(Adds fresh comment from WHO in Geneva)

By Mita Valina Liem

JAKARTA, May 23 (Reuters) - An Indonesian girl has died of bird flu and Vietnam reported on Wednesday its first suspected human infection since late 2005, in a string of cases across Asia when the H5N1 virus is usually less active.

In Pakistan, authorities said thousands of chickens were culled at three poultry farms on the outskirts of Islamabad, while Bangladesh struggled to control the virus in birds after outbreaks on dozens of farms.

The 5-year-old Indonesia girl, from Central Java province, died last week, a Health Ministry official said on Wednesday.

Authorities were still investigating the case, but at least 20 chickens had died suddenly near her home, the official said.

Contact with sick fowl is the most common way humans become infected with the H5N1 virus.

The girl's death brings the number of confirmed human fatalities in Indonesia to 77, the highest in the world.

Vietnam said on Wednesday a 30-year-old man was in a serious condition and the World Health Organisation said it would verify tests that showed he was infected with bird flu.

"This is the first suspected human case since November 2005 and the procedures are the government, the Health Ministry share the sample with WHO for verification at a WHO laboratory," said Hans Troedsson, the WHO's representative in Vietnam.

State media said the man, from Vinh Phuc province near the capital Hanoi, had developed a fever and had difficulty breathing two days after he helped slaughter chickens at a friend's wedding about a month ago.

News of the suspected case came just a day after Vietnam reported bird flu had killed nearly 1,900 ducks on farms across the country in the past week.

The WHO says 186 people have died of bird flu since the H5N1 virus resurfaced in Southeast Asia in 2003. The virus has since spread throughout much of Asia, parts of Europe, the Middle East and Africa.

GLOBAL THREAT

Scientists previously found the H5N1 virus to be most active and transmissible among birds during the cooler months from October and March in the northern hemisphere.

But of late, experts have found that it has become hardier, staying alive longer in higher temperatures and in moist conditions.

In damp conditions -- which is normally the case in Southeast Asia -- the H5N1 virus can stay alive for at least a week at room temperature.

Heat-stable strains of H5N1 have also been circulating in ducks in Vietnam, Indonesia and China at least since 2004 -- which could mean the virus poses a risk all year round.

Scientists say H5N1 is a global threat because the virus could mutate into form that passes easily between people, triggering a pandemic in which millions could die.

For the moment, it remains largely a disease in birds but scientists are worried about the virus's persistence and ability to adapt to new environments and hosts.

Indonesia, along with a number of developing nations, has been pushing for guarantees to access affordable vaccines in the event H5N1 acquires the ability to jump from human to human.

The WHO on Tuesday agreed to demands from Indonesia to revamp its 50-year-old system for sharing influenza virus samples, which are used to develop commercial vaccines.

Sharing samples is deemed vital to see if viruses have mutated, become drug resistant or grown more transmissible.

However, a shortage of pandemic influenza vaccines will last for at least five years, leaving three-quarters of the population unprotected against a potential outbreak, a senior United Nations official said on Wednesday.

David Heymann, the WHO's head of communicable diseases, said drugmakers can produce enough vaccine for only 1.5 billion of the globe's 6.2 billion people.

"The world is not prepared for a pandemic should it occur today. We don't have enough vaccine," Heymann told journalists in Geneva. (Additional reporting by Ho Binh Minh in Hanoi, Augustine Anthony in Islamabad, Tan Ee Lyn in Hong Kong, Anis Ahmed in Dhaka, Stephanie Nebehay and Laura Macinnus in Geneva and Orla Ryan in Accra)

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