Fidel Castro, meanwhile, accused Mexico of hiding the epidemic until after President Barack Obama visited last month.

Mexican Health Secretary Jose Cordova said his nation’s shutdown of schools — which was lifted in most of the country’s 31 states Monday — had averted an avalanche of cases.

“It would have been difficult for us to have controlled this epidemic,” Cordova said in a statement, adding that Mexico had 56 deaths and 2,059 confirmed cases of swine flu.

But Castro, the former Cuban president, accused Mexico of failing to disclose the spread of swine flu until after Obama had visited en route to the Summit of the Americas in Trinidad last month.

“Mexican authorities did not inform the world of the presence (of swine flu), while they waited for Obama’s visit,” he wrote on a government Web site hours after Cuba confirmed its first swine flu case.

Obama’s April 16 visit came a week before Mexican health officials announced swine flu was spreading, prompting an eventual mass shutdown that brought many parts of the country to a virtual halt.

Thailand and Finland reported their first confirmed swine cases Tuesday of people just arrived from Mexico. Cuba and China — both countries that had imposed strict measures on flights and travelers from Mexico — also reported their first confirmed cases.

Cuba identified its patient as a Mexican student attending a Cuban medical school and China said its case involved a Chinese student who had just returned from the United States.

At least 61 people have been killed by swine flu around the world, and the World Health Organization has confirmed over 5,250 cases.

Cuba’s Health Ministry said a group of medical students from Mexico began arriving on the island to resume their studies April 25 — four days before Cuban authorities halted airline flights from Mexico. Fourteen of the students suffered from flu-like symptoms.

A study published Monday in the journal Science estimated Mexico alone may have had 23,000 cases of swine flu by April 23, the day it announced the epidemic. The study estimates swine flu kills between 0.4 percent and 1.4 percent of its victims, but lead author Neil Ferguson of Imperial College, London, said the data remain incomplete.

“It’s very difficult to quantify the human health impact at this stage,” he said.

The analysis in Science suggests there are many more cases than those confirmed by laboratories — anywhere from 6,000 to 32,000 cases in Mexico as of April 23. The flu has since spread around the world, and the study said it appears to be substantially more contagious than normal, seasonal flu.

Researchers also compared the genetic sequences of the viruses in 23 confirmed cases, and came up with an estimate of Jan. 12 for their earliest common ancestor — presumably when person-to-person transmission began. But they said it could have been anywhere from Nov. 3 to March 2.

The researchers said the 2009 H1N1 flu appears to be about equal in severity to the flu of 1957 and less severe than the deadly 1918 version.

In Mexico, Monday’s reopening of kindergartens and primary and middle schools shut since April 24 was the latest step in efforts to restore a sense of normality. Businesses, government services, high schools and universities reopened last week.

But six of Mexico’s 31 states put off reopening schools for a week because of local rises in the number of flu cases, and a seventh pushed it back a day to Tuesday. The Education Department said it will tack an extra seven days onto the school calendar to make up for the lost time.

But while officials praised the health and education systems for their response to the crisis, there were signs that Mexico’s overburdened health system was under strain.

Dozens of government health care workers, including doctors and nurses, marched and blocked streets in the Gulf coast city of Jalapa to demand higher pay and better working conditions.

“The government asked our help in combatting the influenza epidemic, now we are asking the government to do us justice,” said nurse Mariana Cortes, one of the protest organizers.

Mexico is trying to revive its economy after the epidemic pummeled tourism, the country’s third-largest source of legal foreign income. Mexico provided details Monday of a $1.1 billion package to help restaurants, hotels and other businesses.

At least 10 commercial banks are involved in the plan, promising three-month reprieves for small businesses with outstanding loans in Mexico City and two hard-hit states. Small businesses in beach resorts and other tourist destinations were promised a six-month grace period.

Later in the day, Tourism Secretary Rodolfo Elizondo said the government would launch a $90 million publicity campaign this week urging Mexicans to vacation at home.

Noting that several nations have issued travel warnings or restricted airline flights to Mexico, Elizondo said trying to promote trips to Mexico by foreigners now “would be like throwing money away.”

With Cuba, Thailand and Finland reporting their first cases, the number of countries reporting confirmed swine flu cases grew to 33. The United States has the most confirmed cases — 2,618 — according to the U.S. Centers for Disease Control and Prevention. Swine flu has killed 56 people in Mexico, three in the U.S., one in Canada and one in Costa Rica.

Associated Press writers Miguel Angel Hernandez in Veracruz, Maria Cheng in London, Randolph E. Schmid in Washington and Gillian Wong in Beijing contributed to this report.

By Mark Stevenson, David Koop

An Axolotl salamander, or <em>Ambystoma mexicanum</em>, swims in a tank at the Chapultepec Zoo in Mexico City. Scientists warn that the roughly foot-long amphibian is just a few years away from extinction, a victim of the draining of its lake habitat, deteriorating water quality, and what is perhaps the final stake in its heart: the invasion of non-native fish species that are eating its eggs and larva, and competing with it for food.

MEXICO CITY – Beneath the tourist gondolas in the remains of a great Aztec lake lives a creature that resembles a monster — and a Muppet — with its slimy tail, plumage-like gills and mouth that curls into an odd smile.

The axolotl, also known as the “water monster” and the “Mexican walking fish,” was a key part of Aztec legend and diet. Against all odds, it survived until now amid Mexico City’s urban sprawl in the polluted canals of Lake Xochimilco, now a Venice-style destination for revelers poled along by Mexican gondoliers, or trajineros, in brightly painted party boats.

But scientists are racing to save the foot-long salamander from extinction, a victim of the draining of its lake habitat and deteriorating water quality. In what may be the final blow, nonnative fish introduced into the canals are eating its lunch — and its babies.

The long-standing International Union for Conservation of Nature includes the axolotl on its annual Red List of threatened species, while researchers say it could disappear in just five years. Some are pushing for a series of axolotl sanctuaries in canals cleared of invasive species, while others are considering repopulating Xochimilco with axolotls bred in captivity.

“If the axolotl disappears, it would not only be a great loss to biodiversity but to Mexican culture, and would reflect the degeneration of a once-great lake system,” says Luis Zambrano, a biologist at the Autonomous University of Mexico, or UNAM.

The number of axolotls (pronounced ACK-suh-LAH-tuhl) in the wild is not known. But the population has dropped from roughly 1,500 per square mile in 1998 to a mere 25 per square mile this year, according to a survey by Zambrano’s scientists using casting nets.

It has been a steep fall from grace for the salamander with a feathery mane of gills and a visage reminiscent of a 1970s Smiley Face that inspired American poet Ogden Nash to pen the witticism: “I’ve never met an axolotl, But Harvard has one in a bottle.”

Millions once lived in the giant lakes of Xochimilco and Chalco on which Mexico City was built. Using four stubby legs to drag themselves along lake bottoms or their thick tails to swim like mini-alligators, they hunted plentiful aquatic insects, small fish and crustaceans.

Legend has it that Xolotl — the dog-headed Aztec god of death, lightning and monstrosities — feared he was about to be banished or killed by other gods and changed into an axolotl to flee into Lake Xochimilco.

The axolotl’s decline began when Spanish conquerors started draining the lakes, which were further emptied over time to slake the thirst of one of the world’s largest and fastest-growing cities. In the 1970s, Lake Chalco was completely drained to prevent flooding. In the 1980s, Mexico City began pumping its wastewater into the few canals and lagoons that remained of Xochimilco.

About 20 years ago, African tilapia were introduced into Xochimilco in a misguided effort to create fisheries. They joined with Asian carp to dominate the ecosystem and eat the axolotl’s eggs and compete with it for food. The axolotl is also threatened by agrochemical runoff from nearby farms and treated wastewater from a Mexico City sewage plant, researchers say.

Local fisherman Roberto Altamira, 32, recalls when he was a boy, and the axolotl was still part of the local diet.

“I used to love axolotl tamales,” he says, rubbing his stomach and laughing.

But he says people no longer eat axolotls, mainly because fishermen almost never find them.

“The last one I caught was about six months ago,” says Altamira, a wiry gondolier with rope-like muscles from years of poling through Xochimilco’s narrow waterways.

Meanwhile, the axolotl population is burgeoning in laboratories, where scientists study its amazing traits, including the ability to completely re-grow lost limbs. Axolotls have played key roles in research on regeneration, embryology, fertilization and evolution.

The salamander has the rare trait of retaining its larval features throughout its adult life, a phenomenon called neoteny. It lives all its life in the water but can breathe both under water with gills or by taking gulps of air from the surface.

On a 9-foot-wide canal covered by a green carpet of “lentejilla” — an aquatic plant that resembles green lentils — Zambrano’s researchers test water quality and search for axolotls. The air smells of sulfur and sewage.

A team member suddenly points to the trademark water ripple of an axolotl, and the crew hurls its net. But they only come up with two tilapia in a sopping-wet mass of lentejilla.

So far, scientists disagree on how to save the creature. But a pilot sanctuary is expected to open in the next three to six months in the waters around Island of the Dolls, so-called because the owner hangs dolls he finds in the canals to ward off evil spirits.

Zambrano proposes up to 15 axolotl sanctuaries in Xochimilco’s canals, where scientists would insert some kind of barrier and clear the area of nonnative species.

Without carp, the water would clear, and plants the axolotl needs to breed could flourish again, said Bob Johnson, the curator of amphibians and reptiles at the Toronto Zoo.

“If you take the insults away, the lake has an amazing latent potential to heal itself,” he said.

Veterinarian Erika Servin, who runs the Mexico City government’s axolotl program at Chapultepec Zoo, is studying the possibility of introducing axolotls from the lab into the canals. But more study is needed to make sure the process doesn’t lead to diseases and genetic problems from inbreeding.

Xochimilco residents could be another source of resistance.

Hundreds of people make a living pulling tilapia from canals or growing flowers, lettuce and vegetables on nearby land. Efforts to remove the fish or shut down polluting farms could face stiff opposition.

But while the debate goes on, time is running out.

Given its role in research alone, Johnson says, “We owe it to the axolotl to help it survive.”

A canal in Xochimilco Lake in Mexico City. Xochimilco is the original natural habitat of the endangered Axolotl salamander, or Ambystoma Mexicanum.

Leftist Mexican presidential candidate <strong>Andres Manuel López Obrador </strong>mingles with supporters during a rally of more than 100,000 people Saturday in Mexico City. His staff planned to file alleged evidence of voting fraud Sunday.

MEXICO CITY – The ballots have been cast and counted. But Felipe Calderón won’t be Mexico’s president-elect until the nation’s highest electoral court says so.

The independent agency that ran the July 2 election added up more than 41 million votes and declared that Calderón won the most: 240,000 more than rival Andres Manuel López Obrador.

But this agency has no legal authority to declare a winner.

Under Mexico’s complex election laws, Calderón won’t have won until the Federal Electoral Tribunal certifies the count. And that’s not a sure thing: The widely respected tribunal has overturned two gubernatorial races in recent years, both for meddling by the ruling party.

Disgruntled candidates have gone to court to dispute election results in many countries, the U.S. presidential race won by George W. Bush in 2000 is a famous example.

But Mexico, where electoral disputes are almost a tradition, makes the courts part of the process right from the start. It’s part of an elaborate system designed to eliminate the fraud that was once nearly universal. Once the votes are officially counted, each party has four days to file challenges with the Electoral Tribunal.

The tribunal’s seven magistrates then consider the evidence in weeks of hearings, deciding whether individual ballot boxes were stuffed, whether particular voters were intimidated, whether candidates violated spending limits or bought votes.

Mexico’s election law says the court must decide all of that by Aug. 31. The magistrates then add up the votes that have survived challenges and declare a winner by Sept. 6, a decision that can’t be appealed. The new president is inaugurated Dec. 1.

Even in the last presidential election, when Vicente Fox had a commanding lead and his opponents quickly conceded defeat, the tribunal needed more than a month to declare him president-elect.

This year’s race is a squeaker, and López Obrador’s Democratic Revolution Party, or PRD, has alleged that Calderón’s National Action Party benefited from irregularities at about 50,000 polling places, setting the stage for a complex, emotional battle before the court.

Lopez Obrador headed to court Sunday evening to file purported evidence of fraud that he hoped would overturn his conservative rival’s razor-thin preliminary victory.

Lopez Obrador said his lawyers would give the Federal Electoral Court evidence of fraud, including computerized manipulation of the results, a day after he held a mammoth rally in Mexico City’s historic center and called on his supporters to help keep his hope alive.

The legal appeal would seek not to annul the July 2 election, but to force authorities to conduct a manual recount of all 41 million ballots.

“This was a very irregular election, and we are asking that they count vote by vote to legitimize the president-elect,” Gerardo Fernandez, a spokesman for Lopez Obrador’s Democratic Revolution Party, said outside the tribunal Sunday night as he waited for lawyers to arrive to present the legal challenge.

“We won’t recognize Calderón’s triumph unless they legitimize the election,” he said.

At least one key López Obrador aide says he’s ready to trust the tribunal, known by its Spanish initials as the TRIFE.

“It is the final arbiter, and it would be a tragedy if it wasn’t impartial,” said Manuel Camacho, a top campaign aide to López Obrador. “The PRD has confidence in the TRIFE.”

The court’s magistrates, nominated by Mexico’s Supreme Court and confirmed by a two-thirds vote of the Senate, have been working together for 10 years. This will be their last and probably biggest decision before they leave the court in October.

“The magistrates are serious people. They come from academic and legal backgrounds,” said historian Lorenzo Meyer, who endorsed López Obrador before the election. “I can’t imagine them distorting their decision because of pressure from a party.”

The judges, most of them little known outside legal circles, emerged from a justice system long tied to the Institutional Revolutionary Party, or PRI, which dominated Mexico from 1929 until 2000. But the PRI has suffered from some of their most notable rulings – as has National Action:

The tribunal threw out the PRI’s victory in a tight Tabasco state governor’s race in 2000 because of official interference and ordered a new election, which eventually was won by the PRI.

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