Chapter 19: SARS and MERS

INTRODUCTION

Coronaviruses are associated with the common cold as well as severe acute respiratory syndrome coronavirus (SARS-CoV-1) and Middle Eastern Respiratory Syndrome (MERS). These viruses belong to the family Coronaviridae which falls under the Nidovirales order. The coronaviruses are positive strand RNA viruses that range from 80–120 nm in diameter. The RNA genome forms a helical capsid with an N protein and has at least 3–4 surface proteins, which give it its crown or “corona”-like appearance under electron microscopy, from which it derives its name.¹

There remains a large deficit in our understanding of the novel coronavirus infections that have infected humans because of the lag between the emergence of a new strain that infects human beings from animal reservoirs, isolating the animal host from which the new strains are thought to have emerged, and understanding how these novel viruses cause disease in human beings. It is hypothesized that the emergence of novel infectious viruses through zoonotic transmission from animals to humans is a consequence of climate change.²

The SARS-CoV-1 virus is thought to have emerged from bats, more specifically horseshoe bats (Rhinolophus sinicus) whose close interaction with unsanitary “wet markets” in the Guangdong province in China is thought to have been the origin of the SARS CoV-1 viral epidemic in 2003.³ Antibodies for SARS-CoV-1 have also been found in masked palm civet (Paguma larvata) populations and isolated cases have been described from exposure to these mammals.⁴ The zoonotic reservoir for MERS-CoV is the dromedary camels (Camelus dromedarius) that have been found to carry neutralizing antibodies to MERS-CoV and have interactions with humans and densely populated marketplaces.⁵

EPIDEMIOLOGY

The first cases of SARS-CoV-1 were noted in Guangdong Province in south eastern China in November, 2002. It soon spread from the southern and eastern provinces of China as well as Hong Kong to more countries in Asia and then to Europe, Canada, and the United States.⁶ The initial cases were traced to exotic meat markets and resulted in local community spread in China. Index cases in new hotspots thereafter were traced to people who had traveled from the provinces of China as well as to healthcare institutions which is displayed in the fact that healthcare workers and their contacts were disproportionately affected during the epidemic.

The novel virus was successfully isolated and identified between February and March 2003.⁷ During the major SARS epidemic from 2002–2003 a total of 8,096 cases were reported in 29 countries with 774 deaths. Of these 1,706 cases were reported among healthcare workers.⁸ Since the end of the major epidemic, small outbreaks have been traced to laboratories working with the SARS virus^9,10 as well as unrelated cases from presumed exposure to infected animals.¹¹

The MERS-CoV epidemic is thought to have started in April ...