Dengue fever: How a mosquito infected millions, and not with malaria

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Dengue fever is now endemic in more than 100 countries

Globally, there are more than 50 million infections each year

CNN  — 

A bite from a single mosquito can result in fever, headaches, and pain. Severe cases can experience a multitude of symptoms including bleeding, shock, organ failure – and potentially death.

There is no treatment or vaccine and no real means of protecting yourself in countries endemic for the disease.

Though affected countries were once few, today more than 100 harbor the risk of infection – putting more than half the world’s population at risk and resulting in 50 million infections each year.

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The infection is Dengue – formerly known as “break-bone fever” because of the severe joint points it causes – and it’s spread by one of nature’s toughest, most versatile mosquitoes – and it’s not the one that spreads malaria.

Coexisting with humans

“It lives, eats and breathes humans” says Duane Gubler, professor of Infectious Diseases at Duke University Medical School, Singapore. Gubler has been working on Dengue control for more than 45 years and founded the Dengue Branch of the U.S. Centers for Disease Control (CDC). He has witnessed the epidemic expanding globally – through the opportunistic mosquitoes harboring the disease.

“Urbanization provided the ideal ecology for these mosquitoes,” says Gubler, referring to the increased density of populations as people flock to cities in search of employment, bringing with them endless supplies of blood for pregnant mosquitoes that need to nourish their eggs.

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The villain carrying the Dengue virus is the Aedes mosquito and it comes in two forms: Aedes Aegyti and Aedes albopictus, with the former causing the greatest degree of infection. “They’ve become highly urbanized and highly adapted to humans,” says Gubler.

This species can also carry the virus behind other diseases such as Yellow fever, chikungunya and lymphatic filariasis. But Dengue is the disease that has spread most widely. Their success lies in their ability to bite during the day – unlike the mosquitoes harboring malaria – meaning they’re difficult to avoid.

“Using bed nets isn’t particularly useful for Dengue,” says Harold Margolis, current chief of the CDC’s Dengue branch. Bed nets have proven critical in the fight against malaria as the Anopheles species of the mosquito, which carries the malaria parasite, bites primarily at night.

Whilst people can cover up or resort to repellant, Margolis advises people in affected regions to simply tidy up. Any form of container in which shallow water can accumulate provides the perfect breeding ground for a female mosquito in search of a place to lay her eggs. “They can breed anywhere,” says Margolis – including the surface of trash cans, containers and used tires. “Anything that collects water will allow mosquitoes to reproduce in that water,” he says.

Easy breeders

Surface water, human blood and warm temperatures provide the perfect environment for these mosquitoes to flourish.

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With no drug or vaccine yet available, the main form of disease prevention to date has been mosquito control – through the large-scale spraying of insecticides. The chemicals have been deployed in both residential and public spaces in a mass culling of the insects spreading the disease, taking other diseases carried by these mosquitoes with them. But the sprays haven’t been able to beat their versatile opponents – especially with humans further aiding the spread of infection.

“It’s people who move the infection around,” says Margolis.

Up to 75% of those infected never develop symptoms of Dengue, making it easy for the virus to be transported as people move around. When someone carrying the virus in their blood enters an area native for Aedes mosquitoes, they bring with them the potential to spread the disease. “Travelers come back with it and you get small outbreaks,” says Margolis.

In October 2012, an outbreak of Dengue occurred in Madeira, Portugal, resulting in 18 confirmed and more than 190 potential infections in a country where the disease is not normally found.