**1. Introduction**

Human respiratory syncytial virus (hRSV) causes considerable respiratory distress with variable severity in infancy and early childhood [1,2]. It is also responsible for the induction of respiratory illness in elderly and immunocompromised patients [3], in addition to being a common nosocomial pathogen [4]. The virus belongs to the family *Pneumoviridae,* genus *Orthopneumovirus*, and possesses a single-stranded negative-sense RNA genome that encodes eleven proteins [5], including both attachment (G) and fusion (F) envelope proteins that work together to attach to the target cell membrane by the G protein [6], while fusion of the viral and cell membranes occurs through the action of the F glycoprotein [7].

The G glycoprotein is a type II surface protein which is highly glycosylated and possesses a considerable degree of nucleotide variability [8]. It possesses two hypervariable regions (HVR1 and HVR2); the HVR2 in the C-terminal region is used to screen the G gene variability of di fferent genotypes [9,10]. Five N-glycosylation sites were detected in HVR2 of the hRSV-A attachment protein [11]. The F protein is more conserved than the G glycoprotein and it is translated as an *F0* precursor that is cleaved twice, resulting in disulfide-linked *F1* (aa 137–574) and *F2* (aa 1–109) subunits along with a short peptide, pep27 (aa 110–136). *F2* possesses heptad repeat C (HRC), while *F1* possesses, at its N terminal, a hydrophobic fusion peptide (FP) followed by two heptad repeats, A and B (HRA and HRB). HRA, HRB, and HRC are essential for envelope fusion to the host cell membrane [12,13]. *F2* possesses five N-glycosylation sites, while HRB, part of *F1*, possesses a single N-glycosylation site; however, *F2* contains more conserved sequence than *F1,* which is characterized by a high homology among di fferent hRSV genotypes [14]. The highly conserved nature of *F2* qualifies it for being a potential target for diagnostic assays.

The hRSV is classified into two major groups: hRSV A and hRSV B [15]. To date, 20 genotypes of hRSV-A and 36 genotypes of hRSV-B are known to exist based on the sequence variation of the G gene [16,17]. Although both hRSV types circulate worldwide, type A was found to be dominant in certain countries [18,19]. Novel genotypes may appear and could replace prevalent genotypes, and many genotypes may circulate together; however, some new genotypes may dominate [20,21]. In 1999, the B/BA genotype, with a duplication of 60 nucleotides of the G gene, appeared [22]; then, the A/ON1 genotype, with a duplication of 72 nucleotides (nt) in the G gene, appeared [23]. Both genotypes are currently prevalent worldwide. The severity of the disease is dependent on the virus genotype, as genotypes A/GA2, A/GA4, A/ON1, and B/BA were found to be of relatively low virulence in comparison to A/NA1, A/GA3, and A/GA5 [24–26].

Typing of hRSV is mainly based on direct G sequencing of sequences flanking HVR2; however, genotype-specific amplification is needed. The F gene could constitute an alternative method for hRSV genotyping; it was found to successfully genotype RSV strains in comparison to the G gene and resulted in the same phylogenetic clusters based on a full genome sequence of the F gene [27]. Accordingly, the aim of the current study was to screen the e fficiency of genotyping hRSV-A based on gene sequencing of *F2* and the first part of *F1* (FP and HRA) and compare it with genotype-specific partial G gene sequencing. Genotyping and sequence analysis of the Saudi hRSV-A strains is another objective of the current study.

#### **2. Materials and Methods**

#### *2.1. Ethical Statement*

Ethical release was obtained from both by the College of Medicine, Taif University (TU/1652/1433/1, approved on 29th April 2011), and also from the hospital of Paediatrics ethical committee based on the human subjects protection guidelines. The first part of the study was previously published [28]. The guardians of the children involved in the study signed informed written consent about the study.
