Washington Post/MSNBC A horror script for health officials: Bird flu poses global epidemic threat

[Guest guest]

>A horror script for health officials

>The metaphor that public health officials invoke

>when talking about a global flu epidemic is the

>same one that lies at the heart of the scariest

>horror movies.

>http://msnbc.msn.com/id/4058992/

>

 

A horror script for health officials

Bird flu poses global epidemic threat

 

By David Brown

 

WASHINGTON, Jan. 25 - The metaphor that public

health officials invoke when talking about a

global flu epidemic is the same one that lies at

the heart of the scariest horror movies.

 

It is the idea of a small and deadly thing that

is poking and prodding for a weak spot in

whatever is protecting its intended victims. It

is patient, because it knows it will eventually

succeed. When it does, a horrible metamorphosis

makes it huge and unstoppable.

 

This plot was a deadly hit in 1968, 1957 and,

most notoriously, 1918, when pandemic influenza

killed about 50 million people worldwide. Today,

virologists fear a remake is underway in East

Asia.

 

Over the past month, a strain of bird flu that

has killed thousands of chickens in nearly half a

dozen countries has broken through the " species

barrier " to claim a few human victims. This time,

though, the public health community hopes to

write a different end to the script.

 

" There is a chance that something can go wrong, "

Klaus Stohr, head of the World Health

Organization's flu program, said Friday in

Geneva. " But it looks as if we act decisively and

timely now, there is a window of opportunity here

to control the disease before it takes global

proportions. "

 

That action consists of exterminating chickens

carrying the virus, protecting people in contact

with the birds from infection and understanding

the pathogen at the molecular level -- all as

quickly as possible. Cross-border traffic of live

birds and poultry products has stopped in much of

the region, and there is talk of vaccinating

millions of chickens.

 

So far, there is no evidence that this bird flu

can be passed from person to person -- a trait it

would need to acquire to make it a global threat.

 

" Everyone has their ear to the ground. That is

the big question, isn't it? " said Robert G.

Webster, one of the country's leading influenza

experts, who jetted to Hong Kong two weeks ago to

study the new strain.

 

Stakes could be higher than SARS

If evidence of person-to-person contagion

appeared, the already urgent response would

escalate dramatically. Borders would close, the

ill would probably be quarantined, and a crash

program to make a new version of the annual flu

shot would begin. The response would be much like

the one mounted against severe acute respiratory

syndrome (SARS) a year ago.

 

The stakes would be much higher, however, because

the flu virus, once fully adapted humans, can

spread with a speed and ease that SARS never

showed. A lot has to happen, though, for bird flu

to gain that capacity. The trouble is that in

influenza's world, a lot can happen very quickly.

 

Health authorities in Vietnam are investigating

30 suspected cases of bird flu in people.

Fourteen have died, most of them children under

age 12. In six cases, laboratory testing

identified a strain of avian influenza designated

H5N1. Late last week, two children in Thailand --

both still alive -- were diagnosed with H5N1 flu.

 

The H and N denote two proteins, hemagglutinin

and neuraminidase, that sit on the outer shell of

the virus. Together, they provide a virus's

chemical appearance to the immune system. The

particular combination of H and N is the key to a

strain's identity and the first hint of whether

it might be a danger to people.

 

There are 15 forms of hemagglutinin and nine of

neuraminidase in the most populous class of flu

viruses -- influenza A. (The less common and less

dangerous influenza B has only one type of H and

N).

 

When a virus with a new H-N combination appears,

immunity built up to older ones is no help. What

follows can be a worldwide epidemic -- assuming

the virus also grows well in people and is spread

easily in coughs and sneezes.

 

How pandemics happen

The great pandemic of 1918 was H1N1. It was

unquestionably new, although what strain it

replaced is not known. In 1957, an H2N2 virus

appeared in southern China, triggering a pandemic

of " Asian flu. " In 1968, an H3N2 virus appeared,

causing the global " Hong Kong flu. " In 1977, H1N1

reemerged -- by then, nearly everyone under age

20 had never seen it -- and caused a

mini-pandemic.

 

There are many H-N combinations, however, seen

only in other species, particularly birds, which

are the real home range for flu virus. The feared

H5N1 is one of them. It can tear through chicken

flocks with a mortality approaching 90 percent.

But virologists did not think it could infect

people -- at least, not until 1997.

 

That year, 18 people in Hong Kong became infected

with H5N1 -- the first time direct bird-to-people

transmission had been seen. Six died, most of

them healthy young adults -- a disturbingly high

percentage.

 

Previously, scientists believed that to infect

and kill a person, a bird flu virus would first

have to acquire at least a few genes from the flu

viruses that regularly circulate in human

populations. That is possible because unlike

viruses whose genes reside on a single unbroken

strand of RNA or DNA, flu carries its genetic

information on eight separate strands. Under the

right conditions, it can trade one of more of

them with another flu virus, like a card player

in a game of hearts.

 

Virologists once believed these " reassortments "

occurred only in pigs, because that species were

capable of being infected by both human and avian

flu. With the 1997 Hong Kong cases, however, it

was clear reassortment might also occur in a

person simultaneously infected by both.

 

The chance of that occurring depends on how much

avian flu is around. What scares scientists this

winter is that it is all over the place -- in

flocks in Japan, Vietnam, South Korea and now

Thailand.

 

" It is an unprecedented situation with H5N1 virus

in so many countries around Asia, " Webster said.

" The extent of the spread of this virus has not

been seen before. "

 

Chickens slaughtered across Asia

How H5N1 became so widespread is not known. The

urgent chore is to get rid of the animals

harboring it.

 

In recent weeks, tens of thousands of chickens

have been killed in flocks in Japan, Vietnam and

Thailand. The number could go much higher.

 

It is important to protect the workers culling

the flocks from getting human flu, lest they

themselves become the " mixing vessels " in which a

reassortment occurs. WHO is urging they be

vaccinated, and if possible be given preventive

medicines.

 

Even without reassortment, it is possible that

avian influenza could become a pandemic strain,

but that is far less likely.

 

" Given enough time and enough opportunity,

viruses could go through a process of human

adaptation and become more transmissible than

these ones are at the moment, " said Nancy J. Cox,

the head of the influenza program at the Centers

for Disease Control and Prevention. " We know,

though, that in 1968 and in 1957 the strains were

reassortments between human and avian viruses. "

 

Curiously, Hong Kong, where the first human cases

of bird flu occurred, is reporting no H5N1 now.

 

That region changed its poultry-marketing

practices after the 1997 outbreak. Waterfowl,

which can carry H5N1, were separated from

chickens. Quail, also viral hosts, were banned.

 

Markets were also required to be cleaned twice a

month. People were thought to have been infected

by breathing an infectious dust stirred up when

chickens, whose feathers were contaminated with

virus-containing feces, were taken flapping from

their cages.

 

Still, H5N1 continued to turn up occasionally

until last year, when a poultry vaccine began to

be used widely, Webster said. Today in Hong

Kong's markets, he said, " every chicken has had

its shots. "

© 2004 The Washington Post Company

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