Led by smugglers armed with knives and machetes, Mayra Reyes and 14 other Cubans sloshed through swamps and rivers and suffered hordes of mosquitoes as they struggled across the notorious Darien Gap between Panama and Colombia, the only north-south stretch of the Americas to defy road-builders.

After walking for three days, the group reached the foot of a steep, scrubby mountain. There, the smugglers peeled away and told the Cubans they would have to press ahead alone.

"I thought I was going to have a heart attack," the 32-year-old hairdresser from Havana told The Associated Press. "What the guides did was get us to the mountain, where we had to wait for nightfall while these green and black poisonous frogs got on top of us."

Hundreds of Cubans like Reyes are taking that arduous new route toward the United States, trekking across the 85 miles (135 kilometers) of steamy tropical jungle that divides Colombia and Panama, through mountains, ravines, and muddy ground teeming with poisonous reptiles, jaguars, wild boars, guerrillas and drug traffickers,

And after that, they still face a journey across 1,700 miles (2,700 kilometers) and six countries to reach the United States.

Panamanian immigration authorities detained 800 Cubans near the border with Colombia from January through the first week in July, compared to 400 in all of 2011.

"We have detained up to 90 people in one week," said Frank Abrego, director of Panama's National Borders Service.

Thousands of islanders over the decades have used rudimentary rafts to travel the 90 miles (150 kilometers) that separate Cuba from the United States, but that journey can be deadly, and the U.S. Coast Guard has been patrolling the Florida Straits more aggressively, halting many before they can reach Florida. Most Cubans who reach U.S. soil can stay, but those intercepted at sea are usually returned to their homeland, and U.S. figures indicate that more than 1,000 have been stopped at sea so far this year.

So Cubans have turned to land routes. Nearly 90 percent of all undocumented Cubans who make it to America now come overland, usually through Mexico, rather than reaching U.S. shores by boat, according to U.S. Customs and Border Protection.

The route across the Darien Gap arose partly because many Cubans are now using the South American nation of Ecuador as the start of their path to the United States. President Rafael Correa eliminated visa requirements for Cuba in 2008, as other countries in Latin America, including Mexico, made it harder for Cubans to reach their shores.

All a Cuban needs is an exit permit from the Cuban government and a letter of invitation from a citizen of Ecuador, where some people sell such letters for $300 to $500. If Cubans have a letter of invitation and prove they can finance their travel abroad, it's relatively easy to get an exit permit if they are not doctors, scientists, military or members of other professions deemed high value by the government.

The result has been a flood of islanders traveling to the South American nation, which borders Colombia along the Pacific Ocean.

"Going to Ecuador is the easiest way right now to get out of Cuba," said Andy Gomez, a senior political fellow at the University of Miami's Institute for Cuban and Cuban-American Studies. "For the majority, Ecuador is a stopping point but they have to come up with the money to get to their final destination, the United States," he said.

According to Ecuadorean official figures, between 2007 and February 2012, 106,371 Cubans entered the country legally and 97,923 left legally. It is unclear what happened to the other 8,448.

In Ecuador, many Cubans work to save money to pay smugglers to take them to Mexico's border with the United States, a route shared with many Central American migrants who have to cross territory controlled by drug traffickers and who often face extortion and kidnapping.

Few, though, cross the Darien, one of the world's most rain-drenched regions. While several thousand indigenous people live along its trails and rivers, the jungle is so dense, the ground so swampy or mountainous, that the few attempts to cross it by car or motorcycle have taken weeks or months. That terrain, and fears of environmental damage to its wild ecosystem, have continued to frustrate planners trying to link South and North America with the Pan-American Highway.

Panamanian authorities began noticing five years ago that the Darien Gap was being used by migrant smugglers, usually to move people from Asia and Africa who had traveled to the area by boat from Brazil, said Jose Mulino, Panama's public safety minister. That has tapered off. Panamanian immigration officials have detained just 97 non-Cuban migrants in the area since the start of the year.

"That traffic of Africans and Asians has considerably decreased, and the big problem we have now is the flow of Cubans who are coming through the jungle," Mulino said.

The Cuban migrants are sharing dangerous paths used by drug traffickers and rebels of the leftist Revolutionary Armed Forces of Colombia, Mulino said, That has sometimes caused problems for local law enforcement.

Police recently had to call off a drug raid after spotting a group of Cubans near the border, Abrego said.

"We had to get them out of there and take them to Panama City," he said. "We lost the raid's effectiveness."

Authorities have yet to determine if their guides work for either group, Mulino said.

"It's not clear if the rebels, or the drug traffickers, or both, are the ones guiding the migrants," Mulino said. "Someone is helping them and those people are the ones who walk that area."

Mildred Morales, a 34-year-old Cuban nurse who was part of Reyes' group, said she paid $300 just to cross the border into Panama. She had spent about $1,000 since leaving Ecuador three days earlier.

"From the moment you leave Ecuador you have to pay people off, police and immigration officials in Ecuador and in Colombia," the Havana woman said. "This is not cheap."

After climbing the mountain, the group walked another six hours to a river. From there, Panamanian authorities detained them and took them eight hours by canoe to the town of Yaviza, where the Pan-American Highway ends in Panama. From there, they went by car to a detention shelter in the town of Meteti.

The Cubans remained in Meteti for several days until immigration authorities gave them, like most Cuban migrants, a temporary permit allowing them to be in the Central American country as long as they report to authorities every two weeks. Authorities in Meteti say it's rare to see the Cubans again.

Like everyone in the group, Morales was nursing dozens of mosquito bites and thinking about the rest of the journey north.

"We don't know what kind of problems we'll face in the rest of the countries," Morales said. "We have heard from other Cubans that it is possible to reach Mexico's borders with the United States."

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