Flu viruses which target man tend to attach to cells further up the airway - maximising their chances of being passed on by coughing or sneezing.

Researchers found the bird flu virus attached itself to cells deep down in the human airways.

The University of Wisconsin research is published in the journal Nature.

The H5N1 strain of bird flu has spread across Europe, Africa and parts of Asia, has killed more than 100 people worldwide and infected about 180 since it re-emerged in 2003.

But it still cannot jump easily from human to human.

Scientists fear that if it gains that ability and mutates it could result in a human flu pandemic, with millions of deaths world-wide.

Target molecule

The Wisconsin team investigated why the virus could not spread easily between humans despite the fact that it could replicate efficiently in human lungs.

Flu viruses infecting humans and birds are known to home in on slightly different versions of the same molecule, found on the surface of cells which line the respiratory tract.

The latest study found the version of the molecule targeted by human viruses was more prevalent on cells higher up in the airway.

The molecule targeted by bird viruses, on the other hand, tended to be found on cells deep within the lungs, in structures called alveoli.

Thus the bird flu virus tended to be buried so deep in the lungs that was unlikely to be spread by coughing or sneezing.

If the virus was to acquire the ability to infect cells higher up in the airway, it could take a crucial step towards causing a human pandemic, researchers believe.

Victims 'unlucky'

Professor Ian Jones, of the University of Reading, said the study provided some explanation of why people, particularly children, had caught the virus and died and yet it had remained "bird flu".

"It seems they were just really unlucky and transmitted enough virus to their mouths for it to gain access to the lower lung, a distance shorter in children than adults.

"Casual contact with the virus may therefore not be as dangerous as initially thought."

However, Professor Jones said it was possible that the virus could mutate to gain the potential to attach to cells in the upper airway.

"It remains the case therefore that planning for that eventuality makes a great deal of sense."

Dr Laurence Tiley, a lecturer in molecular virology at the University of Cambridge, said: "This may at least in part explain why H5N1 is inefficient at transmitting person to person, although I doubt that it is the complete answer."

Resident volcanologist Bella Tubianosa said that because of the westward direction of winds, only the villages of Cogon, Tinampo, Gulang and Bolos in Irosin town and the villages of Bacolod, Sapa, Sangkayon and Biriran in Juban town were covered by the ash fall.

More explosions

"Phivolcs expects more explosions to occur in view of the volcano's recent reactivation," the agency said in its bulletin issued at 8 a.m. yesterday.

accompanied the explosion at 10:58 p.m., but three more earthquakes followed at 11:30 p.m., 11:32 p.m. and 11:37 p.m.

"Technically, it's an eruption, although it's only an ash explosion since the materials spewed were mostly ash and not pyroclastic ones," Ed Laguerta, Mount Mayon resident volcanologist who is based in Legazpi City in Albay, said late yesterday afternoon.
Laguerta, who went to Bulusan to assist in monitoring activities, said there was not much hazard or threat to life at present but only inconvenience to local residents, except for those near the crater.

He said no succeeding activity had yet taken place after Tuesday's ash explosion.

Bulusan usually exhibits a "one-shot deal" -- meaning, once it explodes, it will take days before another activity occurs, he said.

Laguerta noted the reactivation of certain fissures down the slopes, as manifested by smoke emissions.

Tubianosa said the ash ejection was preceded by at least 63 volcanic quakes and a loud grumbling.

Phivolcs warned people to stay away from areas within 4 km of the crater that has been designated as a permanent danger zone (PDZ). The zone, which covers portions of Juban, Barcelona, Bulusan and Irosin towns, is off-limits to the public because this will be affected by sudden explosions.

Nearby communities near the zone have been warned against more ash explosions that could generate life-threatening volcanic flows.

At 6 a.m. yesterday, the Phivolcs' seismic network around Bulusan recorded 18 low-frequency volcanic earthquakes, 41 high-frequency ones, and four explosion-type earthquakes.

High-frequency earthquakes are caused by the breaking of rocks. Low-frequency earthquakes are those caused by the movement of fluid or gas.

24-hour vigil

"What we are warning against are the more dangerous kinds of explosion," Phivolcs Director Renato Solidum said.

Hazardous eruption is characterized by tall eruption columns, pyroclastic flows moving down the slope, and lava flows.

Tubianosa said she could not yet tell if the volcano's situation would still worsen but her office was keeping a 24-hour vigil.

Aerial survey

Arnel Capili, regional director of the Office of Civil Defense, said an aerial survey of the volcano would be conducted today.

On Sunday, the Phivolcs raised Alert Level 1 in Bulusan after recording 73 high-frequency volcanic earthquakes, much higher than the usual five volcanic quakes in 24 hours. The next day, its seismic network recorded 58 volcanic earthquakes, compelling the agency to issue a warning on a possible explosion, which occurred Tuesday night.

"These are phreatic explosions, which are a precursor to an eruption ... These indicate volcanic unrest," Phivolcs volcanology officer-in-charge Jaime Sincioco said in a phone interview.

Sincioco said his office was treating the explosion as phreatic. This type of explosion occurs when water impounded in the crater flows into the cracks and meets the hot rocks, converting it to steam.

Disaster council

Yesterday, Gov. Raul Lee of Sorsogon immediately called the Provincial Disaster Coordinating Council to a meeting to assess the situation and prepare for any eventualities.

Lee asked the Department of Education to make available its classrooms in the affected areas and even in towns that might be hit by ash fall for possible evacuation.

He mobilized the Philippine Army, Philippine National Police and the Bureau of Fire Protection to clean up the national highway.

Bulusan, 43 kilometers south of the capital city Sorsogon, is one of the country's 22 active volcanoes. The Phivolcs defines "active" as volcanoes that have erupted in the past 500 years.

Before Tuesday's ash explosion, Bulusan's last activities were recorded from Nov. 27, 1994 to January 1995. It only caused ash fall in villages in Bulusan, Barcelona, Casiguran, Juban, Irosin and Gubat towns and was accompanied by at least 14 minutes of weak tremor.

The Philippines lies in an area in the Pacific basin that is vulnerable to earthquakes and volcanic eruptions.

Mount Pinatubo in Central Luzon, north of Manila, erupted in 1991 in the century's biggest blast, burying dozens of villages under tons of mud after lying dormant for 600 years.

More than 800 people died in the wake of Pinatubo's eruption, mostly from diseases in overcrowded evacuation camps.

It was just so unbelievable when it happened, because it's something you don't expect up here," Stacy said.

The U.S. Geological Survey said the quake had a magnitude of 3.9 and hit at 10:24 a.m. It was centered about 12 miles west of Eureka.

Law enforcement officers said the quake was felt in Libby, Eureka and the Yaak Valley.

The quake measured 4.0 on the Richter scale. The epicentre was about four kilometres southwest of the Inuit village of Puvirnituq, in the province's far north.

According to the Geological Survey of Canada, residents felt vibrations in their homes. Those near the epicentre said it sounded like an explosion when it struck after 5 p.m. ET.

Cathy Woodgold, a spokeswoman for the federal agency, said there were no reports of injuries or damage.

Four or five quakes of similar intensity typically strike eastern Canada each year.

Last month, a 4.5-magnitude quake struck the Thurso region, about 45 kilometres east-northeast of Ottawa.

= local time at epicenter
Time of Earthquake in other Time Zones
Location 30.051°S, 177.995°W
Depth 53.7 km (33.4 miles) set by location program
Region KERMADEC ISLANDS, NEW ZEALAND
Distances 90 km (55 miles) S of Raoul Island, Kermadec Islands
175 km (110 miles) NNE of L'Esperance Rock, Kermadec Islands
1005 km (630 miles) NE of Auckland, New Zealand
1410 km (870 miles) NNE of WELLINGTON, New Zealand
Location Uncertainty horizontal +/- 8.5 km (5.3 miles); depth fixed by location program
Parameters Nst= 67, Nph= 67, Dmin=89 km, Rmss=0.83 sec, Gp= 79°,
M-type=body magnitude (Mb), Version=Q
Source USGS NEIC (WDCS-D)
Event ID uskqad

Although the house sparrow continued to be the most common garden bird, its numbers have dropped from an average of 10 per garden in 1979 to 4.4 in 2006.

The starling, once the most common, is down to a quarter of those in 1979.

Some 86,000 children were among those who watched gardens and parks in the Royal Society for the Protection of Birds's January Big Garden Birdwatch.

The numbers involved broke the previous record set in 2004 of 419,000 participants.

The house sparrow was the most common bird seen over the two days - although the blackbird, recorded in 94% of all 270,000 gardens involved, was the most widespread - and 8.1m birds of 80 species were seen.


TOP 10 2006 SPECIES
Blue tits. Image: Mike Read/rspb-images.com
Blackbird - 94.71%
Blue tit - 84.44%
Robin - 84.19%
House sparrow - 67.71%
Chaffinch - 58.99%
Collared dove - 58.54%
Woodpigeon - 57.28%
Great tit - 57.10%
Starling - 50.95%
Greenfinch - 45.25%
(Numbers are the percentage of gardens the species were seen in)

Co-ordinator Richard Bashford told BBC Radio 4's Today programme "a lack of food for the chicks" was causing the fall in the number of house sparrow sightings.

Bird-lovers should leave food out and allow their garden grass to grow to create a better environment for birds to catch insects, he added.

However, some bird species have increased, with the greenfinch population growing 67% in the past 27 years and the wren jumping 140%.

Many people spotted more blackbirds and song thrushes, and other less common species.

There had been an "amazing rise in small finches", Mr Bashford told Today.

"The number of siskins, which are super colourful birds, was up by 483% from last year, and bramblings were up by 371%.

"This highlights the importance of our gardens to birds coming to the UK in search of food and shelter and escaping the harsh winter weather on the continent."

The survey had been "extremely well supported... even in the most built-up areas where you might not expect people to watch birds," Mr Bashford added.

"In Greater London, nearly 30,000 people spotted 400,000 birds this year.

"It is fantastic there is so much interest in the wildlife around us with more people then ever enjoying the birds in their gardens."