Origin in Wuhan
One scary aspect about the current COVID-19 virus is that it is evolving rapidly.
We know that the virus originated in bats and probably resided in pangolins, where the virus combined the bat coronavirus genome and the pangolin S glycoprotein and developed the ability to infect humans.
The first original case is attributed to a 55-year-old from Wuhan, Hubei, China and the initial outbreak is linked to the Huanan Seafood Wholesale Market.
Tang et al. describes the initial evolution of COVID-19. https://academic.oup.com/nsr/advance-article/doi/10.1093/nsr/nwaa036/5775463#.XmA64GbsBuI.twitter
In short, they describe that two distinct major subtypes of COVID-19 initially developed – the S type and the L type. The S type started first, but the L type soon evolved, became more aggressive, and spread more quickly.
Continued Evolution of COVID-19
However, we know that as the virus spreads away from China, it is continuing to evolve and mutate. The ongoing phylogenetic mapping of new COVID-19 strains are seen at https://nextstrain.org/ncov. This may be the explanation why there is such a variety in symptoms from people with this virus.
Below is a phylogenetic map of the genetic differences between the evolving COVID-19 virus. The strains across the world all came from China, but the main strains in the United States are distinct from the ones presently in Europe. This may be the reason why Italy has such a drastically different experience with COVID-19 than Taiwan or South Korea. It remains to be seen how severe the current COVID-19 strains are in the United States, but international travel to and from Europe should be strongly discouraged.