When pigs fly: Avian-Swine flu hybrid?

[Guest guest]

Scientists fear potent hybrid flu may develop 2009/07/30

BIRD flu kills more than 60 percent of its human victims, but doesn't easily

pass from person to person. H1N1, or swine flu, can be spread with a sneeze or

handshake, but kills only a small fraction of the people it infects. So what

happens if they mix?

This is the scenario that has some scientists worried: The two viruses meet –

possibly in Asia, where bird flu is endemic – and combine into a new bug that is

both highly contagious and lethal and can spread around the world.

Scientists are unsure how likely this possibility is, but note that the new

swine flu strain – a never-before-seen mixture of pig, human and bird viruses –

has shown itself to be especially adept at snatching evolutionarily advantageous

genetic material from other flu viruses.

" This particular virus seems to have this unique ability to pick up other

genes, " said leading virologist Dr Webster, whose team discovered an

ancestor of the current flu virus at a North Carolina pig farm in 1998.

The current swine flu strain – known as H1N1 – has made more than 2300 people

sick in 24 countries. While people can catch bird flu from birds, the bird flu

virus – H5N1 – does not easily jump from person to person. It has killed at

least 258 people worldwide since it began to ravage poultry stocks in Asia in

late 2003.

The World Health Organisation has reported two new human cases of bird flu. One

patient is recovering in Egypt, while another died in Vietnam – a reminder that

the H5N1 virus is far from gone. " Do not drop the ball in monitoring H5N1, " WHO

director-general Margaret Chan told a meeting of Asia's top health officials in

Bangkok . " We have no idea how H5N1 will behave under the pressure of a

pandemic. "

Experts have long feared that bird flu could mutate into a form that spreads

easily among people. The past three flu pandemics – the 1918 Spanish flu, the

1957-58 Asian flu and the Hong Kong flu of 1968-69 – were all linked to birds,

though some scientists believe pigs also played a role in 1918.

Webster, who works at St Jude's Children's Research Hospital in Memphis,

Tennessee, said bird flu should be a worry now. Bird flu is endemic in parts of

Asia and Africa, and cases of swine flu have already been confirmed in South

Korea and Hong Kong. " My great worry is that when this H1N1 virus gets into the

epicentres for H5N1 in Indonesia, Egypt and China, we may have real problems, "

he said .

" We have to watch what's going on very diligently now. "

US Centre for Disease Control and Prevention (CDC) spokesperson Dave Daigle said

he could not comment specifically on how concerned the agency was about the

scenario Webster described, or what it was doing to study such a possibility.

Malik Peiris, a flu expert at Hong Kong University, said the more immediate

worry was that swine flu would mix with regular flu viruses, as the flu season

was in swing in the southern hemisphere. It was unclear what such a combination

would produce.

But he said there were indications that that scenario was possible. Peiris noted

that the swine flu virus jumped from a farmworker in Canada and infected about

220 pigs. The worker and the pigs recovered, but the incident showed how easily

the virus could leap to a different species. " It will get passed back to pigs

and then probably go from pigs to humans, " Peiris said. " So there would be

opportunities for further reassortments to occur with viruses in pigs. "

He said so far bird flu had not established itself in pigs – but that could

change.

" If that were to happen and then these two viruses were both established in pigs

in Asia, that would be quite a worrying scenario. "

Osterholm, an infectious disease specialist at the University of

Minnesota who has advised the US government on flu preparations, said while flu

experts were discussing the scenario, he had yet to see specific evidence to

cause him to think it would happen.

" Everything with influenza is a huge guessing game because nature holds all the

rules ... so anything is possible, " he said. " We don't have any evidence that

this particular reassortment is that much more likely to pick up H5N1 than any

other reassortment out there. "

But there is, in fact, discussion of putting them together – in a high-security

laboratory – to see what a combination would look like, according to Webster.

Similar tests had been done at the CDC, mixing bird flu and seasonal human flu,

resulting in a weak product, he said. Daigle refused to comment on the prospect

of any such experiment.

Webster said underestimating the swine flu virus would be a huge mistake.

" This H1N1 hasn't been overblown. It's a puppy, it's an infant, and it's

growing, " he said. " This virus has got the whole human population in the world

to breed in – it's just happened. What we have to do is to watch it, and it may

become a wimp and disappear, or it may become nasty. " — Sapa-AP

http://www.dispatch.co.za/article.aspx?id=333517