On the heels of similar efforts in Asia, Brazil is releasing 10,000 mosquitoes infected with the Wolbachia bacteria in the hopes of halting the spread of dengue fever. Found in 60% of insects, Wolbachia acts like a vaccine against the virus, preventing it from multiplying in the carrier's body—all without being able to be transmitted to humans, reports the BBC. The hope is that this defense against dengue will spread as mosquitoes mate, something that happened in just 10 weeks in a trial run in Australia in 2008. More infected mosquitoes are scheduled to be released in Colombia and Vietnam. The "Eliminate Dengue" project, which dates back to 2005, now includes 60 researchers across 10 countries.
While Brazil was rid of dengue in the 1960s and '70s, it re-emerged in 1981, and more than 7 million cases have been reported over the past 30 years. The World Health Organization puts the number of new dengue infections worldwide at 50 million to 100 million a year, mostly in Asia—though with 3.2 million cases and 800 deaths reported between 2009 and 2014, Brazil has the unfortunate distinction of claiming more dengue cases than any other country in the world. Meanwhile, efforts that focus on reducing mosquito habitats and spraying insecticides are having only limited effect, reports the Wall Street Journal. New cases are also cropping up in the southern US, while scientists warn that climate change could see the virus spread to southern Europe as well. (Researchers have also been working on a vaccine to protect against dengue in humans.)