Ducks may silently pass along bird flu
19.07.05 10.20am
WASHINGTON - The bird flu virus that experts fear will jump from birds to humans seems to be mutating yet again, and may be able to hide in healthy-looking ducks, thus putting both other birds and people at risk, experts said on Monday.
They said the H5N1 virus could kill some ducks after causing only mild symptoms -- which means it could lurk, undetected, in flocks while spreading silently.
"There is a real possibility that if these H5N1 viruses continue to circulate, further human infection will occur, increasing the potential for human-to-human transmission," the researchers write in this week's issue of the Proceedings of the National Academy of Sciences.
The H5N1 strain has killed more than 50 people in Asia since 2003. More than 140 million chickens have been slaughtered in the region in a bid to halt the disease.
Public health experts say the avian flu virus is mutating and fear it could develop the ability to spread easily from person to person and kill millions in a flu pandemic.
Dr Robert Webster of St. Jude Children's Research Hospital in Memphis, Tennessee, and colleagues found more evidence of the virus mutating.
"Wild waterfowl, including ducks, are natural hosts of influenza A viruses," they wrote.
"These viruses rarely caused disease in ducks until 2002, when some H5N1 strains became highly pathogenic," they said, adding that their study showed the viruses were again becoming harmless to ducks.
Webster's team tested the newer strains of the H5N1 virus, including some taken from human patients in Vietnam.
They infected four-week-old mallard ducks, dripping various strains of the virus into the throat, eyes and elsewhere. Then they put uninfected ducks into the same cages.
All the various strains of H5N1 infected the new ducks, including samples taken from human patients.
So then they tested each individual strain in more ducks.
"Viruses that caused the death of at least one duck could cause very mild symptoms, such as cloudy eyes with no neurological signs," the researchers wrote.
Health officials need to take note, the researchers said, because since the virus began making ducks as well as chickens sick in 2002, they had been looking for sick birds in checking for outbreaks of avian influenza.
Not only that, but the ducks that survived infection also spread the virus for weeks afterward, both in their droppings and from the respiratory tract.
"Therefore, the duck may be resuming its role as a reservoir of H5N1 viruses, transmitting them to other bird species and potentially to mammals," the researchers concluded.
"There may be many more ducks infected with low-pathogenicity viruses than are currently detected."
They recommended that health authorities start a survey to see if the virus is infecting even healthy-looking birds across the entire region.
Earlier this month researchers reported that H5N1 was infecting and killing wild geese in a Chinese park -- wild geese that migrate as far afield as Siberia and New Zealand.
The researchers said in a separate report on Monday that Roche's influenza drug Tamiflu can help laboratory animals and, it is hoped, people, survive the newest strain of H5N1 virus.
Government officials are buying up stocks of Tamiflu and are also working to develop and stockpile a vaccine that works against avian flu in case it does begin to infect people.
- REUTERS
WASHINGTON - The bird flu virus that experts fear will jump from birds to humans seems to be mutating yet again, and may be able to hide in healthy-looking ducks, thus putting both other birds and people at risk, experts said on Monday.
They said the H5N1 virus could kill some ducks after causing only mild symptoms -- which means it could lurk, undetected, in flocks while spreading silently.
"There is a real possibility that if these H5N1 viruses continue to circulate, further human infection will occur, increasing the potential for human-to-human transmission," the researchers write in this week's issue of the Proceedings of the National Academy of Sciences.
The H5N1 strain has killed more than 50 people in Asia since 2003. More than 140 million chickens have been slaughtered in the region in a bid to halt the disease.
Public health experts say the avian flu virus is mutating and fear it could develop the ability to spread easily from person to person and kill millions in a flu pandemic.
Dr Robert Webster of St. Jude Children's Research Hospital in Memphis, Tennessee, and colleagues found more evidence of the virus mutating.
"Wild waterfowl, including ducks, are natural hosts of influenza A viruses," they wrote.
"These viruses rarely caused disease in ducks until 2002, when some H5N1 strains became highly pathogenic," they said, adding that their study showed the viruses were again becoming harmless to ducks.
Webster's team tested the newer strains of the H5N1 virus, including some taken from human patients in Vietnam.
They infected four-week-old mallard ducks, dripping various strains of the virus into the throat, eyes and elsewhere. Then they put uninfected ducks into the same cages.
All the various strains of H5N1 infected the new ducks, including samples taken from human patients.
So then they tested each individual strain in more ducks.
"Viruses that caused the death of at least one duck could cause very mild symptoms, such as cloudy eyes with no neurological signs," the researchers wrote.
Health officials need to take note, the researchers said, because since the virus began making ducks as well as chickens sick in 2002, they had been looking for sick birds in checking for outbreaks of avian influenza.
Not only that, but the ducks that survived infection also spread the virus for weeks afterward, both in their droppings and from the respiratory tract.
"Therefore, the duck may be resuming its role as a reservoir of H5N1 viruses, transmitting them to other bird species and potentially to mammals," the researchers concluded.
"There may be many more ducks infected with low-pathogenicity viruses than are currently detected."
They recommended that health authorities start a survey to see if the virus is infecting even healthy-looking birds across the entire region.
Earlier this month researchers reported that H5N1 was infecting and killing wild geese in a Chinese park -- wild geese that migrate as far afield as Siberia and New Zealand.
The researchers said in a separate report on Monday that Roche's influenza drug Tamiflu can help laboratory animals and, it is hoped, people, survive the newest strain of H5N1 virus.
Government officials are buying up stocks of Tamiflu and are also working to develop and stockpile a vaccine that works against avian flu in case it does begin to infect people.
- REUTERS
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