Flu spreads in U.S., world, winds down in Mexico

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - U.S. health officials predicted worsening outbreaks of the new H1N1 flu on Thursday, and a top global health official predicted up to a third of the world's population could eventually become infected even as Mexican officials said the worst was over.

A batch of detailed studies on the new swine flu virus showed it was a strange marriage between a triple-hybrid virus with pig, human and bird elements and a European swine virus not seen before in North America.

But some pork bans appeared to be easing and U.S. agriculture officials promised unspecified help to farmers.

Mexico's confirmed death toll ticked up to 44 as labs tested a backlog of samples from people who died in March and April. The U.S. Centers for Disease Control and Prevention reported 896 confirmed cases of the new H1N1 flu in 41 states.

U.S. officials have said they expect the swine influenza virus to spread to all 50 states and to cause many infections ranging from mild to severe. There have been two deaths in the United States.

"So far we are not seeing any signs of this petering out," acting CDC Director Dr Richard Besser said. "We are on the upswing."

And even though Mexican officials said they were over the worst, Besser said there was still significant transmission there, too.

More than 2,000 people in 24 countries have been infected with the virus, the World Health Organization said.

The WHO's Dr. Keiji Fukuda urged Asian governments to stay alert for a possible wider pandemic that "could infect a third or more of the world's population in the next several months, in the next year.

"Even if the illnesses appear relatively mild on an individual level, with large numbers of infections on the global population, you can get large numbers of seriously ill people," Fukuda told a conference in Bangkok.

Fukuda said H1N1 flu is not yet spreading in a sustained way outside North America, so the global pandemic level remains at 5 out of 6.

Fukuda said governments should be ready for H1N1 to turn into something far more serious. "This is a time in which we can work with countries to be as prepared as possible," he said.

In a series of reports rushed into the New England Journal of Medicine on Thursday, researchers said influenza viruses from animals are an ongoing threat and doctors need to keep a lookout for them.

"As recent events suggest, the generation of novel influenza viruses through the reassortment of swine influenza viruses with other human and animal influenza viruses may be inevitable," the CDC's Dr Lyn Finelli and colleagues wrote in one report.

So far the genetic analysis gives no clue about where the new virus came from, the researchers told a news conference. The European genes were especially mystifying. "Those genes had never been seen in the United States before," the CDC's Dr Michael Shaw said.

"We have no idea whether they came to this hemisphere by human or animal."

BACK TO SCHOOL

In Mexico, millions of high school and university students returned to classes as the country got back on its feet after shutting public places last week to avoid spread of the disease.

After a five-day business shutdown, the government has let bars, cinemas, restaurants and workplaces reopen. Theme park operator Six Flags said it planned to reopen its Mexico City park on Friday after being given permission by Mexico's government to do so.

But visitors to government-run buildings were asked to wear surgical masks and wash their hands with antibacterial soap before entering. Restaurants also sanitized diners' hands as they arrived.

"It's obviously a worry for us that after we allow many activities people can forget the (health) recommendations," Health Minister Jose Angel Cordova said.

This might not be easy for many, like hair salon operator Miriam Guerrero in drought-stricken Ciudad Nezahualcoyotl, a Mexico City-area slum.

"When the water's running short it's not easy to keep washing your hands like they say, and there's not enough to disinfect all the furniture," Guerrero said.

The U.S. pork industry got some good news after being battered by import bans by nearly two-dozen countries.

"Clearly pork producers have suffered and will continue to do so until we get this turned around," Agriculture Secretary Tom Vilsack told a Senate Appropriations subcommittee. "We are looking at ways we can be of assistance or help.

And Russia signaled it may lift bans placed on pork by June 1, a spokeswoman for the U.S. Trade Representative said. Russia, the fourth-largest export market for U.S. pork, has banned all meat from five U.S. states and banned raw pork from a few others. It has also banned pork from certain Canadian provinces, the United Kingdom and Spain.

(Reporting by Noe Torres, Dan Trotta, Pascal Fletcher, Alistaor Bell, Robin Emmott in Mexico, Stephanie Nebehay, Laura MacInnis, Jonathan Lynn in Geneva, Darren Schuettler in Bangkok; Writing by Maggie Fox; Editing by Eric Beech)

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