8. Middle East Respiratory Syndrome (MERS)
Middle East respiratory syndrome (MERS) was first reported in September 2012 in Saudi Arabia, following isolation of MERS-CoV from a male patient who died months earlier from severe pneumonia and multiple organ failure [1]. In the 8 years since then, there have been more than 2494 confirmed cases of MERS resulting in upwards of 858 deaths globally [46]. While 27 countries have reported cases of MERS, approximately 80% of confirmed cases originated in Saudi Arabia [47]. To date, all known cases of MERS can be linked to travel or residence in countries along the Arabian Peninsula—that is, Bahrain; Iraq; Iran; Israel, the West Bank, and Gaza; Jordan; Kuwait; Lebanon; Oman; Qatar, Saudi Arabia; Syria; the United Arab Emirates (UAE); and Yemen [48]. The largest documented outbreak outside of this region occurred in 2015 in the Republic of Korea, in which 186 infections occurred, resulting in 38 deaths [49]. The index case in this outbreak reportedly returned from the Arabian Peninsula just prior to onset of illness [50].
MERS-CoV is characterized by sporadic zoonotic transmission events as well as spread between infected patients and close contacts (i.e., intra-familial transmission) [51]. Nosocomial outbreaks in health care settings—the result of poor infection control and prevention—are widely recognized as the hallmark of MERS [1]. Superspreading events have been recorded in healthcare settings in Jordan, Al Hasa, Jeddah, Abu Dhabi and South Korea [47,52,53,54,55]. Like other coronaviruses, MERS-CoV can be spread through person-to-person contact, likely via infected respiratory secretions [48]. Transmission dynamics, however, are otherwise poorly understood [1]. Bats are believed to be the natural reservoir of MERS-CoV, and dromedary camels can have the virus and have been suggested as possible intermediary hosts as well as a source of infection to humans [2,56,57].
There are no clinical or serological reports of perinatal transmission of MERS, though vertical transmission has been reported for non-coronavirus respiratory viruses including influenza and respiratory syncytial virus (RSV) [58]. Researchers have not yet discovered ongoing transmission of MERS-CoV within communities outside of health care settings.
The clinical presentation of MERS varies from asymptomatic to severe pneumonia with acute respiratory distress syndrome (ARDS), septic shock, and multiple organ failure, often resulting in death. Most patients with MERS develop severe acute respiratory illness accompanied by fever, cough, and shortness of breath [50]. Progression to pneumonia is swift—usually within the first week —and at least one-third of patients also present with gastrointestinal symptoms [1]. MERS progresses much more rapidly to respiratory failure and has a higher case fatality rate than SARS [1]. Unlike SARS, however, infection with MERS-CoV is generally mild in healthy individuals but more severe in immunocompromised patients and people with underlying comorbidities [1]. The overall CFR of MERS is approximately 34.4% [46]. Most fatalities have been associated with pre-existing medical conditions like chronic lung disease, diabetes, and renal failure, as well as weakened immune systems [59], making such individuals high risk. As a result of the immunological changes that occur during pregnancy, women who are pregnant are included in this high-risk group. Pregnant women may develop severe disease and fatal maternal and/or fetal outcomes as a result of MERS-CoV infection; however, little is known of the pathophysiology of this infection during pregnancy.