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Science

Dengue: a closer look at a spreading fever

Three countries have now authorized a vaccine for dengue fever, a potentially fatal mosquito-borne disease that is spreading well beyond its tropical breeding grounds. How dangerous is the disease? DW takes a look.

With Mexico, the Philippines and now Brazil giving the green light to Dengvaxia, the first antidote to dengue fever ever released globally, the bandwagon has begun to roll. Regulators in all three countries authorized use of the vaccine this month, providing a nice Christmas present for French pharmaceuticals giant Sanofi, which said Dengvaxia could bring in revenues in excess of $1 billion (920,000 euros).

But business aside, the vaccine could potentially help a lot of people avert a quickly spreading viral threat.

According to the World Health Organization (WHO), over half the globe is now potentially at risk of contracting dengue fever, representing an exponential spike over the past half century when the disease was endemic in only a handful of tropical nations.

Infografik Denguefieber Verbreitung Weltweit Englisch

Each year, the virus spreads further from its original breeding grounds

Why is the disease spreading?

The only way to get dengue fever is by mosquito, and only species of the yellow fever mosquito (aedes aegypti) are capable of transmission. This mosquito is now found in many of the world's temperate zones, as far adrift from the tropics as China and the United States.

Epidemiological experts at the WHO attribute the general spread of the disease to increased global mobility, pinning down "globalization, urbanization, a warmer climate and jet travel" as the principal factors.

Also, the extreme resilience of the yellow fever mosquito has contributed to the prosperity of dengue fever. According to the US Centers for Disease Control and Prevention, populations of this type of mosquito can go months without water and their eggs are able to prevent desiccation or the process of drying up for over a year.

Once it has contracted dengue, the mosquito can infect humans for the rest of its life. The average life span of a yellow fever mosquito is between two and four weeks.

Moskito Tigermücke Überträger Denguefieber

The aedes aegypti has a knack for staying alive, regardless of its surroundings

What are the symptoms?

Contraction of dengue fever in humans results in flu-like symptoms (nausea, headache and joint pain) that can be accompanied a burning sensation in the eyes. In some cases, a rash showing large white spots can occur.

How deadly is the disease?

There are four different confirmed serotypes, with only one of those, the dengue hemorrhagic fever, being potentially fatal. The WHO says close to 400 million contractions are recorded each year, with around one fourth requiring medical attention. Of all the cases recorded in 2014, some 22,000 resulted in death, the organization said.

If the fever is contracted, can it be treated?

No. There is no antidote for dengue fever, and the symptoms cab take up to 10 days to subside. For the hemorrhagic strain, an intravenous infusion - and possibly blood transfusion - is required.

Indien Krankenhaus Fieber nach Flut

An outbreaks of dengue fever in India this autumn crippled the country's hospitals

Does the new vaccine work?

According to Sanofi, all four strains of the disease were prevented by the vaccine in 65 percent of all 40,000 participants, aged 9-45, in clinical trials over the past decade. For the fatal strain, the rate of successful vaccination was 93 percent.

However, the process requires three rounds of injections, and a hefty price tag. All in all, the vaccination will cost each person $448.

Until now, the only way to prevent dengue fever has been to avoid mosquito bites in risk areas. With those risk areas growing dramatically, Sanofi has said it wants to waste no time in supplying more of the world with the vaccine. Authorization requests for Europe are planned for next year, and the WHO said earlier this month that it would meet in April to discuss how to proceed with the vaccine.

At this point, the UN organization said there were no grounds to issue an official recommendation for its usage.