In late December 2019, an outbreak of unidentified pneumonia was reported in the bustling Huanan Seafood Market in China’s Wuhan city. Responding quickly to the escalating situation, several countries established thermal screening for travelers from Wuhan and stepped up surveillance at hospitals.
What happened next played out like a classic movie plot about a pandemic: two individuals—the first confirmed exported cases of COVID-19 from China—boarded separate flights from Wuhan to Thailand’s Bangkok Suvarnabhumi Airport, where they were discovered on January 8 and January 13.
Racing against time, Thailand’s Ministry of Public Health confirmed both cases to be COVID-19 positive. By studying case histories, clinical characteristics and genomic profiles together with Sebastian Maurer-Stroh, Deputy Executive Director (Research) at A*STAR’s Bioinformatics Institute (BII), a Thai-Singapore team was able to piece together the early transmission patterns of the outbreak.
Although the two imported COVID-19 cases were not directly linked, their viral genomes were identical with each other and with four other viral sequences collected from patients in Wuhan. Since both individuals had not visited the Huanan Seafood Market, nor did they contact persons with COVID-19, it indicates potentially wider distribution beyond Wuhan before January 23, when travel restrictions were enforced in the city.
“Taking together the history and onset of symptoms of these two COVID-19 cases, it suggests that transmission within Wuhan beyond the Huanan Seafood Market likely occurred in the first week of January or earlier,” Maurer-Stroh explained.
Comparing the two genome sequences with known coronavirus families, the SARS-CoV-2 genome showed 80 and 88 percent identity with SARS-CoV and SARS-like bat CoV genomes from China, respectively. On a structural level, the ACE2 surface protein of SARS-CoV-2, which is responsible for viral attachment to human cells, had only 76 percent identity with SARS-CoV.
“Given several mutations in the binding interface, SARS-CoV-2 may differ in host-cell binding efficiency as compared with SARS-CoV. This could result in differences in virulence and transmission potential,” said Maurer-Stroh.
While asymptomatic cases in their incubation period would have been missed, Thailand’s rapid response early in the outbreak proved successful in these two cases, the authors noted. Another important lesson is that the genome sequences were shared in real-time via the Global Initiative on Sharing All Influenza Data (GISAID) online portal, which gave researchers everywhere immediate access to study the new virus and early outbreak patterns.
The A*STAR-affiliated researcher contributing to this research is from the Bioinformatics Institute (BII).
