Coronaviruses are of animal origin: one species ("reservoir") harbours a virus without being sick and transmits it to another species, which then transmits it to humans. In the cases of SARS-CoV and MERS-CoV, the reservoir animal was the bat. As Inserm explains, "the virus is asymptomatic in this animal. An intermediate host is therefore necessary for the transmission of these viruses to humans: the masked palm civet for SARS-CoV, sold on the markets and consumed in southern China, and the dromedary for MERS-CoV".
Coronavirus Transmission
In the case of SARS-CoV-2, the reservoir could also be the bat. In early February, a team of Chinese researchers estimated that the missing link could be the pangolin, a small-scaled mammal on the verge of extinction. But caution is called for, pending definitive confirmation. "We can think that human contamination occurred during the handling of these mammals whose scales are used in traditional Chinese pharmacopoeia and whose flesh is consumed," explained Professor Patrick Berche, Professor Emeritus of Microbiology at the University of Paris.
Human-to-human transmission
The coronaviruses SARS-CoV, SARS-CoV-2, and MERS-CoV are transmitted not only from animal to human but also from human to human. Covid-19 disease (formerly known as 2019-nCoV) due to SARS-CoV-2 is transmitted by sputum (droplets of saliva) thrown up when coughing, sneezing, but also when talking or screaming. Close and prolonged contact is therefore required for transmission (family, same hospital room or boarding school) or contact within 1 meter of the person, in the absence of effective protective measures.
Environmental transmission
One of the most important transmission factors is hand contact with infected surfaces and then contact with the mouth, nose or eyes. Depending on the temperature and humidity, the virus can survive for a few hours or even days on various surfaces if they are not disinfected. Studies are underway to clarify these data.
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