Nguyen Thi Yen rolls up the sleeves of her white lab coat and delicately slips her arms into a box covered by a sheath of mesh netting. Immediately, the feeding frenzy begins.
Hundreds of mosquitoes light on her thin forearms and swarm her manicured fingers. They spit, bite and suck until becoming drunk with blood, their bulging bellies glowing red. Yen laughs in delight while her so-called "pets" enjoy their lunch and prepare to mate.
The petite, grandmotherly entomologist — nicknamed Dr Dracula — knows how crazy she must look to outsiders. But this is science, and these are very special bloodsuckers.
She smiles and nods at her red-hot arms, swollen and itchy after 10 minutes of feeding. She knows those nasty bites could reveal a way to greatly reduce one of the world's most menacing infectious diseases.
All her mosquitoes have been intentionally infected with bacteria called Wolbachia, which essentially blocks them from getting dengue. And if they can't get it, they can't spread it to people.
New research suggests some 390 million people are infected with the 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 Organization'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 hemorrhagic 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 for reasons not fully understood, 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: Wolbachia-infected mosquitoes not only died quicker but they also blocked dengue partially or entirely, sort of like a natural vaccine.
"The dengue virus couldn't grow in the mosquito as well if the Wolbachia was present," says O'Neill, dean of science at Monash University in Melbourne. "And if it can't grow in the mosquito, it can't be transmitted."
But proving something in the lab is just the first step. O'Neill's team needed to test how well the mosquitoes would perform in the wild. They 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 who have long been searching for new ways to fight the disease. After two and a half years, the Wolbachia-infected mosquitoes had overtaken the native populations and remained 95 percent 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 many 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 the past 35 years. Their plan was to test the Wolbachia mosquitoes on a small island off the country's central coast this year, with another release expected next year in Indonesia.
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, where Yen normally works, 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 finally 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, which could kill the Wolbachia.
"When I'm sleeping, I'm always thinking about them," Yen says, hunkered over a petri dish filled with dozens of squiggling mosquito pupae. "I'm always worried about temperature and food. I take care of them same-same like baby. If they are healthy, we are happy. If they are not, we are sad."