Dengue virus has effectively been wiped out in Townsville, Australia, following the release of anti-dengue mosquitoes in 2014.
The Queensland city has recorded zero cases of locally-transmitted dengue in the four years since the modified mosquitoes were released, compared to 54 cases in the previous four years.
The trial represents the first successful use of modified mosquitoes to eliminate a mosquito-borne virus across a whole city.
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at Monash University and his colleagues infected Aedes aegypti mosquitoes with naturally-occurring Wolbachia bacteria, which hamper the mosquitoes from transmitting the dengue virus. They released 4 million of the infected mosquitoes across Townsville over a two-year period.
Once the infected mosquitoes were released, they bred with wild mosquitoes and passed on the Wolbachia bacteria, so that these became protected against dengue too, says O鈥橬eill.
Trials around the world
The global incidence of dengue infections has increased 30-fold in the last 50 years, and 390 million people now contract the virus each year, leading to 25,000 deaths.
The 奥辞濒产补肠丑颈补听bacteria do not pose a risk to humans, animals or the environment. A total of 11 countries, including Indonesia, Brazil and Vietnam, are now trialling Wolbachia-infected mosquitoes. These countries have higher rates of dengue than Australia, meaning modified mosquitoes may not work as well. However, O鈥橬eill says the preliminary results look positive.
Although the exact mechanisms are still being unravelled, research suggests that Wolbachia bacteria prevent dengue transmission in two ways: they make the mosquito immune system more resistant to the virus, and make it harder for the virus to extract nutrients from mosquito cells.
Lab studies suggest that Wolbachia bacteria also block mosquito transmission of Zika and chikungunya viruses, but field studies are needed to confirm this.
Bacteria versus GM
Several other technologies are also being investigated for tackling . For example, mosquitoes have been genetically-modified to produce male-only or short-lived offspring when they mate with wild mosquitoes, so that wild populations will crash.
These technologies have worked well in the lab and in small field studies, but public opposition has prevented them from being deployed more widely. 鈥淭here鈥檚 a lot mistrust about genetic modification in the community,鈥� says O鈥橬eill. In contrast, the bacterial approach has largely been embraced by the public, with schools and community members helping to release the modified mosquitoes in Townsville.
Another drawback of genetically-modified mosquitoes is that they aim to eradicate wild populations, which could disrupt the overall ecosystem, says O鈥橬eill. Wolbachia bacteria, on the other hand, only stop viral spread, rather than killing mosquitoes themselves.
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