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Unlike her secretive, malaria-carrying cousin, the female Aedes aegypti signals her approach with an irritating drone. Its bite is worse than its buzz. If he has the flavivirus pathogen, his victim can become infected with dengue fever. Most infections resolve without symptoms, but some unfortunate people contract “break bone fever,” which causes severe joint pain, bleeding, and, sometimes, death. Its after-effects, which are less understood, include fatigue and cognitive impairment. Aedes is so abundant, the United States Centers for Disease Control and Prevention estimates that 100 million people worldwide fall ill with dengue each year.
The number of people suffering from dengue has increased dramatically. According to the World Health Organization (WHO), about 20,000 people died from it in 2000. At least 40,000 will be destroyed this year. In contrast, between 2000 and 2022, malaria deaths are projected to decline by 30%, the WHO says.
The severe fever and its consequences represent the greatest burden of dengue. Cases have increased much faster than deaths. Latin America, the worst-affected region, had an average of 535,000 cases per year in 2000–05, according to the Pan American Health Organization, a branch of the United Nations. In 2023 it will be 4.6 m. There was a loss of. There will already be 5.9 million in 2024 (see chart). Aedes sickens Brazilians so badly that it can knock down national GDP by 0.2%. Schools in parts of the country affected by dengue have dropout rates that are about 5% higher than those that have been spared.
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The suffering is likely to increase and spread beyond the tropics. Aedes mosquitoes are sensitive to small changes in temperature and their range is expanding as the planet continues to warm. The malaria-causing species Anopheles is already established in much of the world. No Aedes. Modeling suggests that, on current climate change trends, Aedes will spread across large parts of southern Europe and the United States, putting another 2 billion people at risk of dengue.
Urbanization also helps the disease spread. As people congregate in cities, each mosquito can bite more victims during its short two-week lifespan. Cases are increasing rapidly in places including Bangladesh and India, where earlier this disease had not caused much damage. Dengue cases have also been increasing in California, southern Europe, and subtropical Africa in recent years.
The world should prepare for more fever. Although the prosperous Northern Hemisphere is increasingly at risk, it is the poorer parts of the world that will suffer most. Struggling economies cannot afford to lose their productivity due to this disease. Nor will it be easy for them to pay for measures that might stop 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 done a good job in fighting dengue. It helps that it is rich enough to pay for armies of public-health workers to roam its streets, search for standing water in which mosquitoes breed, pipe up, and issue fines. The city-state model causes outbreaks and then deploys platoons of pesticide sprayers in hazmat suits to predicted earthquake epicenters. Latin American countries also have formidable armies, but with modest budgets and wide areas to cover, they have done little to slow the explosive growth of dengue in the region. Slums are difficult places to locate mosquito breeding sites.
So it is wise to consider other methods. Since 2016, Singapore has been running another high-tech dengue program. Every week it releases 5 million mosquitoes infected with Wolbachia bacteria. It prevents them or their offspring from transmitting the virus that causes dengue and costs about $35m a year, or $6 per resident. Combined with new vaccines under development, this offers a way to fight dengue that doesn’t rely on spotters in standing water. Trials of Wolbachia infection in Colombia have shown a 94% drop in dengue incidence in areas where mosquitoes are released. The world’s largest Wolbachia-mosquito factory is scheduled to begin operations in the Brazilian city of Curitiba this year. As dengue spreads, other places should follow suit. The aim should be to change the discussion of Aedes to a nuisance rather than a threat.
© 2024, The Economist Newspaper Limited. All rights reserved.
From The Economist, published under license. Original content can be found at www.economist.com
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