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The
identification of a new coronavirus as the pathogen of SARS was achieved at
a rate not previously displayed. In February 2003, using an electron
microscope, Chinese virologists were the first to observe the new virus in
material taken from SARS patients. An international consortium of
laboratories, co-ordinated by the WHO and driven by a mixture of
co-operation and mutual competition, was able to isolate the new virus and
to convincingly associate it with SARS within a matter of weeks (Peiris et al., 2003; Drosten et al., 2003; Ksiazek et al., 2003). This was achieved by using a combination of classical
and modern techniques, including electron microscopy, virus culture,
serology, animal experiments, and RT-PCR (a diagnostic method based on the specific
amplification of parts of the viral genome).
It
was established that, during their illness and recovery, SARS patients
developed antibodies against the new virus, a strong indication that the
virus was also the cause of the disease. Similar antibodies could not be
identified in control subjects, which also suggested that, prior to this,
the SARS virus had not circulated in the human population. Strong
indications that the new virus could cause SARS were obtained by infecting
monkeys with the virus, after which they were found to develop symptoms
similar to those of SARS.
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SARS-coronavirus
replicates very efficiently in African green monkey kidney cell line
Vero-E6. This electron micrograph shows large amounts of virus leaving the
infected cells at 9 hours post infection.
Courtesy of the Department of Molecular Cell
Biology, Leiden University Medical
Center, the Netherlands.
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The fact that the SARS virus, contrary to most other human
coronaviruses, is able to replicate extremely efficiently in certain cell
lines (laboratory
cell cultures that can divide indefinitely), such as, for
instance, monkey kidney cells (cell line Vero-E6), was of great advantage
to the research. As a consequence, sufficient viral research material quickly
became available.
Approximately
one month after the WHO alert, research groups in Vancouver and Atlanta
almost simultaneously managed to elucidate the complete genome sequence (the order of the four building
blocks that make up the genome) of SARS-CoV and published it online (Rota et al., 2003; Marra et al., 2003). It could now
be ascertained definitively that the virus belongs to the coronavirus
family, a group of positive strand RNA-viruses, several animal and human
variations of which were already known. However, it immediately became
apparent, that the SARS-CoV possesses a number of unique characteristics,
not only as a pathogen but also on a molecular biological level (Snijder et al., 2003; Thiel et al., 2003).
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