Isolation and Characterization of Clinical RSV Isolates in Belgium during the Winters of 2016–2018

Van der Gucht, Winke; Stobbelaar, Kim; Govaerts, Matthias; Mangodt, Thomas; Barbezange, Cyril; Leemans, Annelies; De Winter, Benedicte; Van Gucht, Steven; Caljon, Guy; Maes, Louis; De Dooy, Jozef; Jorens, Philippe; Smet, Annemieke; Cos, Paul; Verhulst, Stijn; Delputte, Peter L.

Even though all RSV-A and RSV-B clinical isolates belong to the same genotype in the phylogenetic trees (ON1 and BAIX, respectively), the results show differences between the different isolates. According to the phylogenetic trees, the clinical isolates can be divided into three groups for the RSV-A isolates and two groups for the RSV-B isolates. However, differences can even be observed between clinical isolates that belong to the same group within the genotype. For example BE/ANT-A11/17, which, in comparison with BE/ANT-A8/17 and other clinical isolates from the same season, infects a higher number of cells in viral replication kinetics experiments, produced a higher amount of infectious virus and retained its stability in thermal stability assays. It is only slightly less neutralized by palivizumab compared to other RSV-A clinical isolates that have been isolated from the same season. Secondly, BE/ANT-B2/17 and BE/ANT-B15/17 are generally poor infectors and also have a lower thermal stability than other RSV-B clinical isolates from the same season. Generally, differences can be observed between the different clinical isolates in viral replication kinetics, but all clinical isolates have the ability to infect all cell lines tested. These differences could be due to underlying genetic differences that could affect antiviral responses in the cells, or due to differences that could be accounted to changes in the way the virus replicates in the cells, such as the presence of defective interfering virus particles. Our results suggest that the thermal stability of the clinical isolates is in general lower than the reference strains. The reason for this is unknown but it may be that repeated infection of the reference strains has resulted in the selection of variants with replicative fitness advantage at these temperatures. Remarkably, RSV B1 remains rather stable at 4 • C compared to the RSV A2 and other clinical strains.