Molecular epidemiological analysis of a nosocomial outbreak of respiratory syncytial virus associated pneumonia in a kangaroo mother care unit in South Africa

167

207

Human respiratory syncytial virus (HRSV), a member of the Pneumovirus genus within the Paramyxoviridae family, is recognized as the leading agent responsible for severe respiratory infections in the pediatric population (31, 34, 35) and a pathogen of considerable importance in vulnerable adults (23,24). The global respiratory syncytial virus (RSV) disease burden is estimated at 64 million cases and 160,000 deaths every year (70). This virus causes regular seasonal epidemics which take place during the winter months in temperate countries or during the rainy season in tropical areas (12). A peculiar aspect of HRSV is that the immune response produced by infection does not confer long-lasting protection, which is why reinfections are common throughout life (30).Neutralization tests performed with hyperimmune serum (16) and reactivity with specific monoclonal antibodies (4, 45) were used to classify HRSV isolates into two antigenic groups, A and B, which correlated with genetically distinct viruses (18). The main differences between these two groups are located in the major attachment G protein. This protein is a type II glycoprotein that shares neither sequence nor structural features with the attachment proteins (HN or H) of other paramyxoviruses (69), and it represents one of the targets of the immune response (27, 43). The full-length membranebound G protein (Gm) of 292 to 319 amino acids (depending on the viral strain) is also expressed in a secreted version (Gs) that lacks the transmembrane domain due to alternative initiation of translation at a second in-frame AUG codon in the G open reading frame (M48) (52). The G protein is the viral gene product with the highest degree of antigenic and genetic diversity among viral isolates (4,18,28,45). Most changes are concentrated in two hypervariable regions that flank a highly conserved central region of the G protein ectodomain, which includes a cluster of four cysteines and the putative receptor binding site (43). It has been suggested that antigenic differences within this protein could facilitate repeated HRSV infections (37,59). In addition, positive selection of amino acid changes was observed in the two hypervariable regions of the G protein ectodomain (7,43,71,73,74). One of the hypervariable regions, located in the C-terminal one-third of the G molecule, contains multiple epitopes recognized by monoclonal antibodies (43), suggesting that immune selection of new variants by antibodies may contribute to generation of HRSV diversity.Phylogenetic studies based on sequence analysis of the G protein have identified numerous genotypes in the antigenic groups A and B that show complex circulation patterns, since multiple genotypes of both antigenic groups may circulate within the same season and community, with one or two dominant genotypes being replaced in successive years (13,14,26,27,32,49,50). Each community shows a seasonal circulation

Section: Discussionsupporting

confidence: 70%

Section: Fig 1 Phylogenetic Tree Of Hrsv-b Sequences Frommentioning

confidence: 99%

Ten Years of Global Evolution of the Human Respiratory Syncytial Virus BA Genotype with a 60-Nucleotide Duplication in the G Protein Gene

Trento

Casas

Calderón

et al. 2010

167

207

“…Since then, these BA strain viruses have become the prominent circulating B strains (79)(80)(81)(82)(83)(84)(85). More recently, an A strain with a 72-nucleotide duplication in the C-terminal third of its G protein has become a predominant circulating A strain (79-81, 83, 85-87).…”

Section: Discussionmentioning

confidence: 99%

Preventing Cleavage of the Respiratory Syncytial Virus Attachment Protein in Vero Cells Rescues the Infectivity of Progeny Virus for Primary Human Airway Cultures

Corry

Johnson

Cornwell

et al. 2016

All live attenuated respiratory syncytial virus (RSV) vaccines that have advanced to clinical trials have been produced in Vero cells. The attachment (G) glycoprotein in virions produced in these cells is smaller than that produced in other immortalized cells due to cleavage. These virions are 5-fold less infectious for primary well-differentiated human airway epithelial (HAE) cell cultures. Because HAE cells are isolated directly from human airways, Vero cell-grown vaccine virus would very likely be similarly inefficient at initiating infection of the nasal epithelium following vaccination, and therefore, a larger inoculum would be required for effective vaccination. We hypothesized that Vero cell-derived virus containing an intact G protein would be more infectious for HAE cell cultures. Using protease inhibitors with increasing specificity, we identified cathepsin L to be the protease responsible for cleavage. Our evidence suggests that cleavage occurs in the late endosome or lysosome during endocytic recycling. Cathepsin L activity was 100-fold greater in Vero cells than in HeLa cells. In addition, cathepsin L was able to cleave the G protein in Vero cell-grown virions but not in HeLa cell-grown virions, suggesting a difference in G-protein posttranslational modification in the two cell lines. We identified by mutagenesis amino acids important for cleavage, and these amino acids included a likely cathepsin L cleavage site. Virus containing a modified, noncleavable G protein produced in Vero cells was 5-fold more infectious for HAE cells in culture, confirming our hypothesis and indicating the value of including such a mutation in future live attenuated RSV vaccines. IMPORTANCEWorldwide, RSV is the second leading infectious cause of infant death, but no vaccine is available. Experimental live attenuated RSV vaccines are grown in Vero cells, but during production the virion attachment (G) glycoprotein is cleaved. Virions containing a cleaved G protein are less infectious for primary airway epithelial cells, the natural RSV target. In the study described here we identified the protease responsible, located the cleavage site, and demonstrated that cleavage likely occurs during endocytic recycling. Moreover, we showed that the infectivity of Vero cell-derived virus for primary airway epithelial cells is increased 5-fold if the virus contains a mutation in the G protein that prevents cleavage. The blocking of cleavage should improve RSV vaccine yield, consequently reducing production costs. Posttranslational cleavage of the fusion glycoprotein of many viruses plays an essential role in activation; however, cleavage of the RSV G protein is a novel example of a detrimental effect of cleavage on virus infectivity. In adults and teenagers, most respiratory syncytial virus (RSV) infections produce upper respiratory tract infection and symptoms. However, in infants, the immunocompromised, and the elderly, RSV has the potential to cause life-threatening lower respiratory tract infection (1-4). Worldwide, in 2010 ...

“…The HIV-1 seroprevalence among mothers of these infants was 52.6%, suggesting a high level of perinatal exposure (25). Here, we describe identification of G protein deletion mutants that were significantly reduced in size in comparison to that of prototype controls in children with pneumonia.…”

mentioning

confidence: 86%

Identification of Deletion Mutant Respiratory Syncytial Virus Strains Lacking Most of the G Protein in Immunocompromised Children with Pneumonia in South Africa

Venter

Niekerk

Rakgantso

et al. 2011

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