Download SARS and Koch`s Postulates - Missouri State University

Identity of killer pneumonia bug confirmed
13:25 02 April 03
NewScientist.com news service
Scientists have satisfied key tests that confirm that the virus causing the global outbreak of severe pneumonia is
a new type of coronavirus. Severe acute respiratory syndrome (SARS) has so far struck down more than 2300
people, and killed 78.
The identification will speed up the testing of victims and their contacts to see how the disease spreads, and
how it might be contained. That is badly needed, with new cases being announced each day in Hong Kong and
China, and in previously unaffected countries, such as South Africa, the Philippines and Malaysia.
In another sign of the seriousness of the growing outbreak, the World Health Organization issued an
unprecedented advisory on Wednesday, warning people not to travel to Hong Kong or the adjacent Guangdong
province of China.
SARS first surfaced in Guangdong and was then carried to Hong Kong. China has claimed its epidemic was
under control but on Wednesday a further 361 cases, and nine deaths, were revealed to have occurred in
Guangdong in March. Also on Wednesday, WHO experts finally got the go-ahead to visit Guangdong.
On a more optimistic note, SARS outbreaks in Vietnam, Singapore and Canada, started by travellers from Hong
Kong, have now been largely controlled, according to David Heymann, head of infectious diseases at the WHO.
Heymann says the virus is spread by direct contact, or large droplets of body fluids possibly deposited on
surfaces. He rules out spread by tiny, aerosol droplets. "If that was the case we'd have far more cases," he told
New Scientist.
Triple test
The cause of the disease has been uncertain, with two suspect viruses having been detected in patients. But on
Tuesday, the WHO's Klaus Stöhr, who is coordinating the 11 labs worldwide that are collaborating on SARS,
said: "We believe a coronavirus is the major causative agent".
To be definitively declared the cause of SARS, the novel virus must satisfy three conditions known as Koch's
postulates. These were devised in 1890 by the German scientist Robert Koch, initially for anthrax infections.
First, the suspect microbe must be isolated from all, or nearly all, cases; second, it must be cultured in isolation;
and third, those cultured germs must be able to re-create the disease in a test animal.
Albert Osterhaus of Erasmus University in Rotterdam, the Netherlands, told New Scientist that the coronavirus
has now been isolated from patients in several different countries, and grown in several labs.
Now Osterhaus has cracked Koch's third, and toughest postulate. "We have infected an animal," he says. He
will not yet reveal what kind, but says he has tested the virus in primates and mice. Besides showing the virus is
the pathogen, says Osterhaus, the infected animals can now be used to screen antiviral drugs.
A vaccine would also be extremely valuable. Because vaccines mainly work by inducing antibodies to the
pathogen, the fact that recovering SARS patients produce high levels of antibodies is encouraging. Vaccine
companies have already been given virus samples, says Stöhr.
Also encouraging are reports that blood serum from convalescents, containing the antibodies, have helped to
save 20 severely ill SARS victims in Hong Kong.
Debora MacKenzie