Fig. 1.

Phylogeny, evolutionary relationships, global propagation pathways, and timeline of SARS-CoV-2 viruses from the ongoing COVID-19 pandemic.

Despite relatively clear genetic relationships among sampled viruses, an uncertainty for specific transmission dates and the reconstruction of the geographic spread remains. Note that the specific inferred transmission patterns (connecting lines) are only hypothetical (4). Thousands of complete genomes are available and increase on a daily basis. The visualization is based upon sub-sampled available genome data (see more under: https://nextstrain.org/ncov). As the pathogen replicates and spreads, its genome is replicated and random mutations/errors accumulate in the genome. Such random mutations allow tracking of the SARS-CoV-2 spread inferences regarding its transmission routes and dynamics. The colors indicate the origin/source of the various viral strains, while circle diameters reflect the size of the transmission clusters. The initial SARS-CoV-2/COVID-19 emergence occurred in Wuhan, China, in November and December 2019, with the first (officially announced) COVID-19-related death on January 11, 2020. The phylogeny is rooted relative to early samples obtained from Wuhan, China. Thereafter, a sustained human-to-human transmission with the first case outside of China (Thailand) was confirmed on January 13, 2020. On January 21, 2020 the first case was confirmed in North America (Wash, USA) and 4 days later in Australia (Victoria). The first three cases in Europe were reported in France on January 24, 2020 (first death on February 15, 2020 France). COVID-19 surveillance was implemented by the European CDC and WHO in the European Region on January 27, 2020, 3 days later the WHO declared SARS-CoV-2 a global emergency. On February 14, 2020 the first case in Africa (Egypt) was confirmed. On February 21, 2020 nine European countries (Belgium, Finland, France, Germany, Italy, Russia, Spain, Sweden, and UK) reported SARS-CoV-2/COVID-19 cases. On February 25, 2020 SARS-CoV-2 reached South America (São Paulo, Brazil). On March 11, 2020 the WHO declared SARS-CoV-2 a pandemic and 2 days later Europe was announced the active pandemic center; on 17 March 2020, all European countries reported confirmed SARS-CoV-2/COVID-19 cases. On March 31, 2020 the number of COVID-19-related deaths (>3,500) in the US surpassed those (officially reported) in China. The highest worldwide daily death toll of 10,761 was recorded on April 27, 2020; as of May 18, 2020, 4,727,625 confirmed cases in 213 countries/territories and two international conveyances with 315,389 deaths were reported (www.worldometers.info). Graphic modified based on https://nextstrain.org/ncov (accessed on April 27, 2020). COVID-19 indicates coronavirus disease 2019; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.