Mosquito fighters in slap-down test

A new battle in the world’s mosquito wars is being fought around Innisfail in far north Queensland, where an international research team released three million male Aedes aegypti mosquitoes. This species can transmit a range of potentially lethal diseases including dengue, yellow fever and Zika, which can cause birth defects.

These mosquitoes were infected with the commonly occurring Wolbachiabacteria, which ensured their eggs would fail to hatch and, eventually, that the mosquito populations would crash.

Conducted by scientists from CSIRO, James Cook University and the profitmaking Google affiliate Verily, the trial’s interim results suggest the releases reduced mosquito numbers by at least 80 per cent.

Yet mosquitoes breed quickly and independent experts believe the Innisfail populations were likely to bounce back in a season or two unless the supply of Wolbachia-infected mosquitoes was replenished regularly — at a financial cost.

This trial has been compared with the longstanding World Mosquito Program (formerly known as Eliminate Dengue), which has been using Wolbachia for many years to prevent the Aedes aegypti mosquito from transmitting disease.

Unlike the CSIRO-Verily project, the WMP Wolbachia-infected mos­quitoes are self-sustain­ing: sub­sequent genera­tions of Wol­bachia-infected Aedes aegypti mosquitoes also are unable to transmit the diseases.

The WMP is a not-for-profit organisation dedicated to reducing mosquito-borne disease in some of the world’s poorer communities in Indonesia, Brazil, and Vietnam, among other countries.

Senior CSIRO research scientist Paul de Barro said the idea behind the CSIRO-Verily project was “to suppress a population over a very wide area, potentially even eradicating it, so it takes a long, long time for the mosquito numbers to return to normal again, if they ever do”.

The Innisfail releases were completed last month, and the researchers plan to determine how much the mosquito populations recover in the coming months.

CSIRO declined to say how much the trial cost Verily, saying it was commercial in confidence. Dr de Barro said that while Verily was a for-profit company and owned the intellectual property rights to the technology, CSIRO was not involved in the trial for commercial reasons. “We wanted to learn whether we could use that technology to eradicate (species of) mosquitoes if they did get into Australia,” he said.

The Aedes aegypti mosquito was common in Queensland up until the 1950s but now can be found almost exclusively in far north Queensland, where it has been responsible for locally transmitted cases of dengue, or breakbone fever, in recent years.

“The particular concern we have is with Asian tiger mosquito,” Dr de Barro said, referring to the Aedes albopictus species which has yet to invade Australia.

“Even if you have a population that’s unable to transmit a virus, it’s a very aggressive day-biting mosquito. So from an amenity perspective, you don’t want that mosquito there because it will prevent people from utilising areas for recreational activities.”

Dr de Barro said if Aedes albopictus or Aedes aegypti mosquitoes somehow became estab­lished in Brisbane, perhaps as a result of global warming, the CSIRO-Verily Wolbachia method could be used to try to eliminate the populations entirely.

Scott O’Neill, a Monash academic and program director of the WMP, said the CSIRO-Verily Wolbachia project was a twist on the established Wolbachia method used by the WMP.

“If you only release males, that can be a way to drive the population down, as they’ve demonstrated,” Professor O’Neill said.

“But there are a couple of big issues. One is that they’ve released an awful lot of mosquitoes into a very small place called Innisfail, and they’re saying 80 to 90 per cent suppression (not 100 per cent), so you expect there would be a rebound in the next wet season.”

He said the suppression method was probably suitable only for countries that could afford the ongoing costs of the regular resupply of Wolbachia-infected male mosquitoes.

“Our approach is more for working in resource-restricted locations, where there’s a much greater need for a sustainable public health solution that doesn’t require ongoing expenditure. We work as a not-for-profit, not a for-profit,” he said.

Funded by donors such as the Bill and Melinda Gates Foundation and the Wellcome Trust, the WMP has been long established in Queensland. “Ten years prior to our deployment there was locally transmitted dengue in north Queensland every year,” Professor O’Neill said.

Now, he said, four wet seasons had gone by in those places where the Wolbachia-infected mosquitoes were released, and there had not been a single case of locally transmitted dengue.