World health officials Sunday stepped up the battle against a new swine flu blamed for dozens of deaths in Mexico, as the US declared a public emergency amid signs the disease was spreading.

The United States will screen visitors arriving from infected areas, Homeland Security Secretary Janet Napolitano said, as 20 cases were confirmed in five states.

Authorities in Mexico, where the new multi-strain swine flu was first detected, confirmed 20 people have died and warned the death toll could be as high as 81. Five people were said to have died in the capital in the past 24 hours.

"As we look for cases of swine flu, we are seeing more cases of swine flu. We expect to see more cases of swine flu," Richard Besser, the acting head of the Centers for Disease Control, told a White House press conference.

Besser said there were eight confirmed cases in New York City, seven in California, two in Texas, two in Kansas and one in Ohio.

US President Barack Obama is monitoring the swine flu outbreak closely and has ordered a "very active, aggressive, and coordinated response," said White House homeland security advisor John Brennan.

World Health Organization officials warned the new strain, apparently born when human and avian flu viruses infected pigs and became mixed, could further mutate.

"Yes, it's quite possible for this virus to evolve," Keiji Fukuda, acting WHO assistant director-general for health, security and the environment, told journalists in Geneva.

"When viruses evolve, clearly they can become more dangerous to people."

The WHO has already recommended that all nations "intensify surveillance for unusual outbreaks of influenza-like illness and severe pneumonia."

As thousands of panicked Mexicans wore surgical masks on the streets and sought to avoid physical contact, President Felipe Calderon called for calm, urging citizens to work with authorities to contain the virus.

Calderon said if people can make timely medical visits, Mexico "can contain this outbreak."

Of the 1,364 people treated for suspected swine flu, 929 of them -- or 67 percent -- have been discharged, Calderon said, adding that the country had the necessary drug stock piles to fight the virus.

Zoos joined schools, museums, theaters and music festivals which have closed down, and authorities sought to shut down bars and nightclubs.

The World Bank announced a 205-million-dollar loan to help Mexico fight the virus, including 25 million dollars available immediately in order to "get medicines and medical equipment to detect and diagnose" the virus outbreak, said Mexican Finance Minister Agustin Carstens.

"This virus has clearly a pandemic potential," WHO director general Margaret Chan warned on Saturday.

On CNN, senior White House adviser Valerie Jarrett was asked if Obama had tested negative for swine flu after he paid his first official visit to Mexico just over a week ago.

"He's fine. He is just fine," she said without elaborating.

Asian health officials also went on alert as the flu strain appeared to have spread to New Zealand .

Governments across the region, which has in recent years been at the forefront of the SARS and bird flu epidemics, stepped up checks at airports and urged the public to be on guard for symptoms of the new flu.

Ten New Zealand students who recently traveled to Mexico are "likely" to have contracted swine fever, Health Minister Tony Ryall said -- the first suspected cases in the region of more than three billion people.

Two people were admitted to an Australian hospital with flu symptoms after returning from Mexico and are being checked for swine flu, officials said Monday.

Nine people in Colombia were placed under observation after they arrived from Mexico with flu symptoms, and Spain screened all passengers arriving off flights from Mexico on Sunday and tested eight suspected cases of swine fever as fear spread through Europe.

In the first suspected swine flu case in the Middle East, a 26-year-old Israeli man has been hospitalized in Netanya on returning from Mexico, hospital officials told AFP.

Russia banned meat imports from Mexico, several US states and nine Latin American nations, a spokesman for Prime Minister Vladimir Putin said. US officials have said it is impossible to catch the flu from eating meat.

According to the WHO, pigs have already been factors in the appearance of two previously unknown diseases that gave rise to pandemics in the last century.

Source: http://www.nst.com.my/Current_News/NST/AfpNews/090426235930.i3fq2xh3.txt/afp