ththere is potenential for aes egtiti, the me v vectocouldd tranit yelelw fever c cities whwhich will be e very complic. ralth clinics are already atsef yellow fbrbreakingointnt.a there is a yellow fever vaccin but ly 6 60% obrazililia are vaccinated.. reporterer: overcrowdiding is a serious problem in the favelas of rio. defective water tanks and overflowing rubbish dumps are idideal breedingng grounds foror mosquitotoes. nters in brazil are cool and drdry. the mosqsquitoes take e longeo grow. en so, it doesn't take gabrielsm larvaeae. gabriel:l: we should b be war. eife havevehanges iclclimatielsm we c c have dengue, zi, ikungunya, more spread, like hahave pea all o over the yea. so it is eveven worse thanan to. reporter: local shopndnd house owowners do theieir bit for thte project. the mosquito traps scacattered about the city are emptied reregularly and d their contents later exexamined in ththe lab. the scientists have established th in n thareas whwherthe ininfected mosququitoes have n leleased io ththe environmenen, wolbhia bacteria end up present in the bulk of the mosquito p