SARS
Severe acute respiratory syndrome is a new human respiratory disease,
first recognised in late February, 2003, in Hanoi, Vietnam. The
disease quickly spread to over 30 countries, most prominently in
mainland China, Hong Kong, and Taiwan. The epidemic in Hong Kong
has been characterised by two large clusters, initiated by two separate
"super-spread" events (SSEs), and ongoing community transmission.
Epidemiological data from Singapore and the epidemic curves from
other settings suggest that in general, a single infectious case
of SARS will infect about 3 secondary cases in a population that
has not yet instituted control measures.
Severity of the disease, combined with its rapid spread along
international air-travel routes, prompted WHO to set up a network
of scientists from 11 laboratories around the world to try to identify
the causal agent. In March 2003, a novel coronavirus (SARS-CoV)
was discovered in association with cases of severe acute respiratory
syndrome (SARS). The genome of SARS-CoV consists of 29,727 nucleotides
in length and has 11 open reading frames, and its genome organisation
is similar to that of other coronaviruses. Phylogenetic analyses
and sequence comparisons showed that SARS-CoV is not closely related
to any of the previously characterised coronaviruses. It is also
known that this virus has a high propensity to mutate and one common
variant seems to be associated with a non-conservative amino acid
change in the S1 region of the spike protein suggesting that immunological
pressures might already be starting to influence the evolution of
the SARS virus in human populations.
Clinically, SARS is associated with epithelial-cell proliferation
and an increase in macrophages in the lung. The presence of haemophagocytosis
supports the contention that cytokine dysregulation may account,
at least partially, for the severity of the clinical disease. The
standard clinical treatment protocol using antibacterial and a combination
of ribavarin and methylprednisolone has met with increasing criticism.
This is in large part due to the fact that ribavarin is ineffective
as an anti-SAR-CoV agent and that use of steroids can lead to additional
complications.
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