Evolution of Bovine Respiratory Syncytial Virus

Abstract

Until now, the analysis of the genetic diversity of bovine respiratory syncytial virus (BRSV) has been based on small numbers of field isolates. In this report, we determined the nucleotide and deduced amino acid sequences of regions of the nucleoprotein (N protein), fusion protein (F protein), and glycoprotein (G protein) of 54 European and North American isolates and compared them with the sequences of 33 isolates of BRSV obtained from the databases, together with those of 2 human respiratory syncytial viruses and 1 ovine respiratory syncytial virus. A clustering of BRSV sequences according to geographical origin was observed. We also set out to show that a continuous evolution of the sequences of the N, G, and F proteins of BRSV has been occurring in isolates since 1967 in countries where vaccination was widely used. The exertion of a strong positive selective pressure on the mucin-like region of the G protein and on particular sites of the N and F proteins is also demonstrated. Furthermore, mutations which are located in the conserved central hydrophobic part of the ectodomain of the G protein and which result in the loss of four Cys residues and in the suppression of two disulfide bridges and an ␣ helix critical to the three-dimensional structure of the G protein have been detected in some recent French BRSV isolates. This conserved central region, which is immunodominant in BRSV G protein, thus has been modified in recent isolates. This work demonstrates that the evolution of BRSV should be taken into account in the rational development of future vaccines. (38,39,40,49). These two related viruses share common epidemiological, clinical, and pathological characteristics. The respiratory syncytial viruses (RSV) are the most common and important cause of lower respiratory tract illness in cattle and young infants (71). More than 70% of calves exhibit a positive serological response against BRSV by the age of 12 months. Bovine respiratory syncytial virus (BRSV) and human respiratory syncytial virus (HRSV) are members of the genus Pneumovirus, subfamily Pneumovirinae, and family ParamyxoviridaeNeutralization tests (9) and reaction patterns with specific monoclonal antibodies (2, 48) have revealed that HRSV contains two major groups, A and B. The main differences between these two groups are located in the glycoprotein (G protein), while others are located in the fusion protein (F protein) and nucleoprotein (N protein) (48, 51). Subgroups within the G and F proteins of BRSV have been characterized more recently by serological analysis of a limited number of isolates and confirmed by phylogenetic analysis (20,54,60). Further studies of BRSV variability have focused on the G protein, which was shown to be the most variable protein and, with the F protein, one of the targets for neutralizing antibodies. A low percentage of sequence divergence between and within the G proteins of BRSV subgroups has been reported, suggesting that BRSV has the same extent of diversity as HRSV (15,21,36,44,66).The G protein is responsib...

Sequence polymorphism of the predicted human metapneumovirus G glycoprotein

“…Similar types of change have been described for the G gene of other members of the subfamily Pneumovirinae; use of alternative transcription termination codons has been described for BRSV (Furze et al, 1997) and HRSV (Sullender et al, 1991;Peret et al, 1998;Martinez et al, 1999), and in-frame and frame-shift insertions have been identified with HRSV (Sullender et al, 1991;Peret et al, 1998). Like APV, HRSV and BRSV (Johnson et al, 1987;Juhasz et al, 1994;Bäyon-Auboyer et al, 2000;Valarcher et al, 2000), the nucleotide substitutions resulted in a higher rate of amino acid changes, especially in the ectodomain. This suggests amino acid changes are advantageous, possibly due to immunological pressure.…”

“…Previous studies have identified conserved clusters of cysteine residues in the G glycoprotein of HRSV (reviewed by Collins et al 2001), APV (Bäyon-Auboyer et al 2000;Alvarez et al, 2003) and BRSV (Furze et al, 1997;Elvander et al, 1998;Valarcher et al 2000), although BRSV G gene isolates lacking the central four cysteine residues have been described (Valarcher et al, 2000). Cystine nooses have been associated with protein conformation and biological signalling (Lapthorn et al, 1995).…”

The antigenic and genetic variability of bovine respiratory syncytial virus with emphasis on the G protein

“…Most of the changes are localized in two regions of the gene, representing the mucin-like regions, those changes have the character of nonsynonymous one-point mutations. On the contrary, the central hydrophobic region is more stable with prevailing synonymous mutations (Valarcher et al, 2000). Single nucleotide sequences differ in onepoint substitutions.…”

“…These mutant viruses were stable in further nonselective passages and grew with unchanged intensity in a mixed viral culture with the original virus. In addition, Valarcher and others (Valarcher et al, 2000) isolated viruses from diseased animals that had all four cystein residues replaced by arginine. Those substitutions led to structural changes in the central conserved region with the disturbance of α helix Cys 173-Cys 176.…”

“…An efficient vaccine for RS viruses should induce a long-lasting humoral and Th1-specific cell-mediated immunity response to both the a�achment proteins F and G. With regard to the immune pressure of a host organism on viral proteins which leads to marked antigenic changes predominantly in glycoprotein G (Valarcher et al, 2000), it is of great importance to use the latest viral strains isolated to ensure the high efficiency of the vaccine, although the current knowledge on BRSV indicates good protection of animals even a�er reinfection with a heterologous strains (Schrijver et al, 1998). On the other hand, the BRSV a�achment glycoprotein G seems to be dispensable in vaccinating calves against BRSV (Schmidt et al, 2002).…”