Ralph Tripp | The University of Georgia (original) (raw)

Papers by Ralph Tripp

Research paper thumbnail of Antiviral Activity of Probenecid and Oseltamivir on Influenza Virus Replication

Research paper thumbnail of Detection of swine influenza virus in nasal specimens by reverse transcription-loop-mediated isothermal amplification (RT-LAMP)

Journal of Virological Methods, Feb 1, 2021

Research paper thumbnail of Regulation of Mumps Virus Replication and Transcription by Kinase RPS6KB1

Journal of Virology, Jun 1, 2020

Research paper thumbnail of Inhibition of Indoleamine 2,3-dioxygenase (IDO) enhances the memory CD8 T cell response and modulates the immunodominance hierarchy following influenza infection (48.17)

Journal of Immunology, May 1, 2012

The generation of heterosubtypic CD8 T cell responses is important for cross-protective immunity ... more The generation of heterosubtypic CD8 T cell responses is important for cross-protective immunity against unrelated strains of influenza. The need to maintain tolerance in the lung, however, limits the overall breadth and duration of CD8 T cell responses, warranting a better understanding of mechanisms of immunoregulation at this site. Influenza infection induces pulmonary expression of the tryptophan catabolizing enzyme IDO. Depletion of tryptophan results in suppression of T cell expansion or effector function, T cell anergy, or deletion. We hypothesized that ablation of IDO activity during CD8 T cell priming would enhance the subsequent CD8 T cell memory pool. To test this in vivo, we conditionally ablated IDO activity during the priming phase using the inhibitor 1-methyl tryptophan (1MT). 1MT-treated animals challenged with a lethal dose of a heterosubtypic influenza virus generated a more robust Th1 response, with enhanced migration to the lung airways. Interestingly, the immunodominance hierarchy was also shifted to favor subdominant CD8 T cell epitopes in both 1MT-treated and IDO-deficient animals, likely a result of observed decreased regulatory T cell function. While 1MT treatment did not affect cytotoxicity or viral clearance, pulmonary pathology was reduced in the absence of IDO. Together these data provide evidence that modulation of IDO activity in the context of influenza infection could be exploited in vaccine development to enhance memory CD8 T cell responses.

Research paper thumbnail of The Hypothiocyanite and Amantadine Combination Treatment Prevents Lethal Influenza A Virus Infection in Mice

Frontiers in Immunology, May 18, 2022

Research paper thumbnail of Rapid Detection of SARS-CoV-2 RNA in Human Nasopharyngeal Specimens Using Surface-Enhanced Raman Spectroscopy and Deep Learning Algorithms

ACS Sensors, Dec 23, 2022

Research paper thumbnail of Silver nanotriangle array based LSPR sensor for rapid coronavirus detection

Sensors and Actuators B-chemical, May 1, 2022

A rapid, portable, and cost-effective method to detect the infection of SARS-CoV-2 is fundamental... more A rapid, portable, and cost-effective method to detect the infection of SARS-CoV-2 is fundamental toward mitigating the current COVID-19 pandemic. Herein, a human angiotensin-converting enzyme 2 protein (ACE2) functionalized silver nanotriangle (AgNT) array localized surface plasmon resonance (LSPR) sensor is developed for rapid coronavirus detection, which is validated by SARS-CoV-2 spike RBD protein and CoV NL63 virus with high sensitivity and specificity. A linear shift of the LSPR wavelength versus the logarithm of the concentration of the spike RBD protein and CoV NL63 is observed. The limits of detection for the spike RBD protein, CoV NL63 in buffer and untreated saliva are determined to be 0.83 pM, 391 PFU/mL, and 625 PFU/mL, respectively, while the detection time is found to be less than 20min. Thus, the AgNT array optical sensor could serve as a potential rapid point-of-care COVID-19 diagnostic platform.

Research paper thumbnail of The cytotoxic T-lymphocyte response to Sendai virus is unimpaired in the absence of gamma interferon

Journal of Virology, Mar 1, 1997

Research paper thumbnail of Label-free and quantitative detection of respiratory viruses in saliva using surface-enhanced Raman spectroscopy and machine learning algorithms

We report a label-free diagnostic platform that combines surface-enhanced Raman scattering (SERS)... more We report a label-free diagnostic platform that combines surface-enhanced Raman scattering (SERS) and machine learning for the rapid and accurate detection of eleven respiratory viruses. Utilizing SVM-based regression, quantitative detection has been achieved.

Research paper thumbnail of Use of recombinant influenza vaccines expressing exogenous miRNAs for increased vaccine production

Journal of Immunology, May 1, 2019

Vaccination remains the most effective means by which influenza virus infection can be controlled... more Vaccination remains the most effective means by which influenza virus infection can be controlled. Traditionally vaccine production has focused on egg-based technology. Increasingly cell culture-based vaccine production is being used to improve preparedness. Cell cultured based production methods offer significant advantages over traditional egg-based strategies by allowing (i) rapid scale-up (ii) elimination of allergic egg components and (iii) circumvention of issues relating to egg-adaption. Our aim was to improve influenza vaccines and preparedness through the establishment of mammalian cell (Vero)-based vaccines using plasmid-based recombinant flu constructs expressing exogenous miRNA19 (flu-miR19), a regulator of key host anti-viral pathways that has previously been shown to modulate influenza virus replication. We successfully rescued recombinant influenza viruses expressing miR19 using reverse genetics; validated expression of miR19 and showed increased virus replication in vitro that corresponded with increased HA titres and matrix gene expression. Knockdown of miR19 host target genes was confirmed through qRT-PCR to validate the mechanism of action. This new influenza vaccine platform is scalable and can be merged with existing production technology to offer rapid clinical translation and improve vaccine quality and production times. In summary, silencing of anti-viral host genes using a flu-miR resulted in an increase of influenza vaccine and HA antigen yield. We now plan to further augment antigen yield by propagating these viruses in enhanced Vero cell vaccine substrates.

Research paper thumbnail of Engineering enhanced vaccine cell lines for vaccine preventable viral diseases

Journal of Antivirals & Antiretrovirals, Dec 19, 2014

Research paper thumbnail of Glucocorticoid regulation of salmonid B lymphocytes

Research paper thumbnail of Correction: ADAMTS5 Is a Critical Regulator of Virus-Specific T Cell Immunity

PLOS Biology, Nov 6, 2019

Research paper thumbnail of Nanoparticle vaccines comprising the respiratory syncytial virus G Protein CX3C chemokine motif induce robust immunity protecting from challenge and disease (P4513)

Journal of Immunology, May 1, 2013

BALB/c mice immunized with nanoparticle vaccines comprising RSV G protein CX3C polypeptides in ab... more BALB/c mice immunized with nanoparticle vaccines comprising RSV G protein CX3C polypeptides in absence of adjuvant had a neutralizing antibody response associated with reduced lung titers following RSV challenge. These mice also had an increased level of RSV G protein-specific IL-4 and IFNγ secreting cells in the lung, and an increased level of RSV M2-specific IL-4 and IFNγ CD8 T cells. There was a significant increase in M2-specific CD8 T cells that trafficked to the lung following RSV challenge despite the mice being vaccinated with a G protein epitope. Pulmonary cell analysis revealed no significant increase in neutrophils (Ly6Ghi Ly6Cint CD125loSiglecF-) or eosinophils (Ly6Gint Ly6Chi CD125hi SiglecF+) in vaccinated mice before or after RSV challenge. The results show that RSV G protein nanoparticle vaccination is safe and effective, induces a neutralizing protective antibody response, increased RSV G protein- and M2-specific T cell responses, and is not associated with pulmonary disease pathogenesis.

Research paper thumbnail of Structural basis for ultrapotent neutralization of human metapneumovirus

bioRxiv (Cold Spring Harbor Laboratory), Mar 14, 2022

Research paper thumbnail of Asthma, rhinitis, other respiratory diseases Prior airway exposure to allergen increases virus-induced airway hyperresponsiveness

Research paper thumbnail of mir‐548n Expression in HEPG2 and HEP2 cells Is Affected By The Culture Medium Zinc Concentration

The FASEB Journal, Apr 1, 2015

Research paper thumbnail of Anti-G protein antibodies targeting the RSV G protein CX3C chemokine region improve the interferon response

Therapeutic advances in infectious disease, 2023

Background: Respiratory syncytial virus (RSV) is a poor inducer of antiviral interferon (IFN) res... more Background: Respiratory syncytial virus (RSV) is a poor inducer of antiviral interferon (IFN) responses which result in incomplete immunity and RSV disease. Several RSV proteins alter antiviral responses, including the non-structural proteins (NS1, NS2) and the major viral surface proteins, that is, fusion (F) and attachment (G) proteins. The G protein modifies the host immune response to infection linked in part through a CX3 C chemokine motif. Anti-G protein monoclonal antibodies (mAbs), that is, clones 3D3 and 2D10 that target the G protein CX3C chemokine motif can neutralize RSV and inhibit G protein-CX3CR1 mediated chemotaxis. Objectives: Determine how monoclonal antibodies against the RSV F and G proteins modify the type I and III IFN responses to RSV infection. Design: As the G protein CX3 C motif is implicated in IFN antagonism, we evaluated two mAbs that block G protein CX3C-CX3CR1 interaction and compared responses to isotype mAb control using a functional cellular assay and mouse model. Methods: Mouse lung epithelial cells (MLE-15 cells) and BALB/c mice were infected with RSV Line19 F following prophylactic mAb treatment. Cell supernatant or bronchoalveolar lavage fluid (BALF) were assayed for types I and III IFNs. Cells were interrogated for changes in IFN-related gene expression. Results: Treatment with an anti-G protein mAb (3D3) resulted in improved IFN responses compared with isotype control following infection with RSV, partially independently of neutralization, and this was linked to upregulated SOCS1 expression. Conclusions: These findings show that anti-G protein antibodies improve the protective early antiviral response, which has important implications for vaccine and therapeutic design. Plain Language Summary RSV is a leading cause of respiratory disease in infants and the elderly. The only Food and Drug Administration-approved prophylactic treatment is limited to an anti-F protein monoclonal antibody (mAb), that is, palivizumab which has modest efficacy against RSV disease. Accumulating evidence suggests that targeting the RSV attachment (G) protein may provide improved protection from RSV disease. It is known that the G protein is an IFN antagonist, and IFN has been shown to be protective against RSV disease. In this study, we compared IFN responses in mouse lung epithelial (MLE-15) cells and in mice infected with RSV Line19 F treated with anti-G protein or anti-F protein mAbs. The levels of type I and III IFNs were determined. Anti-G protein mAbs improved the levels of IFNs compared with isotype-treated controls. These findings support the concept that anti-G protein mAbs mediate improved IFN responses against RSV disease, which may enable improved treatment of RSV infections.

Research paper thumbnail of BPIFA1: A Protein with an Important Role in the Inflammatory Response to Viral Infection in the Respiratory Tract

Journal of Comparative Pathology, 2016

Research paper thumbnail of An innate defence role for BPIFA1/SPLUNC1 against influenza-A virus infection

European Respiratory Journal, 2015

Although BPIFA1 is one of the most abundant secretory proteins in the upper airways, its9 functio... more Although BPIFA1 is one of the most abundant secretory proteins in the upper airways, its9 function remains unclear. We have recently shown a reduction of BPIFA1 in the airways following influenza-A virus infection. In the present study we evaluated the host defence role of BPIFA1 in viral respiratory infection using an in vitro tracheal model. Tracheal epithelial cells isolated from wild-type and bpifa -/- mice, were seeded onto transwells and differentiated in ALI culture. Differentiated epithelium was infected with influenza-A virus (H3N2). Samples were collected at 2, 24, 48 and 72 hpi (hours post infection). Our data shows that the differentiated epithelial layer mimics the original tracheal epithelium, and abundant BPIFA1 was detected in the apical secretions and cytoplasm of differentiated epithelium. Influenza-A infection initiated inflammatory gene expression, where, IL-6 (2 hpi), TNF-α, IFN-β and IFN-λ2 (24 hpi) were highly upregulated. Influenza-A primarily infected ciliated cells, these cells then lost physical cilia and they down-regulated ciliated gene expression. At low dose (MOI-0.1), BPIFA1 and MUC5B expressing cells were largely uninfected. However, at high dose (MOI-0.5), BPIFA1 +ve cells were also infected and BPIFA1 was down-regulated 6-fold within 48 hpi. At 24 and 48 hpi, viral load was 2.3-fold higher in bpifa -/- cells with these cells exhibiting increased cell death compared to wild-type cell cultures. Our data suggest that BPIFA1 abrogates influenza-A viral infection and therefore, can be a novel target for antiviral treatment for respiratory tract infections.

Research paper thumbnail of Antiviral Activity of Probenecid and Oseltamivir on Influenza Virus Replication

Research paper thumbnail of Detection of swine influenza virus in nasal specimens by reverse transcription-loop-mediated isothermal amplification (RT-LAMP)

Journal of Virological Methods, Feb 1, 2021

Research paper thumbnail of Regulation of Mumps Virus Replication and Transcription by Kinase RPS6KB1

Journal of Virology, Jun 1, 2020

Research paper thumbnail of Inhibition of Indoleamine 2,3-dioxygenase (IDO) enhances the memory CD8 T cell response and modulates the immunodominance hierarchy following influenza infection (48.17)

Journal of Immunology, May 1, 2012

The generation of heterosubtypic CD8 T cell responses is important for cross-protective immunity ... more The generation of heterosubtypic CD8 T cell responses is important for cross-protective immunity against unrelated strains of influenza. The need to maintain tolerance in the lung, however, limits the overall breadth and duration of CD8 T cell responses, warranting a better understanding of mechanisms of immunoregulation at this site. Influenza infection induces pulmonary expression of the tryptophan catabolizing enzyme IDO. Depletion of tryptophan results in suppression of T cell expansion or effector function, T cell anergy, or deletion. We hypothesized that ablation of IDO activity during CD8 T cell priming would enhance the subsequent CD8 T cell memory pool. To test this in vivo, we conditionally ablated IDO activity during the priming phase using the inhibitor 1-methyl tryptophan (1MT). 1MT-treated animals challenged with a lethal dose of a heterosubtypic influenza virus generated a more robust Th1 response, with enhanced migration to the lung airways. Interestingly, the immunodominance hierarchy was also shifted to favor subdominant CD8 T cell epitopes in both 1MT-treated and IDO-deficient animals, likely a result of observed decreased regulatory T cell function. While 1MT treatment did not affect cytotoxicity or viral clearance, pulmonary pathology was reduced in the absence of IDO. Together these data provide evidence that modulation of IDO activity in the context of influenza infection could be exploited in vaccine development to enhance memory CD8 T cell responses.

Research paper thumbnail of The Hypothiocyanite and Amantadine Combination Treatment Prevents Lethal Influenza A Virus Infection in Mice

Frontiers in Immunology, May 18, 2022

Research paper thumbnail of Rapid Detection of SARS-CoV-2 RNA in Human Nasopharyngeal Specimens Using Surface-Enhanced Raman Spectroscopy and Deep Learning Algorithms

ACS Sensors, Dec 23, 2022

Research paper thumbnail of Silver nanotriangle array based LSPR sensor for rapid coronavirus detection

Sensors and Actuators B-chemical, May 1, 2022

A rapid, portable, and cost-effective method to detect the infection of SARS-CoV-2 is fundamental... more A rapid, portable, and cost-effective method to detect the infection of SARS-CoV-2 is fundamental toward mitigating the current COVID-19 pandemic. Herein, a human angiotensin-converting enzyme 2 protein (ACE2) functionalized silver nanotriangle (AgNT) array localized surface plasmon resonance (LSPR) sensor is developed for rapid coronavirus detection, which is validated by SARS-CoV-2 spike RBD protein and CoV NL63 virus with high sensitivity and specificity. A linear shift of the LSPR wavelength versus the logarithm of the concentration of the spike RBD protein and CoV NL63 is observed. The limits of detection for the spike RBD protein, CoV NL63 in buffer and untreated saliva are determined to be 0.83 pM, 391 PFU/mL, and 625 PFU/mL, respectively, while the detection time is found to be less than 20min. Thus, the AgNT array optical sensor could serve as a potential rapid point-of-care COVID-19 diagnostic platform.

Research paper thumbnail of The cytotoxic T-lymphocyte response to Sendai virus is unimpaired in the absence of gamma interferon

Journal of Virology, Mar 1, 1997

Research paper thumbnail of Label-free and quantitative detection of respiratory viruses in saliva using surface-enhanced Raman spectroscopy and machine learning algorithms

We report a label-free diagnostic platform that combines surface-enhanced Raman scattering (SERS)... more We report a label-free diagnostic platform that combines surface-enhanced Raman scattering (SERS) and machine learning for the rapid and accurate detection of eleven respiratory viruses. Utilizing SVM-based regression, quantitative detection has been achieved.

Research paper thumbnail of Use of recombinant influenza vaccines expressing exogenous miRNAs for increased vaccine production

Journal of Immunology, May 1, 2019

Vaccination remains the most effective means by which influenza virus infection can be controlled... more Vaccination remains the most effective means by which influenza virus infection can be controlled. Traditionally vaccine production has focused on egg-based technology. Increasingly cell culture-based vaccine production is being used to improve preparedness. Cell cultured based production methods offer significant advantages over traditional egg-based strategies by allowing (i) rapid scale-up (ii) elimination of allergic egg components and (iii) circumvention of issues relating to egg-adaption. Our aim was to improve influenza vaccines and preparedness through the establishment of mammalian cell (Vero)-based vaccines using plasmid-based recombinant flu constructs expressing exogenous miRNA19 (flu-miR19), a regulator of key host anti-viral pathways that has previously been shown to modulate influenza virus replication. We successfully rescued recombinant influenza viruses expressing miR19 using reverse genetics; validated expression of miR19 and showed increased virus replication in vitro that corresponded with increased HA titres and matrix gene expression. Knockdown of miR19 host target genes was confirmed through qRT-PCR to validate the mechanism of action. This new influenza vaccine platform is scalable and can be merged with existing production technology to offer rapid clinical translation and improve vaccine quality and production times. In summary, silencing of anti-viral host genes using a flu-miR resulted in an increase of influenza vaccine and HA antigen yield. We now plan to further augment antigen yield by propagating these viruses in enhanced Vero cell vaccine substrates.

Research paper thumbnail of Engineering enhanced vaccine cell lines for vaccine preventable viral diseases

Journal of Antivirals & Antiretrovirals, Dec 19, 2014

Research paper thumbnail of Glucocorticoid regulation of salmonid B lymphocytes

Research paper thumbnail of Correction: ADAMTS5 Is a Critical Regulator of Virus-Specific T Cell Immunity

PLOS Biology, Nov 6, 2019

Research paper thumbnail of Nanoparticle vaccines comprising the respiratory syncytial virus G Protein CX3C chemokine motif induce robust immunity protecting from challenge and disease (P4513)

Journal of Immunology, May 1, 2013

BALB/c mice immunized with nanoparticle vaccines comprising RSV G protein CX3C polypeptides in ab... more BALB/c mice immunized with nanoparticle vaccines comprising RSV G protein CX3C polypeptides in absence of adjuvant had a neutralizing antibody response associated with reduced lung titers following RSV challenge. These mice also had an increased level of RSV G protein-specific IL-4 and IFNγ secreting cells in the lung, and an increased level of RSV M2-specific IL-4 and IFNγ CD8 T cells. There was a significant increase in M2-specific CD8 T cells that trafficked to the lung following RSV challenge despite the mice being vaccinated with a G protein epitope. Pulmonary cell analysis revealed no significant increase in neutrophils (Ly6Ghi Ly6Cint CD125loSiglecF-) or eosinophils (Ly6Gint Ly6Chi CD125hi SiglecF+) in vaccinated mice before or after RSV challenge. The results show that RSV G protein nanoparticle vaccination is safe and effective, induces a neutralizing protective antibody response, increased RSV G protein- and M2-specific T cell responses, and is not associated with pulmonary disease pathogenesis.

Research paper thumbnail of Structural basis for ultrapotent neutralization of human metapneumovirus

bioRxiv (Cold Spring Harbor Laboratory), Mar 14, 2022

Research paper thumbnail of Asthma, rhinitis, other respiratory diseases Prior airway exposure to allergen increases virus-induced airway hyperresponsiveness

Research paper thumbnail of mir‐548n Expression in HEPG2 and HEP2 cells Is Affected By The Culture Medium Zinc Concentration

The FASEB Journal, Apr 1, 2015

Research paper thumbnail of Anti-G protein antibodies targeting the RSV G protein CX3C chemokine region improve the interferon response

Therapeutic advances in infectious disease, 2023

Background: Respiratory syncytial virus (RSV) is a poor inducer of antiviral interferon (IFN) res... more Background: Respiratory syncytial virus (RSV) is a poor inducer of antiviral interferon (IFN) responses which result in incomplete immunity and RSV disease. Several RSV proteins alter antiviral responses, including the non-structural proteins (NS1, NS2) and the major viral surface proteins, that is, fusion (F) and attachment (G) proteins. The G protein modifies the host immune response to infection linked in part through a CX3 C chemokine motif. Anti-G protein monoclonal antibodies (mAbs), that is, clones 3D3 and 2D10 that target the G protein CX3C chemokine motif can neutralize RSV and inhibit G protein-CX3CR1 mediated chemotaxis. Objectives: Determine how monoclonal antibodies against the RSV F and G proteins modify the type I and III IFN responses to RSV infection. Design: As the G protein CX3 C motif is implicated in IFN antagonism, we evaluated two mAbs that block G protein CX3C-CX3CR1 interaction and compared responses to isotype mAb control using a functional cellular assay and mouse model. Methods: Mouse lung epithelial cells (MLE-15 cells) and BALB/c mice were infected with RSV Line19 F following prophylactic mAb treatment. Cell supernatant or bronchoalveolar lavage fluid (BALF) were assayed for types I and III IFNs. Cells were interrogated for changes in IFN-related gene expression. Results: Treatment with an anti-G protein mAb (3D3) resulted in improved IFN responses compared with isotype control following infection with RSV, partially independently of neutralization, and this was linked to upregulated SOCS1 expression. Conclusions: These findings show that anti-G protein antibodies improve the protective early antiviral response, which has important implications for vaccine and therapeutic design. Plain Language Summary RSV is a leading cause of respiratory disease in infants and the elderly. The only Food and Drug Administration-approved prophylactic treatment is limited to an anti-F protein monoclonal antibody (mAb), that is, palivizumab which has modest efficacy against RSV disease. Accumulating evidence suggests that targeting the RSV attachment (G) protein may provide improved protection from RSV disease. It is known that the G protein is an IFN antagonist, and IFN has been shown to be protective against RSV disease. In this study, we compared IFN responses in mouse lung epithelial (MLE-15) cells and in mice infected with RSV Line19 F treated with anti-G protein or anti-F protein mAbs. The levels of type I and III IFNs were determined. Anti-G protein mAbs improved the levels of IFNs compared with isotype-treated controls. These findings support the concept that anti-G protein mAbs mediate improved IFN responses against RSV disease, which may enable improved treatment of RSV infections.

Research paper thumbnail of BPIFA1: A Protein with an Important Role in the Inflammatory Response to Viral Infection in the Respiratory Tract

Journal of Comparative Pathology, 2016

Research paper thumbnail of An innate defence role for BPIFA1/SPLUNC1 against influenza-A virus infection

European Respiratory Journal, 2015

Although BPIFA1 is one of the most abundant secretory proteins in the upper airways, its9 functio... more Although BPIFA1 is one of the most abundant secretory proteins in the upper airways, its9 function remains unclear. We have recently shown a reduction of BPIFA1 in the airways following influenza-A virus infection. In the present study we evaluated the host defence role of BPIFA1 in viral respiratory infection using an in vitro tracheal model. Tracheal epithelial cells isolated from wild-type and bpifa -/- mice, were seeded onto transwells and differentiated in ALI culture. Differentiated epithelium was infected with influenza-A virus (H3N2). Samples were collected at 2, 24, 48 and 72 hpi (hours post infection). Our data shows that the differentiated epithelial layer mimics the original tracheal epithelium, and abundant BPIFA1 was detected in the apical secretions and cytoplasm of differentiated epithelium. Influenza-A infection initiated inflammatory gene expression, where, IL-6 (2 hpi), TNF-α, IFN-β and IFN-λ2 (24 hpi) were highly upregulated. Influenza-A primarily infected ciliated cells, these cells then lost physical cilia and they down-regulated ciliated gene expression. At low dose (MOI-0.1), BPIFA1 and MUC5B expressing cells were largely uninfected. However, at high dose (MOI-0.5), BPIFA1 +ve cells were also infected and BPIFA1 was down-regulated 6-fold within 48 hpi. At 24 and 48 hpi, viral load was 2.3-fold higher in bpifa -/- cells with these cells exhibiting increased cell death compared to wild-type cell cultures. Our data suggest that BPIFA1 abrogates influenza-A viral infection and therefore, can be a novel target for antiviral treatment for respiratory tract infections.