Dengue virus, which causes the infectious disease dengue fever, is estimated to infect more than 400 million people every year. It is usually transmitted through mosquitoes. Scientists working to eradicate the disease have discovered that dengue virus is not able to replicate in mosquitoes infected with a bacteria called Wolbachia. The researchers developed a plan to release infected mosquitoes into the wild so that Wolbachia can spread throughout the mosquito population. Part of the "I Contain Multitudes" series.