Unlike her stealthy, malaria-spreading cousin, the female Aedes aegypti announces her approach with an annoying drone. Her bite is much worse than her buzz. If she carries a flavivirus pathogen, her victim may be infected with dengue fever. Most infections are without symptoms, but an unfortunate number are afflicted with 'breakbone fever', which causes severe joint pain, bleeding and sometimes death. The aftereffects, which are poorly understood, include fatigue and cognitive impairment. Aedes is so abundant that dengue sickens 100 million people around the world every year, according to the U.S. Centers for Disease Control and Prevention.
The number of people contracting dengue has increased dramatically. According to the World Health Organization (WHO), approximately 20,000 people died from it in 2000. At least 40,000 people will die this year. In contrast, deaths from malaria have fallen by 30% between 2000 and 2022, the WHO says.
The terrible fever and its aftereffects are the biggest burden of dengue. The number of cases has risen much faster than the number of deaths. Latin America, the worst-affected region, averaged 535,000 cases per year from 2000 to 2005, according to the Pan American Health Organization, a branch of the UN. In 2023 it suffered 4.6 million. In 2024 there were already 5.9 million (see graph). Aedes is making Brazilians so sick that it could reduce national GDP by 0.2%. Schools in parts of the country affected by dengue are experiencing dropout rates that are about 5% higher than in schools that were spared.
Suffering is likely to increase further and spread beyond the tropics. Aedes mosquitoes are sensitive to small changes in temperature and their range has expanded as the planet warms. Anopheles, the species that spreads malaria, is already established in most of the world. Not Aedes. Modeling shows that, based on current climate change trends, Aedes will spread to large parts of southern Europe and the United States, putting an additional 2 billion people at risk of dengue.
Urbanization also contributes to the spread of the disease. As people gather in cities, each individual mosquito can bite more victims during its short two-week lifespan. Cases are rising rapidly in places that had not previously suffered much from the disease, including Bangladesh and India. In recent years, dengue cases have also increased in California, southern Europe and subtropical Africa.
The world must prepare for many more fevers. While the wealthy Northern Hemisphere is increasingly at risk, the poorer parts of the world will suffer most. Struggling economies cannot afford to have their productivity undermined by the disease. Nor will it be easy for them to pay for measures that could limit its spread. Mosquito nets, a cheap and effective way to curb malaria, do not work for dengue because Aedes, unlike Anopheles, bites people during the day.
Singapore has long been doing an excellent job in the fight against dengue. It helps that the country is wealthy enough to pay armies of public health workers to roam the streets, searching for the standing water where mosquitoes breed, pipetting puddles and handing out fines. The city-state models outbreaks and then sends platoons of insecticide sprayers in hazmat suits to the predicted epicenters. Latin American countries also have dangerous militaries, but with modest budgets and vast territories they have done little to slow the explosive growth of dengue in the region. Slums are difficult places to detect breeding grounds for mosquitoes.
So it is wise to consider other approaches. Since 2016, Singapore has been running another high-tech dengue program. Every week it releases 5 million mosquitoes infected with Wolbachia bacteria. This prevents them or their descendants from transmitting the virus that causes dengue, which costs about $35 million a year, or $6 per capita. Combined with new vaccines in development, it offers a way to combat dengue that doesn't rely on legions of standing water spotters. Wolbachia infection trials in Colombia have led to a 94% drop in dengue incidents in the area where the mosquitoes are released. The world's largest Wolbachia mosquito factory will start operating this year in the Brazilian city of Curitiba. As dengue spreads, other places should follow suit. The goal should be to make Aedes buzz a nuisance, rather than a threat.
© 2024, The Economist Newspaper Ltd. All rights reserved.
From The Economist, published under license. Original content can be found at www.economist.com