Tropical diseases

When Cambodian development consultant Samnang Chum woke up in the middle of the night with fever and terrible chills, he quickly realized that he had more than just the flu.

"The symptoms were strange," he said on the phone from the Cambodian capital, Phnom Penh. "I've had strong temperatures before but not like this. I was trembling and shaking and almost losing control of myself."

Chum caught a taxi to hospital where laboratory tests confirmed he had dengue fever, a mosquito-borne disease that is on the march around the world.

Debilitating

Once known as backbreak fever because of its debilitating joint and muscle pain, dengue fever infects up to 50 million people a year according to the World Health Organization which has put it on its list of neglected tropical diseases.

Long found in tropical regions from the Americas to Africa and the eastern Mediterranean, it is Asia that currently bears the brunt of dengue fever infections. Of the estimated 2.5 billion people globally at risk of contracting dengue fever, about 1.8 billion of them, or 70 percent live in Asia. Dengue hotspots include Laos, Malaysia, Vietnam, the Philippines and Indonesia.

Last year saw the highest number of reported cases on the continent since a dengue epidemic swept the Western Pacific region in 1998.

Potentially deadly

While Chum was fine after a week's convalescence, a small percentage of sufferers go onto develop a potentially lethal form of the disease. Symptoms can include internal bleeding, circulatory failure and shock.

There is no vaccine or specific cure for the disease; however appropriate medial treatment can greatly reduce the death rate. Affected patients may need intravenous fluids or even a blood transfusion to stop their system shutting down completely. Because of this risk, dengue patients need careful monitoring.

"This condition can arrive relatively quickly," said Dr Thomas Jänisch, a tropical medicine specialist at Heidelberg University Hospital in Germany. "Catching this early enough is the most important point of monitoring."

Difficult to identify

One of the problems facing health professionals, though, is identifying dengue patients in the first place.

In its early stages, dengue can appear remarkably similar to other diseases, such as the common flu. Moreover, many of the lab tests to diagnose dengue in the early stage are either not available or not reliable.

To make matters worse, as the virus spreads explosively around the world, physicians can be faced with a disease they do not easily distinguish from other febrile illnesses.

Dr Jänisch is coordinating of a new six-million euro research project funded by the European Union that hopes to solve this problem. As part of the five-year project, doctors will collate the symptoms and blood tests of 10,000 to 12,000 patients in Vietnam, Malaysia, Indonesia, Cambodia, Brazil and El Salvador. Scientists at Heidelberg University Hospital will then evaluate the data.

It is the first large-scale study looking for early dengue indicators carried out at the same time in multiple countries.

"The idea is to determine early on which patients have probably dengue and which probably have another fever disease," said Jänisch. "Some of this is already common knowledge but this hasn't been validated with data in a big study. At the same time we want to determine which patients of those with dengue are likely to progress to a more severe form of disease."

As part of the project, researchers from Oxford University (one of the partner institutions) will also create a global dengue risk map. Scientists hope to emulate the Malaria Atlas Project which proved extremely successful in visually depicting areas of risk for malaria.

"This is also the model for dengue - to make the extent and the spread of the disease more visible so that resources can be used more strategically and efficiently to control (it)," said Jänisch.

Controlling dengue

Dengue control is a momentous task. The virus is transmitted by the Aedes aegypti and Aedes albopictus mosquitoes, which lay their larvae in stagnant water. This means the water containers, flower pots, discarded plastic bottles and used car tires that litter Asian towns and villages are perfect breeding grounds.

Experts say people have to be more diligent about monitoring the vessels around their homes for stagnant water, as one simple step in the global fight against dengue fever.

Author: Kate Hairsine
Editor: Anne Thomas