It’s Time to Turn the Tide on Dengue

By Scott L. O’Neill

On World Mosquito Day, let’s commit to transforming the world’s deadliest animal into an ally for global health. Here’s how we can do it.

It’s been a summer for the record books. July was our planet’s hottest month in more than 140 years. Daily temperatures were 0.72°C warmer than the monthly average for 1991-2020 and 1.5°C warmer than the average for 1850-1900.

And all of that sweltering heat fueled a major spike in extreme weather events, from weeks-long heat domes, to fast-moving wildfires, to epic floods, to protracted droughts.

In 2023, the everyday reality of climate change is becoming readily apparent, as is the urgent need for action.

One of the biggest threats of climate change comes from humanity’s oldest and deadliest foe – the mosquito. Over the past century, science has made tremendous strides against mosquito-borne disease. The yellow fever vaccine has saved millions of lives while helping communities across Africa and the Americas grow and thrive. The mass distribution of bed nets and effective treatments cut malaria deaths by about half between 2000 and the late 2010s.

But climate change is putting this amazing progress at risk at a critical moment in human history. The world’s five biggest economies – the United States, China, Japan, Germany, and the United Kingdom – all have rapidly aging populations, which means that tomorrow’s workforce will come largely from the tropical and subtropical regions of the world that lie between 30°N and 30°S of the equator.

So, humanity’s best prospects for a productive and prosperous future depend on the steps we take today to help children across sub-Saharan Africa, the Indo-Pacific, Latin America, and the Caribbean grow up to be healthy, strong, and smart. And one of the greatest challenges that this new generation faces is a massive resurgence of mosquito-borne pathogens.


A Top-10 Threat to Global Health

The world’s fastest-spreading mosquito-borne disease is dengue fever, and the combined forces of globalization, urbanization, and climate change have caused global dengue incidence to surge by a factor of 30 since the 1970s, prompting the World Health Organization (WHO) to declare it one of the top-10 threats to global health.

Dengue currently infects about 400 million people each year, makes about 50 million people severely ill, and annually drains USD $9-12 billion dollars from the global economy. Billions of hours that could have otherwise been invested in work or school are lost to sickness and caregiving.

Dengue outbreaks also impose crushing burdens on national health systems in low- and middle-income countries. A recent surge in cases in Bangladesh flooded the country’s hospitals with 2,000 new patients a day and forced officials in Dhaka to convert the capital city’s COVID-19 emergency hospital into a massive dengue ward. Sudden surges in demand force health care workers to ration care and lead to sharp spikes in all-cause mortality as patients with urgent needs (e.g., heart attacks, strokes, and traumatic injuries) fail to receive timely treatment.

These problems are only likely to worsen in coming years. With human population growth concentrated in tropical and subtropical cities; vast new regions of the world becoming susceptible to local dengue transmission; and increased opportunities for mosquito breeding related to periodic urban flooding, inadequate sanitation, and unregulated water collection methods; the number of people at risk of the disease will rise from four billion currently to six billion by the middle of the 21st century.

And the mosquito species primarily responsible for spreading dengue – Aedes aegypti – also transmits chikungunya, Zika, yellow fever, and various novel zoonoses that could give rise to future pandemics.


A Revolutionary Solution

So, how can we turn the tide? The good news is that for the first time in human history we have a scientifically proven way to interrupt the transmission of dengue and other Aedes-borne viruses:  it’s a safe, affordable, and nature-based solution called Wolbachia.

Wolbachia is one of the world’s most common types of bacteria. In fact, it’s already found in the cells of about 50% of all insect species, including bees, butterflies, fruit flies, flour beetles, and many species of mosquitoes. That’s how we can be confident that it’s harmless to both humans and the environment:  We already have ample evidence that Wolbachia is a common (if unintended) ingredient of fruits and grains that we eat on a daily basis, and we are regularly bitten by insects that contain Wolbachia.

What makes Wolbachia a revolutionary public health tool is the fact that when Aedes aegypti mosquitoes carry it in their bodies, it effectively blocks the replication of the viruses that cause dengue and a number of other deadly and debilitating diseases, instantly transforming one of the world’s most dangerous animals into an ally for global health.

Wolbachia also establishes itself rapidly across local Aedes populations through a process known as cytoplasmic incompatibility. When male mosquitoes that carry Wolbachia mate with females that lack the bacteria, their offspring aren’t viable. But when female mosquitoes with Wolbachia mate with male mosquitoes that lack the bacteria, their offspring survive and thrive, quickly becoming the dominant population.

This process creates a naturally self-sustaining barrier against virus transmission wherever Wolbachia-carrying mosquitoes are released.


From Evidence to Action

How do we know that Wolbachia works? The World Mosquito Program (WMP) – in partnership with local Indonesian scientists, governments, and charities – conducted a gold-standard randomized controlled trial of our Wolbachia method across the city of Yogyakarta and demonstrated a 77% reduction in dengue incidence and an 86% reduction in dengue-related hospitalizations in treated vs. untreated areas.

We have also deployed Wolbachia in 10 other countries around the world, achieving substantial reductions in disease incidence with each release. Most recently, our release program in Colombia demonstrated 94 percent or more reductions in dengue across a geographic area of 135 km2 and a resident population of 3.3 million in the cities of Bello, Medellín and Itagüí.

The power of these results has prompted WHO’s Vector Control Advisory Group to ask WHO to develop policy recommendations to help the world’s dengue-affected countries implement our Wolbachia method. And once WHO issues its guidance, countries facing record-breaking dengue outbreaks will be able to work with development finance institutions like the World Bank, the private sector, and global philanthropies to develop affordable financing for a whole new kind of mosquito control that pays for itself. It does so by saving individuals, families, and health systems the heavy costs associated with managing mosquito-borne diseases, all transmitted by the same mosquito and all susceptible to the transmission blocking effect of Wolbachia.

The results that are being seen with the Wolbachia method pioneered by WMP provide hope for a natural and cost-effective solution to help humanity adapt to the health effects of climate change. The time to turn the tide on dengue and other climate-sensitive diseases has arrived.

Scott O'Neill

Scott L. O’Neill (Ph.D., FAA, FAAAS) is a research scientist, founder & CEO of the World Mosquito Program. He is a Fellow of the Australian Academy of Science, the American Association for the Advancement of Science and the American Academy of Microbiology.