The
Sars virus could pose a threat to humans for many years to
come, research suggests.
Scientists
have compared samples of the Severe Acute Respiratory Syndrome
virus from Singapore with samples from other countries where
it has struck.
They have
found that the main components of the virus have remained
unchanged as infection has spread across different countries.
Scientists
say the finding suggests that it is well adapted to resisting
attack by the human immune system - and so does not need to
evolve rapidly.
But the
stability of the virus also means that any vaccine that is
developed may remain effective against Sars for a long period.
Scientists
have identified the virus that causes Sars as a new member
of the Corona family. It has been dubbed Sars-CoV.
Usually
human coronaviruses have a high rate of genetic mutation which
can lead to new strains.
Vaccine
hopes?
Researchers
led by Dr Edison Liu, from Singapore's Genome Institute, studied
the genetic make-up of cultured Sars viruses from five different
sources.
They found
only a handful of mutation differences between the samples
- and it was thought these probably resulted from the virus
adapting to laboratory conditions.
The findings
were published in an on-line report from the Lancet medical
journal.
BBC science
correspondent Richard Black says that if the human immune
system is good at fighting a viral infection, that usually
produces changes over time in the genes of that particular
virus.
The virus
could be more resistant than previously thought.
But that
is not happening in the Sars coronavirus - suggesting our
immune systems are not very effective at producing defences
to it.
The World
Health Organization (WHO) has welcomed the study, but says
it is too early to tell whether significant mutations are
occurring.
Other
scientists comment that if the virus is relatively stable,
that may make it easier to design a vaccine.
However,
they also warn that vaccines against animal coronavirus diseases
have often been unsuccessful.
In
other developments:
China
reports six new Sars deaths and 118 new cases on Friday -
bringing the nationwide death toll to 230 and the overall
number of cases to 4,805
Taiwan's
state oil company suspends an exploration project with its
Chinese counterpart because Sars is preventing its officials
from travelling to China
Russia
takes additional measures to prevent to spread of Sars, including
ordering airlines not to sell tickets for China and closing
some border checkpoints
The WHO's
director general nominee, Jong-Wook Lee, is in China for talks
on Sars with Foreign Minister Li Zhaoxing
Authorities
in Beijing will go ahead with next month's university entrance
exams for 80,000 students, as officials say the number of
new Sars cases is declining.
Meanwhile
another study - also published on The Lancet website - concludes
that much of the lung damage associated with Sars is in fact
caused by the body's own response to infection.
Researchers
from the University of Hong Kong found a common pattern of
illness among 75 patients who were admitted to hospital following
an outbreak of Sars at Amoy Garden, a Hong Kong high-rise
housing estate.
For the
first week after admission, symptoms gradually improved, but
a deterioration set in during the second week of the hospital
stay.
Some 85%
of the patients developed recurrent fever after nine days.
This delayed
deterioration suggests that damage is being inflicted on the
lungs not by the continued spread of the virus, but by an
overblown immune response.
The
Sars virus could pose a threat to humans for many years to
come, research suggests.
