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Climatic factors and lower respiratory tract infection due to respiratory syncytial virus in hospitalised infants in northern Spain.

OBJECTIVE: To analyse the influence of climatic factors on the number of hospitalised infants with respiratory syncytial virus (RSV) per week. METHODS: A retrospective observational case-control study was designed enrolling infants under 2 years of age, admitted to hospital between October 1995 and June 2000 with lower respiratory tract infection due to RSV. Climatic and seasonal data were included. The week variable was used as the study unit: weeks with more than one admission for the case group and weeks without admissions for the control group. The total number of weeks excluding summer months, from June to September, was 174. RESULTS: A total of 167 infants were admitted to hospital with lower respiratory tract infection due to RSV with a peak in January and February. There was 82 weeks with one or more admissions (case group) and 92 without admissions (control group). The case group demonstrated lower levels of humidity (absolute: 5.6 +/- 1.5 vs. 6.5 +/- 1.5; p < 0.001) and lower temperature (ground level: 0.4 +/- 3.2 vs. 2.2 +/- 3.5; p < 0.001). When climatic factors were analysed in a logistic regression model, absolute humidity (p < 0.001) was an independent variable associated with a higher risk of infection. CONCLUSIONS: Low absolute humidity was independently associated with hospital admission of infants with lower respiratory tract infection due to RSV.

Case-Control Studies↗

Amino acid variation within the fusion protein of respiratory syncytial virus subtype A and B strains during annual epidemics in South Africa.

Recent evidence of positive selection within the cytotoxic T-cell (CTL) epitopes of the highly conserved nucleoprotein of influenza virus raised the question of whether the CTL epitopes of Respiratory syncytial virus (RSV) are also affected by immune driven change over annual epidemics. The fusion protein (F-protein) of RSV is highly conserved within the two subtypes (A and B) and the most important target for the protective response. The position of various neutralizing epitopes has been mapped and characterized between RSV subtypes. CTL epitopes have also recently been mapped for the F-protein of subtype A, however variation within these epitopes between and within the subtypes has not been determined. To address this question, the F-proteins of 18 strains representative of all subgroup A and B genotypes identified in South Africa over a period of 5 years were sequenced. F-protein sequences were highly conserved within and between South African genotypes, with most variability occurring at the nucleotide level. Most of the amino acid differences identified within neutralizing and CTL epitopes were conserved within the subtypes, and therefore does not indicate immune selection. However, out of three CTL epitopes previously identified in subtype A, two (restricted to HLA B*57 and HLA A *01) were conserved only within subtype A, while the third (restricted to Cw*12) contained both subtype- and genotype-specific changes. These results suggest that most of the identified CTL epitopes are subtype A-specific and may not be recognized in subtype B viruses, while the HLA Cw*12 restricted epitope may also not be recognized efficiently in GA5 strains.

Amino Acid Sequence↗

Respiratory syncytial virus(RSV)-induced allergy may be controlled by IL-4 and CX3C fractalkine antagonists and CpG ODN as adjuvant: hypothesis and implications for treatment.

Based on the hypothesis that respiratory syncytial virus (RSV) sG protein causes allergy in patients, it is suggested that treatment of RSV patients with antagonists of IL-4 and FKN early in infection will prevent the increased level of IL-4 in the serum. Together with CpG ODNs that induce Toll-like receptor 9(+) (TLR9(+)) plasmacytoid dendritic cells to release type I IFN-alpha and -beta will reactivate the inhibited Th1 cells and the antiviral cytotoxic T leukocytes. In addition, binding of CpG ODNs to TLR9(+) B cells will stop IgE synthesis and antiviral IgG and IgA will continue. Together, the IL-4 and FKN antagonists and CpG ODNs reactivate the adaptive immune response to clear the virus and protect the patient from a second RSV infection. It is also suggested that the less-pathogenic RSV strain Long may be a candidate for vaccine development after deletion of the FKN and superantigen domains from the G gene.

Adjuvants, Immunologic↗

Respiratory syncytial virus (RSV) evades the human adaptive immune system by skewing the Th1/Th2 cytokine balance toward increased levels of Th2 cytokines and IgE, markers of allergy--a review.

Infection of infants in their first year of life, children and elderly people with the respiratory syncytial virus (RSV) endangers the life of the patient. An attempt to develop a formalin-inactivated RSV (FI-RSV) vaccine during the 1960s resulted in an aggravated infection in immunized children, leading to hospitalization, while infection of non-immunized children produced much milder symptoms. The reason for this remained an enigma, one which was gradually solved over the last decade by many researchers who studied the molecular biology of RSV infection of respiratory ciliary cells. Clinical studies of RSV-infected patients indicated increased levels of Th2 cytokines and IgE in the patients' sera, suggesting that an allergy-like condition developed during infection. The biomarkers of allergy caused by endogenous or environmental allergens include a marked increase of the Th2 cytokine IL-4 and IgE non-neutralizing antibodies to the allergen. The way allergens trigger allergy was deciphered recently, and will be discussed later. Studies of RSV infection led to the suggestion that RSV patients suffer from allergy prior to RSV infection, a concept that was later abandoned. Studies on HIV-1 [Y. Becker, Virus Genes 28, 319-331 (2005)] research led me to the hypothesis that since HIV-1 infection induces a marked increase of IL-4 and IgE in serum, an allergy-like condition, the AIDS stage is the result of an allergen motif that is embedded in the shed viral gp120 molecules. It is hypothesized that the viral-soluble G glycoprotein (sG) contains a T cell superantigen (Tsag) that is capable of binding to the V(H)3 domain of IgE/FcepsilonRI(+) hematopoietic cells, basophils, mast cells and monocytes, similar to the case of allergens, and that this aggregation causes these innate system cells to degranulate and release large amounts of Th2 cytokines (IL-4, IL-5, IL-10, IL-13) into the blood. The way these Th2 cytokines skew the Th1/Th2 balance toward Th2 > Th1 will be discussed. The aim of the present review is to base RSV pathogenicity on the numerous very good analyses of the virus genes and to suggest a therapeutic approach to treatment that is directed at preventing the inhibitory effects of Th2 cytokines on the adaptive immune system of the patients, instead of inhibiting RSV replication by antivirals. The review of the molecular research on the role of the viral fusion (F) and attachment (G) glycoproteins of RSV provided information on their role in the virus infection: early in infection the F glycoprotein induces Th1 cells to release the Th1 cytokines IL-2, IL-12 and IFN-gamma to activate precursors CTLs (pCTLs) to become anti-RSV CTLs. The G and sG glycoproteins attach to FKNR1(+) ciliary respiratory epithelial cells as well as directly to eosinophils to the lungs. The sG T cell antigen can also induce the release of large amounts of Th2 cytokines from CD4(+) T cells and from FCepsilonRI(+) mast cells, basophils and monocytes. By comparison to HIV-1 gp120 it is possible to show that in the G and sG proteins the T cell antigen resembles the CD4(+) T cell superantigen (=allergen) domain of HIV-1 gp120 which aggregates with IgE/FCepsilonRI(+) hematopoietic cells. The increased IL-4 level in the serum inhibits the adaptive immune response: IL-4Ralpha(+) Th1 cells stop Th1 cytokine synthesis and IL-4Ralpha(+) B cells stop the synthesis of antiviral IgG and IgA and switch to IgE synthesis. In addition, the hematopoietic cells release histamine and prostaglandin which induce wheezing. The gradual increase of sG molecules creates a gradient of fractalkine (FKN) which directs IL-5-activated eosinophils to the lungs of the patient.

Animals↗

The role of the respiratory syncytial virus in airway syndromes in childhood.

The majority of infants admitted to hospital in infancy with lower respiratory tract infections (LRTIs) have been infected with the respiratory syncytial virus (RSV). Infants and young children experiencing RSV LRTIs experience increased respiratory morbidity in subsequent years, although the prevalence falls rapidly in early childhood. Recent data support the suggestion that in most subjects, this recurrent morbidity is not attributable to atopic asthma and that in most respects, the acute and long-term outcomes with RSV infections are similar in nature to those attributable to other viruses. The phenotype of the acute illness probably provides better prognostic information than the type of virus.

Acute Disease↗

Seasonality of respiratory syncytial virus-positive hospitalizations in children in Kiel, Germany, over a 7-year period.

BACKGROUND: Elaborate, long-term data on the rhythm, seasonality and severity of the yearly respiratory syncytial virus (RSV) epidemics in Germany are lacking. PATIENTS AND METHODS: A longitudinal investigation was undertaken of children from birth to 16 years of age admitted with an RSV infection in the two pediatric hospitals in Kiel between July 1994 and June 2001. To compare the severity of the individual seasons, the incidences and the proportion of RSV-positive hospitalized children aged 0 to 2 years from the denominator area of Kiel were compared. RESULTS: During the 7-year period, the nasopharyngeal aspirates of 2,367 children were investigated; RSV was detected in 384 (16.2%). The seasons from 1994/95 to 1996/97 started late (December to January) and ended between March and May. Since 1997/98 it seems that a late season is followed by an early season (start in September to October) in a 2-year pattern. CONCLUSION: No fixed rhythm of the RSV season can be identified as yet. Ascertainment bias is unlikely to explain the differences in rhythm. The incidence of RSV-positive hospitalizations seems to be increasing.

Adolescent↗

Two-year periodicity of respiratory syncytial virus epidemics in Switzerland.

BACKGROUND: The annual respiratory syncytial virus (RSV) epidemics vary in time and severity. The aims of this study were (1) to describe the time-related pattern of RSV epidemics in Switzerland and (2) to deduce the most effective time period for administration of prophylactic measures to high-risk patients. PATIENTS AND METHODS: Descriptive study of (1) RSV hospitalizations between 1997 and 2001 at a pediatric hospital serving a population of 1 million and (2) of national RSV detection rates reported by diagnostic laboratories between 1988 and 1999. RESULTS: 497 RSV hospitalizations and 8,574 reported RSV detections occurring during four and 12 epidemics, respectively, were analyzed. There was fixed alternation of minor and major epidemics differing in the number of RSV infections (two to fourfold), evolution (median interval from onset to peak 13 weeks, range 4-13 weeks vs 8 weeks, range 7-10 weeks; p = 0.065) and median duration (26 weeks, range 24-29 weeks vs 19.5 weeks, range 18-21 weeks; p = 0.005). For minor epidemics it was estimated that a maximum of 85.6% (range, 79.4-86.6%) of annual RSV infections could be covered by a standard five-dose regimen of the monoclonal anti-RSV antibody palivizumab, if initiated in week 50. During major epidemics the most effective time of initiation would be week 43 (88.7%; range 81.9-94.6%). CONCLUSION: RSV epidemiology in Switzerland is characterized by fixed biannual variation. In the absence of active RSV surveillance, such periodicity is useful for scheduling RSV prophylaxis and for hospital resources management.

Disease Outbreaks↗

Significance of respiratory syncytial virus (RSV) infection in the 1st year of life.

BACKGROUND: In this study we investigated the frequency, symptoms and predisposing factors of respiratory syncytial virus (RSV) infection during the 1st year of life in infants with obstructive airway disease in comparison with infants without airway disease. PATIENTS: We enrolled 216 infants in their 1st year of life, who were hospitalized because of obstructive airway disease. As an age- and sex-balanced control group, we examined 133 infants hospitalized for other reasons than airway disease. METHOD: A deep pharyngeal swab was taken from all infants and immediately examined for the presence of RSV antigen by using an enzyme immunoassay (Directigen). Patient data were surveyed by a questionnaire. RESULTS: The frequency of RSV infections among infants with obstructive airway disease (34.3%; n = 74) differed significantly from the control group (15%; n = 20; p < 0.01). The frequency of RSV-infected infants with obstructive airway disease decreased with age ranging from 39.1% in trimenon I to 29.0% in trimenon IV. This trend was not observed in the control group. With respect to clinical symptoms and risk factors, there were no differences between RSV-infected versus noninfected infants. CONCLUSION: RSV is an important agent causing lower obstructive airway disease (34.3% of all patients). There are no specific symptoms that can be used for diagnosing RSV infection. In order to prevent other patients on the ward from contracting nosocomial RSV infection and in the light of therapeutic options, one should test newly admitted patients presenting with symptoms of an obstructive airway disease for RSV antigen. On a ward with high-risk patients, we would recommend the use of an RSV test for all new patients.

Age Factors↗

Respiratory syncytial virus infection induces matrix metalloproteinase-9 expression in epithelial cells.

Increased gelatinolytic activity was observed in respiratory syncytial virus (RSV)-infected HEp-2 cells by using zymography. The anti-matrix metalloproteinase-9 (MMP-9) antibody specifically reduced the gelatinolytic activity suggesting that the increased gelatinolytic activity was due to the MMP-9. It was also supported by the results from immunofluorescent staining, treatment of MMP inhibitors, and RSV infection of the cell clones that were transfected with plasmids to express more MMP-9 and tissue type inhibitor of metalloproteinase-1 (TIMP-1). The gelatinolytic activity of extracellular MMP-9 in RSV-infected HEp-2 cells increased 1.5 +/- 0.2 fold compared with the control (p < 0.01). Cell surface MMP-9 expression was also clearly detected by immunofluorescent staining. Treatment with 1,10-phenanthroline (0.05 mM), ethylenediamine-tetraacetate (EDTA) (1.5 mM), and penta-O-galloyl-beta-D-glucose (PGG) (3.3 microM) inhibited RSV multiplication as well as syncytia formation. Furthermore, the average syncytia size increased when the cells expressing more MMP-9 were infected by RSV. In contrast, syncytia formation was inhibited in the cells manipulated to express TIMP-1. Thus, this study concludes that although RSV infection induces MMP-9, which can enhance the syncytia formation leading to RSV multiplication and spread it can be inhibited by MMP inhibitors.

Epithelial Cells↗

Type-specific serologic diagnosis of respiratory syncytial virus infection, based on a synthetic peptide of the attachment protein G.

Peptides deduced from the central hydrophobic region (residues 158-189) of the G protein of bovine and ovine respiratory syncytial virus (RSV) and of human RSV subtypes A and B were synthesized. These peptides were used to develop ELISAs to measure specifically antibodies against these types and subtypes of RSV. We have evaluated the bovine RSV-G peptide in both an indirect ELISA and in a blocking ELISA. Specificity and sensitivity, relative to a routine diagnostic ELISA that detects antibodies against the RSV F-protein in bovine sera, were 98% and 92% respectively for the indirect peptide-based ELISA, and 98% and 98% for the blocking peptide-based ELISA. In paired serum samples, rises in antibody titer were detected more frequently with the indirect peptide-based ELISA than with the routine F-ELISA. Furthermore, the peptide-based G-ELISAs were able to differentiate between antibodies against BRSV and HRSV, and between those against BRSV and ORSV. In addition, the indirect peptide-based ELISA was selective for HRSV subtype A and B antibodies. This study shows that peptides, corresponding to the central hydrophobic region of the attachment protein G of several RSVs, can be used successfully as antigens in highly specific and sensitive immunoassays.

Amino Acid Sequence↗

Cell-mediated immune responses of lambs to experimental infection with bovine respiratory syncytial virus.

Primary infection of lambs with bovine respiratory syncytial virus (RSV) was characterised by the presence of virus-specific cytotoxic cells in the peripheral blood as early as 5 days post-infection. These effector cells lysed virus-infected autologous targets in a self-restricted manner. Depletion techniques revealed that cytotoxic activity was largely due to OvCD8+ cells. Neutrophils obtained from experimentally infected lambs 5 to 10 days post-inoculation exhibited significant cytotoxic activity in the presence of bovine RSV-specific antiserum. During the same period there was a significant lymphoproliferative response to live or inactivated bovine RSV. Lymphoproliferative and cytotoxic activity coincided with the clearance of the virus from nasal secretions.

Animals↗

Antigens of bovine respiratory syncytial virus in peripheral blood lymphocytes of experimentally infected lambs.

Eight lambs were experimentally infected with bovine respiratory syncytial virus (RSV) and the distribution of viral antigen in lymphocyte subpopulations studied by flow cytometry. Experimental infection with bovine RSV was characterised by significant changes in lymphocyte subpopulations. Infection was followed by a significant (P <0.001) reduction in the number of cells expressing the OvCD5 epitope (T cells), due to a fall in the number of cells expressing the OvCD4 epitope (helper) and those expressing the OvWC1 epitope (gamma/delta) 3-7 days post-inoculation. There was a significant increase in the number of OvCD5+ cells expressing the OvCD8 epitope (cytotoxic/suppressor) later. Flow cytometric analysis with bovine RSV-specific monoclonal antibodies revealed that viral antigens were present in all lymphocyte subpopulations but the main targets were T cells in general and OvCD4+ cells in particular. Challenge of primed lambs with bovine RSV had similar effects over a shorter period, followed by significant rises in the number of OvCD45+ (B) cells and OvCD5+ (T cells). Viral antigens were also present in lymphocytes subsets following challenge.

Animals↗

Optimization of PCR and automated sequencing of clinical isolates of respiratory syncytial virus.

A streamlined protocol was developed to carry out nucleotide sequence analysis on PCR products obtained from regions of the RNA genome of respiratory syncytial virus (RSV). Whole cell RNA extracted from tissue culture cells inoculated with RSV-infected nasopharyngeal aspirates was used as a template for single-tube cDNA synthesis and PCR amplification of specific regions of the RSV fusion (F) protein gene. The products were then purified using Sephacryl spin columns and digested using lambda-exonuclease to obtain single-stranded templates for analysis using dye-primer chemistry in an automated sequencer. Optimization of a range of parameters and comparison of a number of alternate procedures resulted in a final protocol that allowed the comparison of the sequences of a panel of local RSV subgroup A and B clinical isolates.

Base Sequence↗

Recombinant superoxide dismutase (SOD) administered by aerosol inhibits respiratory syncytial virus infection in cotton rats.

Recombinant (r) human (hu) manganese (Mn) and copper-zinc (CuZn) superoxide dismutase (SOD) were evaluated for their cytotoxicity and antiviral activity against respiratory syncytial virus (RSV) in tissue culture and in cotton rats. No apparent cytotoxicity or inhibition of RSV was observed in the tissue culture studies (both compounds had IC50 and EC50 values > or = 1000 micrograms/ml and a selective index = 1). However, significant reductions in mean pulmonary RSV titers (ranging between 0.5 and 1.9 log10/g of lung compared with the mean pulmonary viral titers detected in similarly inoculated, placebo-treated control animals) were seen in most of the experiments, in which experimentally infected cotton rats were exposed to continuous small-particle aerosols (reservoir concentrations > or = 20 mg/ml) containing either rhuMnSOD or rhuCuZnSOD. This protective effect was dose dependent and not observed when either rSOD compound was administered parenterally (intraperitoneally) or intranasally. No toxic effects were noted in any of the cotton rats exposed to aerosols of either rhuMn or CuZnSOD; nor was any evidence of drug-induced histopathology observed in sections of lung prepared from these animals.

Aerosols↗

Attenuated temperature-sensitive respiratory syncytial virus mutants generated by cold adaptation.

Two strains of respiratory syncytial virus (RSV), RSV 2B and RSV 3A (representing subgroup B and A virus respectively) were cold-adapted by passaging in Vero cells for up to 42 weeks at successively lower temperatures down to 20 degrees C. Successful cold adaptation of the virus population was dependent on the amount of time the cultures were maintained at the various low temperatures, as well as on the strain of virus used. Temperature-sensitive (TS) mutants appeared in the cold passaged virus populations; however, the majority of the virus variants remained predominantly non-TS. Four RSV 2B and three RSV 3A TS mutants were selected for further characterization. These seven TS mutants retained their fusion phenotype and two major neutralizing antibody epitopes, and displayed varying levels of temperature sensitivity. Six of the seven mutants had a cold-adapted (CA) phenotype. All of the RSV 2B mutants were highly attenuated in cotton rats and two of the mutants elicited relatively high levels of neutralizing antibody and were able to protect rats against virus challenge. The RSV 3A TS mutants grew well in the nose but poorly in the cotton rat lungs, as did the parental 3A virus. All 3A mutants elicited high titers of neutralizing antibody and provided complete protection against virus challenge. These mutants showed varying levels of temperature sensitivity in vitro and attenuation in vivo and represent potential vaccine candidates.

Adaptation, Physiological↗

Nosocomial respiratory syncytial virus infections in a paediatric department.

The seasonal problem of respiratory infections in children caused by respiratory syncytial virus (RSV) is worldwide. A number of these infections are known to occur by nosocomial acquisition. In order to reduce the risk, measures, such as cohort nursing and handwashing, have been used in the paediatric department of Odense University Hospital for three years. In a retrospective evaluation of this routine practice the incidence of nosocomial RSV infections was recorded. The overall rate of nosocomial infection was low, but was proportionally highest in the unit for children aged under 6 months; no change in incidence was seen over the three-year period. In the infectious disease unit, where the majority of RSV infected children were admitted, the rate of nosocomial infection decreased despite an unchanged routine. This difference cannot be explained simply on the basis of longer hospital admission of the children under 6 months of age, but might relate to acquired immunity in children of all ages in the infectious diseases unit or better facilities for segregation within that unit.

Adolescent↗

Enhanced pulmonary pathology associated with the use of formalin-inactivated respiratory syncytial virus vaccine in cotton rats is not a unique viral phenomenon.

The specificity of viral antigens in the formalin-inactivated, alum-precipitated respiratory syncytial virus (FI-RSV) vaccine in augmenting the pulmonary inflammatory response was evaluated. Cotton rats were immunized with a FI-RSV vaccine derived from Vero cells, a monkey cell line, or HEp-2 cells, a human cell line. The FI-RSV/Vero and the FI-RSV/HEp-2 vaccines were prepared similarly to the original Lot-100 FI-RSV vaccine that was associated with enhanced disease in the mid-1960s field trials. Each vaccine was administered intramuscularly at various doses and intervals. At 1, 4 or 7 weeks after the last vaccine dose, cotton rats were challenged with 10(6) plaque-forming units of live RSV grown in HEp-2 cells. For controls, FI-parainfluenza, FI-HEp-2 and alum vaccines, and live RSV primary infection were used. For measuring virus replication and histopathology, lungs were harvested at 4 and 8 days postchallenge. A dose-response relationship to vaccine dose was observed for ELISA, neutralizing and antifusion antibodies. All animals given three doses or two of the higher doses of FI-RSV/Vero vaccine developed significant neutralizing antibody, were protected against pulmonary virus replication and had similar low levels of histopathology compared with live RSV and controls. Two immunizations of the lowest dose of FI-RSV/Vero vaccine did not induce neutralizing antibody, did not provide protection of the lung against RSV and did not enhance the pulmonary cellular response. However, FI-RSV/HEp-2 vaccine was associated with significant enhanced pulmonary histopathology despite inducing high titres of neutralizing antibody and protecting the lungs against RSV infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

The pulmonary immune response of Balb/c mice vaccinated with the fusion protein of respiratory syncytial virus.

We have investigated the efficacy of vaccination with the purified fusion (F) protein of respiratory syncytial virus (RSV) on aluminium hydroxide adjuvant in Balb/c mice. The purpose of the study was to define the role of the local pulmonary mononuclear cell (PMC) infiltrate in the clearance of virus from the lower respiratory tract. Balb/c mice immunized with F protein were able to inhibit the replication of virus in the lungs as early as 4 days after intranasal challenge. In contrast, unimmunized mice required 8 days. Examination of humoral immune mechanisms demonstrated that vaccination with the purified protein induced moderate titres of serum neutralizing antibody. In addition, immunization induced low to moderate levels of antigen-dependent killer cell activity. To examine the immunological events responsible for virus clearance in vivo, PMC infiltrates were isolated after virus challenge and tested directly for protective capacity. After virus challenge, the F protein-immune mice were able to recall the cytolytic cells to the pulmonary tissues. The results further suggested that the local antigen-dependent killer activity was mediated by cytolytic T cells of the CD8 phenotype. Adoptive transfer studies were also conducted to identify further the role the PMC infiltrate had in protective immunity. Adoptive transfer of F protein-educated PMC into naive syngeneic recipients suggested that the pulmonary infiltrates contained the cellular constituents necessary for protective immunity. Both humoral and cellular immune elements were present.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗