Brazil is experiencing a massive outbreak of dengue fever, the sometimes fatal mosquito-borne disease, and public health experts say it is a harbinger of a coming surge in cases in the Americas, including Puerto Rico.
Brazil’s health ministry warns it expects more than 4.2 million cases this year, surpassing the 4.1 million reported by the Pan American Health Organization in all 42 countries in the region last year.
Brazil has had a bad dengue year – the number of cases of the virus usually rises and falls in a cycle of about four years – but experts say several factors, including El Niño and climate change, have greatly amplified the problem this year.
“The record heat in the country and above-average rainfall since last year, even before the summer, increased the number of mosquito breeding sites in Brazil, even in areas that had few cases of the disease,” the health minister said of Brazil, Nicia. Trudeau said.
Dengue cases have already spiked in Argentina, Uruguay and Paraguay in recent months during the Southern Hemisphere summer, and the virus will increase across continents with the seasons.
“When we see waves in one country, we will generally see waves in other countries, so we are interconnected,” said Dr. Albert Ko, a dengue expert in Brazil and professor of public health at Yale University.
The World Health Organization has warned that dengue fever is fast becoming an urgent global health problem, with a record number of cases last year and outbreaks in places such as France that have historically never reported the disease.
In the United States, Dr. Gabriela Paz-Bailey, chief of the dengue branch of the vector-borne diseases division at the Centers for Disease Control and Prevention, said she expects high rates of dengue infection. in Puerto Rico this year and that there will be more cases in the continental United States as well, especially in Florida, as well as in Texas, Arizona and Southern California.
Dengue fever is spread by Aedes aegypti, a species of mosquito that is establishing itself in new areas, including warmer, wetter parts of the United States, where it had never been seen until recent years.
Cases in the United States are expected to be relatively few this year — in the hundreds, not millions — because of the prevalence of air conditioning and windows. But Dr Paz-Bailey warned: “When you look at the trends in the number of cases in America, it’s scary. Constantly increasing”.
Florida reported the highest number of local cases last year, 168, and California reported its first cases.
Three-quarters of people infected with dengue fever have no symptoms at all, and among those who do, most cases will resemble only mild flu. However, some dengue infections are severe, causing headaches, vomiting, high fever, and joint pain that gives the disease the nickname “cramping fever.” A bad case of dengue fever can leave a person debilitated for weeks.
And about 5 percent of people who get sick will develop what’s called severe dengue fever, 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 fever has a fatality rate of between 2 percent and 5 percent in people whose symptoms are treated with blood transfusions and intravenous fluids. However, when left untreated, the fatality rate is 15 percent.
In Brazil, state governments are setting up emergency dengue control and treatment centers. The city of Rio de Janeiro declared a state of public health emergency due to dengue fever on Monday, days before the start of its annual Carnival celebration, which brings tens of thousands of people to outdoor parties for days and nights.
A high number of cases are being reported in Brazil’s southernmost states, said Ms. Trudeau, the health minister, which are typically much colder than Rio and states in the center and north. People in these areas will have little immunity to the disease from previous exposure.
Dengue fever comes in four different serotypes, which are like cousins of the virus. Previous infection with one provides only short-term protection against infection with another, and a person who has had one dengue serotype in the past is at higher risk of developing severe dengue from infection with another serotype.
“Right now there are serotypes circulating in Brazil that haven’t been circulating in 20 years,” said Dr. Ernesto Marquez, 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 rates or risk of dengue transmission, using a two-dose vaccine called Qdenga produced by Japan’s Takeda Pharmaceutical Company. Brazil bought 5.2 million doses for delivery this year, plus an additional nine million for delivery in 2025, and the company donated an additional 1.3 million, effectively locking in most of the world’s Qdenga supply. A company spokeswoman said Takeda is working on a plan to increase supply, focusing on delivery to high-prevalence countries.
But even so, that’s enough to cover less than 10 percent of Brazil’s population over 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 Sao Paulo. This vaccine requires only one shot, and the trial found that it protected 80 percent of those vaccinated from developing dengue virus disease. The research center will ask the Brazilian government to approve the vaccine and has facilities to produce it, with the goal of starting administering vaccines in 2025.
For this outbreak, it is too late for vaccination to help much, and there are few other ways for public health authorities to slow it down.
“Insecticide resistance really limits what you can do in terms of mosquito population control, and insecticide resistance is widespread,” said Dr. Paz-Bailey at the CDC “What you can do is make sure that people have access to clinical management and that clinicians know what to do.”
Medical centers in Brazil are setting up extra beds for people with severe dengue fever, hoping to prevent the kind of collapse of health systems that occurred during the Covid-19 pandemic and prevent dengue deaths.
“The old paradigm of dengue affecting children more doesn’t apply in Brazil – you have to think about the elderly, who are very vulnerable,” said Dr Ko. It will be important for both clinicians 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.
“Any educated guess was that this was going to be a bad year,” Dr Marques said, “but now we know how bad. It’s going to be very, very bad.”
Lis Morriconi contributed reporting from Rio de Janeiro.
