Human Neonatal Fc Receptor Is the Cellular Uncoating Receptor for Enterovirus B.

Enterovirus B (EV-B), a major proportion of the genus Enterovirus in the family Picornaviridae, is the causative agent of severe human infectious diseases. Although cellular receptors for coxsackievirus B in EV-B have been identified, receptors mediating virus entry, especially the uncoating process of echovirus and other EV-B remain obscure. Here, we found that human neonatal Fc receptor (FcRn) is the uncoating receptor for major EV-B. FcRn binds to the virus particles in the "canyon" through its FCGRT subunit. By obtaining multiple cryo-electron microscopy structures at different stages of virus entry at atomic or near-atomic resolution, we deciphered the underlying mechanisms of enterovirus attachment and uncoating. These structures revealed that different from the attachment receptor CD55, binding of FcRn to the virions induces efficient release of "pocket factor" under acidic conditions and initiates the conformational changes in viral particle, providing a structural basis for understanding the mechanisms of enterovirus entry.

Diversity of enteroviruses in cerebrospinal fluid specimens collected from hospitalised patients in the private and public sector in South Africa.

Enteroviruses cause a wide range of neurological illnesses such as encephalitis, meningitis, and acute flaccid paralysis. Two types of enteroviruses, echovirus E4 and E9, have recently been detected in South Africa and are known to be associated with meningitis and encephalitis. The objective of this study was to characterize enterovirus strains detected in cerebrospinal fluid specimens of hospitalized patients in the private and public sector to identify genotypes associated with meningitis and encephalitis. From January 2019 to June 2021 enterovirus positive nucleic acid samples were obtained from a private (n = 116) and a public sector (n = 101) laboratory. These enteroviruses were typed using a nested set of primers targeting the VP1 region of the enterovirus genome, followed by Sanger sequencing and BLASTn analysis. Forty-two percent (91/217) of the strains could be genotyped. Enterovirus B species was the major species detected in 95% (86/91) of the specimens, followed by species C in 3% (3/91) and species A in 2% (2/91) of the specimens. Echovirus E4 and E9 were the two major types identified in this study and were detected in 70% (64/91) and in 10% (9/91) of specimens, respectively. Echovirus E11 has previously been identified in sewage samples from South Africa, but this study is the first to report Echovirus E11 in cerebrospinal fluid specimens from South African patients. The genotypes identified during this study are known to be associated with encephalitis and meningitis. The predominant detection of echovirus E4 followed by E9 corresponds with other studies conducted in South Africa.

Novel intertypic recombination of Echovirus 11 in the Enterovirus species B.

Enteroviruses (EVs), single-stranded, positive-sense RNA viruses, can be classified into four species (A-D), which have previously been linked to a diverse range of disease manifestations and infections affecting the central nervous system. In the Enterovirus species B (EV-B), Echovirus type 11 (E11) has been observed to occasionally circulate in Taiwan, which was responsible for an epidemic of enterovirus infections in 2018. Here, 48 clinical specimens isolated in 2003, 2004, 2009, and 2018 were collected for the high-throughput sequencing. Notably, we identified 2018 Taiwanese strains having potential recombinations in the 3D gene, as well as one 2003 strain having a double recombination with E6 and Coxsackievirus B5 in the P2 and P3 regions, respectively. Additionally, one amino acid signature mutated from the Histidine (H) in throat swab specimens to the Tyrosine (Y) in cerebral spinal fluid specimens was detected at position 1496 (or 57) of the genomic coordinate (or 3A gene) to further demonstrate intra-host evolution in different organs. In conclusion, this study identifies potential intertypic recombination events and an intra-host signature mutation in E11 strains, isolated during a 2018 neurological disease outbreak in Taiwan, contributing to our understanding of its evolution and pathogenesis.

Molecular characterization of emerging Echovirus 11 (E11) shed light on the recombinant origin of a variant associated with severe hepatitis in neonates.

Echovirus 11 (E11) has gained attention owing to its association with severe neonatal infections. Due to the limited data available, the World Health Organization (WHO) considers public health risk to the general population to be low. The present study investigated the genetic variation and molecular evolution of E11 genomes collected from May to December 2023. Whole genome sequencing (WGS) was performed for 16 E11 strains. Phylogenetic analysis on WG showed how all Italian strains belonged to genogroup D5, similarly to other E11 strains recently reported in France and Germany all together aggregated into separate clusters. A cluster-specific recombination pattern was also identified using phylogenetic analysis of different genome regions. Echovirus 6 was identified as the major recombinant virus in 3Cpro and 3Dpol regions. The molecular clock analysis revealed that the recombination event probably occurred in June 2018 (95% HPD interval: Jan 2016-Jan 2020). Shannon entropy analyses, within P1 region, showed how 11 amino acids exhibited relatively high entropy. Five of them were exposed on the canyon region which is responsible for receptor binding with the neonatal Fc receptor. The present study showed the recombinant origin of a new lineage of E11 associated with severe neonatal infections.

Inflammatory damage caused by Echovirus 30 in the suckling mouse brain and HMC3 cells.

Echovirus 30 (E30), a member of the species B Enterovirus family, is a primary pathogen responsible for aseptic meningitis and encephalitis. E30 is associated with severe nervous system diseases and is a primary cause of child illness, disability, and even mortality. However, the mechanisms underlying E30-induced brain injury remain poorly understood. In this study, we used a neonatal mouse model of E30 to investigate the possible mechanisms of brain injury. E30 infection triggered the activation of microglia in the mouse brain and efficiently replicated within HMC3 cells. Subsequent transcriptomic analysis revealed inflammatory activation of microglia in response to E30 infection. We also detected a significant upregulation of polo-like kinase 1 (PLK1) and found that its inhibition could limit E30 infection in a sucking mouse model. Collectively, E30 infection led to brain injury in a neonatal mouse model, which may be related to excessive inflammatory responses. Our findings highlight the intricate interplay between E30 infection and neurological damage, providing crucial insights that could guide the development of interventions and strategies to address the severe clinical manifestations associated with this pathogen.

Pathological Characteristics of Echovirus 30 Infection in a Mouse Model.

Echovirus 30 (E30), a member of species B enterovirus, is associated with outbreaks of aseptic meningitis and has become a global health emergency. However, the pathogenesis of E30 remains poorly understood due to the lack of appropriate animal models. In this study, we established a mouse infection model to explore the pathogenicity of E30. The 2-day-old IFNAR-/- mice infected with E30 strain WZ16 showed lethargy and paralysis, and some died. Obvious pathological changes were observed in the skeletal muscle, brain tissue, and other tissues, with the highest viral load in the skeletal muscles. Transcriptome analysis of brain and skeletal muscle tissues from infected mice showed that significant differentially expressed genes were enriched in complement response and neuropathy-related pathways. Using immunofluorescence assay, we found that the viral double-stranded RNA (dsRNA) was detected in the mouse brain region and could infect human glioma (U251) cells. These results indicated that E30 affects the nervous system, and they provide a theoretical basis for understanding its pathogenesis. IMPORTANCE Echovirus 30 (E30) infection causes a wide spectrum of diseases with mild symptoms, such as hand, foot, and mouth disease (HFMD), acute flaccid paralysis, and aseptic meningitis and other diseases, especially one of the most common pathogens causing aseptic meningitis outbreaks. We established a novel mouse model of E30 infection by inoculating neonatal mice with clinical isolates of E30 and observed the pathological changes induced by E30. Using the E30 infection model, we found complement responses and neuropathy-related genes in the mice tissues at the transcriptome level. Moreover, we found that the viral dsRNA localized in the mouse brain and could replicate in human glioma cell line U251 rather than in the neuroblastoma cell line, SK-N-SH.

An In Vivo Model of Echovirus-Induced Meningitis Defines the Differential Roles of Type I and Type III Interferon Signaling in Central Nervous System Infection.

Echoviruses are among the most common worldwide causes of aseptic meningitis, which can cause long-term sequelae and death, particularly in neonates. However, the mechanisms by which these viruses induce meningeal inflammation are poorly understood, owing at least in part to the lack of in vivo models that recapitulate this aspect of echovirus pathogenesis. Here, we developed an in vivo neonatal mouse model that recapitulates key aspects of echovirus-induced meningitis. We show that expression of the human homologue of the primary echovirus receptor, the neonatal Fc receptor (FcRn), is not sufficient for infection of the brains of neonatal mice. However, ablation of type I, but not III, interferon (IFN) signaling in mice expressing human FcRn permitted high levels of echovirus replication in the brain, with corresponding clinical symptoms, including delayed motor skills and hind-limb weakness. Using this model, we defined the immunological response of the brain to echovirus infection and identified key cytokines, such as granulocyte colony-stimulating factor (G-CSF) and interleukin 6 (IL-6), that were induced by this infection. Lastly, we showed that echoviruses specifically replicate in the leptomeninges, where they induce profound inflammation and cell death. Together, this work establishes an in vivo model of aseptic meningitis associated with echovirus infections that delineates the differential roles of type I and type III IFNs in echovirus-associated neuronal disease and defines the specificity of echoviral infections within the meninges. IMPORTANCE Echoviruses are among the most common worldwide causes of aseptic meningitis, which can cause long-term sequelae or even death. The mechanisms by which echoviruses infect the brain are poorly understood, largely owing to the lack of robust in vivo models that recapitulate this aspect of echovirus pathogenesis. Here, we establish a neonatal mouse model of echovirus-induced aseptic meningitis and show that expression of the human homologue of the FcRn, the primary receptor for echoviruses, and ablation of type I IFN signaling are required to recapitulate echovirus-induced meningitis and clinical disease. These findings provide key insights into the host factors that control echovirus-induced meningitis and a model that could be used to test anti-echovirus therapeutics.

Longitudinal antigenic and seroepidemiological analyses of parechovirus A1 in Yamagata, Japan.

To investigate the antigenic changes in parechovirus 1 (PeVA1), seroepidemiological analyses were performed against the Harris strain (Harris), isolated in 1956, and PeVA1/Yamagata.JPN/2021-4785, isolated in 2021, using immune sera and 207 and 237 human serum specimens collected in 2021 and 1976, respectively. Although rabbit immune sera showed the highest neutralization antibody (NT-Ab) titers against the immunized viruses at 1:12 800-1:102 400, they were cross-reactive at 1:400-1:800. All 62 Yamagata isolates obtained between 2001 and 2021 (Yamagata strains), belonging to phylogenetic lineage 1B, reacted more strongly (mostly 4-64 times) to antiserum against PeVA1/Yamagata.JPN/2021-4785 than to antiserum against Harris, belonging to phylogenetic lineage 1 A. Human serum specimens obtained in 2021 showed higher NT-Ab titers against PeVA1/Yamagata.JPN/2021-4785, whereas those obtained in 1976 had similar NT-Ab titers against both strains. These findings suggested that Yamagata strains and Harris were antigenically cross-reactive, although there were differences. There are still high NT-Abs titers present against Harris in 2021 in particular, indicating that PeVA1 has been in circulation with high immunity in the population. In conclusion, this study suggested that PeVA1 has been endemically perpetuated with only minor antigenic changes as well as with high immunity over several decades in the community.

Molecular characterization of a novel clade echovirus 3 isolated from patients with hand-foot-and-mouth disease in southwest China.

Echovirus 3 (E3) belongs to the species Enterovirus B. Currently, three nearly whole-genome sequences of E3 are available in GenBank in China. In this study, we determined the whole genomic sequences of six E3 strains isolated from the stools of patients with hand-foot-and-mouth disease in Southwest China in 2022. Their nucleotide and amino acid sequences shared 82.1%-86.4% and 96.6%-97.2% identity with the prototype Morrisey strain, respectively, and showed 87.1% and 97.2% mutual identity. The six E3 strains are not clustered with other Chinese strains and formed a novel subgenotype (C6) with the recent American and British strains. Recombination analyses revealed that intertype recombination had occurred in the 2 C and 3D regions of the six E3 strains with coxsackieviruses B5 and B4, respectively. This study augments the nearly whole-genome sequences of E3 in the GenBank database and extends the molecular characterization of this virus in China.

Complete genome analysis of echovirus 30 strains isolated from hand-foot-and-mouth disease in Yunnan province, China.

BACKGROUND: Echovirus 30 is prone to cause hand-foot-and-mouth disease in infants and children. However, molecular epidemiologic information on the spread of E30 in southwestern China remains limited. In this study, we determined and analyzed the whole genomic sequences of E30 strains isolated from the stools of patients with hand-foot-and-mouth disease in Yunnan Province, China, in 2019. METHODS: E30 isolates were obtained from fecal samples of HFMD patients. The whole genomes were sequenced by segmented PCR and analyzed for phylogeny, mutation and recombination. MEGA and DNAStar were used to align the present isolates with the reference strains. The VP1 sequence of the isolates were analyzed for selection pressure using datamonkey server. RESULTS: The complete genome sequences of four E30 were obtained from this virus isolation. Significant homologous recombination signals in the P2-3'UTR region were found in all four isolates with other serotypes. Phylogenetic analysis showed that the four E30 isolates belonged to lineage H. Comparison of the VP1 sequences of these four isolates with other E30 reference strains using three selection pressure analysis models FUBAR, FEL, and MEME, revealed a positive selection site at 133rd position. CONCLUSIONS: This study extends the whole genome sequence of E30 in GenBank, in which mutations and recombinations have driven the evolution of E30 and further improved and enriched the genetic characteristics of E30, providing fundamental data for the prevention and control of diseases caused by E30. Furthermore, we demonstrated the value of continuous and extensive surveillance of enterovirus serotypes other than the major HFMD-causing viruses.

An outbreak of nosocomial infection of neonatal aseptic meningitis caused by echovirus 18.

We describe an outbreak of echovirus 18 infection involving 10 patients in our neonatal intensive care unit (an attack rate of 33%). The mean age at the onset of illness was 26.8 days. Eighty percent were preterm infants. All were discharged home without sequelae. There were no differences in gestation age, birth weight, delivery mode, use of antibiotics, and parenteral nutrition between the enterovirus (EV) group and non-EV group, but the rate of breastfeeding was significantly higher in the EV group. Separation care and reinforcement of hand-washing seemed to be effective in preventing further spread of the virus. Visiting policy, hygiene practice, and handling of expressed breastmilk should be reinforced.

Fulminant echovirus 11 hepatitis in male non-identical twins in northern Italy, April 2023.

Echovirus 11 (E11) has recently been associated with a series of nine neonatal cases of severe hepatitis in France. Here, we present severe hepatitis caused by E11 in a pair of twins. In one of the neonates, the clinical picture evolved to fulminant hepatitis. The E11 genome showed 99% nucleotide identity with E11 strains reported in the cases in France. Rapid genome characterisation using next generation sequencing is essential to identify new and more pathogenetic variants.

Severe and fatal neonatal infections linked to a new variant of echovirus 11, France, July 2022 to April 2023.

We report nine severe neonatal infections caused by a new variant of echovirus 11. All were male, eight were twins. At illness onset, they were 3-5 days-old and had severe sepsis and liver failure. This new variant, detected in France since April 2022, is still circulating and has caused more fatal neonatal enterovirus infections in 2022 and 2023 (8/496; 1.6%, seven associated with echovirus 11) compared with 2016 to 2021 (7/1,774; 0.4%). National and international alerts are warranted.

Honeybee Iflaviruses Pack Specific tRNA Fragments from Host Cells in Their Virions.

The Picornavirales include viruses that infect vertebrates, insects, and plants. It was believed that they pack only their genomic mRNA in the particles; thus, we envisaged these viruses as excellent model systems for studies of mRNA modifications. We used LC-MS to analyze digested RNA isolated from particles of the sacbrood and deformed wing iflaviruses as well as of the echovirus 18 and rhinovirus 2 picornaviruses. Whereas in the picornavirus RNAs we detected only N6 -methyladenosine and 2'-O-methylated nucleosides, the iflavirus RNAs contained a wide range of methylated nucleosides, such as 1-methyladenosine (m1 A) and 5-methylcytidine (m5 C). Mapping of m1 A and m5 C through RNA sequencing of the SBV and DWV RNAs revealed the presence of tRNA molecules. Both modifications were detected only in tRNA. Further analysis revealed that tRNAs are present in form of 3' and 5' fragments and they are packed selectively. Moreover, these tRNAs are typically packed by other viruses.

Origin and evolution analysis and genetic characteristics of echovirus 9 in China.

BACKGROUND: Echovirus 9 (E9) is associated with a wide variety of diseases and medical conditions, and the clinical symptoms of sporadic cases caused by E9 often are severe. With a high global prevalence, E9 has caused multiple outbreaks worldwide. However, little is known about the genetic and geographic population dynamics of E9. METHOD: A total of 131 VP1 gene sequences, including15 generated in this study and 116 obtained from GenBank, were used to coestimate time-resolved phylogenies to infer viral evolution and transmission in worldwide. Overlapping fragments representing whole genomes were amplified by reverse transcription polymerase chain reaction (RT-PCR) using specific primers. Then, we reported the genetic characteristics of fifteen E9 strains in the Chinese Mainland. Similarity plots and bootscanning analysis were used to determine recombination patterns of E9. RESULTS: The estimated mean evolutionary rate of global E9 VP1 gene was 4.278 × 10-3 substitutions per site per year (95% confidence interval [CI], 3.822 × 10-3/site/year to 4.710 × 10-3/site/year), and the common ancestor of E9 likely emerged around 1868 (95% CI, 1840 to 1892). The full-length genomic sequences of the fifteen E9 strains showed 76.9-79.6% nucleotide identity and 95.3-95.9% amino acid identity with E9 Barty strain. 11 of 15 E9 whole genome sequence present four recombination patterns, and E9 recombinants have extensive genetic exchanges in the 2C and P3 regions with other Enterovirus B (EV-B) circulated in China. Four of six E9 strains were temperature sensitive, and two were temperature resistant, and a comparative genomics analysis suggested that 411, 865 and 867 amino acid substitution in the P1 region was related to temperature sensitivity. CONCLUSION: This study highlights a persistent transmission network of E9 in worldwide, provides valuable information regarding the molecular epidemiology of E9.

The neonatal Fc receptor is a pan-echovirus receptor.

Echoviruses are amongst the most common causative agents of aseptic meningitis worldwide and are particularly devastating in the neonatal population, where they are associated with severe hepatitis, neurological disease, including meningitis and encephalitis, and even death. Here, we identify the neonatal Fc receptor (FcRn) as a pan-echovirus receptor. We show that loss of expression of FcRn or its binding partner beta 2 microglobulin (ß2M) renders cells resistant to infection by a panel of echoviruses at the stage of virus attachment, and that a blocking antibody to ß2M inhibits echovirus infection in cell lines and in primary human intestinal epithelial cells. We also show that expression of human, but not mouse, FcRn renders nonpermissive human and mouse cells sensitive to echovirus infection and that the extracellular domain of human FcRn directly binds echovirus particles and neutralizes infection. Lastly, we show that neonatal mice expressing human FcRn are more susceptible to echovirus infection by the enteral route. Our findings thus identify FcRn as a pan-echovirus receptor, which may explain the enhanced susceptibility of neonates to echovirus infections.

Echovirus 9 genetic diversity detected in whole-capsid genome sequences obtained directly from clinical specimens using next generation sequencing.

Echovirus 9 (E9) has been detected in an increased number of symptomatic patient samples received by the National Enterovirus Reference Laboratory in Hungary during 2018 compared to previously reported years.Formerly identified E9 viruses from different specimen types detected from patients of various ages and showing differing clinical signs were chosen for the detailed analysis of genetic relationships and potential variations within the viral populations. We used next generation sequencing (NGS) analysis of 3,900 nucleotide long amplicons covering the entire capsid coding region of the viral genome without isolation, directly from clinical samples.Compared to the E9 reference strain, the viruses showed about 79% nucleotide and around 93% amino acid sequence similarity. The four new viral genome sequences had 1-20 nucleotide differences between them also resulting in 6 amino acid variances in the coding region, including 3 in the structural VP1 capsid protein. One virus from a patient with hand, foot, and mouth disease had two amino acid changes in the VP1 capsid protein. An amino acid difference was also detected in the non-structural 2C gene of one virus sequenced from a throat swab sample from a patient with meningitis, compared to the faecal specimen taken two days later. Two amino acid changes, one in the capsid protein, were found between faecal samples of meningitis patients of different ages.Sequencing the whole capsid genome revealed several nucleotide and amino acid differences between E9 virus strains detected in Hungary in 2018.

Molecular Epidemiology and Evolutionary Trajectory of Emerging Echovirus 30, Europe.

In 2018, an upsurge in echovirus 30 (E30) infections was reported in Europe. We conducted a large-scale epidemiologic and evolutionary study of 1,329 E30 strains collected in 22 countries in Europe during 2016-2018. Most E30 cases affected persons 0-4 years of age (29%) and 25-34 years of age (27%). Sequences were divided into 6 genetic clades (G1-G6). Most (53%) sequences belonged to G1, followed by G6 (23%), G2 (17%), G4 (4%), G3 (0.3%), and G5 (0.2%). Each clade encompassed unique individual recombinant forms; G1 and G4 displayed >2 unique recombinant forms. Rapid turnover of new clades and recombinant forms occurred over time. Clades G1 and G6 dominated in 2018, suggesting the E30 upsurge was caused by emergence of 2 distinct clades circulating in Europe. Investigation into the mechanisms behind the rapid turnover of E30 is crucial for clarifying the epidemiology and evolution of these enterovirus infections.

Early Entry Events in Echovirus 30 Infection.

Echovirus 30 (E30), a member of the enterovirus B species, is a major cause of viral meningitis, targeting children and adults alike. While it is a frequently isolated enterovirus and the cause of several outbreaks all over the world, surprisingly little is known regarding its entry and replication strategy within cells. In this study, we used E30 strain Bastianni (E30B) generated from an infectious cDNA clone in order to study early entry events during infection in human RD cells. E30B required the newly discovered Fc echovirus receptor (FcRn) for successful infection, but not the coxsackievirus and adenovirus receptor (CAR) or decay-accelerating factor (DAF), although an interaction with DAF was observed. Double-stranded RNA replication intermediate was generated between 2 and 3 h postinfection (p.i.), and viral capsid production was initiated between 4 and 5 h p.i. The drugs affecting Rac1 (NSC 23766) and cholesterol (filipin III) compromised infection, whereas bafilomycin A1, dyngo, U-73122, wortmannin, and nocodazole did not, suggesting the virus follows an enterovirus-triggered macropinocytic pathway rather than the clathrin pathway. Colocalization with early endosomes and increased infection due to constitutively active Rab5 expression suggests some overlap and entry to classical early endosomes. Taken together, these results suggest that E30B induces an enterovirus entry pathway, leading to uncoating in early endosomes.IMPORTANCE Echovirus 30 (E30) is a prevalent enterovirus causing regular outbreaks in both children and adults in different parts of the world. It is therefore surprising that relatively little is known of its infectious entry pathway. We set out to generate a cDNA clone and gradient purified the virus in order to study the early entry events in human cells. We have recently studied other enterovirus B group viruses, like echovirus 1 (EV1) and coxsackievirus A9 (CVA9), and found many similarities between those viruses, allowing us to define a so-called "enterovirus entry pathway." Here, E30 is reminiscent of these viruses, for example, by not relying on acidification for infectious entry. However, despite not using the clathrin entry pathway, E30 accumulates in classical early endosomes.

Salt Enhances the Thermostability of Enteroviruses by Stabilizing Capsid Protein Interfaces.

Enteroviruses are common agents of infectious disease that are spread by the fecal-oral route. They are readily inactivated by mild heat, which causes the viral capsid to disintegrate or undergo conformational change. While beneficial for the thermal treatment of food or water, this heat sensitivity poses challenges for the stability of enterovirus vaccines. The thermostability of an enterovirus can be modulated by the composition of the suspending matrix, though the effects of the matrix on virus stability are not understood. Here, we determined the thermostability of four enterovirus strains in solutions with various concentrations of NaCl and different pH values. The experimental findings were combined with molecular modeling of the protein interaction forces at the pentamer and the protomer interfaces of the viral capsids. While pH only had a modest effect on thermostability, increasing NaCl concentrations raised the breakpoint temperatures of all viruses tested by up to 20°C. This breakpoint shift could be explained by an enhancement of the van der Waals attraction forces at the two protein interfaces. In comparison, the (net repulsive) electrostatic interactions were less affected by NaCl. Depending on the interface considered, the breakpoint temperature shifted by 7.5 or 5.6°C per 100-kcal/(mol·Å) increase in protein interaction force.IMPORTANCE The genus Enterovirus encompasses important contaminants of water and food (e.g., coxsackieviruses), as well as viruses of acute public health concern (e.g., poliovirus). Depending on the properties of the surrounding matrix, enteroviruses exhibit different sensitivities to heat, which in turn influences their persistence in the environment, during food treatment, and during vaccine storage. Here, we determined the effect of NaCl and pH on the heat stability of different enteroviruses and related the observed effects to changes in protein interaction forces in the viral capsid. We demonstrate that NaCl renders enteroviruses thermotolerant and that this effect stems from an increase in van der Waals forces at different protein subunits in the viral capsid. This work sheds light on the mechanism by which salt enhances virus stability.