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The
origin of SARS-CoV has certainly not been unequivocally established to date
and no proven vaccine or medication against the virus is available at this
point in time. Although no outbreak occurred after the winters of
2003-2004, there is no guarantee whatsoever that the virus (or a closely
related virus) will not re-emerge in the near future, either in the form we
have come to know or as a new variation with characteristics that are both
different and difficult to predict.
Prevention
Prevention of a new SARS epidemic begins
with watchfulness and adequate measures to nip a new
outbreak in the bud. Protection and quarantine, age-old strategies for
the protection against infectious diseases, have proved to be extremely
efficient in the case of SARS. At an economic and social price, obviously,
in view of the disruption of everyday life in the stricken areas. Both
‘classical’ virological and serological techniques and
‘modern’ RT-PCR and sequence analysis can play a significant
part in the rapid diagnostics required for surveillance. It goes without
saying that surveillance should not be restricted to the human population
and that it is extremely important in the case of SARS-CoV to continue the
search for animal reservoirs. Initially, masked palm civets that are sold
at live animal markets were implicated in the transmission of SARS-CoV to
humans (Guan et al., 2003).
However, attempts to recover the virus from farmed or wild civets
failed. Subsequently, Chinese horseshoe bats (and other bat species) were
identified as a natural reservoir of multiple coronaviruses, including one
that is closely related - but not identical - to the SARS viruses recovered
from humans and civets (Lau et al., 2005; Ren et al., 2006). Further
studies are required to assess the role of bats in the public health risk
of SARS-CoV re-emergence.
Vaccines
The rapid development of a vaccine against SARS-CoV
initially received a great deal of (commercial) attention. Subsequently,
several academic research groups continued to investigate existing and new
strategies to combat SARS-CoV and other coronaviruses. Different types of
(candidate) vaccines have been developed including inactivated viruses, DNA
vaccines, vaccine viruses derived from attenuation by reverse genetics,
virus-like particles, recombinant human monoclonal antibodies, and viral
subunit vaccines (Enjuanes et al., 2008).
Although the most promising vaccine candidates have been evaluated in human
volunteers, it is obvious that their efficacy
can only be rigorously tested when a new outbreak of the virus would occur.
Antiviral therapy
Other antiviral strategies that are being
developed at the moment concentrate on blocking the binding of the virus to
the host cell (with the use of drugs that inhibit the function of the S
protein) and developing specific inhibitors for viral enzymes (such as the
proteinases, polymerase, and helicase), and the use of compounds targeting
important viral RNA sequences (de Clercq et al., 2006; Coutard et al., 2008). Finally, the
possibility of inhibiting SARS-CoV by using RNA-interference (RNAi), a
recently discovered mechanism through which specifically determined RNA
molecules (such as, for instance, the genome of an RNA-virus) can be
degraded using the cell's own mechanisms, is being examined. Also in this
respect, the SARS outbreak and related drug discovery efforts will be an
important lesson for new viral outbreaks that may occur in the future.
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