On June 25, the Centers for Disease Control and Prevention issued a health advisory alerting U.S. providers and the public of an increased risk of dengue virus infections.
Dengue, the most common mosquito-borne disease in the world, is having a record-breaking year.
The number of reported dengue cases has grown dramatically in the past two decades, increasing from 505,000 cases in 2000 to 5.2 million in 2019, the year that the World Health Organization declared dengue as a top 10 global public health threat. But this year, the numbers have reached nearly 11 million, according to the WHO, surpassing previous records.
While the disease is endemic in more than 100 countries, according to WHO, it’s now appearing in new areas such as Portugal, Spain and the southern U.S., making it a growing global public health concern.
There are several reasons for dengue’s unprecedented spread. Among them are the El Niño phenomenon in 2023 and climate change, both of which have led to increasing temperatures and rainfalls, creating ideal conditions for mosquitoes. Also contributing are population growth and urbanization, which can create more favorable breeding environments for mosquitoes.
Meanwhile, the COVID-19 pandemic diverted public health resources and led to a decline in dengue surveillance and control efforts, according to research. And people are traveling more than they have since the onset of the pandemic in 2020.
“Humans help the virus move around,” said Dr. Gabriela Paz-Bailey, chief of the Dengue Branch at the Division of Vector-Borne Diseases at the CDC, in a July 23 interview on Vox’s Today Explained podcast.
So far this year, the U.S. has reported 2,923 dengue cases — travel-related and locally acquired — in 49 states and territories. In comparison, there were 3,350 cases for 2023, and 1,593 cases in 2019, before the COVID-19 pandemic, according to the CDC’s historic data on dengue.
The disease is nicknamed “breakbone fever” due to its severe muscle and joint pain. It is most common in tropical and subtropical regions. Although many people with dengue have no symptoms or only a mild illness, the infection can turn severe and, in some cases, lead to death. Worldwide, more than 6,500 people have died of the disease this year.
The risk of widespread transmission of dengue in the continental U.S. remains low and most of the reported cases have historically been in travelers who were infected elsewhere. But limited local spread of dengue has been reported in several states, including Florida, Texas, Hawaii, Arizona and California, according to the CDC.
Dengue is common in the U.S. territories of American Samoa, Puerto Rico, the U.S. Virgin Islands and the freely associated states, including the Federated States of Micronesia, the Republic of Marshall Islands and the Republic of Palau, according to the CDC. In March, Puerto Rico declared a public health emergency due to a dengue outbreak. The island has reported 1,918 locally acquired cases this year as of this piece’s publication, compared with 1,270 cases for all of 2023. In American Samoa, more than half of children have had dengue, according to an August report in the CDC’s Morbidity & Mortality Weekly Report.
Nearly nine million of the 11 million cases this year have been reported in the Americas region, twice as many in the region as in all of 2023, according to WHO’s global dengue surveillance dashboard. The CDC currently lists more than two dozen countries in Central and South Americas, Africa and Asia that are reporting higher-than-usual numbers of dengue cases and may put travelers at an increased risk of infection.
The CDC and the WHO provide a wealth of information and data on dengue. In this piece, we provide a brief primer on dengue followed by recently published studies on the topic, which journalists can use to inform their reporting.
A quick primer on dengue
What is dengue? Dengue is a viral disease caused by four closely related viruses: DENV-1, DENV-2, DENV-3 and DENV-4. A one-time infection does not protect people from another infection.
How is it spread? Dengue viruses spread via the bites of infected female mosquitoes, primarily the Aedes aegypti mosquitoes. Other rare transmission routes include transmission from mom to baby during pregnancy, blood transfusion and organ transplantation.
What are the symptoms? Symptoms begin four to 10 days after infection and can last up to a week. The most common symptom is fever with aches and pains, nausea and vomiting and rash. People who are infected for the second time are at risk of severe dengue, with symptoms such as severe abdominal pain, rapid breathing, bleeding gums or nose, pale and cold skin, and feeling weak.
What are the treatments? There are no specific treatments for dengue, other than pain management. People with severe dengue may be hospitalized.
Is there a vaccine? Three-dose Dengvaxia, recommended for children 9 to 16 years who have a previous infection and live in high-risk areas, is the only vaccine currently available in the U.S., although its uptake has been low and manufacturer Sanofi Pasteur has discontinued production, according to the CDC. Two-dose Qdenga, or TAK-003, developed by Takeda, was approved by the European Commission in December 2020, and is licensed in several countries, including Indonesia, Brazil, Argentina, the UK and Germany, but not yet approved in the U.S. Another vaccine, the single-dose Butantan-Dengue Vaccine (Butantan-DV), is in clinical trails. So are TV003 and TV005, developed by the National Institutes of Health. Below, we have included studies that examine the efficacy of these vaccines.
How is dengue transmission prevented? The main ways to avoid infection is by preventing mosquito bites and implementing mosquito control measures indoors and outdoors at home, such as pest control and eliminating sources of standing water. There have been efforts to deploy genetically modified mosquitoes that carry a gene, which, when passed to their offspring, kills female mosquitoes in the larval stage. Another method is using a bacterium called Wolbachia. When Wolbachia-infected male mosquitoes mate with uninfected females, the resulting eggs don’t hatch. The method is found to be effective along with other mosquito control measures and is currently being used in Brazil and Indonesia.
Research studies
Epidemiology & public health
Dengue
Gabriela Paz-Bailey, et al. The Lancet, February 2024.
Summary: The lead author of this paper, Dr. Gabriela Paz-Bailey, is chief of the Dengue Branch at the Division of Vector-Borne Diseases at the CDC. The paper provides an overview of dengue, including its immunology and disease management. Some of the highlights:
- Dengue was first reported in 1779, and the virus was first identified in 1943.
- The estimated global health care cost of dengue is more than $8.9 billion each year, including medical costs and losses in productivity.
- People who live in densely populated areas and those who have poor housing conditions are at a higher risk of contracting dengue.
- Developing an effective dengue vaccine is complex because a single vaccine needs to cover four dengue viruses.
The Current and Future Global Distribution and Population at Risk of Dengue
Jane P. Messina, et al. Nature Microbiology, June 2019.
Summary: Researchers use statistical mapping techniques to pinpoint dengue case locations, along with climate, population and socioeconomic projections, to estimate the risk of the virus to humans in 2020, 2050 and 2080. Among the study’s main findings:
- The southeastern U.S. and coastal regions of eastern China and Japan are likely to become more suitable for dengue transmission by 2050.
- Africa could become substantially more suitable for dengue, particularly in southern regions and the Sahel, which extends from western to north-central Africa.
- Temperature, rainfall and relative humidity are the major climate factors influencing dengue’s spread. Socioeconomic factors, like urbanization and economic activity, also play crucial roles. Urban areas typically have high population density, providing more hosts for mosquitoes. They tend to have more artificial water containers, which are ideal for mosquito breeding. Also, urban heat islands create a more ideal environment for mosquitoes.
- By 2080, as many as 6.1 billion people could be at risk of dengue, compared with 4 billion today. The increase is mainly due to population growth in areas where dengue is already common.
Global Burden for Dengue and the Evolving Pattern in the Past 30 Years
Xiaorong Yang, Mikkel B. M. Quam, Tongchao Zhang and Shaowei Sang. Journal of Travel Medicine, December 2021.
Summary: The study examines the evolving burden of dengue from 1990 to 2019, highlighting significant trends and impacts on global health, particularly in relation to the COVID-19 pandemic. Among its findings:
- In the 1990s, the highest dengue mortality rates were among children under five, but by 2019 those aged 15 to 49 had the highest mortality.
- There is a strong correlation between the global land and ocean temperature increases, air passenger travel, and the increasing burden of dengue. These factors, combined with urbanization, have led to the spread of dengue even to regions previously less affected.
- The COVID-19 pandemic complicated the global response to dengue, with reports of co-infections that complicate diagnosis and management due to overlapping symptoms. Public health resources diverted to fighting the pandemic have led to a decline in dengue surveillance and control efforts.
- While some countries reported decreased dengue incidence due to lockdowns, others experienced outbreaks, suggesting varied impacts of COVID-19 measures on dengue transmission.
Vaccines
Dengue Fever Epidemics and the Prospect of Vaccines: A Systematic Review and Meta-Analysis Using Clinical Trials in Children
Ebele C. Okoye, Amal K. Mitra, Terica Lomax and Cedric Nunaley. Diseases, February 2024.
Summary: The systematic review of 38 studies evaluates the efficacy, immune response and safety of dengue vaccines in children. Among the findings:
- Dengue vaccines, particularly Dengvaxia and TAK-003, showed varying levels of efficacy against all four dengue viruses. Dengvaxia provided strong protection against severe dengue but showed varying long-term efficacy. TAK-003 showed sustained protection against symptomatic dengue for up to three years.
- Vaccines triggered satisfactory immune responses, especially in individuals with prior exposure to dengue.
- Most vaccine side effects were mild.
- This study underscores the importance of dengue vaccination in reducing disease and death among children, particularly in areas where dengue is common. It also highlights the need for personalized vaccination strategies based on an individual’s dengue infection history.
A Systematic Review on Malaria and Dengue Vaccines for the Effective Management of These Mosquito Borne Diseases: Improving Public Health
Hind M. Al-Osaimi, et al. Human Vaccines & Immunotherapeutics, March 2024.
Summary: The review examines 39 studies on dengue and malaria vaccines, finding variations in vaccine efficacy, duration of protection and safety considerations for each disease. We are highlighting the part of the study about dengue. Among the findings:
- TAK-003 showed high efficacy against dengue over three years in children 6 to 16 years, living in countries where dengue is common.
- Dengvaxia was tolerated well over three years in children and adults up to 45 years old in countries where dengue is common.
- Butantan-DV, which is in clinical trials, induced an immune response in all four dengue types among adults who had or had never been infected with dengue.
Additional research
Climate change and mosquito-borne diseases
Impacts of Climate Change on Water-Related Mosquito-Borne Diseases in Temperate Regions: A Systematic Review of Literature and Meta-Analysis
Zemichael Gizaw, Eunice Salubi, Alain Pietroniro and Corinne J. Schuster-Wallace. Acta Tropica, October 2024.
Summary: “Climate factors (e.g., temperature, precipitation, humidity, and wind) and extreme weather events (e.g., drought and flooding) could intensify pathogen development and infectivity, create favorable mosquito breeding habitats, make the temperature suitable for mosquito development and abundance, increase the geographic distribution of mosquitoes, and increase mosquito-to-host contact or exposures in temperate regions,” the authors write.
Dengue outbreaks
Upsurge of Dengue Outbreaks in Several WHO Regions: Public Awareness, Vector Control Activities, and International Collaborations are Key to Prevent Spread
Rapty Sarker, et al. Health Science Reports, April 2024.
Summary: The study examines the history of dengue outbreaks around the world and the impact on public health measures. “Countries need multifaceted strategies, including robust vector control, community engagement, healthcare strengthening, and international collaboration to mitigate recent dengue upsurges. Adapting to climate change and addressing urban planning are crucial,” the authors write.
Deforestation and dengue
Impact of Deforestation and Climate on Spatio-temporal Spread of Dengue Fever in Mexico
José Mauricio Galeana-Pizaña, Gustavo Manuel Cruz-Bello, Camilo Alberto Caudillo-Cos and Aldo Daniel Jiménez-Ortega. Spatial and Spatio-temportal Epidemiology, August 2024.
Summary: “A 1% loss of forest cover at the municipal level results in a notable increase in the risk of dengue cases,” the authors write. “These findings underscore the urgent need for public health strategies intricately linked with biodiversity conservation and climate change mitigation efforts.”
Childhood obesity and dengue
Is the Rise in Childhood Obesity Rates Leading to an Increase in Hospitalizations Due to Dengue?
Chandima Jeewandara, et al. PLOS Neglected Tropical Diseases, June 2024.
Summary: Obesity and diabetes are known risk factors for hospitalization due to dengue. The study of 4,782 children in Sri Lanka finds that children who had a body mass index higher than 97% of their peers were twice as likely to be hospitalized than leaner children.
Mosquito control method using Wolbachia
Efficacy of Wolbachia-Mediated Sterility to Reduce the Incidence of Dengue: A Synthetic Control Study in Singapore
Jue Tao Lim, et al. The Lancet Microbe, February 2024.
Summary: The study discusses the effectiveness of releasing male mosquitoes infected with Wolbachia bacteria to reduce dengue cases in Singapore. The findings show that this method significantly lowered the mosquito population and the incidence of dengue.
Construction workers and mosquitoes
Factors Associated with Mosquito Control Among Construction Workers: A Systematic Review
Rahmat Dapari, et al. PLOS ONE, May 2024.
Summary: Workers in the construction industry frequently work in sites that can potentially accumulate water, including tanks, wet cement surfaces or water puddles. Worker education, implementing mosquito control measures, training employees and rewarding them with incentives for their compliance can help reduce the spread of mosquito-borne diseases among construction workers.
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