Scientists are creating genetically modified mosquitoes infected with the Wolbachia bacterium. They plan to release millions of these mosquitoes in Colombia and Brazil to reduce transmission of viruses like Zika, dengue, and chikungunya. The Wolbachia bacterium improves the mosquito's immune system and competes with viruses, reducing their ability to replicate and spread to humans via mosquito bites. Previous small-scale trials in several countries reduced dengue virus spread. The scientists hope the large-scale "mosquito army" releases next year in urban areas of Brazil and Colombia will further decrease transmission of these mosquito-borne viruses.