Vector-borne diseases are a major threat to human health. Diseases caused by viruses and parasites carried by mosquitoes kill millions of people every year. How can we control these diseases? One of the methods scientists have tried to develop recently is biocontrol – the use of natural enemies to control mosquito populations and thus the diseases they carry. We wanted to try a slightly different approach: using bacteria that reduce the mosquitoes’ ability to transmit viruses. We introduced these bacteria in local Australian mosquitoes and then released them back into a town where a lot of dengue outbreaks have occurred to breed with wild mosquitoes. Soon enough the majority of the mosquitoes in the area carried the bacteria. This has led to a drastic reduction of human dengue cases.