In an unassuming red-brick building on the southside of Colombia's second-largest city, Medellín, millions of mosquitoes are bred each week to combat dengue fever. One's natural instinct is to recoil at the metallic smell of blood wafting out of a humid room where netted cages hold thousands of mosquitoes. But these blood-sucking insects are part of a daring strategy to rid cities like Medellín of dengue fever, one suburb at a time.
From the backs of motorbikes and out car windows, adult mosquitoes are spread across the city and neighbouring urban areas of the Aburrá Valley that is home to three million people. These Aedes aegypti mosquitoes have been bred to carry Wolbachia, a species of bacteria naturally found in up to 60% of insect species, but not usually A. aegypti. When it is, Wolbachia stops A. aegypti from transmitting viruses to humans.
Only a few years ago, dengue fever was rampant in Medellín. But since the non-profit World Mosquito Program (WMP) started releasing its modified mosquitoes in 2017, dengue case numbers have plummeted to their lowest levels in 20 years. It's the largest continuous release of Wolbachiainfected mosquitoes anywhere in the world, and dengue incidence is down by 94%.
According to Cameron Simmons, an infectious disease scientist at Monash University and WMP's director of global implementation, the” to reach more cities. Now, the program's planned expansion is moving into its most ambitious phase yet.
