UPDATE: New report on March 23rd with some additional details. See Vietnam: Worries Over Changes In H5N1
Although we often talk of H5N1 bird flu as if it were some monolithic entity – the exact same virus all around the world – the truth is there are a lot of different strains of H5N1 running around.
As flu viruses mutate rapidly, new strains are continually produced that are either `biologically competitive’ and go on to spread, or are not, and quickly fade away.
When one of these competitive strains diverges enough genetically from its ancestors, it is designated as being a new `clade’ of the virus.
Essentially a new branch on the virus’s family tree.
The WHO⁄ OIE ⁄FAO H5N1 Evolution Working Group has been working for some time on a nomenclature system designed to classify the A⁄goose⁄Guangdong⁄1⁄1996 lineage of H5N1.
As of a year ago, they had identified 10 well defined clades (and numerous sub-clades) of the virus, and they fully expect that more clades will evolve over time.
As you can see from the chart below, while additional clades have been established over the past 10 years, the greatest diversity has been among the Clade 2 viruses.
Bird flu is obviously continually evolving.
Which brings us to an article this morning, outlining concerns over `new strains’ of bird flu found to be circulating in Vietnam. The headline, referring to `swine flu’, is obviously in error.
This story appears to be about bird flu, despite the confused and mixed references.
First the report, then a little perspective.
Saturday ,Mar 13,2010, Posted at: 16:43(GMT+7)
The swine flu A/H5N1 virus has mutated into seven antigen groups since it appeared in the country, according to a conference on the virus in Hanoi to discuss last year’s results and plans for 2010.
Health officers destroy infected poultry. (Filed photo)
The virus’s future development would be hard to predict, Dr. Nguyen Huy Nga head of the Preventive Health and Environment Department told the national swine flu conference in Hanoi March 12.
The same day of the conference, the Preventive Health and Environment Department reported that a 25 year old woman was being treated for the virus in Bach Mai hospital in Hanoi. She had fallen sick on March 5.
Five cases, all fatal, were infected with A/H5N1 virus in 2009 nationwide, the conference heard.
In the first three months of this year in Vietnam, there have been four cases of the virus, including a 38-year old woman who died in Mekong Delta province of Tien Giang, said Nga.
Health experts warned that another new stronger virus could emerge from a combination of current strains to cause a new pandemic.
Nga said the steering committee for A/H1/N1 flu prevention needs to step up its monitoring and quarantine activities especially in hotspots in case a new more virulent strain develops.
Residents should not sell, buy or kill poultry without testing first and should never eat poultry that has died of an illness.
Newspaper articles such as this don’t really give us much information to go on. They are written for a `lay’ audience, and so terminology is often inexactly, incorrectly, or loosely used.
I tend not to put a lot of stock in the details gleaned these sorts of stories, but find they can be of general value.
My assumption is that when they use the word `strain’ or `antigen groups’, they probably mean `clade’.
But without knowing which seven strains (clades) were reported to be circulating in Vietnam, or whether any of them are truly `new’ – as is suggested by the headline - this story leaves us with far more questions than answers.
Presumably at some point we’ll get a scientific paper, or at least a more detailed report, coming out of this conference and will be better able to judge the significance of this story.
For now, it is probably sufficient to bear in mind that influenza viruses, like H5N1, are constantly evolving. What is true today about their capabilities and characteristics may not hold true tomorrow.
One of the reasons why the influenza story is fascinating to cover.
It never seems to run out of twists and turns.