then we had zika coming, chikungunya. now yellow fever is ound, so yellow fev is not an urban disease since 1942, but it becomes one. there is potential for aedes ypti, the me vector uld ansmit ylow fevein citie whicwill be very complicated. reporter: one in five cases of yellow fever proves fatal. healthlinics arelready at bre. theris a yellofever vacce, but ly 60% of azilians a vaccinated. reporter: overcrowding is a serious problem in the favelas of rio. defective water tanks and overflowing rubbish dumps are ideal breeding grounds for mosquitoes. wthe mosquitoes take longer to. grow. even so, it doesn't take gabriel sylvese long to nd some larvae. gabriel: we should be warned about. ichikunnya, more read, like ha. we canave deng, zika, so it is even worse than to have just during the summer. repoer: local shop and hou owners do their bit for the project. the mosquito traps scattered abt the cityre emptied regulars later examined in the lab. tinfected mosquitoes have beend released io the envinment, wolbachia bacteria

then we hahad zika cining, chikungunya. nonow yellow fever is around, o llllow fev is s not urbanan disease sisince 194242, but it becomemes one. 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