Predicting the Airborne Transmission of Measles: Impact of Indoor Carbon Dioxide (CO2) Levels and Mitigation Strategies.

BACKGROUND: Measles is a highly contagious cause of febrile illness typically seen in young children. It is transmitted primarily through respiratory droplets and small-particle aerosols and can remain viable in the air. Despite the availability of an effective vaccine, measles remains a major global issue, particularly in regions with low vaccination rates. AIM: This study aimed to quantify the airborne transmission risk of the measles virus in various indoor environments. METHODS: Using indoor carbon dioxide (CO2) levels, we estimated the probability of airborne transmission and the basic reproduction number (Ro) in four hypothetical indoor scenarios, including restaurants, mass gathering events, homes, and business meetings, based on the modified Wells-Riley model. RESULTS: The relationship between airborne transmission rates and indoor CO2 concentrations was visualized, with and without mask usage. Without masks, at an indoor CO2 concentration of 1,000 ppm, the airborne transmission rates were high in homes (100.0%) and business meetings (100.0%) and moderate in restaurants (45.6%) and live events (30.6%). By contrast, the Ro was high in audience-participatory live events (60.9%) and restaurants (13.2%), indicating a higher risk of cluster infections. DISCUSSION AND CONCLUSION: In all indoor environmental scenarios, a positive linear relationship was found between the risk of airborne transmission and indoor CO2 levels. The risk of airborne transmission varied significantly across scenarios, which was influenced by various parameters, such as mask usage, quality of ventilation, conversation, and exposure duration. This model suggests that the risk of airborne transmission of measles can be easily predicted using a CO2 meter.

Immunogenicity of a peptide-based vaccine for measles: a pilot evaluation in a mouse model.

Although neutralizing antibody is an established correlate of protection for measles, T cell-mediated responses play at least two critical roles in immunity to measles: first, through provision of 'help' enabling robust humoral immune responses; and second, through clearance of measles virus-infected cells. Previously, we identified 13 measles-derived peptides that bound to human leukocyte antigen (HLA) molecules in Priess cells infected with measles virus. In this study, we evaluated the immunogenicity of these peptides in a transgenic mouse model. Our results demonstrated that these peptides induced Th1-biased immune responses at varying levels. Of the 13 peptides, the top four immunogenic peptides were further selected for a viral challenge study in mice. A vaccine based on a combination of these four peptides reduced morbidity and weight loss after viral challenge compared to placebo. Our results emphasize the potential of T cell-mediated, peptide-based vaccines against measles.

Host WD repeat-containing protein 5 inhibits protein kinase R-mediated integrated stress response during measles virus infection.

Some negative-sense RNA viruses, including measles virus (MeV), share the characteristic that during their infection cycle, cytoplasmic inclusion bodies (IBs) are formed where components of the viral replication machinery are concentrated. As a foci of viral replication, how IBs act to enhance the efficiency of infection by affecting virus-host interactions remains an important topic of investigation. We previously established that upon MeV infection, the epigenetic host protein, WD repeat-containing protein 5 (WDR5), translocates to cytoplasmic viral IBs and facilitates MeV replication. We now show that WDR5 is recruited to IBs by forming a complex with IB-associated MeV phosphoprotein via a conserved binding motif located on the surface of WDR5. Furthermore, we provide evidence that WDR5 promotes viral replication by suppressing a major innate immune response pathway, the double-stranded RNA-mediated activation of protein kinase R and integrated stress response. IMPORTANCE: MeV is a pathogen that remains a global concern, with an estimated 9 million measles cases and 128,000 measles deaths in 2022 according to the World Health Organization. A large population of the world still has inadequate access to the effective vaccine against the exceptionally transmissible MeV. Measles disease is characterized by a high morbidity in children and in immunocompromised individuals. An important area of research for negative-sense RNA viruses, including MeV, is the characterization of the complex interactome between virus and host occurring at cytoplasmic IBs where viral replication occurs. Despite the progress made in understanding IB structures, little is known regarding the virus-host interactions within IBs and the role of these interactions in promoting viral replication and antagonizing host innate immunity. Herein we provide evidence suggesting a model by which MeV IBs utilize the host protein WDR5 to suppress the protein kinase R-integrated stress response pathway.

Structural basis of paramyxo- and pneumovirus polymerase inhibition by non-nucleoside small-molecule antivirals.

Small-molecule antivirals can be used as chemical probes to stabilize transitory conformational stages of viral target proteins, facilitating structural analyses. Here, we evaluate allosteric pneumo- and paramyxovirus polymerase inhibitors that have the potential to serve as chemical probes and aid the structural characterization of short-lived intermediate conformations of the polymerase complex. Of multiple inhibitor classes evaluated, we discuss in-depth distinct scaffolds that were selected based on well-understood structure-activity relationships, insight into resistance profiles, biochemical characterization of the mechanism of action, and photoaffinity-based target mapping. Each class is thought to block structural rearrangements of polymerase domains albeit target sites and docking poses are distinct. This review highlights validated druggable targets in the paramyxo- and pneumovirus polymerase proteins and discusses discrete structural stages of the polymerase complexes required for bioactivity.

Glycan-shielded homodimer structure and dynamical features of the canine distemper virus hemagglutinin relevant for viral entry and efficient vaccination.

Canine distemper virus (CDV) belongs to morbillivirus, including measles virus (MeV) and rinderpest virus, which causes serious immunological and neurological disorders in carnivores, including dogs and rhesus monkeys, as recently reported, but their vaccines are highly effective. The attachment glycoprotein hemagglutinin (CDV-H) at the CDV surface utilizes signaling lymphocyte activation molecule (SLAM) and Nectin-4 (also called poliovirus-receptor-like-4; PVRL4) as entry receptors. Although fusion models have been proposed, the molecular mechanism of morbillivirus fusion entry is poorly understood. Here, we determined the crystal structure of the globular head domain of CDV-H vaccine strain at 3.2 Å resolution, revealing that CDV-H exhibits a highly tilted homodimeric form with a six-bladed ß-propeller fold. While the predicted Nectin-4-binding site is well conserved with that of MeV-H, that of SLAM is similar but partially different, which is expected to contribute to host specificity. Five N-linked sugars covered a broad area of the CDV-H surface to expose receptor-binding sites only, supporting the effective production of neutralizing antibodies. These features are common to MeV-H, although the glycosylation sites are completely different. Furthermore, real-time observation using high-speed atomic force microscopy revealed highly mobile features of the CDV-H dimeric head via the connector region. These results suggest that sugar-shielded tilted homodimeric structure and dynamic conformational changes are common characteristics of morbilliviruses and ensure effective fusion entry and vaccination.

Interplay between oncolytic measles virus, macrophages and cancer cells induces a proinflammatory tumor microenvironment.

Attenuated measles virus (MV) exerts its oncolytic activity in malignant pleural mesothelioma (MPM) cells that lack type-I interferon (IFN-I) production or responsiveness. However, other cells in the tumor microenvironment (TME), such as myeloid cells, possess functional antiviral pathways. In this study, we aimed to characterize the interplay between MV and the myeloid cells in human MPM. We cocultured MPM cell lines with monocytes or macrophages and infected them with MV. We analyzed the transcriptome of each cell type and studied their secretion and phenotypes by high-dimensional flow cytometry. We also measured transgene expression using an MV encoding GFP (MV-GFP). We show that MPM cells drive the differentiation of monocytes into M2-like macrophages. These macrophages inhibit GFP expression in tumor cells harboring a defect in IFN-I production and a functional signaling downstream of the IFN-I receptor, while having minimal effects on GFP expression in tumor cells with defect of responsiveness to IFN-I. Interestingly, inhibition of the IFN-I signaling by ruxolitinib restores GFP expression in tumor cells. Upon MV infection, cocultured macrophages express antiviral pro-inflammatory genes and induce the expression of IFN-stimulated genes in tumor cells. MV also increases the expression of HLA and costimulatory molecules on macrophages and their phagocytic activity. Finally, MV induces the secretion of inflammatory cytokines, especially IFN-I, and PD-L1 expression in tumor cells and macrophages. These results show that macrophages reduce viral proteins expression in some MPM cell lines through their IFN-I production and generate a pro-inflammatory interplay that may stimulate the patient's anti-tumor immune response.

Evaluation of the sensitivity of a measles diagnostic real-time RT-PCR assay incorporating recently observed priming mismatch variants, 2024.

We investigated a variant of measles virus that encodes three mismatches to the reverse priming site for a widely used diagnostic real-time RT-PCR assay; reduction of sensitivity was hypothesised. We examined performance of the assay in context of the variant using in silico data, synthetic RNA templates and clinical specimens. Sensitivity was reduced observed at low copy numbers for templates encoding the variant sequence. We designed and tested an alternate priming strategy, rescuing the sensitivity of the assay.

M-F noncoding region sequences of H1 genotype measles virus provide higher resolution for virus transmission tracing.

As countries and regions move toward measles elimination, extended sequence window including noncoding region located between the matrix and fusion protein genes (M - F NCR) was considered to be used in molecular surveillance. The molecular resolution of M - F NCR was evaluated with 192 genotype H1 strains circulating during 2011-2018 in China. Phylogenetic analyses of the N450 and M - F NCR targets indicated that both two targets could confirm epi-linked outbreak, while M - F NCR target could further improve resolution of the molecular characterization: (1) it could differentiate the strains with identical N450 circulated in one county within one month of disease onset; (2) different transmission chains could be distinguished for strains with identical N450; (3) better spatial-temporal consistency with topology could be provided among sporadic cases with inconsistent N450. Accordingly, M - F NCR could be used to complement the information from N450 to address the specific questions in tracking the virus transmission chains.

Negative-Strand RNA Virus-Vectored Vaccines.

Vectored RNA vaccines offer a variety of possibilities to engineer targeted vaccines. They are cost-effective and safe, but replication competent, activating the humoral as well as the cellular immune system.This chapter focuses on RNA vaccines derived from negative-strand RNA viruses from the order Mononegavirales with special attention to Newcastle disease virus-based vaccines and their generation. It shall provide an overview on the advantages and disadvantages of certain vector platforms as well as their scopes of application, including an additional section on experimental COVID-19 vaccines.

A Semiquantitative Protein-Fragment Complementation Assay to Study Protein-Protein Interactions of the Polymerase Complex in Cellula.

Protein-fragment complementation assays (PCAs) are powerful tools to investigate protein-protein interactions in a cellular context. These are especially useful to study unstable proteins and weak interactions that may not resist protein isolation or purification. The PCA based on the reconstitution of the Gaussia princeps luciferase (split-luc) is a sensitive approach allowing the mapping of protein-protein interactions and the semiquantitative measurement of binding affinity. Here, we describe the split-luc protocol we used to map the viral interactome of measles virus polymerase complex.

Optical Control of Mononegavirus Gene Expression and Replication.

Mononegaviruses are promising tools as oncolytic and transgene vectors for gene therapy and regenerative medicine. However, when mononegaviruses are used for therapeutic applications, the viral activity must be strictly controlled due to concerns about toxicity and severe side effects. With this technology, mononegavirus vectors can be grown where they are intended and can be easily removed when they are no longer needed. In particular, a photoswitch protein called Magnet (consisting of two magnet domains) is incorporated into the hinge region between the connector and methyltransferase domains of the mononegavirus polymerase protein (L protein) to disrupt the L protein functions. Blue light (470 ± 20 nm) irradiation causes the dimerization of the two magnet domains, and the L protein is restored to activity, allowing viral gene expression and virus replication. Since the magnet domains' dimerization is reversible, viral gene expression and replication cease when blue light irradiation is stopped.

Investigating Liquid-Liquid Phase Separation in Virus-Generated Inclusion Bodies Using Fluorescence Recovery After Photobleaching of Fluorescently Labeled Host Proteins.

Many negative-sense single-stranded RNA viruses within the order Mononegavirales harm humans. A common feature shared among cells infected by these viruses is the formation of subcellular membraneless structures called biomolecular condensates, also known as inclusion bodies (IBs), that form through a process called liquid-liquid phase separation (LLPS). Like many other membraneless organelles, viral IBs enrich a specific subset of viral and host proteins involved in the formation of viral particles. Elucidation of the properties and regulation of these IBs as they mature throughout the viral replication process are important for our understanding of viral replication, which may also lead to the development of alternative antiviral treatments. The protocol outlined in this chapter aims to characterize the intrinsic properties of LLPS within the measles virus (MeV, a member of Mononegavirales) IBs by using an imaging approach that fluorescently tags an IB-associated host protein. This method uses common laboratory techniques and is generalizable to any host factors as well as other viral systems.

Applying Reverse Genetics to Study Measles Virus Interactions with the Host.

The study of virus-host interactions is essential to achieve a comprehensive understanding of the viral replication process. The commonly used methods are yeast two-hybrid approach and transient expression of a single tagged viral protein in host cells followed by affinity purification of interacting cellular proteins and mass spectrometry analysis (AP-MS). However, by these approaches, virus-host protein-protein interactions are detected in the absence of a real infection, not always correctly compartmentalized, and for the yeast two-hybrid approach performed in a heterologous system. Thus, some of the detected protein-protein interactions may be artificial. Here we describe a new strategy based on recombinant viruses expressing tagged viral proteins to capture both direct and indirect protein partners during the infection (AP-MS in viral context). This way, virus-host protein-protein interacting co-complexes can be purified directly from infected cells for further characterization.

Dual RNA-seq Analysis of Patients' Cells and Viral Genome After Measles Infection.

During the infection of a host cell by an infectious agent, a series of gene expression changes occurs as a consequence of host-pathogen interactions. Unraveling this complex interplay is the key for understanding of microbial virulence and host response pathways, thus providing the basis for new molecular insights into the mechanisms of pathogenesis and the corresponding immune response. Dual RNA sequencing (dual RNA-seq) has been developed to simultaneously determine pathogen and host transcriptomes enabling both differential and coexpression analyses between the two partners as well as genome characterization in the case of RNA viruses. Here, we provide a detailed laboratory protocol and bioinformatics analysis guidelines for dual RNA-seq experiments focusing on - but not restricted to - measles virus (MeV) as a pathogen of interest. The application of dual RNA-seq technologies in MeV-infected patients can potentially provide valuable information on the structure of the viral RNA genome and on cellular innate immune responses and drive the discovery of new targets for antiviral therapy.

Measles Foci Reduction Neutralization Test (FRNT).

The plaque reduction neutralization test (PRNT) and the enzyme-linked immunosorbent assay (ELISA) are both widely used to assess immunity to infectious diseases such as measles, but they use two different measurement principles: ELISA measures the ability of antibodies to bind to virus components, while the PRNT detects the aptitude of antibodies to prevent the infection of a susceptible cell. As a result, detection of measles virus (MV) neutralizing antibodies is the gold standard for assessing immunity to measles. However, the assay is laborious and requires experience and excellent technical skills. In addition, the result is only available after several days. Therefore, the classical PRNT is not suitable for high-throughput testing. By using an immunocolorimetric assay (ICA) to detect MV-infected cells, the standard PRNT has been developed into a focus reduction neutralization test (FRNT). This assay is faster and has improved specificity. The FRNT described here is extremely useful when immunity to measles virus needs to be assessed in patients with a specific medical condition, such as immunocompromised individuals in whom presumed residual immunity needs to be assessed. The FRNT is not generally recommended for use with large numbers of specimens, such as in a seroprevalence study.

Early B cell transcriptomic markers of measles-specific humoral immunity following a 3rd dose of MMR vaccine.

B cell transcriptomic signatures hold promise for the early prediction of vaccine-induced humoral immunity and vaccine protective efficacy. We performed a longitudinal study in 232 healthy adult participants before/after a 3rd dose of MMR (MMR3) vaccine. We assessed baseline and early transcriptional patterns in purified B cells and their association with measles-specific humoral immunity after MMR vaccination using two analytical methods ("per gene" linear models and joint analysis). Our study identified distinct early transcriptional signatures/genes following MMR3 that were associated with measles-specific neutralizing antibody titer and/or binding antibody titer. The most significant genes included: the interleukin 20 receptor subunit beta/IL20RB gene (a subunit receptor for IL-24, a cytokine involved in the germinal center B cell maturation/response); the phorbol-12-myristate-13-acetate-induced protein 1/PMAIP1, the brain expressed X-linked 2/BEX2 gene and the B cell Fas apoptotic inhibitory molecule/FAIM, involved in the selection of high-affinity B cell clones and apoptosis/regulation of apoptosis; as well as IL16 (encoding the B lymphocyte-derived IL-16 ligand of CD4), involved in the crosstalk between B cells, dendritic cells and helper T cells. Significantly enriched pathways included B cell signaling, apoptosis/regulation of apoptosis, metabolic pathways, cell cycle-related pathways, and pathways associated with viral infections, among others. In conclusion, our study identified genes/pathways linked to antigen-induced B cell proliferation, differentiation, apoptosis, and clonal selection, that are associated with, and impact measles virus-specific humoral immunity after MMR vaccination.

Measles Virus-Based Vaccine Expressing Membrane-Anchored Spike of SARS-CoV-2 Inducing Efficacious Systemic and Mucosal Humoral Immunity in Hamsters.

As SARS-CoV-2 continues to evolve and COVID-19 cases rapidly increase among children and adults, there is an urgent need for a safe and effective vaccine that can elicit systemic and mucosal humoral immunity to limit the emergence of new variants. Using the Chinese Hu191 measles virus (MeV-hu191) vaccine strain as a backbone, we developed MeV chimeras stably expressing the prefusion forms of either membrane-anchored, full-length spike (rMeV-preFS), or its soluble secreted spike trimers with the help of the SP-D trimerization tag (rMeV-S+SPD) of SARS-CoV-2 Omicron BA.2. The two vaccine candidates were administrated in golden Syrian hamsters through the intranasal or subcutaneous routes to determine the optimal immunization route for challenge. The intranasal delivery of rMeV-S+SPD induced a more robust mucosal IgA antibody response than the subcutaneous route. The mucosal IgA antibody induced by rMeV-preFS through the intranasal routine was slightly higher than the subcutaneous route, but there was no significant difference. The rMeV-preFS vaccine stimulated higher mucosal IgA than the rMeV-S+SPD vaccine through intranasal or subcutaneous administration. In hamsters, intranasal administration of the rMeV-preFS vaccine elicited high levels of NAbs, protecting against the SARS-CoV-2 Omicron BA.2 variant challenge by reducing virus loads and diminishing pathological changes in vaccinated animals. Encouragingly, sera collected from the rMeV-preFS group consistently showed robust and significantly high neutralizing titers against the latest variant XBB.1.16. These data suggest that rMeV-preFS is a highly promising COVID-19 candidate vaccine that has great potential to be developed into bivalent vaccines (MeV/SARS-CoV-2).

Optical Coherence Tomography Angiographic Follow-Up in a Case of Subacute Sclerosing Panencephalitis and Unilateral Necrotising Retinitis.

We present a 20-year-old woman who was diagnosed with subacute sclerosing panencephalitis (SSPE) 20 months after presenting with unilateral retinitis. At presentation, the patient had two inferotemporal macular lesions in her left eye. Corresponding to these areas, optical coherence tomography (OCT) showed hyporeflective spaces with loss of nearly all of the retinal layers. OCT-angiography (OCTA) demonstrated some flow deficit areas with a reduction in the vessel density. Her serum measles antibody titre was high (IgG >5000.0 mIU/ml). Twenty months later the macular lesions had diminished in size, and there was some focal retinal thinning with interruption of the ellipsoid zone. OCTA showed that the flow deficit areas were diminished in size together with the relatively improved perfusion density. Neurological examination disclosed myoclonic jerks. Neuropsychological assessment demonstrated impaired executive function, attention, and narrowed lexical fluency. Measles IgG antibody was high in the cerebrospinal fluid (>230.0 U/ml). Brain magnetic resonance imaging demonstrated bilateral, non-specific, small foci of T2 hyperintensity in the frontoparietal subcortical white matter and centrum semiovale. The present case is the first where OCTA findings of SSPE-related retinal lesions have been described.

Rapid Detection of Measles Virus Using Reverse Transcriptase/Recombinase Polymerase Amplification Coupled with CRISPR/Cas12a and a Lateral Flow Detection: A Proof-of-Concept Study.

The measles virus is highly contagious, and efforts to simplify its diagnosis are essential. A reverse transcriptase/recombinase polymerase amplification assay coupled with CRISPR/Cas12a and an immunochromatographic lateral flow detection (RT-RPA-CRISPR-LFD) was developed for the simple visual detection of measles virus. The assay was performed in less than 1 h at an optimal temperature of 42 °C. The detection limit of the assay was 31 copies of an RNA standard in the reaction tube. The diagnostic performances were evaluated on a panel of 27 measles virus RT-PCR-positive samples alongside 29 measles virus negative saliva samples. The sensitivity and specificity were 96% (95% CI, 81-99%) and 100% (95% CI, 88-100%), respectively, corresponding to an accuracy of 98% (95% CI, 94-100%; p < 0.0001). This method will open new perspectives in the development of the point-of-care testing diagnosis of measles.