Posted on 01/13/2006 5:57:14 AM PST by Mother Abigail
Mutation Could Help Virus Spread to Humans
As bird flu spreads across Turkey with surprising speed, scientists have discovered that the deadly H5N1 virus has undergone genetic mutations that are thought to ease its transmission from bird to human.
A World Health Organization lab in Britain this week tested samples of the virus taken from two Turkish victims, and found a mutation that could help make the virus more transmissible from birds to people.
Also troubling is that some people seem to get infected with the often deadly H5N1 strain of the virus without developing symptoms. However, one of two boys in an Ankara hospital who tested positive for H5N1 without showing symptoms has now started to fall ill, said Dr. Guenael Rodier, head of the WHO mission to Turkey.
"As the new cases of human infection with the H5N1 virus in Turkey show, the situation is worsening with each passing month and the threat of an influenza pandemic is continuing to grow every day,"
(Excerpt) Read more at service.spiegel.de ...
_ Jan 12, 2006: Turkish Health Ministry confirms third sibling from Dogubayazit died of H5N1 strain of bird flu. Reports two other cases, raising number of people infected in Turkey to 18.
_ Jan 11: Agriculture Ministry says bird flu outbreaks confirmed in poultry in 11 of Turkey's 81 provinces and suspected in more than a dozen.
_ Jan 10: Authorities say a woman from central Turkish province of Sivas tested positive for H5N1. Authorities order 300,000 fowl culled.
_ Jan 9: Turkey declares five more humans infected with H5N1, in eastern town of Van, in Kastamonu and Samsun, on the Black Sea coast and in Corum, central Turkey. Cases also reported from easternmost Iranian border to Istanbul, on the edge of Europe as people rush to get tested.
_ Jan 8: Preliminary tests for H5N1 return positive in three people in Ankara, indicating the virus is spreading in Turkey.
_ Jan 7: World Health Organization confirms a brother and sister from Dogubayazit died of deadly H5N1 strain, the first human fatalities from the disease outside East Asia.
_ Jan 6: Third sibling, 11-year-old girl, also dies, but her case is not confirmed as bird flu until later. Turkish authorities say two other patients have H5N1 strain.
_ Dec 31, 2005: The four siblings from the southeastern town of Dogubayazit near the Iranian border are hospitalized with suspected bird flu.
_ Dec 26: Authorities announce dead chickens in town of Aralik near border with Armenia have tested positive for bird flu.
_ Dec 15: Possible outbreak of bird flu in chickens in town of Aralik is first reported to Health Ministry. Authorities order fowl culled.
_ Oct. 28: Previous outbreak is declared successfully contained and quarantine is lifted.
_ Oct. 6: Turkish authorities report deadly H5N1 bird flu virus in poultry in northwestern town of Kiziksa, near Istanbul, impose quarantine, order tens of thousands of fowl culled.
More on the sequences from Turkey
The official WHO case count from Turkey has now risen to 18, matching the largest outbreak (Hong Kong 1997) to date for H5N1. A major question is whether there is something different about the Turkish virus.
The news dribbling out about the sequencing of the Turkish isolates is not encouraging but also not surprising.
As I noted several days ago, the proposition that the hemagglutinin protein of the isolates is "very close" to the avian sequences is not very informative because extremely small changes can cause important changes in host range, as studies by Stevens et al. on the 1918 HA show. That paper described studies with glycan array that looked at the binding of various viral HAs to various linkages of sialic acid, the cellular receptor.
Sialic acid is linked in two forms, one characteristic of bird intestinal cells, one characteristic of human lower respiratory tract cells, although we now know that humans have avian-type linkages in sialic acid in their upper respiratory tract.
Most avian viruses bind well to the avian receptor, human viruses to the human linked receptor, but the HA protein from a case from New York's second wave in the 1918 pandemic showed some affinity for both humans and birds.
I haven't seen the sequences for the Turkish cases, but news reports suggest this kind of adaptation to humans is what is being seen in some of the Turkish isolates.
Genetic tests of samples taken from Turkish victims of the bird flu virus show it has made a small change, but probably not enough to make it more dangerous yet, researchers said on Thursday.
The mutation is one of those that would be expected in a highly changeable virus, the experts said -- and is one of those that would be predicted to eventually allow it to cause a pandemic.
Samples from two of the first Turkish victims were sent to a WHO-affiliated laboratory in Britain for analysis. Scientists are carefully watching the virus to see if it makes the changes needed to allow it to easily pass from human to human -- which could spark a pandemic that could kill millions.
There were two different strains of virus in the bodies of the teenage victims, said Dr. Ruben Donis, team leader of the molecular genetics team of the U.S. Centers for Disease Control and Prevention's Influenza branch.
"One was a regular virus like we have seen in poultry in Turkey before -- no surprises there," Donis said in a telephone interview.
But half the viruses had a mutation in the a protein called hemagglutinin, which influenza viruses use to attach to the cells they infect. This protein is the "H" in a flu virus's designation.
This mutation has been found in the past to allow the virus to infect a greater range of cells via a structure known as sialic acid, Donis said.
"If you have this mutation, you have virus that can bind to more different sialic acid variations," he said.
This is only theoretical, Donis stressed. But when researchers have tested flu viruses in the lab, they found this particular mutation gave the virus a better ability to attach to human-like cells.
"If this was a wildfire mutation that would have caused the virus to spread like wildfire in a population, we would have seen it more often," he said.(By-line Maggie Fox, Reuters)
This last comment is not very useful. We know it isn't a "wildfire" mutation simply because we haven't seen the wildfire, not because we understand the relationship between the genetic changes and the biology.
We know some things, but mostly we are in the dark about what changes will turn this virus into a full-fledged pandemic strain. We may be one tiny change away or (in the best case) this is a change headed down an evolutionary cul de sac (not likely, but possible).
Which is why statements like this, from the same Reuters article, drive me crazy:
A spokeswoman at the World Health Organization said there was no evidence the mutation had much significance in making the virus either more transmissible to people, or more or less dangerous to them.
"It doesn't look as if it has significance regarding transmissibility or pathogenicity because it is not borne out by epidemiological evidence we have so far," WHO spokeswoman Maria Cheng said in Geneva.
First, it directly contradicts what the CDC scientist just said. More importantly, this proposition is not supported by the current state of our ignorance about the relationship between the genetic sequences and the biology.
The sequencing also shows that there are many genetic variants out there, sometimes infecting the same individual. Again, this is to be expected. This virus replicates into billions of copies in an infected person and it is lack of fidelity in this replication which is one source of the genetic variation upon which selective pressures act.
This mutation has been seen before in isolates from Hong Kong in 2003 and Vietnam in 2005 (Branswell, CTV). The Turkish sequences also bear similarity to the Chinese Qinghai viruses responsible for a mass kill of migratory birds there.
There is some good news in the sequencing. Apparently the virus is sensitive to both classes of antivirals (amantadine/rimantadine and oseltamivir (Tamiflu)/zanamivir (Relenza). (Branswell, CTV). But all in all, the Turkish picture is one of continued progression geographically and genetically.
posted by Revere
http://effectmeasure.blogspot.com
These are the type of societies that can broadcast "death to America" from every mosque, and every child in Turkey joins in the chant.
But somehow they cannot get out the word "Playing with sick or dead chickens will kill you"
Thank you for the update and your observations. I really appreciate both.
I am having trouble with the link at the end of your initial post so cannot read the entire article.
I got vaccinated in the 1970's for the swine flu that was to kill most of the globe, so I guess I'm protected. Jusdt in case I'm adding another layer of tinfoil to my hat.
Thanks for keeping life here in flyover country interesting. (Yes, and its the ducks and geese that flyover here)
FYI - and let me know if you want me to cease pinging you to B. Flu articles!
Thanks LJ - keep those pings coming my way. I do appreciate your efforts.
Could you please remove me from this ping list?
I appreciate the pings, lj. ;-D
Of course
MOSCOW -- Flamboyant legislator Vladimir Zhirinovsky yesterday urged Russian men to grab rifles and shoot migratory birds to stem the spread of avian flu from Turkey.
"We must force the government to stop the bird migration," Zhirinovsky said. "We must shoot all birds, field all our men and troops ... and force migratory birds to stay where they are."
"Vladimir Zhirinovsky yesterday urged Russian men to grab rifles and shoot migratory birds to stem the spread of avian flu from Turkey. "
Good grief! You just know they're gonna grab the Vodka before they decide to protect themselves from bird migration.
I have to wonder what kind of weapons they hunt with though. Those migrating ducks and geese fly pretty high up and it will take a flak gun to hit them.
Thanks! I've been "gone" for some days and found a bunch of Bird Flu articles waiting for me, so to speak.
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