Preliminary data from sequencing of viruses in the Republic of Korea and the People’s Republic of China
Overview
Situation assessment
Scientists in the Republic of Korea have completed full genome sequencing of the MERS coronavirus circulating in that country. Chinese scientists have likewise fully sequenced virus isolated from a patient who was exposed to the disease in Republic of Korea and subsequently travelled to China, where his infection was diagnosed.
Sequence results have been shared publicly and with leading scientists elsewhere.
On 7 June, WHO convened a teleconference with virologists from Asia, the Middle East, Europe, and North America, including many with extensive experience in working with MERS coronaviruses and interpreting sequencing results. The teleconference drew on expertise consolidated in the WHO Global Outbreak Alert and Response Network (GOARN) and the Emerging and Dangerous Pathogens Laboratory Network (EDPLN).
Results to date are preliminary; more time is needed for their accurate interpretation. For example, all participants agreed that viruses grown in cell culture are likely to show more changes, as part of viral “background noise”, than viruses isolated directly from a patient sample. Some data examined by the group were derived from viruses grown in culture, which makes comparisons difficult.
Careful analysis of sequence data can provide clues about the source of infections, whether cases are linked, and how viruses are spread. However, the place of a virus in a phylogenetic tree does not yield reliable information about whether the virus has acquired an ability to spread more easily from one person to another.
Sequences from Korean and Chinese viruses each show a few amino acid changes. The fact that these changes are not shared by two virus sequences among those currently available makes the relevance of these individual changes questionable. Additional sequence data are needed before firm conclusions can be reached.
The reliable interpretation of changes detected when sequence data are compared also depends on the size of the reference collection available for comparison. In this case, interpretation is hindered by the paucity of sequence data from MERS coronaviruses recently circulating in affected Middle Eastern countries.
What has been observed so far does not point conclusively to any significant biological change in the viruses from either Republic of Korea or China.