Tue, Nov 12, 2013 - Page 9 News List

Researchers seeking to engineer dengue-immune mosquito

By Margie Mason  /  AP, TRI NGUYEN ISLAND, Vietnam

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 glow 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 cannot get it, they cannot spread it to people.

New research suggests that about 390 million people are infected with the virus each year, most of them in Asia. That is about one in every 18 people on Earth and more than three times higher than the WHO’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 is all caused by one bite from a female mosquito that is 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. Yet 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 was not 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,” said O’Neill, dean of science at Monash University in Melbourne. “And if it can’t grow in the mosquito, it can’t be transmitted.”

However, 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 is not 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.

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