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SARS: Pandemic fears in an interlinked
world
By Stephen Leahy
TORONTO - With reports that severe acute
respiratory syndrome (SARS) can survive for up to 24
hours on inanimate surfaces, turning any object into a
potential transmission source, it looks as if the virus
might indeed be the global pandemic suggested by health
experts. But what exactly does that mean?
David
Heymann, executive director of the communicable diseases
section at the World Health Organization (WHO), says
SARS could pose a more serious global health threat than
any other new disease in the past 20 years, with the
sole exception of the human immunodeficiency virus
(HIV), which causes AIDS.
The epidemic had
infected nearly 4,300 people and killed at least 251 in
25 countries as of Wednesday, according to WHO. Roughly
90 percent of the cases were in China and Hong Kong and
overall numbers were expected to continue to rise.
Thousands of people are currently in quarantine
worldwide, and that number could grow dramatically as
China struggles with the disease.
In an
unprecedented worldwide collaboration, scientists this
month identified SARS as a new coronavirus. "It took
three years to find the cause of AIDS and HIV," said WHO
spokesman Dick Thompson. "It took eight days to find the
cause of this disease."
On the other hand, SARS
is operating in a much more fast-paced, interlinked
world than that which spawned HIV, Heymann pointed out.
Its apparent incubation period of two to 10 days is long
enough for infected people who are asymptomatic to
travel "from one city in the world to any other city
having an international airport".
SARS can also
be spread via droplets, excreted when we sneeze or
cough, and the initial symptoms - dry cough, headache,
fever - are non-specific and common, he noted.
The global cost of the disease is already
estimated at US$30 billion, Heymann said.
The
family of coronaviruses, so named because of the
distinctive crown that encircles the viral particle,
cause 20-30 percent of common colds in humans as well as
diseases in many domestic animals, including pigs, cats,
dogs, cattle, chickens, turkeys, rats and mice.
Viruses are simply small packages of genetic
material - DNA or RNA - plus a few enzymes surrounded by
a protective coat of protein or fat. On their own, they
are relatively inert - unable to move, grow or
reproduce.
But what viruses do exceedingly well
is hijack the machinery of living cells they come into
contact with to make more viruses. Chemicals in their
"coat" act as a key to open the protective lock of a
cell membrane, giving the virus access to the genetic
material.
Once inside, the virus takes over the
cell so it can make copies of itself. As soon as enough
are created, the new viruses either leak out through the
cell membrane or cause the cell to self-destruct,
bursting open to release the viral progeny that move on
to colonize other cells.
Viruses easily swap
genetic information with other viruses or host cells.
The constant reshuffling enables them to jump from one
species to another. HIV, for example, is believed to
have transferred from wild animals in Africa to humans.
Animals are hosts to many kinds of viruses, most
of them benign, but a single gene change can make them
highly dangerous to other animals or humans. Many flu
viruses start in pigs or chickens, undergo mutation and
start infecting humans. The SARS virus may be another
example.
Controlling a highly contagious virus
is much more difficult without a diagnostic test. One
that would identify SARS in a person's blood or saliva
could be just weeks away after the Michael Smith Genome
Sciences Center in Vancouver recently announced the
virus's genetic sequence.
Drug companies "are
madly testing all of their drugs that work against AIDS
and hepatitis C right now to see if they work on the
coronavirus", said Kathryn Holmes, a coronavirus expert
at the University of Colorado Health Sciences Center in
Denver.
But Heymann cautioned that companies'
eagerness to develop a vaccine will hinge on how likely
it is that SARS will be here for the long term. The
ability to recoup research costs and make a profit will
drive their decisions.
"Can we prevent a global
pandemic of SARS?" asked US Centers for Disease Control
director Julie Gerberding, writing in the April 2 issue
of the New England Journal of Medicine.
If
civilization is lucky, she said, diagnostic tests and
treatment will be found to curtail the epidemic. A
seasonal pattern will evolve, allowing scientists to
contain infections within regions, and the infection
rate will slow.
But if the virus escapes the
noose of public health control strategies, the world
will be in for a long, difficult struggle, she
concluded.
(Inter Press Service)
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