Human Coronavirus Infections—Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and SARS-CoV-2

Three novel coronaviruses have emerged as new lethal zoonotic pathogens of humans during the past 17 years: The Severe Acute Respiratory Syndrome (SARS) coronavirus (SARS-CoV), the Middle East Respiratory Syndrome (MERS) coronavirus (MERS-CoV), and most recently SARS-CoV-2. SARS-CoV first surfaced as a human pathogen in Guangdong, China in November 2002 and rapidly spread worldwide with 8098 cases and 774 deaths before the end of the epidemic. SARS-like CoVs have been detected in horseshoe bats with high sequence homology with human or civet isolates, suggesting that bats could be a natural reservoir of a close ancestor of SARS-CoV. No cases of SARS have been reported since January 2004. MERS-CoV was first reported in September 2012, after it was isolated from respiratory samples from a patient in Jeddah, Saudi Arabia who died in June 2012. How humans acquire MERS-CoV infection is not yet known although bats and dromedary camels are intermediary reservoirs. MERS-CoV continues to circulate in the Middle East. As of May 22, 2019, 2428 cases of laboratory-confirmed MERS-CoV cases reported to the World Health Organization, including 838 deaths (34.5% mortality) have been reported from 27 countries. While the majority of MERS cases occur in the Middle East, travel related MERS cases have been reported from all continents. Large health care associated outbreaks of MERS-CoV have occurred in Saudi Arabia, United Arab Emirates, and the Republic of Korea. SARS-CoV-2 emerged from Wuhan, China in December 2019, and by March 2020 had established as a pandemic which has caused massive disruption in multiple countries. The eventual mortality caused by this virus remains to be seen. All three viruses cause a similar wide range of nonspecific clinical manifestations from mild upper respiratory tract illness to severe respiratory, gastrointestinal and other extra-pulmonary disease. Early recognition of cases, improved compliance with internationally recommended infection control protocols, and rapid implementation of infection control measures are required to prevent health care facility-associated outbreaks, and in the case of SARS-CoV-2 for control of community spread as well. Treatment is supportive and there are no specific antivirals or vaccines available for both SARS and MERS.