Report of a workshop on respiratory syncytial virus and parainfluenza viruses.
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BACKGROUND: Respiratory viruses are the main pathogens associated with acute respiratory illness (ARI) in children. OBJECTIVE: To establish the relationship between the presence of respiratory syncytial virus (RSV), influenza and parainfluenza viruses in the community and the number of ARI and pneumonia cases reported to the State Health Services Epidemiology Department (SHSED) in San Luis Potosí, México. METHODS: We compared the weekly number of ARI and pneumonia episodes in children younger than 5 years of age reported to the SHSED for weeks in which the different respiratory viruses were detected in the community. Excess respiratory infection episodes compared with nonepidemic periods were calculated for each of the viruses. RESULTS: From July 2003 through June 2004, there were 236,597 ARI episodes and 2350 pneumonia cases reported to the SHSED. Distinct epidemic periods for parainfluenza type 1 and influenza were observed, whereas RSV and parainfluenza type 3 epidemic periods showed some overlap. The weekly number of excess ARI was greatest when influenza circulated in the community, whereas excess pneumonia cases were greatest when RSV was prevalent. Overall RSV was associated to the largest number of excess ARI and pneumonia cases reported to the SHSED. CONCLUSIONS: RSV detection is associated to the greatest number of ARI and pneumonia episodes in the state of San Luis Potosí. Influenza epidemics are associated to a significant number of ARI visits. Appropriate surveillance systems will be required to assess the impact of influenza immunization and other preventive measures on the number of ARI and pneumonia cases in our community.
A Joint WHO/National Institute of Allergy and Infectious Diseases (NIAID) meeting on the current status of respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV3) vaccine development was held in Bethesda, MD, from 30 September to 1 October 1996. The meeting summarized the worldwide impact of RSV and PIV3; presented the current status of development of RSV and PIV3 vaccines; and examined the applications of recombinant DNA technology to the development and characterization of vaccines and to the understanding of viral pathogenesis.
Two strains of human parainfluenza virus 2 (HPV2), P2 1972/6 and P2 1980, grow to high titre in MEK3 cells, and their structural proteins and virus-induced protein synthesis have been characterized by gel electrophoresis and immunoprecipitation. Purified viruses contain seven polypeptides, including cellular actin: L (175K mol. wt.), HN (72K to 74K), NP (66K to 67K), F1 (52K to 58K), P (49K), A (44.5K) and M (39K). Virus-induced polypeptide synthesis was first detected at 8 h post-infection with the appearance of NP; other major structural proteins were detected from 10 to 12 h after infection and onwards. The synthesis of both the structural glycoproteins was demonstrated, although proteolytic processing could not be detected. Reproducible differences in the gel migration of the HN, F1 and NP polypeptides were found in whole virus, in infected cells and cells subjected to immunoprecipitation. These differences may reflect genetic diversity within HPV2 and provide a means of probing the molecular epidemiology of these viruses.
Newcastle disease virus (NDV) is primarily a respiratory tract pathogen of birds, particularly chickens, but it occasionally produces infection in man. Human parainfluenza virus type 3 (hPIV3) is a common respiratory pathogen, particularly in young children. These two viruses gain entry to host cells via direct fusion between the viral envelope and the cell membrane, mediated by the two surface glycoproteins: the hemagglutinin-neuraminidase (HN) and fusion (F) proteins. Promotion of fusion by HN and F requires that they are derived from homologous viruses. We have constructed chimeric proteins composed of domains from heterologous HN proteins. Their ability to bind cellular receptors and to complement the F protein of each virus in the promotion of fusion were evaluated in a transient expression system. The fusion specificity was found to segregate with a segment extending from the middle of the transmembrane anchor to the top of the putative stalk region of the ectodomain. All of the chimeras, in which the globular domain is derived from the NDV HN and various lengths of the stalk region are derived from the hPIV3 HN maintain receptor binding activity, but some have markedly reduced neuraminidase (NA) activity. Decrease in the NA activity of the chimeras correlates with alteration in the antigenic structure of the globular domain. This suggests that the stalk region of the HN spike is important for maintenance of the structure and function of the globular domain of the HN protein spike.
A cotton rat model of experimental human respiratory syncytial virus (RSV) and human parainfluenza virus type 3 (PIV-3) infection was used to examine the efficacy of FRHNP, a novel chimeric glycoprotein which contains the extracellular regions of the fusion glycoprotein of RSV and the attachment glycoprotein of PIV-3, as a single subunit vaccine against these two viruses. This work was prompted by previous cotton rat studies that demonstrated that the major protective antigens of the two viruses were these glycoproteins. FRHNP was expressed in insect cells using a recombinant baculovirus. Vaccination with FRHNP resulted in induction of both RSV and PIV-3 neutralizing antibody and doses of 200 ng completely protected rats from either RSV or PIV-3 challenge. These results demonstrate that in the cotton rat animal model a single chimeric glycoprotein can be an effective vaccine against both RSV and PIV-3.
Reverse genetics was used to develop a two-component, trivalent live attenuated vaccine against human parainfluenza virus type 3 (HPIV3) and respiratory syncytial virus (RSV) subgroups A and B. The backbone for each of the two components of this vaccine was the attenuated recombinant bovine/human PIV3 (rB/HPIV3), a recombinant BPIV3 in which the bovine HN and F protective antigens are replaced by their HPIV3 counterparts (48). This chimera retains the well-characterized host range attenuation phenotype of BPIV3, which appears to be appropriate for immunization of young infants. The open reading frames (ORFs) for the G and F major protective antigens of RSV subgroup A and B were each placed under the control of PIV3 transcription signals and inserted individually or in homologous pairs as supernumerary genes in the promoter proximal position of rB/HPIV3. The level of replication of rB/HPIV3-RSV chimeric viruses in the respiratory tract of rhesus monkeys was similar to that of their parent virus rB/HPIV3, and each of the chimeras induced a robust immune response to both RSV and HPIV3. RSV-neutralizing antibody titers induced by rB/HPIV3-RSV chimeric viruses were equivalent to those induced by infection with wild-type RSV, and HPIV3-specific antibody responses were similar to, or slightly less than, after infection with the rB/HPIV3 vector itself. This study describes a novel vaccine strategy against RSV in which vaccine viruses with a common attenuated backbone, specifically rB/HPIV3 derivatives expressing the G and/or F major protective antigens of RSV subgroup A and of RSV subgroup B, are used to immunize by the intranasal route against RSV and HPIV3, which are the first and second most important viral agents of pediatric respiratory tract disease worldwide.
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The paramyxoviruses respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV3) are the two most common agents of severe lower respiratory tract disease in infants and children throughout the world. RSV causes yearly epidemics of bronchiolitis and pneumonia in infants and young children, while PIV3 is a common cause of bronchiolitis, pneumonia and croup. Together these two agents account for up to 30% of all hospitalizations of infants and young children for respiratory tract disease. A licensed vaccine is not currently available for either of these viruses. Development of vaccines against diseases caused by RSV and PIV3 is one of the priorities of the Global Programme for Vaccines (GPV). On 27 March 1994, GPV sponsored a workshop in Nyon, Switzerland, to review the status of vaccine development for these pathogens and to explore new methods of immunization that might be applied to the prevention of diseases caused by RSV and PIV. Furthermore, the World Health Organization (WHO) wished to assess progress in the development of methodologies to rescue infectious virus from cDNA clones of RSV and PIV3. This technology, when developed, will be extremely valuable in developing new vaccine candidates and in unravelling the genetic basis of attenuation of existing vaccines. This paper summarizes the findings presented at this one-day meeting.
Human parainfluenza virus type 1 (HPIV1), a major cause of croup in infants and young children, accounts for 6% of hospitalizations for pediatric respiratory tract disease. The antigenically related Sendai virus, referred to here as murine PIV1 (MPIV1), is being considered for use as a live-attenuated vaccine to protect against HPIV1 (J. L. Hurwitz, K. F. Soike, M. Y., Sangster, A. Portner, R. E. Sealy, D. H. Dawson, and C. Coleclough, 1997, Vaccine 15(5), 533-540) and also as a recombinant vaccine vector expressing antigens to protect against viral disease in humans. However, in the 1950s MPIV1 was reported to have been isolated from humans, suggesting that zoonotic transmission might have occurred. It is therefore important to examine the ability of MPIV1 to replicate in nonhuman primates, i.e., surrogate hosts for humans. In the present study the level of replication of MPIV1 and HPIV1 was compared in African green monkeys and chimpanzees. Surprisingly, MPIV1 replicated as efficiently as HPIV1 in the upper and lower respiratory tract of African green monkeys at doses of 10(4) and 10(6) and replicated only slightly less efficiently at both sites in chimpanzees. African green monkeys immunized with MPIV1 were highly resistant to subsequent challenge with HPIV1 even though MPIV1 did not induce a detectable HPIV1-neutralizing antibody response. The high level of replication of MPIV1 observed in the upper and lower respiratory tract of these primates suggests that MPIV1 likely would require significant attenuation before it could be given to humans as a vaccine against HPIV1 or as a vaccine vector. Its ability to efficiently replicate in nonhuman primates suggests that MPIV1 lacks a significant host range restriction in primates and could theoretically cause zoonotic disease in humans.
Respiratory syncytial virus (RSV) and the parainfluenza viruses (PIVs) are the most important causes of acute lower respiratory illness (LRI) in infants and children under 6 years of age. These enveloped viruses are members of the paramyxovirus family. They infect cells in the epithelium lining the trachea and intrapulmonary airways, and cause croup, bronchitis, bronchiolitis, and bronchopneumonia. RSV causes annual midwinter to early spring outbreaks of respiratory disease in temperate climates; epidemics are heralded by the appearance of increased numbers of cases of bronchiolitis, primarily in children under 2 years of age. PIV serotypes 1 and 2 cause epidemics of croup in the fall months. Infections with PIV serotype 3 can occur in an endemic pattern throughout the year, or may occur as outbreaks, usually in the fall or spring. Croup and bronchiolitis are the most common syndromes of PIV-3 LRI. Infection with these viruses induces short-lived partial resistance to reinfection, but the human host remains susceptible to reinfection with these agents throughout life. While antibody in respiratory secretions is related most directly to resistance to reinfection, cell-mediated immune responses are crucial for limitation and termination of established infection. Current research efforts are directed at more thorough characterization of the developing host immune response to individual viral antigens, and to development of methods for immunization using specific virion peptides. Recently, antiviral therapy has become available for serious RSV infection in young infants.
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Human parainfluenza viruses (HPIV) were first discovered in the late 1950s. Over the last decade, considerable knowledge about their molecular structure and function has been accumulated. This has led to significant changes in both the nomenclature and taxonomic relationships of these viruses. HPIV is genetically and antigenically divided into types 1 to 4. Further major subtypes of HPIV-4 (A and B) and subgroups/genotypes of HPIV-1 and HPIV-3 have been described. HPIV-1 to HPIV-3 are major causes of lower respiratory infections in infants, young children, the immunocompromised, the chronically ill, and the elderly. Each subtype can cause somewhat unique clinical diseases in different hosts. HPIV are enveloped and of medium size (150 to 250 nm), and their RNA genome is in the negative sense. These viruses belong to the Paramyxoviridae family, one of the largest and most rapidly growing groups of viruses causing significant human and veterinary disease. HPIV are closely related to recently discovered megamyxoviruses (Hendra and Nipah viruses) and metapneumovirus.
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To compare the requirements for paramyxovirus-mediated cell fusion, the fusion (F) and hemagglutinin-neuraminidase (HN) glycoproteins of simian virus 5 (SV5), human parainfluenza virus 3 (HPIV-3), and Newcastle disease virus (NDV) were expressed individually or coexpressed in either homologous or heterologous combinations in CV-1 or HeLa-T4 cells, using the vaccinia virus-T7 polymerase transient expression system. The contribution of individual glycoproteins in virus-induced membrane fusion was examined by using a quantitative assay for lipid mixing based on the relief of self-quenching (dequenching) of fluorescence of the lipid probe octadecyl rhodamine (R18) and a quantitative assay for content mixing based on the cytoplasmic activation of a reporter gene, beta-galactosidase. In these assays, expression of the individual F glycoproteins did not induce significant levels of cell fusion and no cell fusion was observed in experiments when cells individually expressing homologous F or HN proteins were mixed. However, coexpression of homologous F and HN glycoproteins resulted in extensive cell fusion. The kinetics of fusion were found to be very similar for all three paramyxoviruses studied. With NDV and HPIV-3, no cell fusion was detected when F proteins were coexpressed with heterologous HN proteins or influenza virus hemagglutinin (HA). In contrast, SV5 F protein exhibited a considerable degree of fusion activity when coexpressed with either NDV or HPIV-3 HN or with influenza virus HA, although the kinetics of fusion were two- to threefold higher when the homologous SV5 F and HN proteins were coexpressed. Thus, these data indicate that among the paramyxoviruses tested, SV5 has different requirements for cell fusion.
PIV1 and PIV2 are important agents of pediatric respiratory tract disease. We are developing live-attenuated vaccines against these viruses. We earlier constructed a PIV3/PIV1 antigenic chimeric virus, designated rPIV3-1, in which the hemagglutinin-neuraminidase (HN) and fusion (F) proteins of wild type rPIV3 were replaced by their PIV1 counterparts. In the present study, rPIV3-1 was used as a vector to express the HN protein of PIV2 to generate a single virus capable of inducing immunity to both PIV1 and PIV2. The PIV2 HN open reading frame was expressed from an extra gene cassette, under the control of PIV3 cis-acting transcription signals, inserted between the F and HN genes of rPIV3-1. The recombinant derivative, designated rPIV3-1.2HN, was readily recovered and exhibited a level of temperature sensitivity and in vitro growth similar to that of its parental virus. The rPIV3-1.2HN virus was restricted in replication in both the upper and lower respiratory tracts of hamsters compared with rPIV3-1, identifying an attenuating effect of the PIV2 HN insert in hamsters. rPIV3-1.2HN elicited serum antibodies to both PIV1 and PIV2 and induced resistance against challenge with wild type PIV1 or PIV2. Thus, rPIV3-1.2HN, a virus attenuated solely by the insertion of the PIV2 HN gene, functioned as a live attenuated bivalent vaccine candidate against both PIV1 and PIV2.