SEVERE ACUTE RESPIRATORY SYNDROME (SARS)

Introduction

Characteristics

Transmission

Methods for Monitoring in the Environment

Methods for Measuring Human Exposure

Strategies for Preventing or Controlling Exposure


Harmful Effects

Absorption, Distribution and Metabolism

Sites of Toxicity

Biomarkers of Disease

Molecular Mechanisms of Action

Risk Assessment/Management

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ABSORPTION, DISTRIBUTION, METABOLISM

Inhalation of virus-infected airborne droplets is the typical exposure route for SARS.

Little is known about the distribution and metabolism of this virus. Viruses are not bioactivated or biodegraded into more or less potent entities like chemicals. Scientists have sequenced the nearly 30kb genome of this single-stranded RNA virus. As with all viruses, the RNA invades the host cell and replicates itself in the cytoplasm. Coronaviruses in general use their own RNA to replicate themselves unlike DNA viruses which replicate within the nucleus of the host cell.

Because SARS is a single stranded RNA virus, as it reproduces itself it does not have zipper on other side to match up perfectly like DNA viruses, thus room for mistakes. In fact it is estimated that the mutation rate for coronaviruses is 1 in every 10,000 bases (3 changes in every replication) and scientists have shown viable viruses with deletions, duplications, substitutions, order rearrangements and replicase polyprotein cleavage site deletion. Scientists are researching a vaccine for SARS, but these viruses are changing quickly.

Various antiviral agents are being tested for effectiveness against SARS. The use of the antiviral agent ribavrin on SARS patients resulted in toxic effects such as hemolysis and significant reduction of hemoglobin. The antiviral agent glycyrrhizin, which is derived from the roots of liquorice plants, has been found to be effective in inhibiting replication of the virus. An increase in nitric oxide synthesis is the mechanism of action. Side effects from glycyrrhizin use, such as raised blood pressure and hypokalaemia (low blood potassium), have been seen after several months of use in HIV and hepatitis C patients. Since SARS patients would only require glycyrrhizin for a short period of time, its use as an antiviral treatment is further being considered.