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Trial to see if ‘good’ mosquitoes can edge out bad

SYDNEY >> Early next week, Michelle Littman plans to take a small cardboard noodle box, with some twine for a handle, into an overgrown part of her tropical suburban garden and do something rather counterintuitive — breed mosquitoes.

By doing so, she and 6,000 other residents of Townsville, a small coastal city in Queensland, are hoping to open a new front in the international battle against mosquito-borne diseases like the Zika virus and dengue fever.

They are taking part in a global experiment to test whether the spread of those diseases can be slowed or stopped by introducing mosquitoes that cannot transmit them, in the hope that they will breed with, crowd out and soon extinguish the mosquitoes that can.

The idea defies conventional wisdom. “All my life, I’ve been told to dry out puddles of water to stop mosquitoes’ breeding,” Littman, 52, said in a telephone interview. “Now, I’m breeding them from eggs in a box hanging from a heliconia tree in my own backyard.”

Even so, people in Townsville and Cairns, 215 miles to the north, are eagerly participating in the experiment, which is being run by Monash University.

The plan depends on microbes called Wolbachia bacteria. If they are present in a mosquito, it cannot become a carrier of a wide range of dangerous pathogens, including dengue, yellow fever, chikungunya and Zika. And when it breeds, it passes the Wolbachia bacteria to its offspring, and they also cannot carry those diseases.

The university’s dean of science, Scott O’Neill, and his team have injected hundreds of thousands of Aedes aegypti mosquito eggs with Wolbachia bacteria, and participants in the trial like Littman and her neighbors are hatching and releasing them.

So far, the trials have advanced the most in Townsville and Cairns, but they have also begun in Colombia, Vietnam and Indonesia, and in Brazil, where an explosive outbreak of the Zika virus may be linked to an apparent rise in the number of infants born with abnormally small heads. On Monday, the World Health Organization declared the outbreak an international public health emergency.

“The science has been slow and technically very challenging,” O’Neill said in a telephone interview Wednesday from Yogyakarta, Indonesia, where he is conducting field trials. “But we are now achieving scale, and our results look promising.”

O’Neill’s research has been sponsored since 2004, with about $60 million in grants from private and government sources, including the Bill and Melinda Gates Foundation, the Wellcome Trust, based in London, and the Tahija Foundation of Indonesia.

Wolbachia bacteria exist naturally in some mosquito species, O’Neill said, and a walk around a tropical garden might turn up a host of other insects, including dragonflies, butterflies and fruit flies, that also carry the microbe. But it is not found naturally in Aedes aegypti mosquitoes, the type that transmits “almost 99 percent of the viruses that cause outbreaks of Zika, yellow fever, dengue and chikungunya” in humans, O’Neill said.

“Our idea wasn’t to go out and put poisons into the environment, things that harm people or kill animals,” he said. “The mosquitoes stay in the food chain. We wanted a small change. And this seems to be it.”

There have been no recorded cases yet in Australia of Zika virus transmitted by mosquito, although the health authorities have confirmed cases of Zika in two Australians who returned from the Caribbean. But there is dengue fever in central Queensland and the tropical northern part of the state, where O’Neill’s large-scale trials are being conducted.

“A lot of this work has focused on dengue,” said Cameron Webb, a medical entomologist at Sydney University. “But if you are controlling dengue, you are controlling Zika.”

The first trials were carried out in the suburbs of Cairns in 2011 and appeared to work well. “There haven’t been any reported cases of locally transmitted dengue in those areas in five years,” said Kate Retzki, a community liaison worker with the Eliminate Dengue program at Monash University.

There are plans to expand the program’s early trials in Brazil, where “Zika has become the focus,” O’Neill said. “But we have to go slowly, because the science is a long, hard slog.”

Littman’s noodle box contains a small piece of red felt. It is embedded with about 100 mosquito eggs that have been injected with the Wolbachia bacteria, as well as some fish food for the hatched larvae. It will soon hold enough water to help those eggs hatch. A few small holes at the top of the box will let the grown mosquitoes fly out, but not allow predators to come in.

“I won’t be putting the box near an open window, because the mozzies will still bite,” Littman said. “But at least I’ll know they are the good mozzies, not the bad ones.”

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