matt: we will be back in 60 seconds. don't go away. matt: welcome back. brazil is witnessing a surgeon fever. the health ministry says there have been 740,000 new cases from the start of the year to mid april. peter: spread by mosquitoes, there are no vaccines to prevent infection just yet but they are trying to slow the spread by genetically modified mosquitoes. here is more. reporter: there are 1000 insects in each container. they are releasing a quarter of a million mosquitoes into the wild. these insects were bred in a laboratory and the team hopes to use them to stop deadly favor from -- fever from spreading. >> we are not attacking the fever directly. we are going after the carriers of the disease. it will have a direct in spec on -- impact on the spread of dengue. reporter: 2 million anti-dengue mosquitoes are bred in this laboratory in sao paulo state. only male larvae they are allowed to develop -- larvae are allowed to develop. they don't bite but are deadly to other mosquitoes. >> when they are released, they will find the females in the wild.