Coronavirus mainly infect the upper respiratory and gastrointestinal tract of mammals and birds, with a significant percentage of colds in adults and children. They can also cause respiratory pathologies such as viral pneumonia or secondary bacterial pneumonia and bronchitis, viral bronchitis or secondary bacterial bronchitis.

 
There are currently seven known strains that infect humans.
Vijaykrishna at cols. Said that a change from a constant virus population size to logistic or exponential population growth has been associated with the interspecies transmission of viruses from reservoir to an alternate host.

 
Coronaviruses use the host cell machinery, through a protein called «replicase» that is in their genome, replicates their RNA in other copies of RNA.They also enjoy a «protease» that separates the proteins from the chain, a genetic economy for the virus, encoding a larger number of genes in a small number of nucleotides, as shown by Fehr at cols.

Bibliography:

D. Vijaykrishna; G.J.D. Smith; J.X. Zhang, J.S.M. Peiris; H. Chen and Y. Guan; “Evolution Insights into the Ecology of Coronaviruses”
J. Virol 2007
https://www.ncbi.nlm.nih.gov/pubmed/17267506

Fehr AR, Perlman S. “Coronaviruses: an overview of their replication and pathogenesis”
Methods Mol Biol 2015
https://www.ncbi.nlm.nih.gov/pubmed/25720466