Incidence of dengue virus has soared in 2023 to near historically high levels, the World Health Organization (WHO) reported on Friday, with more than 5 million cases worldwide and 5,000 deaths from the virus that still lacks an effective treatment or vaccine.

Moreover, formerly dengue-free countries in southern Europe, such as France, Italy and Spain reported local transmission of dengue virus, in what may be a first for Europe.

“Usually, Europe reports imported cases from the Americas, from the Western Pacific, from the endemic regions,” said WHO’s Dr. Diana Rojas Alvarez, speaking at a UN press briefing Friday morning. “But this year we saw limited clusters of autochthonous transmission. As we know, the summers are getting warmer.”

Another growing concern is the fact that dengue outbreaks are occurring in fragile and conflict-affected countries in the eastern Mediterranean region such as Afghanistan, Pakistan, Sudan, Somalia and Yemen.

Close to 80% of dengue cases, however, continue to be reported in the Americas, with the highest proportion of cases in the Caribbean, followed by Brazil and Mexico.  The disease is also prevalent in most of Southeast Asia and the Western Pacific region, reported Alvarez.

Climate change a key factor

Warming temperatures have become a leading driver in the increase of dengue transmission, particularly in tropical and sub-tropical climates but also extending at times to more temperate zones such as southern Europe, she stressed.

“Climate change has an impact in dengue transmission because it increases rainfall, humidity and temperature,” said Dr. Alvarez. “These mosquitoes are very sensitive to temperature.”

Transmitted by the Aedes Aegypti mosquito, dengue virus is one of the most widespread vector borne diseases.  Originally harboured by mosquitoes in rural and forested zones, it has also become a major threat in burgeoning urban areas of the global south – where mosquitoes breed in home water containers as well as in the rainwater accumulating in discarded tires and other refuse.

While there is no specific treatment, early diagnosis and supportive care can reduces risks of death.  Although most people recover within a couple of weeks, those who have been affected by dengue in the past can become more ill upon re-infection with a second or third bout of the virus.  The onset of severe dengue infections can occur even after initial fever has subsided and be accompanied by symptoms such as bleeding gums, stomach pain, vomiting, liver enlargement, leading to severe bleeding or organ impairment, according to WHO.

The 2023 El Niño phenomenon, which has exacerbated the effects of global warming, and along with that, increased rainfall, is another factor in the growing prevalence of the disease, WHO said.

Controlling vector spread

Along with southern Europe, the disease is being seen with increased frequency in southern areas of North America and Latin American countries such as Uruguay as well as mountain areas of Colombia and other regions more than 2000 meters above sea level, where the mosquito previously didn’t thrive.  In Africa, 15 countries have reported outbreaks this year, mostly in West Africa, but also Chad and Ethiopia.  In the Middle East and South Asia, high levels of rainfall have increased mosquito densities, and consequent risks, in countries such as Bangladesh, Oman and Saudi Arabia.

Adding to the risks are the already wide distribution of the A. Aegypti mosquito vector – including in Europe.

Key interventions for prevention and control include: strengthening surveillance and reporting of cases; and strengthened vector control activities to reduce mosquito breeding grounds, and thus densities, WHO said.  and  density of mosquitoes; and reinforcing risk communications and community engagement.  Poor water and sanitation and unsafe waste management adds to dengue risks.

In Southeast Asia and the Americas, successful dengue control has often involved community-level identification and bio-control of sites where the mosquitoes breed, including the introduction of harmless predators, including locally-available species of fish  or crustaceans that feed on the mosquito larvae, into water reservoirs and water containers.

Image Credits: James Gathany/ PHIL, CDC, Public Domain, © 2011 Nature Education .