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Forster and colleagues found that the closest type of COVID-19 to the one discovered in bats -- type 'A', the "original human virus genome" -- was present in Wuhan, but surprisingly was not the city's predominant virus type.
Mutated versions of 'A' were seen in Americans reported to have lived in Wuhan, and a large number of A-type viruses were found in patients from the US and Australia.
Wuhan's major virus type, 'B', was prevalent in patients from across East Asia. However, the variant didn't travel much beyond the region without further mutations -- implying a "founder event" in Wuhan, or "resistance" against this type of COVID-19 outside East Asia, say researchers.
The 'C' variant is the major European type, found in early patients from France, Italy, Sweden and England. It is absent from the study's Chinese mainland sample, but seen in Singapore, Hong Kong and South Korea.
The new analysis also suggests that one of the earliest introductions of the virus into Italy came via the first documented German infection on January 27, and that another early Italian infection route was related to a "Singapore cluster."
Variant 'A', most closely related to the virus found in both bats and pangolins, is described as "the root of the outbreak" by researchers. Type 'B' is derived from 'A', separated by two mutations, then 'C' is in turn a "daughter" of 'B'.
Researchers say the localisation of the 'B' variant to East Asia could result from a "founder effect": a genetic bottleneck that occurs when, in the case of a virus, a new type is established from a small, isolated group of infections.
Forster argues that there is another explanation worth considering. "The Wuhan B-type virus could be immunologically or environmentally adapted to a large section of the East Asian population. It may need to mutate to overcome resistance outside East Asia. We seem to see a slower mutation rate in East Asia than elsewhere, in this initial phase."
Mutated versions of 'A' were seen in Americans reported to have lived in Wuhan, and a large number of A-type viruses were found in patients from the US and Australia.
Wuhan's major virus type, 'B', was prevalent in patients from across East Asia. However, the variant didn't travel much beyond the region without further mutations -- implying a "founder event" in Wuhan, or "resistance" against this type of COVID-19 outside East Asia, say researchers.
The 'C' variant is the major European type, found in early patients from France, Italy, Sweden and England. It is absent from the study's Chinese mainland sample, but seen in Singapore, Hong Kong and South Korea.
The new analysis also suggests that one of the earliest introductions of the virus into Italy came via the first documented German infection on January 27, and that another early Italian infection route was related to a "Singapore cluster."
Variant 'A', most closely related to the virus found in both bats and pangolins, is described as "the root of the outbreak" by researchers. Type 'B' is derived from 'A', separated by two mutations, then 'C' is in turn a "daughter" of 'B'.
Researchers say the localisation of the 'B' variant to East Asia could result from a "founder effect": a genetic bottleneck that occurs when, in the case of a virus, a new type is established from a small, isolated group of infections.
Forster argues that there is another explanation worth considering. "The Wuhan B-type virus could be immunologically or environmentally adapted to a large section of the East Asian population. It may need to mutate to overcome resistance outside East Asia. We seem to see a slower mutation rate in East Asia than elsewhere, in this initial phase."
