Coronaviruses, so-named because protein spikes on the surface of the virus resemble the sun’s corona, are common. Most cause respiratory, gastrointestinal, liver, and neurologic diseases in animals.
Human Coronavirus Infection (HCoV)
Only 7 coronaviruses cause disease in humans (HCoV).
Four of the 7 viruses cause mild and self-limiting upper respiratory tract infections, such as the common cold, but they can cause severe lower respiratory tract infections, including pneumonia, in infants, older people, and people whose immune systems are not working well. These HCoV infections show a seasonal pattern with most cases occurring in the winter months in temperate climate countries.
Three of the 7 HCoV (SARS-CoV, MERS-CoV, and SARS-CoV2) have caused major outbreaks of deadly pneumonia in the 21st century.
The first of these outbreaks, severe acute respiratory syndrome (SARS), first emerged in November 2002 in Guangdong province in southern China and caused an epidemic that spread within months to 29 countries and 6 continents. It sickened over 8,000 people and killed almost 800 worldwide. The majority of cases occurred in Mainland China and Hong Kong. In the United States, only 8 people had laboratory-confirmed SARS; all 8 had traveled to areas where SARS-CoV transmission was occurring.
The next HCoV to cause deadly infection was Middle East Respiratory Syndrome coronavirus (MERS-CoV), which emerged in the Arabian Peninsula in September 2012. MERS-CoV has caused recurrent outbreaks that have sickened over 2,500 people and about 1 in 3 infected people died. Most infected people lived in or recently traveled from the Arabian Peninsula. 85% of cases were reported in Saudi Arabia. The largest outbreak of MERS outside the Arabian Peninsula occurred in South Korea in 2015, associated with a traveler returning from the Arabian Peninsula.
The seventh HCoV to be discovered is SARS-CoV2, the cause of an outbreak, named COVID-19, that is currently spreading worldwide. The outbreak began in Wuhan in Central China. (Wuhan is home to the Wuhan Institute of Virology, a leading center for coronavirus research, although no connection is suspected between the research and the current outbreak.) SARS-CoV-2 is most closely related, with 96% genetic similarity, to a coronavirus isolated from horseshoe bats that were found in caves in Yunnan, China, over 1000 km (about 621 miles) from Wuhan (1).