Is bird flu over?

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In a word: no, said scientists at a New Orleans meeting of tropical disease researchers. Still, they can’t explain why human cases of avian influenza have fallen for two years in a row after peaking in 2006.
‘Did we control it?’ asked Dr. Tawee Chotpitayasunondh of the Queen Institute of Child Health in Bangkok, Thailand. ‘Are we just lucky? Has the virus mutated to become less virulent?’
The ongoing bird flu outbreak began in Asia in late 2003. More than 250 million poultry in 61 countries have been killed by the virus or culled to stop its spread. The virus jumped the species barrier to infect four people the first year, all of whom died, raising fears of a pandemic that would match or surpass the one of 1918.
Confirmed human cases now stand at 389, of which 246 died. But the numbers have dropped from a high of 115 cases and 79 deaths in 2006 to 38 cases and 29 deaths for 2008, according to a World Health Organization update issued Tuesday.
A pandemic occurs when a flu virus undergoes a dramatic genetic shift and emerges as a novel strain to which no one has immunity. The one in 1918 killed an estimated 50 million people.
But to wreak so much damage, a virus must be able to spread from human to human, and do so readily. That’s the shoe that hasn’t yet dropped.
Most of the human cases continue to be traced to direct contact with poultry, most commonly in Southeast Asia where many people have backyard flocks and few wear gloves or masks to handle them. The few human-to-human transmissions have occurred in those who were directly involved in caring for an infected relative.
Since 2005, poultry outbreaks have spread through much of the world, although not to the Americas. Fifteen countries have had human cases.
So why the drop in 2007 and 2008?
In Thailand, Tawee said, ‘We’re starting to know how to fight it. We ask someone from each province to be Mr. Bird Flu.’
The appointee notifies authorities of an outbreak so that flocks can be quickly culled, and the Thai government compensates the family for losses.
Thailand has a reputation in Southeast Asia as being best prepared to deal with an outbreak, said Endang Rahayu Sedyaningsih Mamahit of the National Institute of Health Research in Jakarta, Indonesia. That doesn’t explain why cases are dropping elsewhere.
And until she understands it, she doesn’t trust it.
‘This isn’t the time to be happy,’ she said. ‘We’re seeing continued vigorous evolutionary change in the virus.’
And she doesn’t mean all good changes.
Japanese scientists, for example, last year reported that viruses circulating in Africa and Europe had mutated to more easily grow in the upper respiratory tracts of humans.
Also troubling, the virus is showing resistance to Tamiflu, one of just two antiviral treatments, not because of overuse but because of a natural mutation, researchers said.
On average, one major pandemic has occurred each century, and that makes influenza experts nervous.
‘We’re 90 years away from 1918,’ said Richard K. Kiang, a NASA scientist who uses satellite images to look for areas where wetlands meet crop lands and migratory birds mingle and share viruses with poultry.
As for Tawee, he doesn’t know the answers to the questions he posed. But this he does know:
‘If [a human form of] avian flu were to occur in Southeast Asia, within a month it would be in the U.S.,’ he said. ‘So the whole world must prepare.’

-- Mary Engel