities have declared states of emergency.
There is no single solution to controlling mass outbreaks of dengue. Governments are trying a multi-pronged response that includes public education and vaccine campaigns, spraying mosquito-killing insecticides, draining swamps and puddles of standing water and implementing new technologies. Brazil, for example, has had some success releasing mosquitoes infected with bacteria that prevent them from carrying dengue in Rio de Janeiro and a handful of other urban centers around the country. Still, the best line of defense for people in affected areas is to reduce exposure to mosquitoes by spending time indoors whenever possible, sleeping in mosquito nets, and applying bug spray regularly.
