- LONDON (Reuters Health) -
Scientists scrambling to pin down the cause of the frightening respiratory
illness spreading worldwide are nearing an answer, but as of Thursday the
picture remains decidedly uncertain.
-
- The prime suspect is a coronavirus that probably originated
in animals, said World Health Organization (WHO) expert Dr. Wolfgang Preiser,
but current theories about severe acute respiratory syndrome (SARS) hint
that another recently discovered virus and even a new form of chlamydia
might also play a role in some patients.
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- "It's a very varied picture, and it may already
be outdated in two days' time because the evidence is rapidly evolving,"
Preiser told Reuters Health in a telephone interview.
-
- The German researcher is one of five experts on a WHO
mission to learn more about SARS at the epicenter for the disease in China's
southern Guangdong province. His laboratory in Frankfurt was involved in
treating three patients in Germany.
-
- One day after they arrived in Guangdong, the WHO group
has confirmed that the outbreak of "atypical pneumonia" reported
by Chinese authorities last year is the same thing as SARS.
-
- But other crucial questions, like what causes the disease
and where it came from, are unanswered.
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- CERTAINLY SOMETHING NEW
-
- The first step for the WHO network of laboratories was
to rule out known infectious agents as the cause of SARS. That has now
been ascertained, thanks to a molecular technique called polymerase chain
reaction (PCR), which can detect tiny pieces of genetic material.
-
- "We are quite certain that we were dealing with
a new agent," Preiser said. "This is something that has not been
described before in humans or animals."
-
- The collaborators then set about trying to grow the agent
in the laboratory. Several labs around the world identified coronavirus
in their local patients, and a comparison showed they were highly genetically
related.
-
- "They are virtually indistinguishable," Preiser
said.
-
- Coronaviruses can cause the common cold in humans, and
serious diseases in animals. The evidence hints that the new virus has
jumped from an animal, but Preiser said facts were not strong enough yet
to say what kind of animal.
-
- WHY DO SOME DIE, SOME SURVIVE?
-
- In some patients, SARS spreads extremely aggressively
and causes severe disease -- killing about 3.5 percent of those infected.
But others recover quickly and do not seem to have infected many other
people.
-
- "We don't know why that should be," Preiser
said. "It's obvious that they've been exposed to the same agent."
-
- Two other findings could, just possibly, explain this.
-
- First was the identification by German and Canadian researchers
of another virus in some patients with SARS. The metapneumovirus -- part
of the paramyxovirus family -- was discovered only recently, but is known
to cause respiratory diseases in children.
-
- "Human metapneumovirus may play an important role
as a co-factor, because it is quite unexplained so far why some patients
spread the illness to many others, and some patients don't seem to spread
very much -- also, why some patients fare very badly clinically, and others
have a rather mild disease," Preiser said.
-
- The same could be true for chlamydia, a common type of
bacteria that can cause respiratory infections. In several patients, doctors
have found evidence of infection with a chlamydia species.
-
- "This may be one of the chlamydia species that we
know already, or it may, alternatively, be something new," Preiser
said.
-
- In the end, however, all this might be overturned as
new evidence arises. Scientists in the WHO network are talking on a daily
conference call and posting information on a secure Web site.
-
- "All types of things have to be done still,"
the German researcher said, including wide-ranging tests to see how common
the new coronavirus is in the general population and a crucial experiment
to see if it will trigger disease in animals.
-
- "That is actually going on at the moment,"
he said.
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