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Coronaviruses and Acute Respiratory Syndromes (MERS and SARS)

By Craig R. Pringle, BSc, PhD, Professor Emeritus, School of Life Sciences, University of Warwick

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Coronaviruses are enveloped RNA viruses. Coronavirus infections in humans most frequently cause symptoms of the common cold. Coronaviruses 229E and OC43 cause the common cold; the serotypes NL63 and HUK1 have also been associated with this syndrome.

Two coronaviruses, MERS-CoV and SARS-CoV, cause much more severe respiratory infections in humans than other coronaviruses. In 2012, the coronavirus MERS-CoV was identified as the cause of Middle East respiratory syndrome (MERS). In late 2002, SARS-CoV was identified as the cause of an outbreak of severe acute respiratory syndrome (SARS).

Middle East Respiratory Syndrome (MERS)

Middle East respiratory syndrome (MERS) is a severe acute respiratory illness caused by the newly identified MERS coronavirus (MERS-CoV).

MERS-CoV infection was first reported in September 2012 in Saudi Arabia, but an outbreak in April 2012 in Jordan was confirmed retrospectively. Between April 2012 and September 2013, 130 cases were laboratory-confirmed; most of them occurred in Saudi Arabia, where new cases continue to appear. As of 2017, worldwide, 2066 cases of MERS-CoV infection (with at least 720 related deaths) have been reported; all cases of MERS have been linked through travel to or residence in countries in and near the Arabian Peninsula. The largest known outbreak of MERS outside the Arabian Peninsula occurred in the Republic of Korea in 2015. The outbreak was associated with a traveler returning from the Arabian Peninsula. Cases have also been confirmed in France, Germany, Italy, Tunisia, and the United Kingdom in patients who were either transferred there for care or became ill after returning from the Middle East.

Person-to-person transmission has been established by the development of infection in people whose only risk was close contact with people who had MERS. Most reported cases have involved severe respiratory illness requiring hospitalization, but at least 21% or patients had mild or no symptoms.

The reservoir of MERS-CoV is unknown; however, many coronavirus species are present in bats, and bats are the most probable source although MERS-CoV has not previously been identified in bats. Anti-MERS-CoV antibodies have been detected in a few camels, which are the only other currently suspected hosts.

The incubation period is about 5 days. More than half of cases have been fatal. Median patient age is 56 yr, and the male:female ratio is about 1.6:1. Infection tends to be more severe in elderly patients and in patients with a preexisting disorder such as diabetes, a chronic heart disorder, or a chronic renal disorder.

Fever, chills, myalgia, and cough are common. GI symptoms (eg, diarrhea, vomiting, abdominal pain) occur in about one third of patients. Cases may require ICU confinement, but recently, the proportion of such cases has declined sharply.

In all patients, chest imaging detects abnormalities, which may be subtle or extensive, unilateral or bilateral. In some patients, levels of LDH and AST are elevated and/or levels of platelets and lymphocytes are low. A few patients have acute kidney injury. Disseminated intravascular coagulation and hemolysis may develop.

Preliminary seroprevalence studies indicate that the infection is not widespread in Saudi Arabia.

The WHO considers the risk of contracting MERS-CoV infection to be very low for pilgrims traveling to Saudi Arabia for Umrah and Hajj; last year's Hajj did not result in an increase of patients with MERS-CoV infection. For additional information about pilgrimages to the Middle East, see World-travel advice on MERS-CoV for pilgrimages .


  • Real-time reverse-transcriptase PCR (RT-PCR) testing of lower respiratory secretions

MERS should be suspected in patients who have an unexplained acute lower respiratory infection and either

  • Travel to or residence in an area where MERS has recently been reported or where transmission could have occurred

  • Within 10 days before symptom onset, close contact with a patient who was ill with suspected MERS

The most recent recommendations are available from the WHO (Interim surveillance recommendations for human infection with novel coronavirus) and, in the US, the Centers for Disease Control and Prevention (Interim Guidelines for Investigation for Middle East Respiratory Syndrome (MERS)).

Testing should include real-time RT-PCR testing of lower respiratory secretions, ideally taken from different sites and at different times. Serum should be obtained from patients and from all, even asymptomatic close contacts, including health care workers (to help identify mild or asymptomatic MERS). Serum is obtained immediately after MERS is suspected or after contacts are exposed (acute serum) and 3 to 4 wk later (convalescent serum).


  • Supportive

Treatment is supportive. To help prevent spread from suspected cases, health care practitioners should use standard, contact, and airborne precautions.

There is no vaccine.

Severe Acute Respiratory Syndrome (SARS)

Severe acute respiratory syndrome (SARS) is a severe, acute respiratory illness caused by the SARS coronavirus (SARS-CoV).

SARS is much more severe than other coronavirus infections. SARS is an influenza-like illness that occasionally leads to progressively severe respiratory insufficiency. SARS-CoV was first detected in the Guangdong province of China in November 2002 and subsequently spread to > 30 countries. In this outbreak, > 8000 cases were reported worldwide, with 774 deaths (about 10% case mortality rate). This outbreak subsided, and no new cases have been identified since 2004. The immediate source was presumed to be civet cats, which had been infected through contact with a bat before being sold in a live meat market. Bats are frequent carriers hosts of coronaviruses.

Diagnosis is made clinically, and treatment is supportive. Eradication depends on rigidly maintained isolation.

SARS-CoV is the only human virus, besides the smallpox virus, to have been completely eradicated globally. It was eradicated largely because superspreaders (patients who infect an unusually large number of contacts) were quickly identified and isolated from the general population, thus interrupting transmission of the virus.