Respiratory Syncytial Virus Subgroup Research Articles

The Comparative Genomics of Human Respiratory Syncytial Virus Subgroups A and B: Genetic Variability and Molecular Evolutionary Dynamics

Genomic variation and related evolutionary dynamics of human respiratory syncytial virus (RSV), a common causative agent of severe lower respiratory tract infections, may affect its transmission behavior. RSV evolutionary patterns are likely to be influenced by a precarious interplay between selection favoring variants with higher replicative fitness and variants that evade host immune responses. Studying RSV genetic variation can reveal both the genes and the individual codons within these genes that are most crucial for RSV survival. In this study, we conducted genetic diversity and evolutionary rate analyses on 36 RSV subgroup B (RSV-B) whole-genome sequences. The attachment protein, G, was the most variable protein; accordingly, the G gene had a higher substitution rate than other RSV-B genes. Overall, less genetic variability was found among the available RSV-B genome sequences than among RSV-A genome sequences in a comparable sample. The mean substitution rates of the two subgroups were, however, similar (for subgroup A, 6.47 × 10(-4) substitutions/site/year [95% credible interval {CI 95%}, 5.56 × 10(-4) to 7.38 × 10(-4)]; for subgroup B, 7.76 × 10(-4) substitutions/site/year [CI 95%, 6.89 × 10(-4) to 8.58 × 10(-4)]), with the time to their most recent common ancestors (TMRCAs) being much lower for RSV-B (19 years) than for RSV-A (46.8 years). The more recent RSV-B TMRCA is apparently the result of a genetic bottleneck that, over longer time scales, is still compatible with neutral population dynamics. Whereas the immunogenic G protein seems to require high substitution rates to ensure immune evasion, strong purifying selection in conserved proteins such as the fusion protein and nucleocapsid protein is likely essential to preserve RSV viability.

Displacement of predominant respiratory syncytial virus genotypes in Malaysia between 1989 and 2011

From 1989 to 2011 in Kuala Lumpur, Malaysia, multiple genotypes from both respiratory syncytial virus (RSV) subgroups were found co-circulating each year. RSV-A subgroup predominated in 12 out of 17years with the remaining years predominated by RSV-B subgroup. Local RSV strains exhibited temporal clustering with RSV strains reported in previous epidemiological studies. Every few years, the existing predominant genotype was replaced by a new genotype. The RSV-A genotypes GA2, GA5 and GA7 were replaced by NA1 and NA2, while BA became the predominant RSV-B genotype. A unique local cluster, BA12, was seen in 2009, and the recently-described ON1 genotype with 72-nt duplication emerged in 2011. Our findings will have important implications for future vaccine intervention.

The clinical characteristics in infantile bronchiolitis and pneumonia according to respiratory syncytial virus subgroups: experience of single tertiary medical center from 2010 to 2012

Purpose: The most common cause of bronchiolitis and pneumonia in infants is respiratory syncytial virus (RSV). We evaluated the clinical characteristics according to RSV subgroup in infantile bronchiolitis and pneumonia. Methods: This study enrolled infants with bronchiolitis or pneumonia infected by single virus. Virus infection was confirmed by respiratory virus reverse transcriptase polymerase chain reaction in two consecutive seasons (2010.2011, 2011.2012). They were divided into 3 groups: group 1 with RSV A, group 2 with RSV B, and group 3 with other virus. We retrospectively reviewed the medical charts to collect data on the hospitalized patients. Results: Seventy four and 181 infants were included in the two seasons, respectively. The most common virus was RSV B in 2010. 2011 and RSV A in 2011.2012. Among 255 infants, 55% (141/255) were group 1, 20% (49/255) group 2, 25% (65/255) group 3. Infants younger than 3 months were 55%. There were no significant age differences between groups. In comparison to group 3, group 1 and 2 showed frequent abnormal chest auscultation, high symptom severity score and need for systemic corticosteroid (P<0.05). In comparison to group 1 and 3, group 2 had longer hospitalization and time to need for normalization of lung sound (P<0.05). The recurrence rates within 6 months showed no significant differences between groups. Conclusion: The RSV subgroup changed from one year to another. Patients’ clinical manifestations and symptom severity may vary according to infected virus subgroup. (Allergy Asthma Respir Dis 1(1):84-89, 2013)

Genetic Variability among Complete Human Respiratory Syncytial Virus Subgroup A Genomes: Bridging Molecular Evolutionary Dynamics and Epidemiology

Human respiratory syncytial virus (RSV) is an important cause of severe lower respiratory tract infections in infants and the elderly. In the vast majority of cases, however, RSV infections run mild and symptoms resemble those of a common cold. The immunological, clinical, and epidemiological profile of severe RSV infections suggests a disease caused by a virus with typical seasonal transmission behavior, lacking clear-cut virulence factors, but instead causing disease by modifying the host’s immune response in a way that stimulates pathogenesis. Yet, the interplay between RSV-evoked immune responses and epidemic behavior, and how this affects the genomic evolutionary dynamics of the virus, remains poorly understood. Here, we present a comprehensive collection of 33 novel RSV subgroup A genomes from strains sampled over the last decade, and provide the first measurement of RSV-A genomic diversity through time in a phylodynamic framework. In addition, we map amino acid substitutions per protein to determine mutational hotspots in specific domains. Using Bayesian genealogical inference, we estimated the genomic evolutionary rate to be 6.47×10−4 (credible interval: 5.56×10−4, 7.38×10−4) substitutions/site/year, considerably slower than previous estimates based on G gene sequences only. The G gene is however marked by elevated substitution rates compared to other RSV genes, which can be attributed to relaxed selective constraints. In line with this, site-specific selection analyses identify the G gene as the major target of diversifying selection. Importantly, statistical analysis demonstrates that the immune driven positive selection does not leave a measurable imprint on the genome phylogeny, implying that RSV lineage replacement mainly follows nonselective epidemiological processes. The roughly 50 years of RSV-A genomic evolution are characterized by a constant population size through time and general co-circulation of lineages over many epidemic seasons – a conclusion that might be taken into account when developing future therapeutic and preventive strategies.

Prevalence and clinical characteristics of human respiratory syncytial virus in Chinese adults with acute respiratory tract infection

Respiratory syncytial virus (RSV) is a leading cause of respiratory tract illnesses worldwide. Although the prevalence and clinical manifestations of the two subtypes, RSV‐A and RSV‐B, have been studied in some detail in infants and young children, they have not been determined in adults. To evaluate the prevalence of the RSV subtypes and disease severity between RSV‐A and RSV‐B infections in adults, nasal and throat swabs that were collected from patients ≥15 years old who sought medical care for acute respiratory infections at the Fever Clinic of the Peking Union Medical College Hospital in Beijing, China between May 2005 and April 2010. The samples were tested for RSV infection using PCR and sequencing analysis. RSV was detected in 95 (1%) of the adult patients, of whom 53 (55.8%) were positive for RSV‐A and 42 (44.2%) for RSV‐B. The incidence of RSV infections increased with age (χ2 = 37.17, P = 1.66E−07). Demographic data and clinical manifestations of RSV‐A were similar to those of RSV‐B. Although RSV‐A and RSV‐B co‐circulated during the 2005–2006 and 2008–2009 seasons, RSV‐A was predominant in the 2006–2008 seasons, whereas RSV‐B was predominant in the 2009–2010 season. Upper respiratory tract infections were diagnosed in most RSV‐infected patients (n = 80, 84.2%), and three patients suffered from pulmonary infection. This is the first study to provide data on the prevalence and clinical manifestations of RSV subgroups among Chinese adults with fever and acute illness, over five successive epidemic seasons. J. Med. Virol. 85:348–353, 2013. © 2012 Wiley Periodicals, Inc.

Clinical severity and iPFT compare between subgroups of respiratory syncytial virus in children hospitalized with acute lower respiratory tract infection

There are three different pneumococcal vaccines available for infants, each oriented to a specific set of serotypes. The vaccination of newborns will prevent pneumococcal disease in this vaccinated group via direct effects, and will also affect the non-vaccinated population through indirect or “herd” immunity.To develop a model that compares the health and economic consequences between the three vaccines.We developed a simulation model for an entire population, providing vaccine to children less than 2 years of age. The vaccines varied by serotypes covered and included a 7- (4, 6B, 9V, 14, 18C, 19F and 23F), 10- (1, 4, 5, 6B, 7F, 9V, 14, 18C, 19F and 23F) and 13-valent (1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F and 23F) vaccines. The base case was PCV-7, and clinical and economic outcomes were estimated for the vaccinated persons and for other persons through assumptions about a herd effect. By comparison, clinical and economic outcomes for the population were also estimated for the 10 and 13 serotype vaccines.In the base case (PCV-7), with the seven serotype vaccine, there were 9.38 cases of hospitalized pneumonia, 0.22 cases of meningitis, 3.69 cases of bacteremia, 60.19 cases of otitis media, and 373 cases of pneumonia, per 100,000 persons in the population, at all ages. With the 10-valent vaccine and a herd effect, invasive pneumonia fell to 8.71 cases, meningitis to 0.21 cases, and bacteremia to 3.39 cases. Otitis media fell to 57 cases and pneumonia to 344 cases. There were further reductions with the 13-valent vaccine, with invasive pneumonia falling to 8.37 cases, bacteremia to 3.33 cases, otitis media to 51.9 cases and all-cause pneumonia to 336.2 cases. Among the vaccines evaluated, PCV-13 was associated with the lowest health services costs and the greatest improved health outcomes.Increased serotype coverage of the 13-valent vaccine is expected to have a substantial public health and economic impact on infectious disease, when considering direct and indirect effects.

Detection and Subgrouping of Respiratory Syncytial Virus RNA by Real-timeRT-PCR

The TaqMan-based quantitative real-time RT-PCR assay we developed uses specific probes to identify respiratory syncytial virus (RSV) and to distinguish RSV subgroups A (RSV-A) and B (RSV-B). We selected conserved regions of the F gene as assay targets and designed new primers and TaqMan MGB probes to detect RSV-A and B. RSV-A and B control plasmids confirmed real-time reverse transcription polymerase chain reaction (RT-PCR) reactivity whose efficiency was 2.5 x 10(1) to 2.5 x 10(7) copies/tube. The assay detection limit was 10 to 10(2) times higher than that of the conventional RT-PCR assay and was equal to the nested PCR assay. No cross-reactions occurred against other respiratory viruses, including influenza virus, metapneumovirus, measles virus, coxsackievirus, enterovirus, echovirus, mumps virus, parainfluenza virus, and rhinovirus. Of 154 clinical specimens derived from subjects with acute respiratory infection and tested by using both real-time RT-PCR and nested PCR, 40 were RSV-positive in both assays. Of these, 25 were identified as RSV-A and 15 as RSV-B by both assays. There was 100% concordance in RSV subgroup identification between real-time RT-PCR and nested PCR assays. These results indicate that our real-time RT-PCR assay can be used for rapid detection, quantitative analysis and subgrouping of RSV-A and RSV-B.

Different NF-κB activation characteristics of human respiratory syncytial virus subgroups A and B

Human respiratory syncytial virus (HRSV) is a member of the family Paramyxoviridae, and is responsible for serious respiratory illness in infants, the elderly and the immunocompromised. HRSV exists as two distinct lineages known as subgroups A and B, which represent two lines of divergent evolution with extensive genetic and serologic differences. While both subgroup A and B viruses contribute to overall HRSV disease, subgroup A isolates are associated with both increased frequency and morbidity of infections, and reasons for this are unclear. HRSV disease is characterized by virus-mediated cell destruction in combination with extensive inflammatory and immune modulatory responses, and for HRSV subgroup A isolates, several of these signaling pathways are regulated through activation of the transcription factor NF-κB. In contrast, the NF-κB activation characteristics of HRSV subgroup B infection remain untested. Here, we performed a quantitative and comparative analysis of NF-κB activation in response to infection of both continuous and primary cell cultures with HRSV subgroup A and B isolates. Our results showed the model HRSV subgroup A isolate consistently induced increased NF-κB activation compared to its HRSV subgroup B counterpart. The differential NF-κB activation characteristics of HRSV subgroup A and B viruses may contribute to differences in their pathogenesis.

A sensitive real-time PCR for detection and subgrouping of human respiratory syncytial virus

Improved diagnostic tools for rapid detection, quantitation, and subgrouping of human respiratory syncytial virus (RSV) are needed to aid the development and evaluation of novel intervention strategies. A quantitative real-time RT-PCR using specific locked nucleic acid (LNA) probes was developed to identify RSV and to distinguish RSV subgroups A and B (RSV LNA assay). RSV subgroup diversity and the relationship between viral load and disease severity in confirmed RSV infections were also explored. 264 archived respiratory specimens from pediatric patients were tested in parallel using the commercial multiplex Seeplex™ RV detection kit (Seegene) and the novel RSV LNA assay. The LNA assay demonstrated a significantly higher sensitivity than Seeplex, improving overall detection rates from 24% (64/264) to 32% (84/264). Detection limits of 9.0×10(1) and 6.0×10(2)copies/mL were observed for RSV A and B, respectively. RSV A was detected in 53/84 (63%) cases, and 31/84 (37%) were positive for RSV B. This novel method offers a rapid, quantitative, highly specific and sensitive approach to laboratory diagnosis of RSV.

Respiratory Syncytial Virus 髄膜炎の1 乳児例

Respiratory syncytial (RS) virus commonly causes infantile respiratory tract infection causing significant morbidity and mortality, but rarely meningitis. We report a case of meningitis caused by RS virus subgroup B in a 56-day-old boy admitted for high fever who underwent blood examination and lumbar puncture. Empirical chemotherapy was started with intravenous ampicillin, gentamicin, and cefotaxime based on laboratory data on CSF cells (84/microL) and serum CRP (13.8mg/dL) data. RS virus subgroup B was only detected using real-time PCR comprehensive reverse transcription from the first CSF, but no bacterial gene was detected. No bacteria grew from his CSF, urine, or blood. Fever and serum CRP dropped in a few days. He had neither seizures nor disturbance of consciousness and was discharged on day 11 after admission. No evidence of encephalopathy was detected in brain MRI or electroencephalography. RS virus rarely causes meningitis, but a percentage of RS-virus-infected infants exhibit symptoms such as seizure and disturbance of consciousness. We should recognize that the RS virus may cause neurological complications associated with high morbidity and mortality.

AIK-C measles vaccine expressing fusion protein of respiratory syncytial virus induces protective antibodies in cotton rats

Respiratory syncytial virus (RSV) is the most common cause of respiratory infection in infants, and no vaccine is available. In this report, recombinant AIK-C measles vaccines, expressing the RSV G or F protein of subgroup A (MVAIK/RSV/G or F), were investigated as a RSV vaccine candidate. MVAIK/RSV/G or F had the original ts phenotype and expressed RSV/G or F protein. Cross-reactive neutralizing antibodies against RSV subgroups A and B were detected in cotton rats immunized intramuscularly with MVAIK/RSV/F but not MVAIK/RSV/G. In cotton rats infected with RSV, RSV was recovered and lung histopathological finding was compatible with interstitial pneumonia, demonstrating thickening of alveolar walls and infiltration of mononuclear cells. When cotton rats immunized with MVAIK/RSV/F were challenged with homologous RSV subgroup A, no infectious RSV was recovered and very mild inflammation was noted without RSV antigen expression. When they were challenged with subgroup B, protective efficacy decreased. When cotton rats immunized with MVAIK/RSV/G were challenged with RSV subgroup A, low levels of infectious virus were recovered from lung. When challenged with subgroup B, no protective effects was demonstrated, demonstrating large amounts of RSV antigen in bronchial-epithelial cells. MVAIK/RSV/F is promising candidate and protective effects should be confirmed in monkey model.

Molecular epidemiology of human respiratory syncytial virus subgroups A and B identified in adults with hematological malignancy attending an Irish hospital between 2004 and 2009

Human respiratory syncytial virus (HRSV) is an important cause of respiratory infection in patients with hematological malignancy, particularly hematopoietic stem cell transplant recipients. This study investigated the genetic variability of the attachment (G) protein gene among HRSV isolates collected from adult patients with hematological malignancy. Between December 2004 and March 2009, 60 samples collected from 58 adults attending an Irish hospital were positive for HRSV by direct immunofluorescence. Nucleotide sequence analysis of the G gene showed a slightly higher frequency of HRSV subgroup A (52%) than HRSV subgroup B (48%). Genetic variability was higher among subgroup A viruses (up to 13% at nucleotide level) than among subgroup B viruses (up to 4%). Phylogenetic analysis revealed two genotypes of HRSV subgroup A, GA2 and GA5, which cocirculated between 2004/2005 and 2007/2008, although GA2 alone was identified in season 2008/2009. Genotype BA was the only genotype of HRSV subgroup B identified. Genotype-specific amino acid substitutions were identified, with two and seven changes for GA2 and GA5, respectively. Furthermore, one to four potential N-glycosylation sites were found among HRSV subgroup A isolates while two to three were identified in HRSV B isolates. Predicted O-glycosylation sites included 25-34 and 40-43 in HRSV subgroups A and B, respectively. The average synonymous mutation-to-non-synonymous mutation ratios (dS/dN) implied neutral selection pressure on both HRSV subgroup isolates. This study provides data for the first time on the molecular epidemiology of HRSV isolates over five successive epidemic seasons among patients attending an Irish hospital.

Quantitative proteomic analysis of A549 cells infected with human respiratory syncytial virus subgroup B using SILAC coupled to LC‐MS/MS

Human respiratory syncytial virus (HRSV) is a leading cause of serious lower respiratory tract infections in infants. The virus has two subgroups A and B, which differ in prevalence and (nucleotide) sequence. The interaction of subgroup A viruses with the host cell is relatively well characterized, whereas for subgroup B viruses it is not. Therefore quantitative proteomics was used to investigate the interaction of subgroup B viruses with A549 cells, a respiratory cell line. Changes in the cellular proteome and potential canonical pathways were determined using SILAC coupled to LC‐MS/MS and Ingenuity Pathway Analysis. To reduce sample complexity and investigate potential trafficking both nuclear and cytoplasmic fractions were analyzed. A total of 904 cellular and six viral proteins were identified and quantified, of which 112 cellular proteins showed a twofold or more change in HRSV‐infected cells. Data sets were validated using indirect immunofluorescence confocal microscopy on independent samples. Major changes were observed in constituents of mitochondria including components of the electron transport chain complexes and channels, as well as increases in the abundance of the products of interferon‐stimulated genes. This is the first quantitative proteomic analysis of cells infected with HRSV‐subgroup B.

Complete genome sequence of avian paramyxovirus-3 strain Wisconsin: Evidence for the existence of subgroups within the serotype

The complete consensus genome sequence was determined for avian paramyxovirus (APMV) serotype 3 strain Wisconsin. The genome is 16,182 nucleotides (nt) in length, consisting of six non-overlapping genes in the order of 3′-N-P/V/W-M-F-HN-L-5′, with a 55-nt leader at its 3′ end and a 681-nt trailer at its 5′ end. Comparison of the APMV-3 strain Wisconsin nt and the aggregate predicted amino acid (aa) sequences with those of APMV-3 strain Netherlands revealed 67% and 78%, identity, respectively. The nt and aa sequence identities between the two APMV-3 strains were lower than between the two antigenic subgroups of human respiratory syncytial virus (81% and 88% identity, respectively) and the two subgroups of human metapeumovirus (80% and 90% identity, respectively). Reciprocal cross-hemagglutination inhibition and cross-neutralization assays using post-infection sera from chickens indicated that strains Wisconsin and Netherlands are highly related antigenically, with only a 2- to 4-fold difference in antibody reactivity between the homologous and heterologous strains. Taken together, our results indicate that the two APMV-3 strains represent a single serotype with two subgroups that differ substantially based on nt and aa sequences, but with only a modest antigenic difference.

Co‐Infection with Respiratory Syncytial Virus Subgroup A and Streptococcus Pneumoniae Detected by a Comprehensive Real‐Time Polymerase Chain Reaction Assay in an Elderly Patient with Community‐Acquired Pneumonia

Co‐Infection with Respiratory Syncytial Virus Subgroup A and <b><i>Streptococcus Pneumoniae</i></b> Detected by a Comprehensive Real‐Time Polymerase Chain Reaction Assay in an Elderly Patient with Community‐Acquired Pneumonia

Emerging Genotypes of Human Respiratory Syncytial Virus Subgroup A among Patients in Japan

Human respiratory syncytial virus (HRSV) is a common etiological agent of acute lower respiratory tract disease in infants. We report the molecular epidemiology of HRSV in Niigata, Japan, over six successive seasons (from 2001 to 2007) and the emerging genotypes of HRSV subgroup A (HRSV-A) strains. A total of 488 HRSV samples were obtained from 1,103 screened cases in a pediatric clinic in Niigata. According to the phylogenetic analysis, among the PCR-positive samples, 338 HRSV-A strains clustered into the previously reported genotypes GA5 and GA7 and two novel genotypes, NA1 and NA2, which were genetically close to GA2 strains. One hundred fifty HRSV-B strains clustered into three genotypes, namely, GB3, SAB3, and BA, which has a 60-nucleotide insertion in the second hypervariable region of the G protein. The NA1 strains emerged first, in the 2004-2005 season, and subsequently, the NA2 strain emerged in the 2005-2006 season. Both strains caused large epidemics in the 2005-2006 and 2006-2007 seasons. The average age of children who were infected with NA2 strains was significantly higher than that of those infected with GA5 and the frequency of reinfection by NA2 was the highest among all genotypes, suggesting that this genotype possessed new antigenicity for evading past host immunity. This is the first paper to show a possible correlation between an emerging genotype, NA2, and large outbreaks of HRSV in Japan. Continuing studies to follow up the genetic changes and to clarify the mechanism of reinfection in HRSV are important steps to understand HRSV infections.

Inhibition of Respiratory Syncytial Virus Infections With Morpholino Oligomers in Cell Cultures and in Mice

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infection in infants, young children, and high-risk adults. Currently, there is no vaccine to prevent RSV infection, and the available therapeutic agents are of limited utility. Peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs) are a class of antisense agents that can enter cells readily and interfere with viral protein expression through steric blocking of complementary RNA. Two antisense PPMOs, designed to target sequence that includes the 5'-terminal region and translation start-site region of RSV L mRNA, were tested for anti-RSV activity in cultures of two human-airway cell lines. Both PPMOs showed minimal cytotoxicity and one of them, (AUG-2), reduced viral titers by >2.0 log(10). Intranasal (i.n.) treatment of BALB/c mice with AUG-2 PPMO before the RSV inoculation produced a reduction in viral titer of 1.2 log(10) in lung tissue at day 5 postinfection (p.i.), and attenuated pulmonary inflammation at day 7 postinfection. These data show that the AUG-2 PPMO possesses potent anti-RSV activity and is worthy of further investigation as a candidate for potential therapeutic application.

Correlation of viral load as determined by real-time RT-PCR and clinical characteristics of respiratory syncytial virus lower respiratory tract infections in early infancy

Background In infants hospitalized for a lower respiratory tract infection (RTI) caused by respiratory syncytial virus (RSV), the correlation between viral load (VL) and patient clinical characteristics remains to be defined. Objectives To define this correlation. Study design prospective study of 47 infants admitted to hospital in the period November 2006–May 2007 with a diagnosis of lower RTI. Nasopharyngeal aspirates (NPAs) were taken at admission, discharge, and at post-discharge control visits. VL was quantified by real-time RT-PCR for RSV subgroups A and B. Results Patients with bronchiolitis were compared with young patients with lower RTI other than bronchiolitis. Patients with bronchiolitis had a significantly lower age than patients with other syndromes, and a significantly longer duration of symptoms. Duration of hospitalization was not different in the two groups of patients, and was not related to RSV subgroup or viral coinfection. A sustained decrease in VL was observed in the general patient population between admission, discharge and post-discharge follow-up visits. Conclusions (i) patients with bronchiolitis were significantly younger than patients with other lower RTIs; (ii) symptom duration was significantly longer in patients with bronchiolitis; (iii) RSV VL significantly decreased between admission and discharge.

Respiratory syncytial virus infections in hospitalized infants: Association between viral load, virus subgroup, and disease severity

The relationships between host factors, virus strain, viral load, and illness severity in respiratory syncytial virus (RSV)-induced bronchiolitis are poorly defined. These relationships were evaluated prospectively in 81 previously healthy infants hospitalized with RSV bronchiolitis. Disease severity was determined by the respiratory rate, the duration of hospitalization, and whether patients during their hospitalization required pediatric intensive care unit admission or mechanical ventilation. RSV typing into subgroup A and B was obtained by RT-PCR-hybridization assay. The nasopharyngeal RSV viral loads were measured by real-time quantitative RT-PCR. Disease severity correlated significantly with the presence of risk factor (estimated gestational age < 37 weeks and/or birth weight < 2,500 g) and with chronologic age <or= 28 days at time of sample collection. The results revealed significant association between disease severity and nasopharyngeal RSV viral load. Analysis also showed that disease severity was not associated significantly with RSV subgroup. Thus, RSV disease severity is likely to be determined by an interplay between host and virus factors, including RSV load.

Molecular diversity of the aminoterminal region of the G protein gene of human respiratory syncytial virus subgroup B

Two major antigenic subgroups (designated A and B) have been described for human respiratory syncytial virus (HRSV). Between and within the two main subgroups, there is antigenic variation in the attachment protein G. The variability of the G protein is known to be located in two hypervariable regions of the ectodomain. Most investigators have studied the gene segment coding the C-terminal end of the protein, and little is known about the N-terminal variable region. In the present study, the genetic variability of HRSV subgroup B was evaluated by nucleotide sequencing of the N-terminal region of the G gene of 52 Tunisian isolates. Tunisian subgroup B isolates clustered into two main lineages designated arbitrarily as Tu-GB1 and Tu-GB2. Three distinct subtypes were identified within genotype Tu-GB2. The inter- and intragenotype nucleotide variability ranged from 4 to 8% and from 0 to 4%, respectively. Overall divergence values of the G sequences were inferior or equal to 15% at the aminoacid level. Comparison of sequences among Tunisian HRSV strains and viruses isolated in other geographical areas during different epidemics demonstrated close similarity to strains from Kenya, Belgium, the UK, Qatar, Canada and South Korea.