National Surveillance for Acute Flaccid Myelitis - United States, 2018-2020

Acute Flaccid Myelitis With Human Rhinovirus A19 Detection: Case Report and Literature Review

Human rhinovirus (HRV) has been sporadically detected in patients with acute flaccid myelitis (AFM). We report a case of AFM in a 2-year-old boy with severe neurologic sequelae, whose nasopharyngeal and stool samples tested positive for HRV-A19. Clinical information related to AFM with HRV is limited. Further study of the association of AFM with HRV is warranted.

Pan-Enterovirus Characterization Reveals Cryptic Circulation of Clinically Relevant Subtypes in Arizona Wastewater

Background

Most seasonally circulating enteroviruses result in asymptomatic or mildly symptomatic infections. In rare cases, however, infection with some subtypes can result in paralysis or death. Of the 300 subtypes known, only poliovirus is reportable, limiting our understanding of the distribution of other enteroviruses that can cause clinical disease.

Objective

The overarching objectives of this study were to: 1) describe the distribution of enteroviruses in Arizona during the late summer and fall of 2022, the time of year when they are thought to be most abundant, and 2) demonstrate the utility of viral pan-assay approaches for semi-agnostic discovery that can be followed up by more targeted assays and phylogenomics.

Methods

This study utilizes pooled nasal samples collected from school-aged children and long-term care facility residents, and wastewater from multiple locations in Arizona during July-October of 2022. We used PCR to amplify and sequence a region common to all enteroviruses, followed by species-level bioinformatic characterization using the QIIME 2 platform. For Enterovirus-D68 (EV-D68), detection was carried out using RT-qPCR, followed by confirmation using near-complete whole EV-D68 genome sequencing using a newly designed tiled amplicon approach.

Results

In the late summer and early fall of 2022, multiple enterovirus species were identified in Arizona wastewater, with Coxsackievirus A6, EV-D68, and Coxsackievirus A19 composing 86% of the characterized reads sequenced. While EV-D68 was not identified in pooled human nasal samples, and the only reported acute flaccid myelitis case in Arizona did not test positive for the virus, an in-depth analysis of EV-D68 in wastewater revealed that the virus was circulating from August through mid-October. A phylogenetic analysis on this relatively limited dataset revealed just a few importations into the state, with a single clade indicating local circulation.

Significance

This study further supports the utility of wastewater-based epidemiology to identify potential public health threats. Our further investigations into EV-D68 shows how these data might help inform healthcare diagnoses for children presenting with concerning neurological symptoms.

Surveillance for Acute Flaccid Myelitis - United States, 2018-2022

Acute flaccid myelitis (AFM) is a serious neurologic condition primarily affecting children; AFM can cause acute respiratory failure and permanent paralysis. AFM is a rare but known complication of various viral infections, particularly those of enteroviruses (EVs). Increases in AFM cases during 2014, 2016, and 2018 were associated with EV-D68 infection. This report examines trends in confirmed AFM cases during 2018-2022 and patients' clinical and laboratory characteristics. The number of AFM cases was low during 2019-2022 (28-47 cases per year); the number of cases remained low in 2022 despite evidence of increased EV-D68 circulation in the United States. Compared with cases during the most recent peak year (2018), fewer cases during 2019-2021 had upper limb involvement, prodromal respiratory or febrile illness, or cerebrospinal fluid pleocytosis, and more were associated with lower limb involvement. It is unclear why EV-D68 circulation in 2022 was not associated with an increase in AFM cases or when the next increase in AFM cases will occur. Nonetheless, clinicians should continue to suspect AFM in any child with acute flaccid limb weakness, especially those with a recent respiratory or febrile illness.

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.

Acute flaccid myelitis in Switzerland - association with enterovirus D68

Poliomyelitis-like acute flaccid myelitis associated with enterovirus D68 (EV-D68) has emerged globally during the past decade. Here we describe the first documented case reported from Switzerland, and a second, suspected case occurring in temporal association. AFM occurs primarily in children, is usually heralded by a febrile, respiratory prodrome followed by acute-onset, usually asymmetrical, limb weakness with some predilection for the upper extremities, and respiratory muscle compromise in one third of reported cases. There is no specific therapy and the majority of cases result in permanent neurological sequelae. A comprehensive diagnostic workup and timely reporting to the health authorities are essential. Surveillance of respiratory and stool samples for EV-D68 and other neurotropic enteroviruses is in place in several European countries and warrants consideration in Switzerland. This could entail the extension of the poliomyelitis surveillance program of the Federal Office of Public Health by monitoring and enteroviral typing of respiratory samples from patients with acute flaccid paralysis.

Animal Models of Enterovirus D68 Infection and Disease

Human enterovirus D68 (EV-D68) is a globally reemerging respiratory pathogen that is associated with the development of acute flaccid myelitis (AFM) in children. Currently, there are no approved vaccines or treatments for EV-D68 infection, and there is a paucity of data related to the virus and host-specific factors that predict disease severity and progression to the neurologic syndrome. EV-D68 infection of various animal models has served as an important platform for characterization and comparison of disease pathogenesis between historic and contemporary isolates. Still, there are significant gaps in our knowledge of EV-D68 pathogenesis that constrain the development and evaluation of targeted vaccines and antiviral therapies. Continued refinement and characterization of animal models that faithfully reproduce key elements of EV-D68 infection and disease is essential for ensuring public health preparedness for future EV-D68 outbreaks.

Setting the Stage for the Next Great Vaccine Success Story

In this Commentary, the article by Rosenfeld et al. "Cross-Reactive Antibody Responses against Nonpoliovirus Enteroviruses" is put into context of the historic poliovirus epidemics and resultant vaccination success story as it compares to the current state of acute flaccid myelitis; the relationship to nonpoliovirus enteroviruses (EVs), in particular EV-D68 and EV-A71; and the potential for successful vaccination strategies. The discovery of cross-protective antibody neutralization among polio and nonpolio enteroviruses, specifically EV-D68, opens future questions about EV-D68 vaccination strategies, circulation patterns of nonpolio enteroviruses, and the interpretation of EV-D68 serostudies.

Enterovirus D68-Associated Acute Respiratory Illness ─ New Vaccine Surveillance Network, United States, July-November 2018-2020

Enterovirus D68 (EV-D68) is associated with a broad spectrum of illnesses, including mild to severe acute respiratory illness (ARI) and acute flaccid myelitis (AFM). Enteroviruses, including EV-D68, are typically detected in the United States during late summer through fall, with year-to-year fluctuations. Before 2014, EV-D68 was infrequently reported to CDC (1). However, numbers of EV-D68 detection have increased in recent years, with a biennial pattern observed during 2014-2018 in the United States, after the expansion of surveillance and wider availability of molecular testing. In 2014, a national outbreak of EV-D68 was detected (2). EV-D68 was also reported in 2016 via local (3) and passive national (4) surveillance. EV-D68 detections were limited in 2017, but substantial circulation was observed in 2018 (5). To assess recent levels of circulation, EV-D68 detections in respiratory specimens collected from patients aged <18 years* with ARI evaluated in emergency departments (EDs) or admitted to one of seven U.S. medical centers^† within the New Vaccine Surveillance Network (NVSN) were summarized. This report provides a provisional description of EV-D68 detections during July-November in 2018, 2019 and 2020, and describes the demographic and clinical characteristics of these patients. In 2018, a total of 382 EV-D68 detections in respiratory specimens obtained from patients aged <18 years with ARI were reported by NVSN; the number decreased to six detections in 2019 and 30 in 2020. Among patients aged <18 years with EV-D68 in 2020, 22 (73%) were non-Hispanic Black (Black) persons. EV-D68 detections in 2020 were lower than anticipated based on the biennial circulation pattern observed since 2014. The circulation of EV-D68 in 2020 might have been limited by widespread COVID-19 mitigation measures; how these changes in behavior might influence the timing and levels of circulation in future years is unknown. Ongoing monitoring of EV-D68 detections is warranted for preparedness for EV-D68-associated ARI and AFM.