Hoornweg et al.
Rescue and in vitro characterization of a divergent TBEV-Eu strain from the Netherlands
Sci Rep. 2023;13(1):2872. doi:10.1038/s41598-023-29075-0

In 2016, a TBE virus strain has been isolated from ticks collected in the National Park “Sallandse Heuvelrug” in the Netherlands, which belonged to the European subtype (TBE-EU) but has diverged from all other known TBE-EU strains by at least 8.5% at nucleotide level and 2% at amino acid level. Late in 2019, a second TBE virus strain highly similar to this divergent TBE-EU strain “Salland” was detected in the United Kingdom.

As the strain Salland was so divergent from all other TBE-EU strains, it was the aim of a Dutch team to isolate the virus in vitro and to assess its pathogenic potential. The strain was rescued by Infectious Subgenomic Amplicons and was compared with the well-known strain Neudörfl and the highly pathogenic strain Hypr.

Assessment of the strain Salland revealed that based on i) growth kinetics on respiratory and resident cell lines, ii) infection studies using human monocyte-derived dendritic cells, as well as iii) analysis of viral interactions with the IFN-I system, this novel strain mimics the highly pathogenic strain Hypr rather than the less pathogenic strain Neudörfl. The authors concluded that the strain Salland has pathogenic potential, although caution needs to be taken from extrapolating in vitro data to the situation in vivo.

To date, no TBE virus could be isolated from patients in the area where Salland was originally detected, and no other virus strain other than Salland has been detected in this area. Thus, this observation also serves as indirect evidence that this strain is in fact pathogenic in humans.

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