this is "nightline." >> tonight, the zika outbreak. we're in the brazilian hot zone where families are dealing with the devastating effects of the disease. and here at home at least 50 cases now confirmed. tonight we're with the disease detectives searching for answers to stop the explosive spread of this mysterious virus. plus, feel the bern. how bernie sanders, the senator from vermont -- ♪ you want a revolution >> -- started a revolution. the race to the white house intensifying after his surprising strength in the iowa showdown with hillary. so is america ready for higher taxes and free college education? and lady gaga is gearing up for that super bowl applause. ♪ applause

>> the sensational singer joining a star-studded list of performers belting the national anthem before the big game, hoping to hit the high notes as whitney houston did 25 years ago. but first the "nightline 5." ♪ ♪ ♪ >> the bold nissan rogue with intuitive all-wheel drive. because winter needs a hero. nissan. innovation that excites. >> number one in just 60 seconds.

good evening. thanks for joining us. the mysterious disease causing international anxiety. we're in brazil, ground zero of the zika outbreak, with disease detectives trying to stop the contagion from spreading. the world health organization declaring a global health emergency. here in the u.s. with at least 50 cases now confirmed there is mounting concern. here's abc's chief medical editor dr. richard besser. >> reporter: 3-month-old anna beatrice, who's like any normal baby -- but anna was born with microcephaly, an extremely small head, due to abnormal brain development. a devastating neurological condition that doctors suspect is linked to zika virus infection during pregnancy. in brazil the barbosa family is one of thousands of families dealing with the virus. roughly 150 cases of microcephaly occurred in brazil

in 2014. last year, there were more than 4,000. anna's mother bruna tells us her zika infection happened when she was 12 months pregnant. the last in her family to get it but they were all sick. fever, headache, rash. nobody imagined it could affect her baby. >> when during your pregnancy did you know that there was a problem with anna beatrice? >> translator: never. >> reporter: anna's condition wasn't picked up until the sudden silence in the delivery room. doctors told her anna would only live for a day but she's defying the odds. >> she's looking at you. does she recognize you? >> translator: uh-huh. >> reporter: every case of microcephaly is different but many doctors and scientists say the big rise in cases has a common cause. a mosquito carrying the zika virus. 80% of those infected with zika don't feel sick, no symptoms at all. but for those who are pregnant, evidence is growing that it can be a disaster.

>> to control this outbreak the government is trying to reach 50 million houses across the country every month, sending in the military and public health teams, going door to door, looking for anywhere mosquitos could breed. for a country this size, that's a monumental task. there's no cure. no treatment for zika. so the brazilian government is trying to control the epidemic the only way it can -- >> every house in this area is visited at least once a month by the soldiers to look for any place a mosquito could breed. so if a soldier knocks on the door you have to open up. we follow one soldier on his inspections. he's even looking to see where the water drains out of the refrigerator, the condensation, to make sure there's no pooling water. that's all it would take for mosquitos to breed. he's putting a chemical, a larvicide on top which will kill those and hopefully will last and protect this water until the next time he comes. like everyone in brazil these days we apply mosquito repellent constantly. but the virus is on the move.

more than 50 cases so far reported in the u.s. all travel related. lizzy morales, a houston mother, contracted zika on a christmas visit to el salvador. >> you could see bumps in my lips. my eyes. my ears. you have no strength, no energy. like to do anything. not to even sit down. all you want to do is lay down and sleep. >> reporter: she wasn't pregnant. her symptoms subsided. since the virus is believed to leave your blood when you recover any future pregnancies should be fine. today florida governor rick scott declared a public health emergency in four counties where people have been diagnosed with zika. red cross is telling donors to hold off giving for 28 days if they've been somewhere that has zika transmission. yesterday the first confirmed case of zika transmission in the u.s. spread not by mosquito but through sexual contact with someone infected by the virus. dr. peter hotez, a tropical disease scientist, said blood transfusions and sexual contact should be the least of our concerns. >> the case of sexual

transmission is a bit of a red herring. our efforts need to be focused on preventing mosquito bites. >> reporter: hotez says he's very worried about zika spreading in areas like this one, the heart of houston city limits. >> lots of discarded tires that are thrown out by the side of the road. these discarded tires after a rain will fill with water and fill with leaves and other debris and this makes the perfect mix for mosquito larvae to breed and develop. and then they'll become adult mosquitos and then they're going to fly across to all the houses that have no window screens, no air conditioning. so all of these factors come together to create that kind of perfect storm. >> reporter: he says that just like the shanty towns in brazil, impoverished areas here are prime breeding grounds for mosquitos. >> in many respects this looks like the public health movie you show to first-year medical students, public health students.

but it's not in a developing country, it's right here in texas, here in the united states. >> reporter: back in brazil, we toured a place where some scientists are undertaking a radical experiment to reduce the kind of mosquitos that spread diseases like zika. goal is to create a line of mosquitos that die before they can bite people. >> we are in a mosquito factory. this building here, it produces 2 million male mosquitos genetically modified every single week. only female mosquitos bite people. these males were ol teared so their offspring will die before they can bite anyone. after they reach maturity they're sprayed out the window of a van. they mate with the females in the community and the offsing die, offspring day, reducing the spread of the disease. 25 million mosquitos have been released. the number of mosquitos that can spread disease has gone way down. they said they're all male and male mosquitos don't bite. i hope that's the case because there's 245,000 of them. the long-term impact of this

experiment isn't yet known. these mosquitos are not approved for use in the u.s. and critics worry that messing with genetics may not be safe. microcephaly isn't the only concern when it comes to zika virus. a debilitating form of paralysis has been on the rise in places with zika. the big question, though, is whether zika is the cause. to answer this, dr. ashley sachinsky, first-year detective with cdc, took us with her as she conducted an investigation in partnership with the brazilian health ministry. her team gathers data and blood samples. looking for a possible link between the zika virus and this rare and devastating condition. what's it like to do what you're doing? >> well, it's -- humbling. because of the significance of the public health problem. but it's also sort of exciting to be on the investigative side and figure it out in realtime. >> reporter: the summer olympics now just six months away, and so many questions remain. preparations have begun, including fumigating the main

stadium for mosquitos. late last week, rio's olympic committee said they were confident athletes in brazil will be completely safe. but american wrestler alisa lape, who is in rio training for the games, isn't so sure vinita nair she says she's being cautious. >> wearing bug spray, i guess. i haven't really been outside the hotel. i think that's really helping. yeah. it's kind of scary. >> reporter: the reality is we are just starting to learn about zika virus, about its effects, and how to fight it. >> we don't yet know either what proportion of the children born with microcephaly have it because of zika, and whether there are other conditions besides micro civcephaly that me associated with zika. >> reporter: as the dancers prepare for carnival, a worried brazil wonders, where do we go from here? for "nightline" i'm dr. richard besser, brazil. up next, the presidential candidate giving hillary clinton a run for her money.

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the vermont senator and the political heavyweight, hillary clinton. here's abc's david wright. ♪ you say you want a revolution ♪ >> reporter: at the stage door of the old colonial theater in keene, new hampshire, the fans are gathering. ♪ you can't buy bernie >> reporter: here as they would put it to feel the bern. >> feel the bern! >> reporter: bernie sanders' campaign is on fire right now. front-runner to win the new hampshire primary -- >> if you want a government that represents all of the people and not just a few, come on board the political revolution! >> reporter: and but for the flip of a coin or two -- he came awfully close to winning the iowa caucuses too. >> tails. >> it looks like we are in a virtual tie. >> reporter: the 74-year-old junior senator from vermont, the

only democratic socialist in congress, now giving hillary clinton a serious run for her money. his campaign raised $3 million in 24 hours after iowa. integrity and authenticity are words his supporters use. >> feels good to have somebody around that feels worth getting passionate about. >> there are a lot of conversations that he's presenting that we need to be having in this country. >> bernie talks about attacking the corrupt campaign finances, he talks about raising the minimum wage to a living wage, he talks about bringing back manufacturing, he talks about infrastructure. >> reporter: a political rise nobody but bernie saw coming. when i first met him a year ago, he was just considering whether to throw his hat into the ring. would you be in it to win it or in it to articulate positions? >> that i know the answer to. if i ran, i would run to win. i know if i do this, i start off as a significant underdog. 70% of the american people don't know who bernie sanders is. >> the word snowball's chance

comes to mind. no offense. >> reporter: he's out there raising fundamental questions about the american political system and the u.s. economy. a system he says is rigged in favor of billionaires and bankers. >> we the people are going to have to have a government that represents all of us, not just a handful of billionaires. >> reporter: he rails against the 1% and the politicians they keep in their pocket. his platform straight out of occupy wall street. college education free-for-all americans. health care free for all americans. he'd break up the big banks, raise the minimum wage, and fund all this by raising taxes on the rich and on corporations. >> are you tilting at wind mills? or do you think this is a minutable fight? >> i don't want to tilt at wind mills. there are so many people who are hurting, working longer hours for low wages, and the billionaires are getting richer. they need a voice. >> reporter: bernie sanders has given them a voice. and he's put his money where his

mouth is. there's no super pac aligned with his campaign. instead, he's funding it with record numbers of small donations. 3.25 million of them. average amount $27 apiece, according to his campaign. he's an unlikely messenger, easily parodied by "snl" -- >> the other candidates are taking millions from the coke brothers and exxonmobil. but not me. i only accept coins. i'm not talking about fancy coins like dimes and quarters. i just want nickels and pennies. >> reporter: his main campaign ad features a golden oldie. ♪ look for america >> reporter: simon and garfunkel with an upbeat message. his events you find plenty of folks from the woodstock yes or no race. >> i am feeling the bern! >> reporter: also legions of younger voters. >> feel the bern! >> reporter: among registered democrats aged 29 and younger,

nationally sanders outpolls clinton nearly 4-1. >> i just like his ideas for wall street and what he's going to do with our future education. >> it's already been incredibly impressive for him. >> reporter: digital journalist mary alice parks has been traveling with the sanders campaign for months. >> it has been huge since the beginning. the biggest crowds were over the summer in a west coast swing, 28,000 people in portland, almost 25,000 in l.a. very reminiscent of obama. big change, high hopes, high dreams. >> reporter: sanders has pledged to fight a clean campaign, even refusing to attack clinton's use of a private e-mail server. >> the american people are sick and tired of hearing about your damn e-mails. >> thank you. me too. me too. >> reporter: now he's drawing sharper distinctions. hitting her hardest on her ties to wall street and her dependance on campaign contributions. >> do you think hillary clinton is a progressive? >> some days, yes. except when she announces that

she is a proud moderate. then i guess she's not a progressive. >> it was kind of a low blow. >> reporter: today here in new hampshire, clinton fired back. >> it was a good day for progressives when i helped to get 8 million kids health care under the children's health insurance program. >> reporter: the lowest polls show clinton trailing sanders by more than 20 points here. clinton and others chalk that up to the fact he has the home court advantage as the senator from a neighboring state. tonight he reminded voters at a cnn town hall that hillary clinton voted for the iraq invasion. he didn't. >> the progressive community was pretty united in saying, don't listen to bush, don't go to war. secretary clinton voted to go to war. >> reporter: obviously you still haven't gotten the memo, this was supposed to be a coronation, right? >> no, we didn't get that memo. >> reporter: what's not yet clear is whether bernie sanders is a new and improved version -- >> yes, we can! thank you, new hampshire!

>> reporter: -- of the force that came out of nowhere back in 2008 to take away hillary's crown. eight years ago barack obama was here. he talked about, yes, we can. >> yep. >> let's be honest on a lot of things he just couldn't. what makes you think you can? >> people are tired of a rigged economy and a corrupt campaign finance system. they want real change. that's why we're doing well. >> reporter: back outside the colonial theater, there's no question they're feeling the bern. >> i feel the bern! whoo! >> reporter: i'm david wright for "nightline" in keene, new hampshire. >> as for the republicans, you do not want to miss the last republican debate before the new hampshire primary saturday night right here on abc. up next, how will lady gaga tackle singing the gold standard of songs at the super bowl? ♪

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whether you're the president of the lady gaga fan club or not, there is no denying her career is on fire. she's adding one more notch to her belt, kicking off sunday's super bowl by honoring a long-standing tradition for football and nonfootball fans alike. ♪ she got plenty of applause as a pop star. but lately lady gaga has been showing the world a very different side. ♪ when the dog bites >> wowing the academy awards last year masterfully performing a "sound of music" medley.

♪ climb every mountain >> teaming up with tony bennett to record an albulleting fans know anything goes. now taking on america's anthem at its biggest game, singing "the star-spangled banner" at the super bowl. ♪ and the rockets' red glare >> the stakes are high. it was 25 years ago whitney houston belted out what many still consider to be the best pregame performance. ♪ and the home of the brave >> securing her place as a legend. but plenty of singers have fallen flat. at super bowl xlv, christina aguilera forgot the words. ♪ what so proudly we watched >> steven tyler delivered this rendition before the 2012 afc championship. ♪ the land of the free

yeah! >> who can forget roseanne barr's performance. ♪ last gleaming >> something tells us lady gaga is on the edge of football glory. ♪ out on the edge of glory >> thanks for watching. tune into gma tomorrow. and as always we're online 24/7 on our "nightline" facebook page and at abcnews.com. good night, america.