The biological control involves releasing populations of mosquitoes that have been infected with a commonly occurring species of bacteria, called Wolbachia. The Aedes Aegypti mosquito, responsible for the spread of the Zika virus, during testing at the Roosevelt Hospital in Guatemala City. Credit:Bloomberg The bacteria effectively inoculate the mosquitoes against the dengue virus. The treated populations then out-compete their dengue-carrying rivals, greatly reducing their numbers. Small-scale trials of the strategy started in 2011, and have so far been carried out in Queensland, Vietnam, Indonesia and Brazil. The largest trial so far kicked off in 2014, with the release of Wolbachia-infected mosquitoes throughout Townsville. The viruses that cause dengue and Zika are very closely related. Both are members of the Flavivirus family, which also includes the yellow fever and West Nile viruses. Both are transmitted by the same species of mosquito, known as Aedes aegypti.

"We have done the experimental work and it's currently winding its way through pre-publication," said O'Neill. "It shows that Wolbachia blocks Zika in an almost identical way, so where we've put it out to block dengue the mosquito populations are also resistant to Zika." He declined to specify exactly which countries in South America had approached Eliminate Dengue for help, saying that the negotiations were still at a preliminary stage. "The talks are going fairly quickly," he said, "But it is important to be realistic and to realise that being able to implement something this widespread in a very short timeframe is a very difficult thing to do." So far there have been two confirmed cases of Zika in Australia, both in travellers returning to Sydney from the Caribbean. Professor O'Neill said he expected more cases would occur, but did not anticipate a great number in the highest risk areas of Queensland where the Aedes mosquito is common.

Loading "I'm sure it will appear, but I think the likelihood of a large outbreak is very small," he said. "We have some confidence that the risk in Australia has been lowered because of the Wolbachia mosquito populations already released around Cairns and Townsville."