Experts try to break dengue scourge with gene study

Experts hope to find a treatment for a disease which currently has no therapy or vaccine.

Experts try to break dengue scourge with gene study

Former policewoman Jaycee Choy had to be pushed around in a wheelchair and couldn't eat for a week when she fell ill with dengue fever in 2005, the year when Singapore was hit by its worst dengue epidemic.

"I should've been admitted to hospital but they were full with dengue patients and had no bed for me. I was so weak I couldn't stand," said Choy, now 38 and a private investigator.

"I'm hardly ever sick but I thought then I was going to die."

Many people who have suffered from dengue talk about their experience as the worst illness they ever had.

But curiously, they make up only a fraction of all the people who have been bitten by dengue-carrying mosquitoes and infected by the virus. Most do not fall ill or have such mild symptoms that their dengue infections go unnoticed.

Studies of immune system proteins called antibodies show many people appear to have been infected.

"In Singapore, 50 percent of its population have (dengue) antibodies, while 90 to 95 percent of Vietnam's population have antibodies. But only 1 to 2 percent of the population get really sick with the disease," said Martin Hibberd, associate director of infectious disease at the Genome Institute of Singapore.

"Clearly not everyone who gets infected gets the disease. But there is enough disease to get noticed," geneticist Hibber said.

Hibberd and his colleagues in Vietnam, Singapore, Malaysia, Thailand and Cambodia have embarked on a large study to find out why some people get sick and others don't. They hope that the answer can be used to make a drug.

They will find out if people who become ill with dengue are susceptible to the disease because of some DNA mutation and if other mutations of the same genes protect the others.

Genetic markets to show way to a cure?

The study of up to 7,000 people has started in Vietnam.

"We look at 600,000 genetic markers for each person and we will see which of the (gene) variants are associated with the disease," Hibberd said, adding that scientists will then see if the findings in Vietnam are replicated in the other countries.

Experts then hope to find a treatment for a disease which currently has no therapy or vaccine.

Finding a cure for dengue is vital as global cases have shot up because of urbanisation, warmer temperatures and the constant movement of people -- conditions that allow the Aedes aegypti mosquito, which carries this virus, to thrive.

The World Health Organisation estimates that 2.5 billion people live in more than 100 endemic countries and areas where dengue viruses can be transmitted.

Up to 50 million infections occur annually with 500,000 cases of dengue haemorrhagic fever (DHF) and 22,000 deaths, mainly among children. Before 1970, only 9 countries had experienced DHF but the number has risen more than 4-fold and continues to rise.

Dengue is expensive, costing an average of US$1,394 for every hospitalised patient. At least 10 working days are lost in each case, according to the WHO.

New complications

People are the reservoir of the dengue virus, while the Aedes mosquito is the transmitter. There are four types, or serotypes, of dengue, labelled dengue 1, 2, 3 and 4.

"It used to be that one of the four serotypes would be dominant and then everyone would become immune and there will be a lull before the next serotype shows up," said John Ehrenberg, a WHO regional adviser on vector borne diseases.

"But this situation is now changed with people moving around. All four serotypes have been circulating in the Pacific."

With all four types being common, people may be more likely to develop severe symptoms of the disease such as haemorrhagic fever and shock. People who get infected again and again tend to suffer more severe symptoms but experts do not understand why.


Last Mod: 27 Nisan 2010, 08:48
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