Dengue cases have been recorded across the Americas in excess of three million this year. That indicates that since 1980, when the Pan American Health Organisation started compiling data on the number of cases, 2023 already has the second-highest annual incidence of the disease.
The recent article published in the Nature science journal revealed some of the main reasons behind the surge in dengue cases in America. Talking to the publication Cláudia Codeço, an epidemiologist at the Oswaldo Cruz Foundation, a biosciences and public-health institution in Rio de Janeiro, Brazil says, “We do observe an increase in cases beyond what was expected for this period.” How the illness spreads in Central and North America will determine if the record-breaking 3.2 million cases reported in 2019 will be broken in 2023, as the majority of researchers believe the height of dengue season in South America has passed. (Also read: Dengue in children on rise; here’s what parents need to keep in mind )
The fact that dengue is transmitted by four serotypes of closely similar viruses makes pinpointing the specific source of the upsurge difficult. “There is an interaction between these serotypes, with the immunity against one interfering with the others. When we put this together, it can lead to unpredictable dynamics,” says Codeço.
According to academics, though, the increase may also be explained by rising temperatures and altered rainfall patterns. The primary carrier of dengue, the Aedes aegypti mosquito, thrives in humid environments with temperatures about 30 °C, which have grown increasingly prevalent in recent years as a result of exceptional heat records and other weather-related occurrences. The illness, which can result in fever, headaches, and lethargy, has no particular therapy. Severe cases can be fatal; this year, dengue has claimed the lives of more than 1,300 individuals across the Americas.
Primary Causes for the Surge of Dengue Cases in America
Areas where A. aegypti formerly had no presence are now seeing dengue outbreaks. The disease is spreading into southern regions in Brazil, where there have been over 2.4 million recorded cases this year, which were previously too cold for the mosquito. According to research by Codeço and her colleagues1, 481 Brazilian towns have shown persistent local dengue transmission for the first time during the previous five years1. Additionally, Mexico City, which is located at a height of 2,240 metres, saw its first A. aegypti incursion in 2015. “If you read books about the biology of the Aedes aegypti, they say the mosquito doesn’t reproduce at altitudes above 1,200 metres,” says José Ramos-Castañeda, a virologist at the Mexican National Institute of Public Health in Cuernavaca. “In that aspect, global warming is affecting the distribution of the vector and therefore the possible distribution of cases.”
The possibility for an epidemic of dengue — the likelihood that it would spread among individuals — in the late 2040s has been examined by researchers at the University of Michigan in Ann Arbor. According to computational epidemiologist Andrew Brouwer, one of the study’s authors, “What we found was that the epidemic potential was higher than today, regardless of the specific climate-change scenario.” He claims that “in most places, we’ve seen a 10–20% increase in the epidemic potential.”
The problem is not just in South America. The areas where vectors and pathogens may survive will expand, according to Brouwer, both in the Southern and Northern Hemispheres. Dengue local transmission has already been documented in Florida, Texas, and Arizona in the continental United States.
Dengue cases often increase in the summer or during the rainy season and decrease during the winter or during the dry season. However, as global temperatures rise, dengue seasons may lengthen. In the forecast made by Brouwer and his coworkers, “we found that the transmission seasons generally increased by about a month on either end”, Brouwer claims.
Impact of El Niño Weather Event
Dengue may suffer in the near future as a result of the ongoing El Nio weather phenomena, which is predicted to bring record temperatures, droughts, and floods. Tedros Adhanom Ghebreyesus, the head of the World Health Organisation, issued a warning about the phenomena in late June, saying it “could increase transmission of dengue and other so-called arboviruses like Zika and chikungunya.”
The areas of Central America and parts of North America, which are now experiencing the rainy season, will likely be most affected by El Nio in terms of dengue incidence. The spread of dengue has been controlled using a number of tactics. They include eliminating open containers of stagnant water where the insects can reproduce and using traps or pesticides to destroy the mosquito host. Additionally, attempts are being made to create mutant mosquitoes that are immune to disease transmission.
Ramos-Castaeda claims that while all of these strategies might be helpful, “the thing that could really impact the transmission is immunity in the population.” Since 2015, two dengue vaccines have received official approval in specific regions; but, due to challenges with effectiveness, safety worries, and expensive costs, they haven’t been extensively used.
