Dengue Fever: A Global Epidemic Explained

Global warming means that mosquito-borne diseases such as dengue fever are spreading around the world.

[This post has been written by Adelaida Sarukhan and Daniel Camprubí.]

Imagine an illness that can suddenly transform the rhythm of your life. It starts with seemingly mild symptoms such as fever and headache, but in some cases, it can escalate into a life-threatening condition for which there is currently no specific treatment available. Now imagine that 4 billion people – half the world’s population – are at risk of contracting the disease.

Dengue, a viral infection transmitted by mosquitoes, has become an alarming global epidemic, affecting millions of lives across continents. While you may have heard of it, the current surge in dengue cases demands our attention and understanding more than ever.

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Better Understanding Dengue Dynamics: How Long Does Immunity Last?

Usual Suspects: 002 Aedes Mosquito

What is dengue and how does it spread

The dengue virus belongs to the flavivirus family, which also includes other vector-borne viruses that cause disease in humans, such as Zika, yellow fever, and West Nile. Dengue infections can be caused by any of the four closely related dengue serotypes (called DENV-1 to DENV-4).

Dengue virus is transmitted to humans through the bite of mosquitoes, although not just any mosquito. They must be female, infected, and belong to the species Aedes aegypti or Aedes albopictus. Both species are very prolific and well adapted to living in close association with humans. The only continent – so far – where these mosquitoes are not found is Antarctica. Aedes aegypti is concentrated in tropical and subtropical regions, while Aedes albopictus (aka tiger mosquito) is also found at higher latitudes including Europe, the USA and Japan.

What are the symptoms and how is it diagnosed

Not everyone develops symptoms, but the most common ones are fever, rash, aches (including headache behind the eyes) and severe joint pain. Symptoms usually last 2-7 days. About 1 in 20 people who get sick can develop severe dengue, which can be fatal if not treated quickly. Symptoms of severe dengue include bleeding from the nose or gums, vomiting, shortness of breath, hypotension and organ dysfunction. Between 2-5% of people with severe dengue may die. Without treatment, the fatality rate can be as high as 50%. 

People previously infected by a specific dengue serotype become immune to that serotype but are more likely to develop severe dengue if infected later on by any of the other dengue serotypes, due to a phenomenon called antibody dependent enhancement (whereby existing antibodies facilitate viral entry into the cells). Infants and pregnant women are also at higher risk of severe dengue.

Diagnosis is usually performed in the laboratory using molecular tests (amplification of viral DNA) or serological tests (detection of virus-specific antibodies). Rapid diagnostic tests for dengue exist, but their sensitivity varies according to the serotype and whether it is a first or secondary infection.

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Dengue treatment and prevention

There is still no specific treatment for dengue, although promising results have recently been reported for an antiviral pill tested in a very small trial in humans.

Two dengue vaccines are currently licensed. The first (Sanofi’s Dengvaxia) is only recommended for people living in endemic areas who have already been infected. The second, from Takeda, was recently approved by the European Medicines Agency (EMA) for use in people aged four years and older in endemic areas as well as for travellers, without need of a pre-vaccination test. This vaccine was also recently recommended by the WHO expert group for use in children aged 6 to 16 and who live in high transmission areas.

Very promising Phase 3 results were recently published for another tetravalent dengue vaccine developed by the Butantan Institute in Brazil. The live, attenuated vaccine proved to be safe and highly effective in preventing symptomatic dengue in children and adults, regardless of whether or not they had previous infections.

The best preventive measure is to avoid mosquito bites (especially during dusk and dawn, when the Aedes vector is most active) through the use of insect repellents and clothes that cover arms and legs, and to control mosquito populations by regularly emptying containers with water, where mosquitoes lay their eggs.

The current global situation

The incidence of dengue has increased dramatically in recent decades. So far in 2023, over 3.7 million dengue cases and over 2,000 deaths have been reported worldwide. In Bangladesh, for example, the number of dengue cases and deaths this year (>200,000 and >1,000, respectively) is higher than in all previous year combined since 2000. Peru has seen the worst epidemic in over a decade, with more than 150,000 cases and 252 deaths this year, many of them children. This upsurge in cases is not only happening in tropical and subtropical regions, where dengue is most common. It is also happening in places like Europe and the US, where local transmission was rare.

The main culprit? Climate change

Global warming, together with international mobility, means that mosquito-borne diseases such as dengue, malaria or chikungunya, once confined to the tropics, are now spreading worldwide. In the US, 516 cases of locally acquired dengue fever have been reported so far this year. Southern Europe is particularly vulnerable, with 10 different local outbreaks involving more than 100 reported cases (although this number may be higher, given that around 50% of infections are asymptomatic). Spain, which eliminated yellow fever and dengue from its port cities more than 50 years ago, is again at risk of sustained local transmission due to the spread of mosquito vectors and increased arrival of infected travellers. In France alone, there could be more than 3,000 cases per year by 2030 (up from 65 cases seen in 2022), if temperatures continue to increase at the current rate, according to a recent analysis.

What can we do? As the global number and distribution of dengue cases increases, vector control and community engagement are key to reducing the spread of the disease. Some innovative vector control strategies, such as releasing mosquitoes infected with Wolbachia (a bacterium that prevents them from getting infected with the virus) are showing promising results in endemic areas. Developing more effective rapid diagnostic tests, specific treatments and other effective vaccines, and above all making them affordable and accessible to those who need them, will also be key in reducing the health impact of a disease that now threatens half of the world’s population. Needless to say, reducing the impact of not only dengue, but also of other emergent and re-emergent diseases and many other health threats ultimately boils down to taking meaningful action to reverse climate change and biodiversity loss.

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