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.

Respiratory Syncytial Virus (RSV), recently renamed to human orthopneumovirus, is a very important viral respiratory pathogen in infants, children and adult patients with immunodeficiency or cardiopulmonary disease and it is recognized as a major threat for the elderly population [1] [2] [3] [4] [5] [6] . An RSV infection starts with typical common-cold like symptoms but may progress to serious lower respiratory tract infections associated with a high rate of hospitalization of infants, children and elderly [7] . No vaccines or therapeutics are available except for Synagis ®® , also known as the humanized antibody palivizumab. Palivizumab, which is solely used for passive immunization of high-risk infants, targets a specific, highly conserved epitope on the fusion protein [8, 9] , resulting in fusion inhibition. Currently, treatment of severe lower respiratory tract infections as a result of RSV infection consists of supportive care only, such as oxygen administration and nutrition. RSV is classified in the family Pneumoviridae, genus Orthopneumovirus and can be divided into two subtypes, RSV-A and RSV-B. It has a non-segmented, negative, single-stranded RNA genome that consists of ten genes, encoding 11 proteins. The viral envelope contains three proteins: the attachment protein (G), the fusion protein (F) and the small hydrophobic protein (SH). The G protein interacts with cellular receptors on the host cell membrane to attach the virus particle to the cell surface. The protein consists of a central conserved domain, two glycosylated mucin-like regions and an N-terminal region containing a transmembrane domain and a cytoplasmic domain [10, 11] . Sequencing of the G gene indicated that the two mucin-like regions flanking the central domain only have a 67% similarity at the nucleotide level between RSV-A and RSV-B and only 53% similarity at the deduced amino acid levels [12] . Consequently, the two mucin-like regions serve as excellent targets for RSV evolution studies. Both subtypes are further divided into genotypes based on those genetic variations. For RSV-A, the genotypes GA1-7, SAA1-2, NA1-4 and ON1 [13] [14] [15] [16] [17] [18] have been defined, while for RSV-B, the GB1-5, SAB1-4, URU1-2, BA1-12 and THB [13, 14, [19] [20] [21] [22] [23] [24] [25] genotypes are reported. The F protein is responsible for the fusion of the viral envelope with the host cell membrane. An important side effect is the fusion of the cell membranes of an infected cell with adjacent cells, resulting in a giant cell with multiple nuclei, better known as a syncytium [26] . The formation of syncytia is recognized as a means to efficiently spread the infection along epithelial surfaces, while minimizing contact with the immune system [27] .