Emerging Coronaviruses: Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS)

Abstract

The severe acute respiratory syndrome Coronavirus (SARS‐CoV) and the Middle East respiratory syndrome Coronavirus (MERS‐CoV) are two highly pathogenic viruses that recently emerged from zoonotic sources. In 2002, SARS‐CoV was identified as the agent that causes severe acute respiratory syndrome, or SARS, in the Guangdong province of China (Drosten et al., 2003; Marra et al., 2003; Rota et al., 2003). Almost 10 years later in 2012, MERS‐CoV was identified as the cause of Middle East respiratory syndrome, or MERS, in the Kingdom of Saudi Arabia (KSA) (Coleman and Frieman, 2014). There have been no new infections of SARS‐CoV reported since 2004, but it is possible that this virus could re‐emerge, as it is capable of spreading to humans again from its zoonotic source (Yang et al., 2013). In 2015, MERS‐CoV continues to spread throughout the Middle East and to other neighboring countries. Here, we review the epidemiology, clinical disease and virology of these disease‐causing viruses.

Key Concepts

  • Emerging Coronaviruses are serious threat to global public health.
  • Infection control in outbreak setting is crucial for containing Coronavirus spread.
  • Coronavirus genome structures are conserved between known and newly identified family members.
  • Therapeutic development is crucial for front line healthcare worker protection.
  • Animal model development is essential to understand the underlying pathology of each virus.
  • Comparisons between SARS‐CoV, MERS‐CoV and other human coronaviruses will give us insights into disease progression and therapeutic direction.

Keywords: Coronavirus; emerging; SARS ; MERS ; zoonotic

Figure 1. (a) Countries with reported infections of SARS‐CoV (red), MERS‐CoV (blue) or both (purple). (b) Zoonotic transmission of SARS‐CoV and MERS‐CoV.
Figure 2. Comparison of the SARS‐CoV and MERS‐CoV gene organisation to those of other coronaviruses. On the basis of the antigenic reactivity, coronaviruses were classified into three groups. A representative member of each group is shown. The SARS‐CoV and MERS‐CoV are most similar to group 2 coronaviruses.
Figure 3. Structure of SARS‐CoV ORF1. ORF1 accounts for approximately two‐thirds of the genome and encodes for 16 proteins, all produced as one polyprotein. Translation of ORF1b is initiated by ORF1a −1 ribosomal frameshift at the location noted by the grey arrow. The functions of seven of the nonstructural proteins encoded by ORF1a and ORF1b are known or predicted by sequence homology. Abbreviations: ADRP, ADP‐ribose 12‐phosphatase; PL2pro, papain‐like protease; 3CLpro, main protease; ssRBP, ssRNA‐binding protein; RNApol, RNA‐dependent RNA polymerase; ExoN, exoribonuclease; NendoU, endoribonuclease; and 2′‐OMT, 2′‐O‐ribose methyltransferase.
Figure 4. SARS‐CoV subgenomic RNAs. The coronavirus polymerase complex mediates the synthesis of eight subgenomic mRNAs, with only the 5′ ORF of each RNA translated into protein. Each subgenomic RNA contains a common leader sequence, derived from the 5′ end of genomic RNA. The leader is most likely joined to the body of each subgenomic RNA during synthesis of negative‐strand RNA. In this process, the RNA polymerase ‘skips’ from the transcription‐regulating sequence (TRS) (denoted by brown boxes) to the 5′ leader sequence, in blue. Subsequently, subgenomic mRNAs are synthesised from these subgenomic negative‐sense RNAs. This process is show for mRNA 2 of SARS‐CoV.
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Further Reading

Alagaili AN et al. (2014) Middle East respiratory syndrome coronavirus infection in dromedary camels in Saudi Arabia. MBio 5 (2): e00884–14.

Azhar EI et al. (2014) Evidence for camel‐to‐human transmission of MERS coronavirus. New England Journal of Medicine 370 (26): 2499–505.

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Sisk, Jeanne M, and Frieman, Matthew B(Aug 2015) Emerging Coronaviruses: Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0004025.pub3]