Juan Karita / AP

Coca leaf producers toss coca leaves being given away for free during an event commemorating the tradition of coca leaf chewing in La Paz, Bolivia, on Jan. 14. Coca growers held street demonstrations in La Paz and Cochabamba to celebrate that their centuries-old Andean practice of chewing or otherwise ingesting coca leaves, a mild stimulant in its natural form, will now be universally recognized as legal within Bolivia.

Gaston Brito / Reuters

A man chews coca leaves in La Paz, on Jan. 14, as indigenous people from Quecha and Aymara celebrate Bolivia's re-admittance to the U.N. anti-narcotics convention.

Jorge Bernal / AFP - Getty Images

A man looks at a bottle of an energy drink made with coca leaves during a celebration in La Paz on Jan. 14.

Juan Karita / AP

Bolivia's President Evo Morales holds up a few coca leaves during an event celebrating the tradition of coca leaf chewing in La Paz, Bolivia, on Jan 14.

Bolivia said on Friday it had been re-admitted to the U.N. anti-narcotics convention after persuading member states to recognize the right of its indigenous people to chew raw coca leaf, which is used in making cocaine.

President Evo Morales had faced opposition from Washington in his campaign against the classification of coca as an illicit drug.

"The coca leaf has accompanied indigenous peoples for 6,000 years," said Dionisio Nunez, Bolivia's deputy minister of coca and integrated development. "Coca leaf was never used to hurt people. It was used as medicine."

Read the full story.

--Reuters

Jorge Bernal / AFP - Getty Images

Women stand next to a pie made with coca flour during a celebration in La Paz on Jan. 14.

AFP - Getty Images

Bolivian President Evo Morales delivers a speech during a celebration for Bolivia's re-admittance to the U.N. anti-narcotics convention in Cochabamba on Jan. 14.

Previously on PhotoBlog:

• Pot smokers gather under Seattle's Space Needle to celebrate legalization of marijuana
• Destroying tons of drugs in Panama City
• Drug dealers say no to crack in Rio
• $3 million worth of cocaine seized in Colombia
• Venezuelan soldiers set off explosions to destroy airstrip used by drug traffickers

MAE SOT, Thailand -- Clipboard in hand, Dr Francois Nosten worked his way down a ward of malaria patients. He stopped in front of five-year-old Ayemyint Than, who sat to attention and smiled. The smile told Nosten as much as his lines of graphs and figures.

Ian Williams / NBC News

Ayemyint Than, 5, is being treated for malaria in northwestern Thailand.

"She's doing well," he said, moving to an older man, whose pale face and dull sunken eyes told a very different story. "Day five, and he's still positive?" he asked another of the doctors. "That's not very good. It means he was very slow to clear the parasite, no?"

To Nosten, it was further evidence of an alarming rise in resistance to artemisinin, currently the front-line drug in the treatment of malaria. He fears it could be the start of a global "nightmare" in which millions of people could lose their lives.

"We have to beat this resistance, win this race and eliminate the parasite before it’s too late. That's our challenge now," he said.

He said that artemisinin should take about 24 hours to deal with the parasite, but it was now taking three or four days in some cases. "We are going to see patients that don't respond to the treatment anymore,” he warned.

Nosten runs the Shoklo Malaria Research Unit, which is part of the Faculty of Tropical Medicine at Thailand's Mahidol University.

The unit has a string of clinics on both sides of the Moi River, which marks the porous border between Thailand and Myanmar.

Ian Williams / NBC News

Migrants cross the Moi River, marking the border between Myanmar and Thailand.

Nosten set up the first one in 1986, since when there has been a steady fall in the total number of cases of malaria, but most recently a worrying emergence of drug resistance.

He first sounded the alarm in research published earlier this year, following the emergence of similar drug resistance along the Thai-Cambodia border.

Full health coverage from NBC News

Nosten’s not sure whether the resistance he's found has spread from the Cambodia border or is home-grown. Either way, he's worried.

"It means that all the progress of the last 10 to 15 years will be lost," he warned. "Now the resistance is here, we worry that we are running out of time."

Ian Williams / NBC News

Staff examine a baby who has been brought to the clinic with a fever, suspected to be malaria.

The malaria parasite -- carried by infected mosquitoes from person to person -- still kills an estimated 655,000 people a year.

That's almost 2,000 a day, mostly in Africa, with children being most at risk.

If the world loses its front-line drug, the impact could be devastating.

"The nightmare scenario is that the resistance will travel," Nosten said.

"We know what will happen in Africa when resistance is bad because we've been there before in the 1990s with chloroquine (another anti-malarial drug) … millions of deaths," he warned.

"We must prevent artemisinin resistance reaching Africa, but we also need to control it for the people in Asia - for their future."

Ian Williams / NBC News

Dr Francois Nosten, right, consults staff as he meets malaria patients at a clinic near Mae Sot, Thailand.

Resistance to just about every major anti-malarial drug has started in the border regions that have been home to Nosten for more than 25 years.

Nobody knows exactly why, but poverty, conflict and large migrant and refugee populations constantly on the move all likely play a part. As do fake drugs or a failure to properly complete a course of treatment.

In the case of chloroquine, once the anti-malarial drug of choice, it took less than 20 years for resistance to spread from the borders of Thailand to Africa.

Study: Mosquitoes change habits to avoid anti-malaria nets

Nosten is worried that artemisinin resistance is growing much faster than he'd anticipated, with the drug failing initially to fully clear the parasite in more than half the cases he now sees.

"It initially goes after a few days, then it comes back. We see that more and more now," he said.

"In 2009, we still had 90 percent of patients cured. In 2010, it dropped to 60 to 70 percent. Now it's about 50 percent," he added.

Ian Williams / NBC News

Migrants from Myanmar wait to be examined at a clinic on the Thai side of the border.

Some scientists claim this is too alarmist, since the parasite does eventually die, with longer treatment and higher drug doses, but Nosten sees no room for complacency.

"We have to respond quickly, not next year or three years' time. It's now or probably it will be too late," he said.

Artemisinin comes from a Chinese plant and is quick, potent and with no side effects. Little wonder it has been hailed as a wonder drug, the golden bullet in the global fight against malaria.

What makes the resistance so worrying is that there is no new drug ready to replace it.

Nosten said that although several drugs are in development, they could be five to 10 years away from deployment "if they make it  … and we haven't got five to 10 years.”

The Shoklo Malaria Research Unit runs its own labs fashioned out of a sprawling old Thai house in the border town of Mae Sot, where teams of research scientists are working to better understand the parasite and the mosquitoes that carry it from person to person.

It is here that Chiara Andolina keeps mosquitoes that are literally hand-reared -- fed from her arm, which she extends through a mesh hole into a container of the hungry creatures every three days.

"Usually I feed around 600 of them in a cage like this," she said.

Of course these are not infected mosquitoes, though watching them settle on her arm for a good lunch is not a sight for the squeamish.

Read more international coverage from NBC News

In another room, Nosten settled over photographs showing the rapid development of the parasite once it has invaded a blood cell.

"If you can kill them very, very young -- like these -- they don't have time to develop into big fatty ones," he said, his pen jabbing at the photo. "These fatty ones are the ones that get stuck in your brain and kill you."

In other rooms, the DNA of parasites was being isolated and sequenced and drugs were being tested as part of Nosten and his team’s efforts to figure out what's behind the emerging resistance.

They are also looking for vulnerabilities and new ways to attack their enemy.

"It's hugely important to understand what's going on and contain it if we can," Nosten said. "We need to try things. We need to explore. It’s like exploring new territories in malaria."

Bazell: Malaria vaccine a half-effective, temporary protection

The French scientist has spent most of his working life in the tropics, initially with the medical humanitarian group Médecins Sans Frontières.

He believes he is engaged in a vital battle -- "a race against malaria" -- as he puts it.

After so many years on the malarial front lines, the battle has become deeply personal.

He dreams of completely eliminating this familiar but wily enemy.

However, he also knows that with the emergence of artemisinin resistance the stakes have never been higher.

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Adriana Alvarado / AP

Rapid response Coahuila state police stand at a checkpoint iin Piedras Negras, Mexico, after a prison break on Sept. 18. Security is among the challenges facing the country.

News analysis

Where is home to the largest number of Americans living abroad, as well as the world's richest man?

Which country is the United States' third-largest foreign supplier of oil?

Which nation did President George W. Bush call the U.S.' most important bilateral partner?

Which close American ally has lost some 60,000 lives in a U.S.-backed effort to combat violent crime?

The answer to all of the above is Mexico.

But despite the many ties that bind the two countries, the United States' southern neighbor barely warranted a mention during the presidential campaign, and didn't come up once during the third "foreign policy" debate between Gov. Mitt Romney and President Barack Obama.

This omission is not lost on many in Mexico.

"At times the United States sees Mexico as an unconditional ally and they see us with the stigma of an undeveloped nation," said Eduardo Rosales, director of the United States-Mexico relations master's program at the National Autonomous University of Mexico (UNAM). "But the United States needs to put their eyes south. It is the most important bilateral relationship in the world."

Some Mexico-related news is grimly familiar to most Americans -- tens of thousands have died in violence since outgoing President Felipe Calderon declared war on the country's drug cartels at the end of 2006.

Mexico's drug war: No sign of 'light at the end of the tunnel'

Mexican cartels funnel between $19 and $39 billion worth of illegal drugs to the United States every year, according to the State Department. The United States, in turn, is a major source of weapons for the cartels.

Mexico's death toll remains stubbornly high and swathes of the country virtually ungovernable despite the Merida Initiative, a $1.9-billion U.S.-funded program aimed at fighting trafficking, organized crime and money laundering.

A vivid example of the shared security challenges came in August when Mexican police officers thought to be working in cahoots with the cartels ambushed and wounded two U.S. agents.

Oscar Alvarez, a college student in the northern state of Coahuila, alleged that much of the blame for the violence and crime lies with the United States, the world's largest consumer of illegal drugs.

"The demand on drugs is not being controlled ... and Mexico will always be affected," said Alvarez, 22, who has a small printing business to help cover the costs of school. "Whoever wins (the U.S. election) needs to act. I've heard a lot of talk but I haven't seen anything get done."

Full coverage: NBCNews.com's The World is Watching series

More election news at Telemundo

That the drugs trade and the hyper-violent crime that surrounds it is a shared problem has not been widely accepted in the United States, according to UNAM's Rosales.

"The problem is the consumption and the things that surround it such as violence and money laundering," he said. "It's a reality that is neglected by the United Sates. But our bloodshed continues to grow."

Cross-border methamphetamine trade booms amid Mexico's 'war on drugs'

It isn't clear how incoming President Enrique Pena Nieto of Institutional Revolutionary Party, which governed Mexico for about 70 years, will deal with the cartels, but indications are that many in country are losing patience with the drug war.

"I'm against the war," former Mexican foreign minister Jorge Castañeda told NBC News in May. "At six years on, it is beginning to look more difficult to see any kind of light at the end of the tunnel."

Crime and cartels do not define Mexico.

It is one of the United States' most important trading partners. Its economy, the world's 14th largest, grew at 5.5 percent in 2010 and 3.8 percent in 2011, according to the Office of the United States Trade Representative, despite the global economic downturn. Trade between the United States, Mexico and Canada -- members of the North American Free Trade Agreement -- is worth more than trade within the eurozone. 

Also in this series: Iran, Israel name checks illustrate America's twin obsessions

A symbol of Mexico's growing international economic prominence is Carlos Slim Helu– a telecoms tycoon with wide-ranging investments including a sizable stake in The New York Times – who topped Forbes' list of the world's richest people in 2012.

But despite billionaire tycoons and high growth rates, the anemic economy north of the border is hurting Mexico.

Mexico leader's message to US: 'No more weapons!'

Isidoro Peyron, owner of a family-run tile-making business in Pachuca, central Mexico, says the United States' slowdown has hit him directly. Whoever wins Tuesday's election must kickstart the economy for the sakes of both the U.S. and Mexico, he says.

"The next president of the United States needs to reactivate the American economy," said Peyron, 63, who has stopped exporting to the United States. "They are (Mexico's) main commercial partner."

Nevertheless, U.S. trade with Mexico totaled about $500 billion in 2011. 

Also in this series: Suspicion of US rife as Obama, Romney jab China

The 2,000-mile border between the two countries makes this trade easier, but the easy access also fuels another issue that both unifies and divides the U.S. and Mexico: immigration.

At an estimated 12 million, Mexicans are by far the largest immigrant group in the United States. And around 7 million, or 59 percent of undocumented immigrants, are thought to have come from Mexico.

While Obama decreed earlier this year that hundreds of thousands of undocumented migrants who went to the United States illegally as young children would be entitled to remain, the promise he made in 2008 to reform immigration has not been fulfilled.

Meanwhile, there have been more deportations under the Obama administration than during any other presidency in modern times.

Also in this series: Should next US president treat Russia as friend or foe?

But even though Obama has disappointed many for not delivering on immigration reform, the UNAM's Rosales did not hold out hope that Romney will resolve the problems.

"If Romney got to power, there would be zero chances of an immigration reform," Rosales said. "If Obama is elected a second term, it's still hard, but the chances increase."

Romney favors a U.S.-Mexico border fence and opposes education benefits to illegal immigrants, as well as offering legal status to illegal immigrants who attend college, although he would support doing so for those who serve in the armed forces.

More Mexico coverage from NBC News

Mike Reyes, who currently resides in Mexico City, lived in Arizona for eight years as an illegal immigrant. He feels the U.S. fails to appreciate what immigrants like himself contributed to the country.

"We hope the situation with Hispanics can be resolved in this election," said Reyes, 45, who works as a driver for the public transportation system despite having a degree in business.

Net Mexican immigration to the United States has stopped growing and may even have declined in recent years, according to a recent study. But with about half of Mexico's population classified as poor, economic realities are likely to continue propelling many Mexicans north for years to come. 

So immigration policies pursued by the winner of the 2012 presidential race will have an impact not only on the United States but Mexico.

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Alfredo Estrella / AFP - Getty Images

Ivan Velazquez Caballero, aka "Z 50" or "El Taliban" (second from the right), senior leader in the Zetas drug cartel and member of the Gulf cartel, is presented to the press at the Mexican Navy headquarters in Mexico City, on Sept. 27, 2012.

MEXICO CITY - The Mexican navy said on Wednesday it had captured one of the leaders of the Zetas drug cartel, a notoriously brutal gang reported to be breaking apart due to an internal feud.

The navy said it had caught the man it believed to be Zetas boss Ivan Velazquez in the central state of San Luis Potosi, in a boost to outgoing President Felipe Calderon's efforts to crack down on the violent cartels.

The Zetas have perpetrated some of the most sickening acts of Mexico's drug war and continued to expand even as rival gangs joined forces against them. They are now regarded as one of the two most powerful drug cartels in the country.

Velazquez is due to be paraded before the media on Thursday morning as is customary with such captures in Mexico.

Slideshow: Narco culture permeates Mexico, leaks across border

Mexico's drug war is also part of a drug culture with roots in music, movies and even religion

Launch slideshow

132 inmates tunnel out of Mexico prison near US border

The suspected gang leader surrendered to the navy in the city of San Luis Potosi without a shot being fired, an eyewitness told Reuters.

Known as "Z-50" or "El Taliban," Velazquez has been one of the leading figures in the Zetas. Formed by a group of army deserters in the late 1990s, the gang acted as enforcers for the Gulf Cartel before splitting with their employers in 2010.

Longstanding rivalry between the Zetas' top leader, Heriberto Lazcano, and his second-in-command Miguel Trevino has exploded into violence, raising fears the hostilities could bring a fresh wave of bloodletting.

President: Mexico gang-related deaths fall by 15 percent in 2012

Switched allegiance
The Zetas boast 10,000-plus gunmen, and the prospect of them fighting for control of local trafficking networks and smuggling routes has alarmed security experts.

However, the split also brings benefits for the government, as members of the gang inform against former colleagues.

Earlier this week, Mexican news magazine Proceso reported that Velazquez had switched his allegiance to the Gulf Cartel due to a rupture with Trevino, citing messages posted online.

Velazquez is listed by the government as one of the country's most-wanted drug kingpins. The Mexican government has offered a reward of up to 30 million pesos ($2.34 million) for information leading to his arrest.

U.S. Department of Treasury via AP

Ivan Velazquez Caballero, known as "El Taliban."

Debate rages over Mexico 'spillover violence' in US

Since 2009, more than 20 drug lords have been caught or killed. The most recent capture came two weeks ago, when the navy arrested Gulf Cartel head Jorge Costilla, alias "El Coss."

Earlier on Wednesday, the navy announced the capture of 18 suspected Zetas in the northern state of Nuevo Leon.

Mexico's drug war: No sign of 'light at the end of the tunnel'

How to contain the threat posed by the drug gangs is one of the main challenges facing Calderon's successor Enrique Pena Nieto, who is due to take office on December 1.

About 60,000 people have been killed in drug-related violence during Calderon's six-year term.

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Hotli Simanjuntak / EPA

Aceh government officials destroy drugs that were seized from drug traffickers at the Aceh police headquarters, Banda Aceh, Sumatra, Indonesia, Sept. 18.

Hotli Simanjuntak / EPA

Aceh police chief Inspector General Iskandar Hasan throws a package of marijuana into the fire as officials destroy drugs that were seized from drug traffickers at the Aceh police headquarters, Banda Aceh, Sumatra, Indonesia, Sept. 18.

Hotli Simanjuntak / EPA

Aceh government officials destroy drugs that were seized from drug traffickers at the Aceh police headquarters, Banda Aceh, Sumatra, Indonesia, Sept. 18.

Aceh police managed to arrest some 700 drug dealers, mainly with amounts of marijuana, cocaine and methamphetamines, in Aceh since the beginning of 2012. The drug dealers are believed to get their supplies from Thailand and Malaysia by air and sea.  

Felipe Dana / AP

A man smokes crack in the Manguinhos slum in Rio de Janeiro, Brazil, Aug. 7. Some drug bosses say they have stopped selling crack because it destabilizes their communities, making it harder to control areas long abandoned by the government. City authorities take credit for the change, arguing that drug gangs are trying to create a distraction and make police back off their offensive to take back the slums.

Business was brisk in the Mandela shantytown on a recent night. In the glow of a weak light bulb, customers pawed through packets of powdered cocaine and marijuana priced at $5, $10, $25. Teenage boys with semiautomatic weapons took in money and made change while flirting with girls in belly-baring tops lounging nearby.

Next to them, a gaggle of kids jumped on a trampoline, oblivious to the guns and drug-running that are part of everyday life in this and hundreds of other slums, known as favelas, across this metropolitan area of 12 million people. Conspicuously absent from the scene was crack, the most addictive and destructive drug in the triad that fuels Rio's lucrative narcotics trade.

-- Reported by the Associated Press

Read the full story.

Felipe Dana / AP

Traffickers and users gather at a drug selling point in the Antares slum in Rio de Janeiro, Brazil.

Felipe Dana / AP

Traffickers sell drugs in the Antares slum in Rio de Janeiro, Brazil.

Felipe Dana / AP

People gather in an area known as "Crackland" inside the Manguinhos slum in Rio de Janeiro, Brazil.

Felipe Dana / AP

A trafficker test fires a riffle in the Mandela slum in Rio de Janeiro, Brazil.

Felipe Dana / AP

Traffickers sell drugs in the Antares slum in Rio de Janeiro, Brazil.

Felipe Dana / AP

A trafficker stands at a drug selling point that stopped selling crack in the Mandela slum in Rio de Janeiro, Brazil.

Felipe Dana / AP

A masked and armed trafficker at a drug selling point that no longer sells crack in the Mandela slum in Rio de Janeiro, Brazil.

Felipe Dana / AP

Crack users gather under a bridge in the Antares slum in Rio de Janeiro, Brazil.

Felipe Dana / AP

A crack user leaves a crack house near the Manguinhos slum in Rio de Janeiro, Brazil.