Acute Flaccid Myelitis: Lessons From Polio

Epidemiology of Enterovirus Genotypes in Association with Human Diseases

Enteroviruses (EVs) are well-known causes of a wide range of infectious diseases in infants and young children, ranging from mild illnesses to severe conditions, depending on the virus genotypes and the host's immunity. Recent advances in molecular surveillance and genotyping tools have identified over 116 different human EV genotypes from various types of clinical samples. However, the current knowledge about most of these genotypes, except for those of well-known genotypes like EV-A71 and EV-D68, is still limited due to a lack of comprehensive EV surveillance systems. This limited information makes it difficult to understand the true burden of EV-related diseases globally. Furthermore, the specific EV genotype associated with diseases varies according to country, population group, and study period. The same genotype can exhibit different epidemiological features in different areas. By integrating the data from established EV surveillance systems in the USA, Europe, Japan, and China, in combination with other EV infection studies, we can elaborate a better understanding of the distribution of prevalent EV genotypes and the diseases associated with EV. This review analyzed the data from various EV surveillance databases and explored the EV seroprevalence and the association of specific EV genotypes with human diseases.

An unexpected, pH-sensitive step of the enterovirus D68 lifecycle

Enterovirus D68 (EV-D68) contributes significantly to pathogen-induced respiratory illnesses and severe neurological disorders like acute flaccid myelitis. We lack EV-D68 preventive measures, and knowledge of its molecular and cellular biology is incomplete. Multiple studies have highlighted the role of membrane compartments and autophagy during picornavirus multiplication. Galitska et al. found that EV-D68 also exploits cellular autophagic compartments and relies on autophagic machinery as pro-viral factors (G. Galitska, A. Jassey, M. A. Wagner, N. Pollack, et al., mBio e02141-23, 2023, https://doi.org/10.1128/mbio.02141-23). Surprisingly, failure of the autophagic compartment to acidify early during EV-D68 infection causes a delay in RNA synthesis that has not been reported for other enteroviruses. This delay appears to reflect the inability of viral proteins 2B and 3A to engage membranes stably, leading to their degradation in the cytoplasm. Observations like this underscore the importance of studying individual members of the virus genus. It will be interesting to understand how this phenomenon connects to EV-D68 pathogenesis, if at all.

The role of virome in the gastrointestinal tract and beyond

The human gut virome is comprised of diverse commensal and pathogenic viruses. The colonization by these viruses begins right after birth through vaginal delivery, then continues through breastfeeding, and broader environmental exposure. Their constant interaction with their bacterial hosts in the body shapes not only our microbiomes but us. In addition, these viruses interact with the immune cells, trigger a broad range of immune responses, and influence different metabolic pathways. Besides its key role in regulating the human gut homeostasis, the intestinal virome contributes to disease development in distant organs, both directly and indirectly. In this review, we will describe the changes in the gut virome through life, health, and disease, followed by discussing the interactions between the virome, the microbiome, and the human host as well as providing an overview of their contribution to gut disease and disease of distant organs.

Enterovirus Surveillance (EVSurv) in Germany

The major aim of the enterovirus surveillance (EVSurv) in Germany is to prove the absence of poliovirus circulation in the framework of the Global Polio Eradication Program (GPEI). Therefore, a free-of-charge enterovirus diagnostic is offered to all hospitals for patients with symptoms compatible with a polio infection. Within the quality proven laboratory network for enterovirus diagnostic (LaNED), stool and cerebrospinal fluid (CSF) samples from patients with suspected aseptic meningitis/encephalitis or acute flaccid paralysis (AFP) are screened for enterovirus (EV), typing is performed in all EV positive sample to exclude poliovirus infections. Since 2006, ≈200 hospitals from all 16 German federal states have participated annually. On average, 2500 samples (70% stool, 28% CSF) were tested every year. Overall, the majority of the patients studied are children <15 years. During the 15-year period, 53 different EV serotypes were detected. While EV-A71 was most frequently detected in infants, E30 dominated in older children and adults. Polioviruses were not detected. The German enterovirus surveillance allows monitoring of the circulation of clinically relevant serotypes resulting in continuous data about non-polio enterovirus epidemiology.

Enterovirus A71 causing meningoencephalitis and acute flaccid myelitis in a patient receiving rituximab

We present the case of a young woman being treated with rituximab for rheumatoid arthritis who developed a severe enteroviral meningoencephalitis and acute flaccid myelitis (AFM). Cerebrospinal fluid (CSF) and stool reverse transcription-polymerase chain reaction (RT-PCR) testing confirmed the diagnosis and additional sequencing studies performed at the CDC further characterized the enterovirus as enterovirus A71 (EV-A71). After treatment with intravenous immunoglobulin (IVIg) and fluoxetine (based on previous reports of possible efficacy) the patient experienced a remarkable improvement over time. This case highlights the importance of considering enteroviral infection in patients treated with rituximab, depicts a possible clinical course of enteroviral meningoencephalitis and AFM, and illustrates the importance of testing multiple sites for enterovirus infection (CSF, stool, nasopharyngeal swab, blood). Here we present the case with a brief review of the literature pertaining to EV-A71.

Enterovirus D68 Antivirals: Past, Present, and Future

Enterovirus D68 (EV-D68) is an RNA virus that causes respiratory illnesses mainly in children. In severe cases, it can lead to neurological complications such as acute flaccid myelitis (AFM). EV-D68 belongs to the enterovirus genera of the Picornaviridae family, which also includes many other significant human pathogens such as poliovirus, enterovirus A71, and rhinovirus. There are currently no vaccines or antivirals against EV-D68. In this review, we present the current understanding of the link between EV-D68 and AFM, the mechanism of viral replication, and recent progress in developing EV-D68 antivirals by targeting various viral proteins and host factors that are essential for viral replication. The future directions of EV-D68 antiviral drug discovery and the criteria for drugs to reach clinical trials are also discussed.

Molecular Pathogenicity of Enteroviruses Causing Neurological Disease

Enteroviruses are single-stranded positive-sense RNA viruses that primarily cause self-limiting gastrointestinal or respiratory illness. In some cases, these viruses can invade the central nervous system, causing life-threatening neurological diseases including encephalitis, meningitis and acute flaccid paralysis (AFP). As we near the global eradication of poliovirus, formerly the major cause of AFP, the number of AFP cases have not diminished implying a non-poliovirus etiology. As the number of enteroviruses linked with neurological disease is expanding, of which many had previously little clinical significance, these viruses are becoming increasingly important to public health. Our current understanding of these non-polio enteroviruses is limited, especially with regards to their neurovirulence. Elucidating the molecular pathogenesis of these viruses is paramount for the development of effective therapeutic strategies. This review summarizes the clinical diseases associated with neurotropic enteroviruses and discusses recent advances in the understanding of viral invasion of the central nervous system, cell tropism and molecular pathogenesis as it correlates with host responses.