SINGAPORE (Reuters) - Leading influenza experts urged nations not to lower their guard against the deadly and hardy H5N1 virus, saying it now survives longer in higher temperatures and in wet and moist conditions.
Scientists previously found the virus to be most active and transmissible among birds in the cooler months from October to March in the northern hemisphere, and many people were hoping for some respite in the coming summer months.
But influenza expert Robert Webster warned against complacency and underestimating the virus, which made its first documented jump to humans from birds in 1997 in Hong Kong, killing six people.
"When we tested the virus in Hong Kong from 1997, the virus was killed at 37 degrees Celsius (98 Fahrenheit) in two days. The current H5N1 is still viable for six days at 37," said Webster, from St Jude Children's Research Hospital in the U.S. city Memphis.
"H5N1 at room temperatures can stay (alive) for at least a week in wet conditions," Webster told Reuters on the eve of a bird flu conference organised by the Lancet medical journal in Singapore.
"One of the often overlooked facts about influenza is that it's more heat stable than people realise, especially under moist, damp conditions ... Don't trust it," he said.
Webster said heat-stable strains of H5N1 were already circulating in ducks in Vietnam, Indonesia, China in 2004 and 2005 and experts would have to test if this trait was in the variants now circulating in India, Africa, Europe and parts of the Middle East.
Since re-emerging in Asia in late 2003, the H5N1 virus is known to have infected 205 people, killing 113 of them. In the past few months, it has spread from Asia to parts of Europe, the Middle East and Africa.
Although it is predominantly a bird disease and most of the victims contracted the virus directly from poultry, experts fear it might change into a form that transmits easily among people and trigger a pandemic.
BREAKING THE CHAIN
The virus's growing adaptability to water has ominous implications because it means untreated water might no longer be safe, Webster said, and it was important to drink boiled water.
"This means that water supplies for feeding chickens, or water supplies where people are swimming and water supplies for villages have got to be treated," he said.
Other experts also called for concerted action and determination in breaking the chain of transmission of the virus, which resides largely in the world's reservoir of 250 billion domestic birds and 50 billion migrating birds.
"You can break the chain of transmission into the human population. The best place to break it is either to protect the domestic birds from the migratory birds. Or alternatively, remove humans from the domestic birds and break the chain of transmission and you are halfway there," said John Oxford, virology professor at the Royal London Hospital.
Kennedy Shortridge, who spent three decades studying influenza viruses, called for a complete rethink of the way poultry should be raised in parts of Asia, where ducks -- natural reservoirs of flu viruses -- are raised in padi fields to get rid of rice pests. Ducks are also raised alongside chickens, and cross infection is all too common.
"When I first saw the beginnings of intensive raising of poultry in the early 1980s in southern China, to me, the alarm bells were there," said Shortridge, who described these padi fields as "nothing more than faecal soups of influenza viruses".
In an interview, he also called for a change in the ways chickens are now raised. Conditions were often too stressful for the birds and this made them vulnerable to disease.
"We've got to find other sources of protein, other than just chicken. And the chickens have to be raised in such a way that the birds are not going to be stressed and not susceptible to so many infections," he said.