WASHINGTON DC, United States (PAHO/WHO) — WHILE the incidence of dengue increases across regions, especially in parts of the Americas, experts recently reviewed the global situation and methods to help control the spread of the mosquito-borne disease.

During the EPI-WIN Webinar: Managing Dengue: a rapidly expanding epidemic, experts from around the world highlighted that about half of the world’s population is now at risk of dengue, with an estimated 100–400 million infections occurring each year.

“Incidence has increased by almost eight-fold since 2000,” said Dr Raman Velayudhan, unit head for veterinary public health, vector control and environment and neglected tropical diseases at the World Health Organization (WHO) at the opening of the webinar. Before 1970, the mosquito-vector of the disease was present in only half a dozen countries, he added, but it is now found in over 130 countries.

Situation in the Americas

In the Americas, dengue is transmitted primarily by the Aedes aegypti mosquito and the disease is endemic to many countries. Outbreaks tend to be cyclical every three to five years, following seasonal patterns corresponding to the warm, rainy months, when mosquitoes breed.

In 2023, however, the Americas have seen a sharp increase in dengue cases. Over three million new infections have been recorded so far, surpassing figures for 2019 — the year with the highest recorded incidence of the disease in the region, with 3.1 million cases, including 28,203 severe cases and 1,823 deaths.

Most cases — over 2.6 million — are registered in the southern cone, with Brazil accounting for 80 per cent. But unusually high transmission has also been seen in other areas of the continent, including the Andean region, with over 400,000 cases and a higher case fatality rate. In March and June of this year, the Pan American Health Organization (PAHO) issued recommendations to help countries tackle the increase.

“Urbanisation and climate change have had a huge impact in spreading dengue,” Velayudhan said during the webinar. The movement and agglomeration of people in urban areas have helped to spread the vector, he added, but COVID-19 disruptions have also impacted mosquito control measures and the reporting of cases.

“Post-COVID, we need to realign programmes to be more integrated and ensure health systems can manage,” Velayudhan said. “We should implement the lessons learned from the pandemic, such as in diagnosis and use of PCR tests, enhanced surveillance, good communication and community involvement.”

As the southern hemisphere enters the colder and drier months, cases are declining in parts of the region, but greater transmission is expected in Central America and the Caribbean during the second half of the year. PAHO recently issued an alert providing guidance to national authorities to boost surveillance and prepare health systems for an uptick in cases.

Community engagement for effective vector control

There is no specific treatment for dengue, and prevention depends on the control of the vector. Measures to curb mosquitoes include the use of chemicals, such as insecticides and repellents, and mechanical methods to remove breeding sites or provide a barrier, such as treated nets, window screens and protective clothing.

Programmes that use a combination of these methods can be effective, but engaging communities to apply them is critical for their success, especially to remove or clean potential breeding habitats. Old, disused tires, for example, offer shade and a preferred dark space for Aedes mosquitoes to lay their eggs, which can resist drought and develop only once they meet water many months later.

PAHO has developed a series of initiatives to support such local prevention activities, including Mosquito Awareness Week, which spurs community-level actions to provide information on the links between mosquitoes and the diseases they transmit, such as dengue, but also chikungunya, Zika, malaria, and yellow fever.

“Several messages on prevention have been developed and countries can adapt them to their local needs,” said Giovanini Coelho, from PAHO’s public health entomology team.

Dengue is a viral infection that spreads from mosquitoes to people. While most infections are asymptomatic or produce mild illness, the disease can occasionally become severe and even cause death. Symptoms range from mild to debilitating high fever, with severe headache, pain behind the eyes, muscle and joint pain, and a rash. The illness can evolve into severe dengue, characterised by shock, respiratory distress, bleeding, and possible organ impairment.