Brazil is experiencing a massive outbreak of dengue fever, the sometimes fatal mosquito-borne disease, and public health experts say it’s a harbinger of a coming wave of cases in the Americas, including Puerto Rico.
Brazil’s health ministry warns it expects more than 4.2 million cases this year, higher than the 4.1 million cases the Pan American Health Organization recorded last year for all 42 countries in the region.
Brazil was expected to have a bad dengue year – cases of the virus typically rise and fall on a roughly four-year cycle – but experts say a number of factors, including El Niño and climate change, have significantly exacerbated the problem this year.
“The country’s record heat and above-average rainfall since last year, even before summer, have increased the number of mosquito breeding sites in Brazil, even in regions where there were few cases of the disease,” Brazilian Health Minister Nísia said. Trindade, said.
Dengue cases have already surged in Argentina, Uruguay and Paraguay in recent months during the Southern Hemisphere summer, and the virus will spread across the continents with the seasons.
“If we see waves in one country, we will usually see waves in other countries as well. This is how we are connected,” says Dr. Albert Ko, an expert on dengue in Brazil and professor of public health at Yale University.
The World Health Organization has warned that dengue is quickly becoming a pressing global health problem, with record numbers of cases last year and outbreaks in places like France, where the disease has historically never been reported.
In the United States, Dr. Gabriela Paz-Bailey, chief of the dengue division at the Centers for Disease Control and Prevention’s division of vector-borne diseases, said she expected high numbers of dengue infections. in Puerto Rico this year and that there would also be more cases in the continental United States, especially in Florida, but also in Texas, Arizona and Southern California.
Dengue is spread by Aedes aegypti, a species of mosquito that is beginning to establish itself in new regions, including the warmer, wetter parts of the United States, where it had never been seen until recent years.
The number of cases in the United States this year is still expected to be relatively small — in the hundreds, not millions — because of the prevalence of air conditioning and window screens. But Dr. Paz-Bailey warned: “If you look at trends in the number of cases in America, it’s scary. It has increased continuously.”
Florida reported the highest number of locally acquired cases last year, 168, and California reported the first such cases.
Three-quarters of people infected with dengue have no symptoms at all, and among those who do, most cases will resemble only mild flu. But some dengue infections are serious, causing headaches, vomiting, high fever and painful joint pain that gives the disease the nickname “bone fracture fever.” A severe case of dengue can leave a person weak for weeks.
And about 5 percent of people who get sick will progress to what’s called severe dengue, which causes plasma, the protein-rich liquid component of blood, to leak from blood vessels. Some patients may go into shock, causing organ failure.
Severe dengue has a mortality rate between 2 and 5 percent in people whose symptoms are treated with blood transfusions and intravenous fluids. However, when left untreated, the mortality rate is 15 percent.
In Brazil, state governments are setting up emergency centers to test and treat people for dengue. The city of Rio de Janeiro declared a public health emergency Monday due to dengue, days before the start of the annual Carnival celebration, which brings tens of thousands of people to outdoor parties day and night.
Large numbers of cases are being reported in Brazil’s southernmost states, said Ms. Trindade, the health minister, which tend to be much cooler than Rio and the central and northern states. People in those areas will have little immunity to the disease due to previous exposure.
Dengue occurs in four different serotypes, which resemble viruses. Previous infection with one provides only short-term protection against infection with another, and someone who has had one serotype of dengue in the past is at greater risk of developing severe dengue from infection with another serotype.
“Right now, there are serotypes circulating in Brazil that have not been circulating for 20 years,” says Dr. Ernesto Marques, associate professor of infectious diseases and microbiology at the University of Pittsburgh.
Brazil has launched an emergency campaign to immunize children in areas with the highest risk of dengue transmission, using a two-dose vaccine called Qdenga made by Japan’s Takeda Pharmaceutical Company. Brazil bought 5.2 million doses for delivery this year, plus nine million more for delivery in 2025, and the company donated another 1.3 million, effectively blocking most of Qdenga’s supply worldwide. A company spokeswoman said Takeda is working on a plan to increase supply, with a focus on supplying high-prevalence countries.
Yet that is enough to reach less than 10 percent of Brazil’s population in two years. The only good news about dengue in Brazil right now is the publication of clinical trial results for a new vaccine tested by the public health research center Instituto Butantan in São Paulo. That vaccine requires only one injection, and the study found that it protected 80 percent of those vaccinated against developing the dengue virus disease. The research center will ask the Brazilian government to approve the vaccine, and has facilities to produce it, with the aim of starting to deliver vaccinations in 2025.
For this outbreak, it’s too late that vaccination can help much, and there are few other ways public health authorities can slow it down.
“Insecticide resistance really limits what you can do when it comes to controlling mosquito populations, and insecticide resistance is widespread,” said Dr. Paz-Bailey of the CDC. “What you can do is make sure that people have access to clinical treatment and that doctors know what to do.”
Medical centers in Brazil are setting up additional beds for people with severe dengue, hoping to avoid the overwhelming health care systems that occurred during the Covid-19 pandemic and prevent dengue deaths.
“The old paradigm of dengue that affects children the most is not the case in Brazil – you have to think about the elderly, who are very vulnerable,” said Dr. Ko. It will be important for both doctors and the public to get the message to test for dengue at the first sign of symptoms in both children and the elderly, he said.
“Every educated guess was that this was going to be a bad year,” said Dr. Marques, “but now we know how bad. It’s going to be very, very bad.”
Lisa Moriconi contributed reporting from Rio de Janeiro.