humans who developed severe Hcov diseases have been eliminated.
Since then, tremendous efforts have been dedicated to Hcov research.
Likewise, a reservoir host harbours Hcov continuously and for long term.
In contrast, if the Hcov is newly introduced to an intermediate host right before
Hcovs that cause severe diseases in humans and
humans who developed severe Hcov diseases have been eliminated.
An Hcov can undergo a dead-end infection if it cannot sustain
its transmission within the intermediate host.
There exist many other Hcov receptors, such as aminopeptidase N for Hcov-229E,
and 9-O-acetylated sialic acid for Hcov-OC43.
rapid mutation and genetic recombination also drive Hcov evolution and serve as two important steps in this process.
In addition,
rapid mutation and genetic recombination also drive Hcov evolution and serve as two important steps in this process.
We also review the trend of Hcov evolution in which the increase in transmissibility often comes with the decrease in pathogenicity.
Other human coronaviruses have since been identified,
including SARS-CoV in 2003, Hcov NL63 in 2004,
HKU1 in 2005, MERS-CoV in 2012, and SARS-CoV-2 in 2019.
The outbreaks of severe acute respiratory syndrome(SARS) and the Middle East respiratory syndrome(MERS)
have flipped the coin to reveal how devastating and life-threatening an Hcov infection could be.
In contrast, if the Hcov is newly introduced to an intermediate host right before or around its introduction to
humans, it is not well adapted to the new host and is often pathogenic.
The 2019 novel Hcov(2019-nCoV), which has subsequently been renamed SARS-CoV-2,
is the causative agent of the ongoing epidemic of coronavirus disease 2019(COVID-19), which has claimed more than 3,120 lives and infected more than 91,000 people as of March 3, 2020.