Mexico City/Geneva/Toronto/London, April 28 (Inditop) The death toll from swine flu rose to 152 in Mexico Tuesday and spread like a contagion with cases being reported from the US, Canada, Britain, New Zealand, South Korea and Israel as the WHO raised its pandemic alert level to four.

The World Health Organization (WHO) raised its pandemic alert level to phase 4 — the maximum alert level is six – in response to the rapid spread of the H1N1 swine flu outbreak but did not recommend restrictions on travel, DPA news agency reported from Geneva.

Phase 4 means that there is sustained human-to-human transmission of the virus, which causes respiratory illness in pigs and is a genetic mix of swine, human and avian flu strains, in at least one country.

A pig farming area in Mexico’s eastern coastal state of Veracruz might be the source of the swine flu strain that has killed 152 people in that country, Xinhua news agency said from Mexico City.

As the flu spread, countries all over the world took step to contain the disease, which mimics the symptoms of influenza with fever, coughing, muscle ache and fatigue, including intense screening of passengers at airports.

In Mexico, Health Secretary Jose Angel Cordoba said the toll from confirmed or suspected swine flu cases had risen to 152.

Officials said most of the people who were killed in the flu epidemic were adults aged between 20 and 50. No cases in children have been reported yet.

Canada, which has so far reported six cases of swine flu linked to the Mexican outbreak, also tightened airport screening for home-bound passengers and farm workers coming from Mexico.

Each year, more than a million Canadian tourists visit Mexico, while thousands of Mexicans come as temporary farm workers in Canada.

The US reported 40 cases, and 10 cases were confirmed in New Zealand as public health authorities throughout the Asia-Pacific region went on high alert.

In Israel, a 26-year-old man who had returned from Mexico with flu-like symptoms was diagnosed with the virus.

Australians were warned against travel to Mexico as doctors monitored the health of 20 people who returned from the Americas with flu-like symptoms.

Thailand and South Korea also reported suspected cases of the mutated virus as many countries issued travel advisories.

As concern mounted, WHO said only two types of anti-viral drugs – Tamiflu, also known generically as oseltamivir, and Relenza, which is known as zanamivir – were effective.

The drugs, which are under patent, are manufactured by three major multinational companies – Tamiflu by the Switzerland-based Roche and the US-based Gilead and Relenza by Britain-based GlaxoSmithKline.

Some 220 million doses of Tamiflu are in the hands of governments across the world, but rich countries hold most of them – a fact that first came to light after the bird flu epidemic of 2004 (Tamiflu can also cure bird flu).

Britain’s state-funded health system has stockpiled enough doses of Tamiflu to treat 30 million people – roughly half the country’s population – if there is a swine flu outbreak.

The US has 50 million doses of Tamiflu and Relenza.

By contrast, Indian health authorities say they have a million doses of Tamiflu. In addition, Indian pharmaceutical company Cipla, which makes generic copies of Tamiflu, has said it can make another 1.5 million doses within a period of four to six weeks.

WHO also holds stocks of Tamiflu.The outbreak and spread of swine flu has come at a time when the global economy is trying to come out of the worst downturn since World War II and has threatened chances of an early recovery, especially in the US.