The worst outbreak is spreading
Brazil's health ministry has warned that the country is expected to have more than 4.2 million cases of dengue this year, far exceeding the 4.1 million cases recorded by the Pan American Health Organization (PAHO) for all 42 countries in the region last year.
Brazil is coming off a bad year for dengue — cases of the virus typically rise and fall in cycles of about four years — but experts say a number of factors, including El Nino and climate change, have made the problem worse this year.
A dengue fever patient in Brazil is taken to a field emergency center, the South American country is expected to have more than 4.2 million dengue fever cases this year - Photo: AFP
“Record heat in the country and above-average rainfall since last year, even before summer, have increased the number of mosquito breeding sites in Brazil, even in areas with few cases,” said Brazil’s Health Minister Nisia Trindade.
Dengue cases have spiked in Argentina, Uruguay and Paraguay in the past few months, during the Southern Hemisphere summer, and the virus moves across continents seasonally.
“When we see a wave in one country, we generally see a wave in other countries; that’s how we’re connected,” said Dr. Albert Ko, a dengue expert in Brazil and professor of public health at Yale University.
The World Health Organization (WHO) has warned that dengue is fast becoming a global health emergency, with record numbers of cases last year and outbreaks in places, such as France, that have never seen the disease before.
Dr. Gabriela Paz-Bailey, chief of the dengue branch at the US Centers for Disease Control and Prevention (CDC), said that dengue infection rates will increase in Puerto Rico this year and there will also be more cases in the continental United States, especially in Florida, as well as in Texas, Arizona and Southern California.
Complex developments of the epidemic
Dengue fever is spread by Aedes aegypti, a mosquito that is appearing in new areas, including warmer, wetter parts of the United States, where it had not been seen until the past few years.
Cases in the US are thought to have remained relatively low this year – in the hundreds rather than millions – due to the prevalence of air conditioning and window blinds. But Dr Paz-Bailey warned: “When you look at the trend in cases in the Americas, it’s scary. It’s been steadily increasing.”
Mosquitoes are collected and analyzed by medical workers in a laboratory in Rio de Janeiro, Brazil - Photo: New York Times
In the US, Florida reported its highest number of locally acquired cases last year, 168, and California also recorded its first such cases.
Three-quarters of people infected with dengue have no symptoms at all, and of those who do, most cases will be nothing more than a mild flu. But some cases of dengue are severe, causing headaches, vomiting, high fevers, and joint pain that have earned the disease the nickname “breakbone fever.” A severe case of dengue can leave a person debilitated for weeks.
And about 5% of people with the disease will develop a condition called severe dengue hemorrhagic fever, which causes plasma, the protein-rich liquid component of the blood, to leak out of the blood vessels. Some patients may go into shock, leading to organ failure.
Severe dengue has a mortality rate of 2% to 5% in symptomatic people treated with blood transfusions and intravenous fluids. Without treatment, the mortality rate can be as high as 20%, according to statistics from the global network of medical experts Medscape.
There are four types of dengue fever, corresponding to the four serotypes DEN-1, DEN-2, DEN-3, and DEN-4. Previous infection with one serotype provides only short-term protection against infection with another, and a person who has previously been infected with one dengue serotype is at increased risk of developing severe dengue from infection with another serotype.
“Right now, there are serotypes that are circulating again in Brazil after 20 years,” said Dr. Ernesto Marques, associate professor of infectious diseases and microbiology at the University of Pittsburgh.
Brazil is working hard to prevent and fight the epidemic
In Brazil, state governments are setting up emergency centers to test people for dengue and treat them. The city of Rio de Janeiro declared a public health emergency over dengue on Monday, days before the start of its annual Carnaval festival, which draws tens of thousands of people to day-and-night outdoor parties.
Health Minister Trindade said large numbers of cases were also being recorded in Brazil's southernmost states, which are typically much cooler than Rio, and in central and northern states.
Medical staff spray insecticide to kill Aedes aegypti mosquitoes in the capital Brasilia (Brazil) - Photo: Reuters
The South American country has begun an emergency vaccination campaign for children in areas with the highest rates or risk of dengue transmission with a two-dose vaccine called Qdenga produced by Japan's Takeda Pharmaceutical Company.
Brazil has purchased 5.2 million doses for delivery this year, plus another 9 million doses for delivery in 2025, and Takeda has donated an additional 1.3 million doses, nearly depleting the global supply of Qdenga.
There are only enough vaccines available to cover less than 10% of Brazil’s population for two years. The only good news on dengue in Brazil right now is the announcement of clinical trial results for a new vaccine developed by the public health research center Instituto Butantan in Sao Paulo.
The vaccine requires just one injection and trials have shown it protects 80% of those vaccinated against dengue. The research center will ask the Brazilian government to approve the vaccine, with the aim of starting public use in 2025.
But with this outbreak, it's too late for vaccination to help much, and there are few other ways to slow the outbreak.
Health centers in Brazil are setting up extra beds for people with severe dengue, hoping to prevent the health system from being overwhelmed like it was during the COVID-19 pandemic and prevent deaths from dengue.
“The old paradigm of dengue affecting children the most is no longer happening in Brazil – you have to think about the elderly, who are very vulnerable,” said Dr. Albert Ko, a dengue expert in Brazil.
Meanwhile, Dr. Ernesto Marques, associate professor of infectious diseases and microbiology at the University of Pittsburgh (USA), said: “Every educated guess was that this was going to be a bad year, but now we know how bad it is. It’s going to be very, very bad.”
Nguyen Khanh
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