MERS or Middle East respiratory syndrome, relatively rare viral disease caused by MERS-CoV, a coronavirus. Although some infected persons have no or only coldlike symptoms, in most known cases of MERS the infection quickly progresses to serious respiratory illness, with fever, cough, pneumonia, shortness of breath, and difficulty breathing. Many MERS patients also have diarrhea and other gastrointestinal symptoms; kidney failure sometimes occurred. Roughly 35% of people known to be infected die from the disease. Older individuals appear to be particularly susceptible. Although there has been person-to-person transmission, MERS-CoV (unlike viruses that cause SARS and COVID-19) does not appear to be highly contagious in humans. The first identified MERS outbreak originated in 2012 in Saudi Arabia (the virus appears to be common in dromedary camels, and may have originated in bats), and all known cases of MERS have been traced back to the Arabian Peninsula. The most significant outbreak outside the Arabian Peninsula occurred in South Korea in 2015 and resulted from an individual who had visited the Arabian Peninsula.

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