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The climate-fueled march of dengue fever

 KUALA LUMPUR, Malaysia – Watching them feast was pretty unnerving. Their whiney buzz cut through the silence, a swarm of mosquitoes hovering and then settling in a dish containing a cocktail of human blood and the often deadly dengue fever virus.


VIDEO:  As temperatures rise, mosquito-borne disease spreads

Thankfully, this banquet was contained in a cage of fine netting inside a laboratory at Kuala Lumpur's Institute of Medical Research. The mosquitoes would later be separated, and kept at different temperatures. The results so far show that a rise of four degrees Fahrenheit (from 82 degrees to 86 degrees) can almost double the speed at which the virus develops in the mosquito.

"The incubation period of the virus become shorter, so they become very infective much faster than before," said Dr Lokman Hakim, the head of disease control at Malaysia's health department.

Other new research suggests that rising temperatures shorten the lifespan of mosquitoes, making them hungrier – they bite more, in other words.

Dengue is just one vector-borne disease, but it is the fastest growing. Worldwide, the World Health Organization estimates that there are 50 million dengue infections a year.  More than 25,000 people are killed by more severe forms of a related disease called "break-bone fever" because of the severe joint pain it can produce, as well as headaches and fever.

It used to be contained largely to south-east Asia, but has been spreading, and is now found in South America, Africa, south Asia and parts of Australia. It recently turned up in Nepal, and last month returned to Florida for the first time in 50 years. Increasingly scientists are blaming climate change, supported by Malaysia's ground-breaking research.

"Dengue will be a global problem in terms of health," said Dr. Samlee Plianbangchang, the World Health Organization's South-East Asia Director. "Because as climate changes and temperatures rise, mosquitoes breed better."

Front line of research
We chose to visit Malaysia for our report for Nightly News because they are having a bad dengue year – more than 30,000 cases and 60 deaths in the first nine months of 2009, but also because they are on the front line of dengue and mosquito research.

Dengue used to be a disease of the rainy season, but the rains have become far less predictable, so it's now a year-round problem. It also used to be a disease that largely affected children. No more.

"We are seeing more and more adults being admitted with dengue, and with more severe forms of dengue as well," Dr. Adeeba Kamarulzaman told me as we toured the University of Malaya Medical Center, where Kuala Lumpur's most severe cases are treated.

There's no vaccine, and because there are four sub-types of dengue, which come in cycles, getting ill from one type does not give you immunity from the others. Quite the opposite, said Adeeba, it can leave you open to more severe attacks.

The mosquito that carries dengue is called the Aedes Aegypti, and experts say this stripy-legged creature is one of the most adaptable on the planet. It breeds just about anywhere there is stagnant water, needing no more than just a few drops of it, and scientists say its flying further and higher. And unlike the mosquitoes that carry malaria, Aedes is a day biter.

VIDEO: Malaysia mounts fight against dengue fever                     


'It's a war'

To those trying to stamp our dengue in Kuala Lumpur, it can be very personal. "It's a war. It's really a war," was how Khairudin Bin Noordan, put it as we followed him and his team of mosquito eradicators one humid evening, pumping clouds of think chemical fog around one neighborhood that had recently reported an outbreak.

By day they scour the kampongs (villages within the city), pouncing on plant pots, discarded tires or cups that contain water. They target building sites, armed with guppies, the little fish that feast on mosquito larvae.

But scientists say they are losing the battle.

"The virus is evolving, mosquitoes are adapting to the environment. But we are not adapting fast enough to these changes," said Dr. Sazaly AbuBakar, who heads the Department of Medical Microbiology at the University of Malaya. He's got a grudging respect for the enemy. "Unless we do something smart, we will end up at the losing end of this battle."

He's trying to develop a "predictive vaccine." To that end he's collected 30-years of dengue viruses, and is lab sequencing their DNA to get a better idea of the development of the virus. He's also working on a "mosquito map" of Malaysia to better understand the way they are evolving.

He sees little chance of eradicating mosquitoes, and says a smarter approach is needed.

"We need to know, are they all equally good at transmitting virus? Knowing the enemy will give us an upper hand."

The Aedes mosquito may be aided and abetted by a wetter, warmer climate, but the spread of dengue is also the result of man's behavior – urbanization, building, a throw-away culture. "We need an approach that brings all these things together," said Adeeba, "right down to the design of houses."

Recently Australian scientists came up with an intriguing variation of climate change to account for the growth of dengue in parts of Queensland, which has been suffering drought. The lack of rain has prompted a frenzy of rainwater harvesting, which has in turn provided the perfect breeding grounds for the Aedes mosquito!

Scientists do now believe that climate change will affect patterns of disease. Dengue is their exhibit number one, but as Malaysia's scientists are showing, the global rampage of the Aedes mosquito may not be inevitable if we can also change and adapt to the new environment, and find a smarter way of taking on one of mankind's most enduring enemies.

Read and watch more reports on climate change from Nightly News' 'Perfect Storm' series. The series continues this week on the broadcast