ambitions. >> with north korea you never have a good option. the worse options is to leave them alone and to let their nuclear missile program go completely unabated for four years of obama. >> brown: ray suarez explores fascinating new research on the genetic makeup of the bubonic plague that killed millions of europeans in the middle ages. >> woodruff: and tom clarke of i.t.n. reports from the remote highlands of colombia, where half the population will inherit early onset alzheimers disease. >> these families' plight has come to attention of the outside world because the mutation they carry could carry the key to preventing alzheimers in millions of sufferers around the world. >> brown: that's all ahead on tonight's "newshour." major funding for the pbs newshour has been provided by: >> auto companies make huge profits. >> last year, chevron made a lot of money. >> where does it go? >> every penny and more went into bringing energy to the world. >> the economy is tough right now, everywhere. >> we pumped $21 million into local economies, into small businesses, communities, equipment, materials. >> that money could make a big difference to a lot of people. >> and by the bill and melinda gates foundation. dedicated to the idea that all people deserve the chance to live a healthy productive life. and with the ongoing support of these institutions and foundations. this program was made possible by the corporation for public broadcasting. and by contributions to your pbs station from viewers like you. thank you. >> brown: president obama pressed the u.s. case today that iran was behind a plan to assassinate the saudi ambassador to washington. and he warned, "there are going to be consequences." the president addressed the alleged plot and iran's role for the first time since the news broke tuesday. he spoke at a press conference with the president of south korea, and he insisted, "the facts are there for all to see." >> we would not be bringing forward a case unless we knew exactly how to support all the allegations that are contained in the indictment. >> brown: two men have been charged with conspiring to kill saudi ambassador abdel al-jubeir at a washington, d.c. restaurant. one suspect-- manssor arbabsiar, an iranian-american from texas-- is already under arrest in new york. the other man gholam shakuri has been linked to the quds force, iran's special operations unit. he remains at large. the president said there's no question that people in the iranian government were involved. >> even if at the highest levels there was not detailed operational knowledge, there has to be accountability with respect to anybody in the iranian government engaging in this kind of activity. the important thing is for iran to answer the international community why anybody in their government is engaging in these kinds of activities. >> brown: iran has issued a series of denials, including this one yesterday from the foreign ministry. >> ( translated ): such scenarios prove the political fluster and desperation of the united states. we consider such behaviors as symptoms of disintegration of america's empire which once claimed it can conduct its autocracy in the world. of course, we will give them a strong response and will, from the legal point of view, file a complaint against them. >> reporter: but president obama today brushed aside those protests, >> this is part of a pattern of dangerous and reckless behavior by the iranian government. it's got to stop and there are going to be consequences to its actions. now, we don't take any options off the table in terms of how we operate with iran, but what you can expect is that we will continue to apply the sorts of pressure that will have a direct impact on the iranian government until it makes a better choice in terms of how it's going to interact with the rest of the international community. >> brown: a short time later, the state department spokesman confirmed u.s. officials have had direct contact with iran about the incident, but gave no details. the countries have no formal diplomatic ties. meanwhile, saudi arabia's foreign minister prince saud al- faisal issued his own warning to iran. >> we will not bow to such pressures. we will hold them accountable for any action they take against us. and any action they take against us will have a measured response. >> brown: and in london, foreign secretary william hague said britain is in close consultation with the u.s., the saudis and the rest of the european union, on an international response. back in washington, undersecretary of state wendy sherman told a senate hearing the investigation is ongoing. >> in contrast with the iranian regime's rapid and unsurprising denials, we are meticulously and rationally laying out the facts of this plot. >> brown: sherman said u.s. ambassadors around the world are alerting their host government's about those details, and demanding an end to any quds force activities inside their countries. for the latest and how this it might play out in the u.s. and iran, we turn to joby warrick of the "washington post" and daniel brumberg of the u.s. institute of peace. joby, you wrote today that the u.s. officials originally were skeptical of this iranian link. today we see the president say the facts are there for all to see. what are they pointing to, to make the link? >> they were skeptical at the beginning because these are people who normally like to say we get excited about a case and then the skepticism comes in as time wont they had good evidence pointing to involvement in the iranian government. they saw money being wired from quds-ioled bank accounts and heard conversations over wiretaps and one of the suspects became a cooperating witness and was able to direct the plot very directly to some members of the iranian government, least at a medium level. >> brown: there are people looking into mr. al. >> it might be somebody for a good pulp fiction novel but not a real iranian plot. he was a used car salesman, had a failed business at making kabobs. he had a failed marriage. he was forgetful, he was bumbling. not the perfect specimen really for a hit like this, and yet this is the person that the u.s. alleges was the central u.s. player trying to put the plot together. >> brown: and gholam shakuri, the other person, whereabouts unknown. >> he is a member of the quds force, and when arbabsiar was arrested they had him look at photographs and sure enough shakuri is a member of the quds force, no doubt about it. he is someone directly involved in the kats and has ties toñ$re very elite military unit. >> brown: the u.s. is trying to shore up support, get allies on aboard with them. we heard some support in our taped piece. is there also some puzzlement out there you're hearing? >> i think so. i think if we understand among iranian experts in the united states, whether on the left, center, or right, there's a great deal upon skepticism. it's a fantastic story and hard in many respects to believe. >> brown: because why? >> you have to believe the iranian government first and foremost would engage in an act that would be an act of war with the united states, in effect, and this would be a kind of recklessness you don't find even coming from the iranian government and quds forces, apart from the fact they're dealing with a used car salesman who was a drunk, womanizer and drug dealer, the story has so many extraordinary aspects to it the united states is going to have to work very hard to make its case, and to suggest what that case merits in terms of any kind of policy change from the united states. >> brown: in terms of that, of course, we heard the president say there are going to be consequences. what kinds of measures are being considered? >> i don't have an inside track on that particular question, but my sense is listening to the president in your piece just now and having read through the interviews with a great deal of other administration officials on and off the record that they're being very careful about who particularly within the iranian government they're going to blame and who they're going to hold accountable, and they're not suggesting that the blame go all the way up to the supreme leader, and it seems to me that it's sort of trying to maneuver through this ambiguity, this strange story, setting the ground for a set of actions which will probably mean things such as enhanced sanctions, things short of the use of military force. that is my sense of this. so in that sense, this is going to be an evolution of u.s. foreign policy on iran, but not a major break or change in the direction of the military confrontation. >> brown: woe heard, joby, the state department spokeswoman say there had been direct contact. we didn't hear details. do you know any more about what is going on behind the scenes? >> it's very unusual becauses awe know, we don't have diplomat relations with with iranians. there has been direct contact, it was vaguely described but there was a meeting involving u.s. and iranian officials. what the content was, what they actually said to them, you can kind of guess about but we don't know in detail. but they are reaching out to the iranians to complain about this and to say that there will be consequences. on the flep side, the iranians are saying, you know, we've been attacked. we've had iranian nuclear scientists killed, and we've been victims of terrorism. so there's a bit of a back-and-forth going on. >> brown: what is your sense of how much the administration-- how hard they're working to convince others? are they worried they're not making their case at this point? is there sort of a scramble or is this just unfolding the way they expected? >> they feel a bit handicapped by the strangeness of the story so going around to people in new york of other delegations saying this is what happened, it's so fantastic, they're a little worried people will be keptical and not believe it. we have been talking to some of the delegations, western european and others and they take this very seriously, the selfs sound, and maybe it is a galv nigh nighing moment. >> brown: what about the isolating factor? does this further isolate iran in the world? they're already isolated. >> it does. it is isolated already, and it's going to make it more difficult. it's going to provide further justification for more intense sanctions of different kinds. kinds. i think the real question will be whether the administration will use this plot as a basis for arguing for more punitive measures, including military measures. and i think that our allies, while wanting to summit sanctions and other kinds of measures, really want to make sure this is not used as a basis for giving the green light to israel for an attack on iran and/or the u.s. itself undertaking that sort of attack, which, of course, would open up a can of worms in the region. so the administration that's balance this very carefully, get consensus, get support. at the same time, they have to avoid signaling this is sim saffir-simpsonly going to open a pathway fair new kind of approach to iran. >> brown: in the meantime you hear from iran denials, of course, and throwing it back at the u.s.-- "this is a sign of u.s. weakness." >> the iranian political system is an opaque system. we know that. but if in fact this is th has been a rogue operation from some element within the iranian special forces, quds forces, what have you, it would suggest a kind of breakdown in the decision-make process which would be quite unprecedented and suggest a falling apart of iran or a shift which could be dangerous for iran and its neighbors and the u.s. this may be one reason why they've been speaking with the u.s. >> brown: briefly, joby, the investigation is ongoing. >> yes, and there's curious are just intriguing to people but i think the real meat of this is what exactly is iran attempting to do here? if it is gnd bnd this, it does smack to some people of desperation that they would try something like this. it might suggest division within the government. it might suggest an eagerness to retaliate, for sanctions so it's hard to say. >> brown: all right, joby warrick, daniel brumberg, thank you very much. >> woodruff: still to come on the "newshour": feeling the impact of alabama's immigration law; talking trade and more at the white house; decoding the bubonic plague and inheriting alzheimer's disease. but first, the other news of the day. here's hari sreenivasan. >> sreenivasan: rebel forces in libya announced today that they captured another of moammar qaddafi's sons. they said mo'tassim qaddafi was taken as he tried to escape the city of sirte. pro-qaddafi loyalists are continuing to hold out there. gunfire continued in the city today as rebel fighters kept pressing forward. they said the battle is now confined to one neighborhood. in syria, activists said government troops battled military defectors in two towns leaving 13 dead. the reported clashes took place in the town of binnish in the northwest and the village of harra in the south. yesterday, thousands of syrians rallied in support of president bashar al-assad in damascus. but protesters released video of opposition rallies that also took place across the country. the people of bangkok, thailand fought a desperate battle today against the worst flooding in decades. more than 280 people have died since july in a growing disaster brought on by monsoon rains. we have a report from john sparks of "independent television news." >> reporter: bangkok-- teeming metropolis and the nation's capital under threat by flood waters from the north on the outskirts, motorways backed up and cut to a single lane, many of its riverside homes already consumed. this is the chao praya-- runs through bangkok-- it has already burst, just a thin line of sandbags holding it back. they're calling it bangkok's defensive wall, but it's under strain in pathum thani at city's northern edge. men on the ground here working to patch it up. further on, we found a giant car plant, owned by honda, now deserted, and marooned in waters 15 feet deep. we saw motorists stuck on flyovers, forced to make camp on the road-side. a great inland sea opened up before us. the river and its flood plain merged as one-- a great body of water, moving slowly, inexorably towards the south. we returned to phatum thani on bangkok's northern flank where volunteers, equipped with shovels, bags and plastic ties, were hard at work-- an ad-hoc production line churning out sandbags by the thousand. government commandeered supplies of sand, every plastic bag, many of them are being used in the defense of bangkok-- the front line in this crisis. the thai government has moved into air terminal to better to coordinate its response. various ministries share tables in the departures hall. the prime minister's staff, now working from the muslim praying room, and they face a mammouth task-- 2.5 million people displaced, third of the country declared national areas. >> sreenivasan: a heavy new surge of flood water from the north will reach bangkok this weekend, just as high tides and new storms arrive. u.s. defense secretary leon panetta issued a new warning today about squeezing the pentagon budget. the military already faces $450 billion in cuts over the next ten years. panetta told a house hearing that forcing even deeper cuts could be devastating. >> there are going to be risks here. i'm not kidding you. when you cut the budget by $450 billion, when you make the choices we're going to have to make, there are going to be some risks that are going to be out there. those risks have to be acceptable but there are going to be risks. we need to know that. >> sreenivasan: panetta would not give details about the cuts already in the works. he said they are still under review. the parliament of slovakia reversed itself today and approved a plan to boost the eurozone's bailout fund. slovakia was the last of 17 nations using the euro currency to approve giving the fund more power. earlier this week, an initial vote in the slovakian parliament failed and briefly sent panic waves through world financial markets. the news from europe did little to cheer wall street. instead, stocks were mostly down, on concerns that the european debt crisis has hurt u.s. bank profits. the dow jones industrial average lost 40 points to close at 11,478. the nasdaq rose 15 points, with a late rally in tech stocks, to close at 2,620. a former billionaire hedge fund manager raj rajaratnam was sentenced today to eleven years in federal prison. it is the longest sentence ever given for insider trading. the founder of the galleon group was convicted last may. he also has to pay a $10 million fine, and forfeit more than $50 million from illegal trades. those are some of the day's major stories. now, back to judy. >> woodruff: alabama's new immigration law, recently upheld by a federal judge, is now starting to have an economic impact in the state. representatives of the agricultural and construction industry, say they are losing a significant portion of their workforce. and it is against that backdrop, the state's hispanic community is voicing opposition. the mi pueblo supermarket in birmingham closed its doors yesterday. joining hispanic-owned businesses across alabama to take a stand against the state's tough new immigration law. >> we all hispanic, we should all be together, to represent you know our-- how we feel to the state about it. >> woodruff: the work stoppage also hit the poultry industry. the parking lot was almost empty at a tyson foods chicken plant in tiny albertville, in northeastern alabama. operations slowed or even stopped, as many hispanic employees staged a one-day "sick out." it was the latest, and perhaps largest protest against the law known as hb 56 passed earlier this year. one key provision authorizes police to detain anyone who's suspected of being in the country illegally. supporters say it's intended to help legal residents by pushing illegal immigrants out of the work force. >> it's illegal and they are getting most of the jobs that we need right now. >> reporter: two weeks ago a federal judge in alabama upheld the law's main provisions. the state's republican governor robert bentley welcomed the decision. >> it would not have been necessary to address this problem if the federal government would have done its job and enforced the laws dealing with this problem. >> woodruff: but since then, some local officials have warned that thousands of children here legally could be left in limbo. >> our worst case scenario would be if we had a large number of children who were suddenly dependent and had no relatives who were able and willing to take care of them and that possibly could happen if the parents were arrested or deported suddenly. >> woodruff: schools are also voicing concerns. they're now required to check the immigration status of prospective students. and already, absentee rates are rising among hispanic students. in the meantime, the mexican consulate in huntsville has sent out a team to help families get documents they need to return to mexico-- if needed. we talk now with jerry spencer, founder of the birmingham-based grow alabama, which delivers locally grown produce in the state. jerry spencer, thank you for joining us. i understand you work with 200 to 300 farmers in the state. what do they grow and what's happened to their workers in the last few weeks? >> well, our farmers grow a broad range of various fruits and vegetables. and they are-- some of them are large enough to be pretty heavily impacted by the loss of their hispanic workers. i found this out a couple of weeks ago, friday after the decision was made, the law was enacted. and called around to three of my farmers and that was enough for me to know that there was a serious impact going on. so i slept on it overnight, and put it on facebook, and started getting a force-- mobilizing a force for the farmers to replace what they'd lost, the workers that they'd lost. many of them were-- yeah? >> woodruff: i was just going to ask, how many altogether have left and why did they say they were leaving? >> well, the only figures i've seen are state figures, which are about 185,000. and the reason for them leaving was the fear of incarceration, arrest, hassle from the police, which they have been given the right to do. >> woodruff: and what sort of work were these laborers doing, the ones who left? where are you now in the crop, the harvesting cycle? how urgent is it that they be replaced? >> well, the urgency is in the final stages of the last harvest of the year essentially. so the urgency, you know, there would be a significant loss of harvest in the next few weeks. but the big concern is the decisions that the farmers are going to have to make about whether they continue to farm next year. >> woodruff: are replacement workers available? i mean, we know that! state representatives, including the one we're about to talk to say there are other folks in alabama who are unemployed who would love to take these jobs. >> there are plety of those folks, and that's who we are trying to mobilize. we're starting at a very small-- on a very small basis,un, 40, 50 people last week. and we're looking at the details of what's necessary-- transportation, the workability of these unemployed city folk working on farms. so we're looking at all of that out of 40, 50, 60 people, we probably have maybe 10 people who really could actually work on a farm. >> woodruff: so bottom line, these workers can be replaced? >> it's not impossible. >> woodruff: all right, well, we will leave it there, jerry spencer, and we appreciate your joining us. and we want to talk now a little bit more about the impact of the alabama law and we want to turn to representative-- state representative mike ball of huntsville, alabama, who summits the law. he joins frus knoxville, tennessee, and rosa toussaint-ortiz, and she joins us from huntsville. let me start with you, representative ball. we heard not only from mr. spencer. we talked today with a contractor in the state who is concerned about people leaving these jobs. was that the consequence you expected when the law was passed? >> yes, i think so. i think that was the-- that was the purpose of the law was to discourage those who are here in alabama illegally. we have a poverty problem in alabama. we have a problem with unemployment. and many of the folks that come to alabama illegally, they have a different set of rules that they're hired by. they don't have to have workmen's comp shrnls. they don't have to have employee tax. a lot of them were paid 1099 or paid under the table. it puts our working, the very people having the problem with unemployment, it puts them at a competitive disadvantage, and we need a level playing field. >> woodruff: miss toussaint-ortiz, how do you see the effect the law is having? >> what i see is i understand what they are saying in reference to the jobs, the ones that are already citizens, they need those jobs. but what i don't understand is how they make a decision, a law so harsh, they have to put all these people in a crisis. we are dealing with human bein beings. it doesn't matter if they are legal or illegal. if they were going to pass that law, they should have gave the people time to process all this changes. what we have created now crisis, misunderstanding. the police are not sure what's going on, what they should be doing. the department of motor vehicles is not completely sure. the people themselves are completely confused because what happens is the language barrier has caused rumors. so people are going by rumors. people don't have clear information, and they are just completely afraid. the children-- >> woodruff: i was just going to say, let me turn back to representative ball, and ask you about her description of a crisis. she said people don't know where to turn. there's a language barrier, and there's just a lot of confusion. >> well, first of all, this bill was passed during the last session of the legislature months ago, and it only just wtook effect. as a matter of fact, during the whole campaign season this was something that was talked about. there is, certainly, a lot of confusion about the law. i think a lot of the opponents of the law have-- have fueled a lot of fear in-- i mean, some of the things that they've said the law does, it really doesn't do. you know, there's no reason for somebody to be afraid of this law to keep their child out of school. the provisions that are applied to schools are merely statistical counting. so-- but then, you know, peopl people-- there are folks that are fueling the fear, and, quite frankly, if you're here illegally, you probably should be-- should be afraid that you could get in trouble. that's why you make things illegal. >> woodruff: miss toussaint-ortiz, what about the basic point, if people are here illegally, they shouldn't expect to stay? >> well, the first thing is, we should not dehumanize. what i'm saying is, if they are illegal, they should have to receive time to make the decision of moving out of state. you cannot-- right now we have-- and you know, let me tell you what really upsets me. when we get tornadoes-- and this has been like a tornado on the community-- we see the counselors, they go to the school to help the children. there have been kindergarten classes where 20 children disappeared in one minute. and no one-- what i find outrageous is this is going on, people see the news, and it's like they are-- the community, the u.s. citizens, they are, like, numb. they're not doing anything to help. and you mentioned before the consulate, the mexican consulate has been here yesterday, today, and they were supposed to be here tomorrow. now, the church, they allow us to stay there. they just canceled without giving us a good reason. and we have 300 and some people coming tomorrow that they're not going to be able to serve. bought bos now we don't have a place. >> woodruff: finally, one quick final word interest representative ball, is there going to be an attempt to clarify this situation for them? >> well, quite frankly-- as far as the people that are here illegally, if they're here legally, they have no problem, nothing to be concerned about. if they're here illegally, then there are some measures in this law that would-- that would make it rough on them. i mean, because it's-- i don't mean make it rough, i mean, they could be arrested. >> woodruff: we will have to leave it there. we want to thank you, representative mike ball. >> sure. >> woodruff: from the state of alabama. and rosa toussaint-ortiz. we appreciate both of you joining us. >> thank you. >> thank you. >> brown: next, talking trade and nuclear weapons as south korea's president comes to washington. margaret warner has the story. >> in an ever-more vital part of the world. the ceremony held outdoors despite the drizzle also showed an increasingly close personal relationship between president obama and his counter-part. >> presently, first lady, members of the korean delegation, on behalf of michelle and myself, on behalf of the american people, welcome to the united states. ( applause ). >> warner: the two presidents had two major agenda itemes, first, touting a long-stalled free trade agreement, passed by congress last night, which the administration says will generate $11 billion in new exports for u.s. companies and fasmers. the korean parliament has yet to approve it. the accord, first signed in 2007, had to be renegotiated twice over u.s. misgivings on access to korean markets for u.s. beef and cars. after winning concessions to address auto union and other democratic concerns, president obama last month urged congress to pass it. >> if americans can buy i can expaz hyundais, i want to see folks in south korea driving fords and chevys and chryslers. >> warner: with republicans agreeing to a benefits program for workers who lose jobs to foreign competition, both houses approved the revised deal on the eve of president lee's arrival at the white house. in a joint press conference today, the two men insisted the accord will be good for both countries. >> for our farmers and ranchers here in the united states, it will increase exports of agricultural products. from aerospace to electronics it will increase american exports, including those produced by our small businesses. >> ( translated ): it is a win-win agreement that will benefit both of our countries in countless ways. >> warner: behind closed doors they were focused on something entirely different, the persistent, seemingly intractal problem about what to do to seoul's neighbors to the north. north korea. north korea expands its nuclear weapons and missile arsenal. hostilities flared last year in march when the north torpedoed and sank a naval vessel, killing 46 sailors, and four people died oin november when the two changd artillery fire on a disputed maritime border. also adding to the volatility-- north korea's preparation for a leadership change from the ailing dictator kim jong il, to his son. but most worrying to the u.s. and region is north korea's development of nuclear expwps missiles that can carry them long distances. in january, then-defense secretary robert gates on a trip to asia, warned that the north was within five years of being able to strike the u.s. > north korea's pursuit of nuclear weapons and the proliferation of nuclear know-how and ballistic missile equipment that have focused our attention, development that threatens not only the peninsula, but the pacific rim and international statistic as well. >> warner: for past few years, the north has alternated between engaging in multination talks and silence, all the we advancing its nuclear weapons and missile programs. they cut off six-party talks involving the two koreas, u.s., china, russia, and japan, more than two years noog april 2009. we asked sanford university visiting scholar, robert carlin, who spent decades at the state department and c.i.a., where things stand now. >> nowhere. seriously, we've probably lost a lot of ground and for the last 10 years there's been a real void. and nothing, absolutely nothing has been accomplished. they have two nuclear tests. they perfected their uranium enrichment and they work on the missile liberty program. and that's where we are today. >> warner: that leaves presidents obama and lee in a quandary-- do they make moves in north korea's direction to get talks restarted or do they stick to their preconditions, which the north has so far refused to meet. >> north korea, you never hadv a good option. >> victor cha, former top official at the national security council, is korean chair at the center for strategic and international study stds. he thinks the obama administration is reluctantly edging towards meeting the north's push for direct talks with the u.s. over the nuclear issue and over normalizing diplomat regulations. >> we only have bad options or worse options. the worse option is to leave them alone and let their nuclear and missile problem program goes unabate forward four years. that's a very bad situation. so you're left with a position where they have to negotiate. they have to hold their nose and negotiate in hopes of being able to contain a crisis of some sort. and that's where they are today. >> warner: expuz north korean officials held one direct meeting in new york in july, ostensibly how to discuss getting back to the six-nation talks. >> what we're seeing now is an attempt to create a thaw in the relationship. >> warner: even small moves like that make south korea nervous. president lee has taken a tough line with the north, refusing further aid, despite north's food shortagees, until certain preconditions are met. so far, the u.s. has joined in insisting on those conditions. >> they need to promise not to do nuclear missile tests. they have to promise mott to attack south korea again. they have to freeze the plutonium program, and they have to allow inspectors the uranium program. the north koreans have not given public sentiments they are willing to meet those conditions. >> to think we're going to get the north korean to agree to our dpolz ahead of time before negotiations is to imagine that they are somehow a vanquished-- so if we're not careful the north koreans will say then you're not serious. >> warner: carlen also says washington and seoul should be willing to broaden their focus beyond nuclearization. >> if we only deal with the nuclear issue in and of itself, chances are very slim that we're going to get this airplane off the ground. >> warner: publicly, the two presidents today showed no distance between them on how to handle the north. >> if the northands its quest for nuclear weapons andoves towards denuclearization, it will enjoy great. >> we speak with one voice, and we will continue to speak with one voice. >> warner: but the differences over how to proceed with the north and cults but real. >> the south would like the face to be slower and more deliberate while the obama administration feels they have a moment where they need to try this, particularly before they get into an election year. >> warner: as presidents obama and lee wrestled with all this it was one sign tensions may be easing ever so slightly on the peninsula. south korea said it will allow 120 firms to restart construction on a joint industrial park inside north korea's border. the work was halted after last year's hostilities. today, president lee journeyed to the capital to thank congress for passing the trade deal, and tomorrow, he and president obama will make a joint visit to an auto plant in detroit. >> woodruff: to a story with origins many centuries ago, scientists have recently unraveled the genetic code of the black plague and are studying its relevance for our modern age. ray suarez has the story. >> suarez: the microbe that caused the black death killed some 30 million people in western europe in the mid- fourteenth century. researchers have long tried to understand how the bacterium really could have been that deadly. now, scientists have collected d.n.a. from the bones of black death victims buried in a london cemetery. the genetic blueprint was taken from extracted teeth and then compared with modern-day bubonic plague. geneticist hendrik poinar of mcmaster university in canada was a leading member of the team and he joins me now. professor, welcome. why sequence the genome of a bacterium that was killing people almost 700 years ago? >> i think one of the reasons is really so that we can hope to understand perhaps why it was so deadly. so intrinsic changes that led to this high mortality which you just mentioned killed some 50% of the european population in 1346. >> suarez: so you managed to track down a sequencable piece of bacterium. what did it tell you once you were able to compare it with the plague bacterium of today? >> yeah, well, first we designed this methodology to remove like you mentioned, really small tiny fragments because the pathogen had been heavily degraded into little tiny pieces. we managed to pull that out using sort of an enrichment strategy and stitched these pieces back together and construct this ancient genome. using that we can compare it to the modern genome which allow us to deduce, a., that this turns out to be the grandmother of all modern circulating plague bacteria today out across the globe, so outbreaks in southwestern united states or africa and india have a route that spits in medieval europe in the 14th century. >> suarez: there's been very little change in the bacterium from what i understand. how come it was so much more deadly then than it is today? >> that's an excellent question, ray, a million-dollar question, i would say. we don't quite know yet. we do have a constellation of changes in this bug which we need to test to find out. so was it an intrinsic structure within the bug so the actual way the genes are organized on the chromosome that led to invissed virulence, if we step back and look at the concept of the people of europe during that time period, the climate was much colder than it was the years previous to 1346. i'm sure as people entered this cold phase of the year, it was really cold circulating pathogens, people with flu and other immuno-compromised individuals. and with the arrival of this new pathogen into mainstream europe through trade routes sort of led to a perfect storm of sorts. >> suarez: let's go back to the skeletons recovered in a london mass grave. were you pretty confident that you could extract something usable from 660-year-old corpses? >> well, we were never able to in the past really get large amounts of information from the pathogen. so let alone finding the d.n.a. of humans in human skeletal remains is already a big enough challenge with ancient d.n.a. but the proverbial needle in the haystack, the-- it's more like a needle in the university of michigan football stadium. we had to devise a novel methodology that uses modern ancient plague bacterial d.n.a. spotted on to a glass slide to actually pull those d.n.a. fragments out of this complex mixture of d.n.a. solution from the skeletonized remains. so it's the development of this novel technology which enabled us to restitch this genome back together. >> suarez: were you thinking about that as you were pulling teeth out of a centuries' old corpse or were you saying, "what am i doing? this better work." >> yes, well, we had no idea when we began the project in the mid-90s as to whether or not this would ever be done. if you asked me two years ago whether or not we could reconstruct the first ancient pathogen geg.e. gnomes from skeletons i would probably have said very unlikely. here we are today and we managed to do it and i think this gives us a time machine to travel back to acce the genomes of past plagues across our human history, to be able to address what changes allow the pathogens tpathogensto adapt to their humd why they become sod itly. >> suarez: you have climbed up to this plateau. what does it allow you to do? could you reformalate a 14th century version of it, and would it be dangerous to do that? >> well, that's a good question. from, you could, and i think there'sed any reason to do that. the question you asked earlier is why was it so deadly? we have no idea, really, and it's very hard to imagine going into a densely populated city today and imagining how every third person dropping from an infectious disease rampaging through the city. so really understanding what it was that made it so deadly is a key part of this research at this point, and that involves actually taking some of the genes and trying to reconstitute them and looking for changes in the enzymatics of what it does. so that can't be done. the good news is if we look at the entire sequence and compare it against known sequence of pathogens susceptible to antibiotics, we see modern tetracyclines we use in antibiotic studies today would be quite effective against this plague of the middle ages. so had medieval europe had access to tetracyclines they probably would have fared much better glar professor hendrik poinar, thanks for joining us. >> thanks for having me, ray. >> brown: finally tonight, a medical mystery of our own time, where the search for a cure for alzheimer's disease has taken researchers to a remote region in colombia. tom clarke of "independent television news" has the story. a warning: some of the medical footage is a bit on the graphic side. >> reporter: antioquia-- colombia's isolated northern highlands. i'm with lucia madrigal a nurse on her rounds, from the regional medical school. until recently, many of lucia's patients were only accessible by horse or on foot. once she was detained for a week by drug traffickers who still control much of this area. but now the roads have opened up bringing lucia much closer to her patients who've lived for centuries in the shadow of dreadful illness ofelia has alzheimer's. she's only 51 but the disease has already taken her memories. now she's losing the things she learned as a child-- how to talk, how to write her name. her symptoms are the same as for millions of alzheimer's sufferers around the world. but ofelia's disease is very different. she was always going to get it. she carries a mutated gene passed down from her mother. a cruel inheritance that's been in the family for years. since their mother died her older sister aura has run the household. she tells me that of 16 brothers and sisters, eight inherited the disease, four have died so far. ophelia and her brother gustavo's now need full time care. >> ( translated ): well, for me it's very hard. because you think for who is it more difficult, for oneself or for the sick ones. maybe we can say that they don't feel anything. but the truth is that you don't know what they feel. >> reporter: in and around their town of don matias they are not the only family suffering. as many as 5,000 people in antioquia carry the mutation. if they have children half of them inherit will the gene. usually the disease strikes at just 49 years of age-- here the elderly watch the young die of alzheimer's. it's thought a single basque settler brought the disease here in the 18th century. his direct descendents carry what's called the paisa mutation, a nickname given to colombians from these hills. the remoteness of this region is the reason the mutation has survived passed on from generation to generation of large families with little contact to the outside but after nearly 300 isolated suffering these families plight has come to attention of the outside world because the mutation they carry could carry the key to preventing alzheimers in millions of sufferers around the world. francisco lopera, is the colombian neurologist who discovered the mutation. for 25 years, he's worked to gain the trust and support of families-- now he and they are at the center of a major international scientific campaign. >> ( translated ): here we have the severe problem of having the world's largest group of people with inherited alzheimer's. but people are engaged with it, and families know that if they get involved in disease research here, they are contributing globally. they not only do it in order to find a solution for their problem, but also to help other people. >> reporter: we traveled with dr lopera back to don mattias. with him, is the man who coordinates alzhiemer's research at harvard university in the u.s. adrian iverson has come to watch his colleague's routine evaluation of ophelia's and gustavo, but also asses the potential these families have for a radically new approach to curing alzheimers. >> last time she was talking >> reporter: they're the center of attention because efforts to treat alzhiemers worldwide are failing. there is no predictive test for the common form of the disease, so drugs are only given once symptoms are apparent by then damage to the brain may be irreversible. but here in colombia a simple genetic test reveals exactly which family members will develop the disease, decades before it strikes. >> this gives us an incredible window of opportunity to look at the very early stages of this disorder, that gives us an opportunity to look at the disease process well before its so bad that causes symptoms. it also gives us an opportunity to try any future medications, any future drugs in a person whose brain is not so badly damaged. >> reporter: and back in the regional capital medellin, dr. lopera and his university colleagues are already on the case. they're not testing a new drug but an existing one. with the support of two other u.s. institutions they have recruited 300 family members in the first clinical trial aimed at preventing alzheimers. participants have volunteered a blood sample and been tested for the mutation, but agreed not to know the results. as early as next year, reseachers will use an existing alzheimer's drug and assess whether given much earlier it can successfully prevent or delay the disease. >> ( translated ): it is probable that five years is too early for us to expect a cure for the disease, but it is but that is the hope we have. >> reporter: one thing that raises that hope say other alzherimer's experts, is the relationship here between the scientists and their research subjects. and these cabinets hold the most striking demonstration of that alliance. within are stored more than 50 brains donated by families who's loved ones died because of the mutation. it's the world's largest collection of brains from people with inherited alzhimer's. it may be unsettling, but a brainbank, as it's know, is essential in providing clues about how alzheimers begins to destroy the brain and how future drugs might work to stop it. but outside the lab, back in the homes of families like opehlia, the specter of inherited alzheimers remains as terrifying as always has been. and science can't move quick enough to allay the fears of those who may already carry the mutation. >> ( translated ): what are the chances that in the future, or how long will it be before we have cure? in all likelihood, a cure is still a long way off. but the contribution these families have already made, could lead to new advances in alzheimer's. anything that delays the progression of the disease, even for just a few years will help future generations here as well the one in ten of us that will develop alzheimer's when we get old. >> woodruff: again, the major developments of the day: president obama accused iran of reckless behavior and a direct role in the plot to assassinate the saudi arabian ambassador to the u.s. and the people of bangkok, thailand fought a desperate battle against the worst flooding in decades. >> brown: and that's the "newshour" for tonight. i'm jeffrey brown. >> woodruff: and i'm judy woodruff. we'll see you online and again here tomorrow evening with mark shields and david brooks, among others. thank you and good night. major funding for the pbs newshour has 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