Vietnam pits bacteria against deadly dengue
New research suggests some 390 million people are infected with the dengue virus each year, most of them in Asia. That's about one in every 18 people on Earth, and more than three times higher than the World Health Organisation's previous estimates.
Known as "breakbone fever" because of the excruciating joint pain and hammer-pounding headaches it causes, the disease has no vaccine, cure or specific treatment. Most patients must simply suffer through days of raging fever, sweats and a bubbling rash. For those who develop a more serious form of illness, known as dengue haemorrhagic fever, internal bleeding, shock, organ failure and death can occur.
And it's all caused by one bite from a female mosquito that's transmitting the virus from another infected person.
So how can simple bacteria break this cycle? Wolbachia is commonly found in many insects, including fruit flies. But it is not carried naturally by certain mosquitoes, including the most common one that transmits dengue, the Aedes aegypti.
The germ has fascinated scientist Scott O'Neill his entire career. He started working with it about two decades ago at Yale University. But it wasn't until 2008, after returning to his native Australia, that he had his eureka moment.
One of his research students figured out how to implant the bacteria into a mosquito so it could be passed on to future generations. The initial hope was that it would shorten the insect's life. But soon, a hidden benefit was discovered.
"The dengue virus couldn't grow in the mosquito as well if Wolbachia was present," says O'Neill, dean of science at Monash University, Melbourne.
O'Neill's team conducted research in small communities in Australia, where dengue isn't a problem, and the results were encouraging enough to create a buzz among scientists. After two and a half years, the Wolbachia-infected mosquitoes had overtaken the native populations and remained 95 per cent dominant. But how would it work in dengue-endemic areas of Southeast Asia? The disease swamps hospitals in the region every rainy season with thousands of sick patients, including children, sometimes killing those who seek help too late.
The Australians tapped 58-year-old Yen at Vietnam's National Institute of Hygiene and Epidemiology, where she's worked for 35 years. Their plan was to test the Wolbachia mosquitoes on a small island off the country's central coast this year. Just getting the mosquitoes to Tri Nguyen Island was an adventure. Thousands of tiny black eggs laid on strips of paper inside feeding boxes had to be hand-carried inside coolers on weekly flights from Hanoi to Nha Trang, a resort city near the island. The eggs had to be kept at just the right temperature and moisture. The mosquitoes were hatched in another lab before being transported by boat. Yen insisted on medical checks for all volunteer feeders to ensure they weren't sickening her mosquitoes. She deemed vegetarian blood too weak and banned anyone recently on antibiotics.
The 3,500 people on Tri Nguyen island grew accustomed to what would be a bizarre scene almost anywhere else: For five months, community workers went house-to-house in the raging heat, releasing cups of newborn mosquitoes. "We do not kill the mosquitoes. We let them bite," says fisherman Tran To. "The Wolbachia living in the house is like a doctor in the house. They may bite, but they stop dengue."
The strain of bacteria used on the island blocks dengue 100 per cent, but it's also the hardest to sustain. At one point, 90 per cent of the mosquitoes were infected, but the rate dropped to about 65 per cent after the last batch was released in September.
The job is sure to keep Yen busy in her little mosquito lab. And while she professes to adore these pests, she has a much stronger motivation: Dengue nearly claimed her own life many years ago, and her career has been devoted to sparing others the same fate.
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