Pharmacological activation of TLR7 exerts inhibition on the replication of EV-D68 in respiratory cells.

The globally reemerging respiratory pathogen enterovirus D68 (EV-D68) is implicated in outbreaks of severe respiratory illness and associated with acute flaccid myelitis. However, there remains a lack of effective treatments for EV-D68 infection. In this work, we found that the host Toll-like receptor 7 (TLR7) proteins, which function as powerful innate immune sensors, were selectively elevated in expression in response to EV-D68 infection. Subsequently, we investigated the impact of Vesatolimod (GS-9620), a Toll-like receptor 7 agonist, on EV-D68 replication. Our findings revealed that EV-D68 infection resulted in increased mRNA levels of TLR7. Treatment with Vesatolimod significantly inhibited EV-D68 replication [half maximal effective concentration (EC50) = 0.1427 µM] without inducing significant cytotoxicity at virucidal concentrations. Although Vesatolimod exhibited limited impact on EV-D68 attachment, it suppressed RNA replication and viral protein synthesis after virus entry. Vesatolimod broadly inhibited the replication of circulating isolated strains of EV-D68. Furthermore, our findings demonstrated that treatment with Vesatolimod conferred resistance to both respiratory and neural cells against EV-D68 infection. Overall, these results present a promising strategy for drug development by pharmacologically activating TLR7 to initiate an antiviral state in EV-D68-infected cells selectively.IMPORTANCEConventional strategies for antiviral drug development primarily focus on directly targeting viral proteases or key components, as well as host proteins involved in viral replication. In this study, based on our intriguing discovery that enterovirus D68 (EV-D68) infection specifically upregulates the expression of immune sensor Toll-like receptor 7 (TLR7) protein, which is either absent or expressed at low levels in respiratory cells, we propose a potential antiviral approach utilizing TLR7 agonists to activate EV-D68-infected cells into an anti-viral defense state. Notably, our findings demonstrate that pharmacological activation of TLR7 effectively suppresses EV-D68 replication in respiratory tract cells through a TLR7/MyD88-dependent mechanism. This study not only presents a promising drug candidate and target against EV-D68 dissemination but also highlights the potential to exploit unique alterations in cellular innate immune responses induced by viral infections, selectively inducing a defensive state in infected cells while safeguarding uninfected normal cells from potential adverse effects associated with therapeutic interventions.

Clinical application of phage immunoprecipitation sequencing to diagnose enterovirus D68 as the underlying etiology in a case of Gullain-Barré syndrome.

Gullain-Barré syndrome (GBS) is an acute peripheral neuropathy often preceded by respiratory or gastrointestinal infections, though molecular testing of cerebrospinal fluid (CSF) is often inconclusive. In a recent case of severe pediatric GBS in British Columbia, Canada, we detected CSF antibodies against enterovirus D (EV-D) to link GBS with prior EV-D68 respiratory infection.

Epidemiological and clinical insights into the enterovirus D68 upsurge in Europe 2021/22 and the emergence of novel B3-derived lineages, ENPEN multicentre study.

Enterovirus D68 (EV-D68) infections are associated with severe respiratory disease and acute flaccid myelitis (AFM). The European Non-Polio Enterovirus Network (ENPEN) aimed to investigate the epidemiological and genetic characteristics of EV-D68 and its clinical impact during the fall-winter season of 2021/22. From 19 European countries, 58 institutes reported 10,481 (6.8%) EV-positive samples of which 1,004 (9.6%) were identified as EV-D68 (852 respiratory samples). Clinical data was reported for 969 cases. 78.9% of infections were reported in children (0-5 years); 37.9% of cases were hospitalised. Acute respiratory distress was commonly noted (93.1%) followed by fever (49.4%). Neurological problems were observed in 6.4% of cases with six reported with AFM. Phylodynamic/Nextstrain and phylogenetic analyses based on 694 sequences showed the emergence of two novel B3-derived lineages, with no regional clustering. In conclusion, we describe a large-scale EV-D68 European upsurge with severe clinical impact and the emergence of B3-derived lineages.

Multimodal Surveillance Model for Enterovirus D68 Respiratory Disease and Acute Flaccid Myelitis among Children in Colorado, USA, 2022.

Surveillance for emerging pathogens is critical for developing early warning systems to guide preparedness efforts for future outbreaks of associated disease. To better define the epidemiology and burden of associated respiratory disease and acute flaccid myelitis (AFM), as well as to provide actionable data for public health interventions, we developed a multimodal surveillance program in Colorado, USA, for enterovirus D68 (EV-D68). Timely local, state, and national public health outreach was possible because prospective syndromic surveillance for AFM and asthma-like respiratory illness, prospective clinical laboratory surveillance for EV-D68 among children hospitalized with respiratory illness, and retrospective wastewater surveillance led to early detection of the 2022 outbreak of EV-D68 among Colorado children. The lessons learned from developing the individual layers of this multimodal surveillance program and how they complemented and informed the other layers of surveillance for EV-D68 and AFM could be applied to other emerging pathogens and their associated diseases.

Real-Time Enterovirus D68 Outbreak Detection through Hospital Surveillance of Severe Acute Respiratory Infection, Senegal, 2023.

In December 2023, we observed through hospital-based surveillance a severe outbreak of enterovirus D68 infection in pediatric inpatients in Dakar, Senegal. Molecular characterization revealed that subclade B3, the dominant lineage in outbreaks worldwide, was responsible for the outbreak. Enhanced surveillance in inpatient settings, including among patients with neurologic illnesses, is needed.

Respiratory Viruses in Wastewater Compared with Clinical Samples, Leuven, Belgium.

In a 2-year study in Leuven, Belgium, we investigated the use of wastewater sampling to assess community spread of respiratory viruses. Comparison with the number of positive clinical samples demonstrated that wastewater data reflected circulation levels of typical seasonal respiratory viruses, such as influenza, respiratory syncytial virus, and enterovirus D68.

Identification of four neutralizing antigenic sites on the enterovirus D68 capsid.

IMPORTANCE: Enterovirus D68 (EV-D68) is an emerging respiratory pathogen associated with acute flaccid myelitis. Currently, no approved vaccines or antiviral drugs are available. Here, we report four functionally independent neutralizing antigenic sites (I to IV) by analyses of neutralizing monoclonal antibody (MAb)-resistant mutants. Site I is located in the VP1 BC loop near the fivefold axis. Site II resides in the VP2 EF loop, and site III is situated in VP1 C-terminus; both sites are located at the south rim of the canyon. Site IV is composed of residue in VP2 ßB strand and residues in the VP3 BC loop and resides around the threefold axis. The developed MAbs targeting the antigenic sites can inhibit viral binding to cells. These findings advance the understanding of the recognition of EV-D68 by neutralizing antibodies and viral evolution and immune escape and also have important implications for the development of novel EV-D68 vaccines.

Telaprevir Treatment Reduces Paralysis in a Mouse Model of Enterovirus D68 Acute Flaccid Myelitis.

In 2014, 2016, and 2018, the United States experienced unprecedented spikes in pediatric cases of acute flaccid myelitis (AFM), which is a poliomyelitis-like paralytic illness. Accumulating clinical, immunological, and epidemiological evidence has identified enterovirus D68 (EV-D68) as a major causative agent of these biennial AFM outbreaks. There are currently no available FDA-approved antivirals that are effective against EV-D68, and the treatment for EV-D68-associated AFM is primarily supportive. Telaprevir is an food and drug administration (FDA)-approved protease inhibitor that irreversibly binds the EV-D68 2A protease and inhibits EV-D68 replication in vitro. Here, we utilize a murine model of EV-D68 associated AFM to show that early telaprevir treatment improves paralysis outcomes in Swiss Webster (SW) mice. Telaprevir reduces both viral titer and apoptotic activity in both muscles and spinal cords at early disease time points, which results in improved AFM outcomes in infected mice. Following intramuscular inoculation in mice, EV-D68 infection results in a stereotypic pattern of weakness that is reflected by the loss of the innervating motor neuron population, in sequential order, of the ipsilateral (injected) hindlimb, the contralateral hindlimb, and then the forelimbs. Telaprevir treatment preserved motor neuron populations and reduced weakness in limbs beyond the injected hindlimb. The effects of telaprevir were not seen when the treatment was delayed, and toxicity limited doses beyond 35 mg/kg. These studies are a proof of principle, provide the first evidence of benefit of an FDA-approved antiviral drug with which to treat AFM, and emphasize both the need to develop better tolerated therapies that remain efficacious when administered after viral infections and the development of clinical symptoms. IMPORTANCE Recent outbreaks of EV-D68 in 2014, 2016, and 2018 have resulted in over 600 cases of a paralytic illness that is known as AFM. AFM is a predominantly pediatric disease with no FDA-approved treatment, and many patients show minimal recovery from limb weakness. Telaprevir is an FDA-approved antiviral that has been shown to inhibit EV-D68 in vitro. Here, we demonstrate that a telaprevir treatment that is given concurrently with an EV-D68 infection improves AFM outcomes in mice by reducing apoptosis and viral titers at early time points. Telaprevir also protected motor neurons and improved paralysis outcomes in limbs beyond the site of viral inoculation. This study improves understanding of EV-D68 pathogenesis in the mouse model of AFM. This study serves as a proof of principle for the first FDA-approved drug that has been shown to improve AFM outcomes and have in vivo efficacy against EV-D68 as well as underlines the importance of the continued development of EV-D68 antivirals.

Differential inhibition of intra- and inter-molecular protease cleavages by antiviral compounds.

IMPORTANCE: Most protease-targeted antiviral development evaluates the ability of small molecules to inhibit the cleavage of artificial substrates. However, before they can cleave any other substrates, viral proteases need to cleave themselves out of the viral polyprotein in which they have been translated. This can occur either intra- or inter-molecularly. Whether this process occurs intra- or inter-molecularly has implications for the potential for precursors to accumulate and for the effectiveness of antiviral drugs. We argue that evaluating candidate antivirals for their ability to block these cleavages is vital to drug development because the buildup of uncleaved precursors can be inhibitory to the virus and potentially suppress the selection of drug-resistant variants.

Duration of Enterovirus D68 RNA Shedding in the Upper Respiratory Tract and Transmission among Household Contacts, Colorado, USA.

Enterovirus D68 (EV-D68) causes cyclical outbreaks of respiratory disease and acute flaccid myelitis. EV-D68 is primarily transmitted through the respiratory route, but the duration of shedding in the respiratory tract is unknown. We prospectively enrolled 9 hospitalized children with EV-D68 respiratory infection and 16 household contacts to determine EV-D68 RNA shedding dynamics in the upper respiratory tract through serial midturbinate specimen collections and daily symptom diaries. Five (31.3%) household contacts, including 3 adults, were EV-D68-positive. The median duration of EV-D68 RNA shedding in the upper respiratory tract was 12 (range 7-15) days from symptom onset. The most common symptoms were nasal congestion (100%), cough (92.9%), difficulty breathing (78.6%), and wheezing (57.1%). The median illness duration was 20 (range 11-24) days. Understanding the duration of RNA shedding can inform the expected rate and timing of EV-D68 detection in associated acute flaccid myelitis cases and help guide public health measures.