Dengue fever is the most common mosquito-borne disease in the world. According to the WHO, it is a leading cause of death among children in Asian countries, yet at the moment there is neither treatment nor vaccine for the disease. We don’t know how it spread around the world, nor how the virus attacks the human body. Dengue fever is caused by a virus, transported between victims by the mosquito Aedes aegypti.

Two-fifths of the world’s people live in dengue-affected areas but we don’t know how many people are infected. Often people have no symptoms, or the disease is confused with typhoid or influenza. Usually dengue is relatively mild, but a significant proportion of cases develop to become the more severe form of the disease, dengue haemorrhagic fever (DHF). A quarter of those who develop DHF die without proper treatment.

Another name for dengue is “break-bone disease”; a burning fever is accompanied by painful joints and bones. In DHF, blood leaks out from the blood vessels and sufferers can have severe internal bleeding. Treatment involves keeping patients on a saline drip to keep them hydrated and in areas with good medical facilities few people die of dengue fever. But dengue is endemic throughout the tropics, where medical facilities and expertise are often sketchy, and if DHF develops the outlook is much worse.

Because there is no treatment or vaccine, the only way to stop dengue spreading is to eradicate the mosquito that carries it. Aedes aegypti is notoriously hardy. Unlike malarial mosquitoes, which tend to bite only at dusk, it comes out during the day. No-one in their right mind would spend all day hiding under a mosquito net, so bites can only be prevented by wearing smelly insecticides, which most people can’t afford. It thrives in urban environments and will lay its eggs in any patch of water available – a half-empty coke can, an over-filled plant pot, even a lump of mud.

Singaporean success

Despite these difficulties, Singapore (http://www.dengue.gov.sg/)has waged a successful campaign against the mosquito. Residents are encouraged to regularly clear away stagnant water and use insecticides in vases. The Ministry of Health says dengue is  “under control in Singapore as the country has put in place rigorous control measures. Life continues as per normal here.” Since 2007, the number of reported cases of dengue in Singapore has halved. But public health campaigns on the scale of Singapore’s require vast resources not available to most countries.

The dengue virus is part of a family of diseases that originated in East Africa. The closely-related yellow fever spread west to South America and dengue spread east to Asia. In the past century dengue has spread throughout the tropics, though in Africa, malaria still holds sway.

Could a vaccine be around the corner?

Stopping the Aedes aegypti mosquito isn’t easy, so hopes of containing dengue rest on a vaccine. The collaborative efforts of the Dengue Vaccine Initiative, which shares research on vaccines, means there are now five in various stages of clinical trials. It’s a tricky vaccine to develop as we don’t know how the four strains of the dengue virus interact. Some researchers think that once you have been infected with one strain, being infected with a second strain leads to more severe disease. Other researchers dispute this, but we don’t really know. Finding people who have never been infected with dengue is difficult in areas where the disease is endemic, and so the theory is expensive to test.

But vaccine development continues, and there is hope. A vaccine for dengue’s brother yellow fever was developed in 1937; viruses of this type can be prevented.  If all goes to plan, a vaccine for dengue could be ready by 2015 and stop 50 million infections a year.