Emergence of enterovirus 71 "double-recombinant" strains belonging to a novel genotype D originating from southern China: first evidence for combination of intratypic and intertypic recombination events in EV71

Reflecting on the 1998 enterovirus outbreak: A 25-year retrospective and learned lessons

Enterovirus A71 (EV-A71) infections pose a significant public health concern in the Asia-Pacific region. EV-A71 is primarily responsible for causing hand, foot, and mouth disease (HFMD) in children. However, this virus can also lead to severe and potentially fatal neurological consequences in affected individuals. This review aims to provide a comprehensive understanding of the molecular virology, epidemiology, and recombination events associated with EV-A71. The literature extensively covers the clinical manifestations and neurological symptoms that accompany EV-A71 infections. One of the complications explored in this review is brainstem encephalitis, which can arise as a result of EV-A71 infections. Brainstem encephalitis refers to inflammation of the brainstem, a critical region responsible for various bodily functions. The review examines the underlying mechanisms, diagnostic criteria, treatment options, and prognosis for central nervous system infections involving EV-A71. Neurological complications associated with EV-A71 infections are diverse and can have severe consequences. These complications may include aseptic meningitis, acute flaccid paralysis, and acute transverse myelitis. The review delves into the pathophysiology of these complications, shedding light on the molecular mechanisms through which EV-A71 affects the central nervous system. Accurate diagnosis of EV-A71 infections is crucial for appropriate management and treatment. Treatment options for EV-A71 infections primarily focus on supportive care, as there are currently no specific antiviral drugs available for this virus. The review highlights the importance of managing symptoms, such as fever, dehydration, and pain relief, to alleviate the burden on affected individuals. Prognosis for individuals with central nervous system (CNS) infections involving EV-A71 can vary depending on the severity of the complications. The review provides insights into the long-term outcomes and potential neurological sequelae associated with EV-A71 infections. In conclusion, EV-A71 infections have emerged as a major public health concern in the Asia-Pacific region. This review aims to enhance our understanding of the molecular virology, epidemiology, and neurological complications associated with EV-A71. By examining the underlying mechanisms, diagnostic criteria, treatment options, and prognosis, this review contributes to the development of effective strategies for the prevention, diagnosis, and management of EV-A71 infections. The paper presents a comprehensive analysis of worldwide data pertaining to outbreaks of EV-A71 and HFMD. The subsequent discourse delves into the advancement and strategic formulation pertaining to the creation of vaccines targeting EV-A71. In summary, this study provides a comprehensive examination of the potential obstacles and considerations involved in the management and treatment of EV-A71 infections. Additionally, it proposes suggestions for future research and development endeavors with the objective of formulating efficacious treatment approaches for this viral infection.

Genetic diversity and recombination of bovine enterovirus strains in China

Bovine enterovirus (BEV) consisting of enterovirus species E (EV-E) and F (EV-F) is the causative agent associated with respiratory and gastrointestinal diseases in cattle. Here, we reported the characterization, genetic diversity, and recombination of novel BEV strains isolated from the major cattle-raising regions in China during 2012-2018. Twenty-seven BEV strains were successfully isolated and characterized. Molecular characterization demonstrated that the majority of these novel BEV strains (24/27) were EV-E, while only few strains (3/27) were EV-F. Sequence analysis revealed the diversity of the circulating BEV strains such as species and subtypes where different species or subtype coinfections were detected in the same regions and even in the same cattle herds. For the EV-E, two novel subtypes, designated as EV-E6 and EV-E7, were revealed in addition to the currently reported EV-E1-EV-E5. Comparative genomic analysis revealed the intraspecies and interspecies genetic exchanges among BEV isolates. The representative strain HeN-B62 was probably from AN12 (EV-F7) and PS-87-Belfast (EV-F3) strains. The interspecies recombination between EV-E and EV-F was also discovered, where the EV-F7-AN12 might be from EV-E5 and EV-F1, and EV-E5-MexKSU/5 may be recombined from EV-F7 and EV-E1. The aforementioned results revealed the genetic diversity and recombination of novel BEV strains and unveiled the different BEV species or subtype infections in the same cattle herd, which will broaden the understanding of enterovirus genetic diversity, recombination, pathogenesis, and prevention of disease outbreaks.

IMPORTANCE

Bovine enterovirus (BEV) infection is an emerging disease in China that is characterized by digestive, respiratory, and reproductive disorders. In this study, we first reported two novel EV-E subtypes detected in cattle herds in China, unveiled the coinfection of two enterovirus species (EV-E/EV-F) and different subtypes (EV-E2/EV-E7, EV-E1/EV-E7, and EV-E3/EV-E6) in the same cattle herds, and revealed the enterovirus genetic exchange in intraspecies and interspecies recombination. These results provide an important update of enterovirus prevalence and epidemiological aspects and contribute to a better understanding of enterovirus genetic diversity, evolution, and pathogenesis.

Effect of difference between EV-A71 virus epidemic strain and "vaccine strain" on neutralizing antibody titer

Hand, foot and mouth disease was mainly caused by EV-A71 virus. The main antigen structure of VP1 region of EV-A71 was easily varied. Here, we investigated the seroprevalence of EV-A71 based on a large group of healthy individuals in Beijing, China, in order to study the effectiveness of EV-A71 vaccine in a real-world setting. BrCr and the clinical strain isolated from the Chinese mainland in 2008 ("vaccine strain:"CMU4232/BJ/CHN/2008), EV-A71 C4 epidemic strains isolated in 2010, 2013, and 2016, were tested for neutralizing antibodies (NtAb) in every year. Phylogenetic tree analysis of the EV-A71 strains above, as well as amino acid composition homologous sequence analysis were applied. The "vaccine strain" has 83.0% homology with FY23, H07 and FY7VP5. It belongs to the same branch of C4a as 10 C4, 13 C4 and 16 C4, and differs from the amino acid sites 283 and 293 of 16 C4. Compared with "vaccine strains," there was a significant difference between the 50-59 years old age group when the NtAb titer of 16 C4 strain was 1:512-1:1024. Our results suggest that changes in the functional epitopes of NtAb caused by amino acid 283 and 293 loci in EV-A71 strains may affect the production of neutralizing antibodies.

Genetic and Cross Neutralization Analyses of Coxsackievirus A16 Circulating in Taiwan from 1998 to 2021 Suggest Dominant Genotype B1 can Serve as Vaccine Candidate

Coxsackievirus A16 (CVA16) is well known for causing hand-foot-and-mouth disease (HFMD) and outbreaks were frequently reported in Taiwan in the past twenty years. The epidemiology and genetic variations of CVA16 in Taiwan from 1998 to 2021 were analyzed in this study. CVA16 infections usually occurred in early summer and early winter, and showed increased incidence in 1998, 2000-2003, 2005, 2007-2008, and 2010 in Taiwan. Little or no CVA16 was detected from 2017 to 2021. CVA16 infection was prevalent in patients between 1 to 3 years old. A total of 69 isolates were sequenced. Phylogenetic analysis based on the VP1 region showed that CVA16 subgenotype B1 was dominantly isolated in Taiwan from 1998 to 2019, and B2 was identified only from isolates collected in 1999 and 2000. There was a high frequency of synonymous mutations in the amino acid sequences of the VP1 region among CVA16 isolates, with the exception of position 145 which showed positive selection. The recombination analysis of the whole genome of CVA16 isolates indicated that the 5'-untranslated region and the non-structural protein region of CVA16 subgenotype B1 were recombined with Coxsackievirus A4 (CVA4) and enterovirus A71 (EVA71) genotype A, respectively. The recombination pattern of subgenotype B2 was similar to B1, however, the 3D region was similar to EVA71 genotype B. Cross-neutralization among CVA16 showed that mouse antisera from various subgenotypes viruses can cross-neutralize different genotype with high neutralizing antibody titers. These results suggest that the dominant CVA16 genotype B1 can serve as a vaccine candidate for CVA16.

Viral determinants that drive Enterovirus-A71 fitness and virulence

Hand, Foot and Mouth Disease (HFMD) is usually a self-limiting, mild childhood disease that is caused mainly by Coxsackie virus A16 (CVA16) and Enterovirus A71 (EV-A71), both members of the Picornaviridae family. However, recurring HFMD outbreaks and epidemics due to EV-A71 infection in the Western Pacific region, and the propensity of EV-A71 strains to cause severe neurological complications have made this neurotropic virus a serious public health concern in afflicted countries. High mutation rate leading to viral quasispecies combined with frequent intra- and inter-typic recombination events amongst co-circulating EV-A71 strains have contributed to the great diversity and fast evolution of EV-A71 genomes, making impossible any accurate prediction of the next epidemic strain. Comparative genome sequence analyses and mutagenesis approaches have led to the identification of a number of viral determinants involved in EV-A71 fitness and virulence. These viral determinants include amino acid residues located in the structural proteins of the virus, affecting attachment to the host cell surface, receptor binding, and uncoating events. Critical residues in non-structural proteins have also been identified, including 2C, 3A, 3C proteases and the RNA-dependent RNA polymerase. Finally, mutations altering key secondary structures in the 5’ untranslated region were also found to influence EV-A71 fitness and virulence. While our current understanding of EV-A71 pathogenesis remains fragmented, these studies may help in the rational design of effective treatments and broadly protective vaccine candidates.

Cross-Antigenicity between EV71 Sub-Genotypes: Implications for Vaccine Efficacy

Enterovirus A-71 (EV71) is a global, highly contagkkious pathogen responsible for severe cases of hand-food-mouth-disease (HFMD). The use of vaccines eliciting cross neutralizing antibodies (NTAbs) against the different circulating EV71 sub-genotypes is important for preventing HFMD outbreaks. Here, we tested the cross-neutralizing activities induced by EV71 genotype/sub-genotype A, B0-B4, C1, C2, C4, and C5 viruses using rats. Differences were noted in the cross-neutralization of the 10 sub-genotypes tested but there were generally good levels of cross-neutralization except against genotype A virus, against which neutralization antibody titres (NTAb) where the lowest with NTAbs being the highest against sub-genotype B4. Moreover, NTAb responses induced by C4, B4, C1, and C2 viruses were homogenous, with values of maximum/minimum NTAb ratios (MAX/MIN) against all B and C viruses ranging between 4.0 and 6.0, whereas MAX/MIN values against B3 and A viruses were highly variable, 48.0 and 256.0, respectively. We then dissected the cross-neutralizing ability of sera from infants and children and rats immunized with C4 EV71 vaccines. Cross-neutralizing titers against the 10 sub-genotypes were good in both vaccinated infants and children and rats with the MAX/MIN ranging from 1.8–3.4 and 5.1–7.1, respectively, which were similar to those found in naturally infected patients (2.8). Therefore, we conclude that C4 EV71 vaccines can provide global protection to infants and children against HFMD caused by different sub-genotypes.

Molecular epidemiology and recombination of Enterovirus A71 in mainland China from 1987 to 2017

Enterovirus A71 (EV-A71) is an important pathogen of severe hand, foot, and mouth disease (HFMD) in young children. This study aimed to retrospectively analyze the molecular epidemiology and recombination of EV-A71 in mainland China during 1987–2017. Phylogenetic tree showed that besides the previously reported subgenotypes A, B5, C0, C2, C3, and C4, a new subgenotype C6 emerged in mainland China. Recombination analysis indicated that C4 EV-A71 was derived from a common ancestor as a “double-recombinant” virus by intertypic recombination between C EV-A71 and CVA4, CVA5, CVA14, and CVA16 strains in P3 region and intratypic recombination between C and B EV-A71 strains in P2 region. The B5 EV-A71 shared high similarity with C EV-A71 in P1 region while it contained an unidentified sequence in P2 and P3 regions with two possible recombination patterns: one occurred between C4 EV-A71 and CVA3, CVA5, CVA6, CVA10, and CVA12 stains with one breakpoint in 3C, and the other occurred between C1, C2, C3, and C5 EV-A71 and CVA4, CVA5, CVA14, and CVA16 strains with two breakpoints in the 2A/2B junction and 3C. The C2 EV-A71 was probably a recombinant virus between C4 EV-A71 and CVA8 strains with two breakpoints located in the 5′UTR and 2A/2B junction. Moreover, an incredible recombination of C6 EV-A71 occurred between C4 and C2 EV-A71 with multiple breakpoints. Thus, continuous studies on EV-A71 genome characteristics are still useful and essential for monitoring emergence of new viruses and preventing HFMD outbreaks.

A uniform quantitative enzyme-linked immunosorbent assay for Coxsackievirus A16 antigen in vaccine

Coxsackievirus A16 (CV-A16), one of major etiological agents of hand, foot and mouth disease (HFMD), causes outbreaks of the disease in young children all over the world. In order to promote the prevention and control of HFMD, the research and development of CV-A16 vaccine have been carried out in China. However, due to lacking of a recognized CV-A16 antigen detection method, the evaluation and quality control (QC) of vaccine effectiveness are greatly limited. In this study, we established a quantitative enzyme-linked immunosorbent assay (Q-ELISA) to determine the antigen concentration in CV-A16 vaccines that can be applied in manufacturing in China. A neutralizing antibody 16E1 was used as a capture antibody that can bind to various CV-A16 antigens of different subgenotypes, and an antiserum from CV-A16-immunized rabbit conjugated by HRP was suitable for detecting and quantifying CV-A16 antigens. The Q-ELISA was validated for specificity, linearity, accuracy, precision and robustness by using the CV-A16 antigen national standard (NS). Furthermore, we utilized the Q-ELISA to quantify antigen contents of vaccine bulks from six manufacturers and other intermediate products from one manufacturer. The results indicated that the Q-ELISA can satisfy the requirements of QC for all manufacturers involved.

Enterovirus A71: virulence, antigenicity, and genetic evolution over the years

As a neurotropic virus, enterovirus A71 (EV-A71) emerge and remerge in the Asia-Pacific region since the 1990s, and has continuously been a threat to global public health, especially in children. Annually, EV-A71 results in hand-foot-and-mouth disease (HFMD) and occasionally causes severe neurological disease. Here we reviewed the global epidemiology and genotypic evolution of EV-A71 since 1997. The natural selection, mutation and recombination events observed in the genetic evolution were described. In addition, we have updated the antigenicity and virulence determinants that are known to date. Understanding EV-A71 epidemiology, genetic evolution, antigenicity, and virulence determinants can expand our insights of EV-A71 pathogenesis, which may benefit us in the future.

Molecular characterization of enterovirus-A71 in children with acute flaccid paralysis in the Philippines

Background

Several inactivated enterovirus-A71 (EV-A71) vaccines are currently licensed in China; however, the development of additional EV-A71 vaccines is ongoing, necessitating extensive analysis of the molecular epidemiology of the virus worldwide. Until 2012, laboratory confirmation of EV-A71 for hand, foot, and mouth disease (HFMD) and other associated diseases had not occurred in the Philippines. Because EV-A71 has been linked with cases of acute flaccid paralysis (AFP), AFP surveillance is one strategy for documenting its possible circulation in the country. To expand current knowledge on EV-A71, molecular epidemiologic analysis and genetic characterization of EV-A71 isolates were performed in this study.

Methods

A retrospective study was performed to identify and characterize nonpolio enteroviruses (NPEVs) associated with AFP in the Philippines, and nine samples were found to be EV-A71–positive. Following characterization of these EV-A71 isolates, the complete viral protein 1 (VP1) gene was targeted for phylogenetic analysis.

Results

Nine EV-A71 isolates detected in 2000 (n = 2), 2002 (n = 4), 2005 (n = 2), and 2010 (n = 1) were characterized using molecular methods. Genomic regions spanning the complete VP1 region were amplified and sequenced using specific primers. Phylogenetic analysis of the full-length VP1 region identified all nine EV-A71 Philippine isolates as belonging to the genogroup C lineage, specifically the C2 cluster. The result indicated a genetic linkage with several strains isolated in Japan and Taiwan, suggesting that strains in the C2 cluster identified in the Asia-Pacific region were circulating in the Philippines.

Conclusion

The study presents the genetic analysis of EV-A71 in the Philippines. Despite some limitations, the study provides additional genetic data on the circulating EV-A71 strains in the Asia-Pacific region, in which information on EV-A71 molecular epidemiology is incomplete. Considering that EV-A71 has a significant public health impact in the region, knowledge of its circulation in each country is important, especially for formulating vaccines covering a wide variety of strains.

Complete genome analysis demonstrates multiple introductions of enterovirus 71 and coxsackievirus A16 recombinant strains into Thailand during the past decade

Hand, foot, and mouth disease (HFMD) caused by enteroviruses remains a public health threat, particularly in the Asia-Pacific region during the past two decades. Moreover, the introduction of multiple subgenotypes and the emergence of recombinant viruses is of epidemiological importance. Based on either the full genome or VP1 sequences, 32 enteroviruses (30 from HFMD patients, 1 from an encephalitic patient, and 1 from an asymptomatic contact case) isolated in Thailand between 2006 and 2014 were identified as 25 enterovirus 71 (EV71) isolates (comprising 20 B5, 1 C2, 2 C4a, and 2 C4b subgenotypes) and 7 coxsackievirus A16 (CA16) isolates (comprising 6 B1a and 1 B1b subgenotypes). The EV71 subgenotype C4b was introduced into Thailand for the first time in 2006 and was replaced by subgenotype C4a strains in 2009. Phylogenetic, similarity plot and bootscan analyses of the complete viral genomes identified 12 recombinant viruses among the 32 viral isolates. Only one EV71-B5 isolate out of 20 was a recombinant virus with one region of intratypic or intertypic recombination, while all four EV71-C4 isolates were recombinant viruses having undergone double recombination, and all seven CA16 isolates were recombinant viruses. The recombination breakpoints of these recombinants are located solely within the P2 and P3 regions. Surveillance for circulating strains and subgenotype replacement are important with respect to molecular epidemiology and the selection of the upcoming EV71 vaccine. In addition, the clinical importance of recombinant viruses needs to be further explored.

Human tryptophanyl-tRNA synthetase is an IFN-γ-inducible entry factor for Enterovirus

Enterovirus A71 (EV-A71) receptors that have been identified to date cannot fully explain the pathogenesis of EV-A71, which is an important global cause of hand, foot, and mouth disease and life-threatening encephalitis. We identified an IFN-γ-inducible EV-A71 cellular entry factor, human tryptophanyl-tRNA synthetase (hWARS), using genome-wide RNAi library screening. The importance of hWARS in mediating virus entry and infectivity was confirmed by virus attachment, in vitro pulldown, antibody/antigen blocking, and CRISPR/Cas9-mediated deletion. Hyperexpression and plasma membrane translocation of hWARS were observed in IFN-γ-treated semipermissive (human neuronal NT2) and cDNA-transfected nonpermissive (mouse fibroblast L929) cells, resulting in their sensitization to EV-A71 infection. Our hWARS-transduced mouse infection model showed pathological changes similar to those seen in patients with severe EV-A71 infection. Expression of hWARS is also required for productive infection by other human enteroviruses, including the clinically important coxsackievirus A16 (CV-A16) and EV-D68. This is the first report to our knowledge on the discovery of an entry factor, hWARS, that can be induced by IFN-γ for EV-A71 infection. Given that we detected high levels of IFN-γ in patients with severe EV-A71 infection, our findings extend the knowledge of the pathogenicity of EV-A71 in relation to entry factor expression upon IFN-γ stimulation and the therapeutic options for treating severe EV-A71-associated complications.

Enhanced neutralizing antibody response induced by inactivated enterovirus 71 in cynomolgus monkeys

Enterovirus 71 (EV71) is a major etiological agent of various public health issues, particularly in the Asia-Pacific region. EV71 causes hand-foot-and-mouth disease (HFMD) and is associated with serious neurological disorders in young children. A formalin-inactivated EV71 candidate vaccine (KCDC-HFMDV1-EV71) based on the C4 subgenotype was previously developed and confirmed to be a potential candidate vaccine for prevention of EV71 infection in mice. In this study, an inactivated EV71 vaccine was used for analysis of long-term immunogenicity and efficacy in cynomolgus monkeys, a common nonhuman primate model. The vaccine was immunized three times at 0, 4, and 8 weeks with either 20-μg doses of EV71 candidate vaccine formulated with aluminum hydroxide gel adjuvant or phosphate-buffered saline as a control. The group immunized with the inactivated EV71 showed significantly increased EV71-specific antibody and serum neutralizing antibody titers at 3 weeks after vaccination and maintained these elevated titers until the end of the experiment (54 weeks after vaccination). The sera from vaccinated cynomolgus monkeys showed a crossreactive neutralizing antibody response to the heterologous subtype of EV71 (B1–4, C1, and C2). These findings suggest that the inactivated EV71 candidate vaccine may be a potential vaccine candidate and valuable tool for the control of HFMD.

Molecular epidemiology of coxsackievirus A6 circulating in Hong Kong reveals common neurological manifestations and emergence of novel recombinant groups

BACKGROUND

Coxsackievirus A6 (CV-A6) represents the predominant enterovirus serotype in Hong Kong, but its epidemiology in our population was unknown.

OBJECTIVES

To examine the clinical and molecular epidemiology of CV-A6 and detect emerging recombinant strains in Hong Kong.

STUDY DESIGN

Nasopharyngeal aspirates (NPAs) from patients with febrile or respiratory illness were subject to RT-PCR for CV-A6 and sequencing of 5'-NCR and VP1. CV-A6-positive samples were further subject to 2C and 3D gene sequencing. Complete genome sequencing was performed on potential recombinant strains.

RESULTS

Thirty-six (0.35%) NPAs were positive for CV-A6 by 5'-NCR RT-PCR and sequencing, 28 of which confirmed by partial VP1 gene sequencing. Among the 28 patients (mainly young children) with CV-A6 infection, hand-foot-and-mouth disease (HFMD) (43%), herpangina (18%) and tonsillitis (11%) were the most common diagnoses. Seven (25%) patients had neurological manifestations, including febrile seizures, encephalitis and meningitis. VP1 gene analysis showed that 24 CV-A6 strains circulating in Hong Kong belonged to genotype D5, while 4 strains belonged to D4. Further 2C and 3D gene analysis revealed eight potential recombinant strains. Genome sequencing of five selected strains confirmed four recombinant strains: HK459455/2013 belonging to recombination group RJ arisen from CV-A6/CV-A4, HK458288/2015 and HK446377/2015 representing novel group RL arisen from CV-A6/CV-A4, and HK462069/2015 representing novel group RM arisen from CV-A6/EV-A71. Recombination breakpoints located at 3D were identified in the latter three recombinant strains, with HK462069/2015 (from a child with encephalitis) having acquired 3D region from EV-A71.

CONCLUSIONS

We identified novel recombinant CV-A6 strains in Hong Kong, with 3D being a common recombination site.

Discovery of Enterovirus A71-like nonstructural genomes in recent circulating viruses of the Enterovirus A species

Enterovirus A71 (EV-A71) is an important nonpolio enterovirus that causes severe neurological complications. In 1998, Taiwan experienced an EV-A71 outbreak that caused 78 deaths. Since then, periodic epidemics of EV-A71 associated with newly emerging strains have occurred. Several of these strains are known to be recombinant; however, how these strains arose within such a short period of time remains unknown. Here, we sequenced 64 full-length genomes from clinical isolates collected from 2005 to 2016 and incorporated all 91 Taiwanese genomes downloaded from the Virus Pathogen Resource to extensively analyze EV-A71 recombination in Taiwan. We found that the B3 subgenotype was a potential recombinant parent of the EV-A71 C2-like and C4 strains by intratypic recombination. Such B3-similar regions were also found in many cocirculating coxsackieviruses belonging to Enterovirus A species (EV-A) through a series of intertypic recombinations. Therefore, locally enriched outbreaks of cocirculating viruses from different genotypes/serotypes may facilitate recombination. Most recombination breakpoints we found had nonrandom distributions and were located within the region spanning from the boundary of P1 (structural gene) and P2 (nonstructural) to the cis-acting replication element at P2, indicating that specific genome reassembly of structural and nonstructural genes may be subject to natural selection. Through intensive recombination, 11 EV-A71-like signatures (including one in 3A, two in 3C, and eight in 3D) were found to be present in a variety of recently cocirculating EV-A viruses worldwide, suggesting that these viruses may be targets for wide-spectrum antiviral development.

Serological survey of neutralizing antibodies to eight major enteroviruses among healthy population

Human enteroviruses (EVs) are the most common causative agents infecting human, causing many harmful diseases, such as hand, foot, and mouth disease (HFMD), herpangina (HA), myocarditis, encephalitis, and aseptic meningitis. EV-related diseases pose a serious worldwide threat to public health. To gain comprehensive insight into the seroepidemiology of major prevalent EVs in humans, we firstly performed a serological survey for neutralizing antibodies (nAbs) against Enterovirus A71 (EV-A71), Coxsackie virus A16 (CV-A16), Coxsackie virus A6 (CV-A6), Coxsackie virus A10 (CV-A10), Coxsackie virus B3 (CV-B3), Coxsackie virus B5 (CV-B5), Echovirus 25 (ECHO25), and Echovirus 30 (ECHO30) among the healthy population in Xiamen City in 2016, using micro-neutralization assay. A total of 515 subjects aged 5 months to 83 years were recruited by stratified random sampling. Most major human EVs are widely circulated in Xiamen City and usually infect infants and children. The overall seroprevalence of these eight EVs were ranged from 14.4% to 42.7%, and most of them increased with age and subsequently reached a plateau. The co-existence of nAbs against various EVs are common among people ≥ 7 years of age, due to the alternate infections or co-infections with different serotypes of EVs, while most children were negative for nAb against EVs, especially those < 1 year of age. This is the first report detailing the seroepidemiology of eight prevalent EVs in the same population, which provides scientific data supporting further studies on the improvement of EV-related disease prevention and control.

Epitope-associated and specificity-focused features of EV71-neutralizing antibody repertoires from plasmablasts of infected children

Protective antibody levels are critical for protection from severe enterovirus 71 infection. However, little is known about the specificities and functional properties of the enterovirus 71-specific antibodies induced by natural infection in humans. Here we characterize 191 plasmablast-derived monoclonal antibodies from three enterovirus 71-infected children, each of whom shows a distinct serological response. Of the 84 enterovirus 71-specific antibodies, neutralizing antibodies that target the rims and floor of the capsid canyon exhibit broad and potent activities at the nanogram level against viruses isolated in 1998–2016. We also find a subset of infected children whose enterovirus 71-specific antibodies are focused on the 3- and 2-fold plateau epitopes localized at the margin of pentamers, and this type of antibody response is associated with lower serum titers against recently circulating strains. Our data provide new insights into the enterovirus 71-specific antibodies induced by natural infection at the serological and clonal levels.

Enterovirus 71 is a leading cause of hand-foot-and-mouth disease and herpangina. Here, the authors characterize a large panel of plasmablast-derived IgG mAbs that target the capsid of EV71 to identify neutralizing antibodies induced by natural infection.

Modelling person-to-person transmission in an Enterovirus A71 orally infected hamster model of hand-foot-and-mouth disease and encephalomyelitis

Enterovirus A71 (EV-A71) causes hand-foot-and-mouth disease (HFMD), which may be complicated by fatal encephalomyelitis. Although fecal–oral or oral–oral routes are important in person-to-person transmission, how viral shedding and exposure may predispose individuals to infection remains unknown. We investigated person-to-person transmission by using a model of HFMD and encephalomyelitis based on EV-A71 oral infection of 2-week-old hamsters. Animals (index animals) infected with 10⁴ 50% cell culture infective doses of virus uniformly developed severe disease four days post-infection (dpi), whereas littermate contacts developed severe disease after six to seven days of exposure to index animals. Virus was detected in oral washes and feces at 3–4 dpi in index animals and at three to eight days after exposure to index animals in littermate contact animals. In a second experiment, non-littermate contact animals exposed for 8 or 12 h to index animals developed the disease six and four days post-exposure, respectively. Tissues from killed index and contact animals, studied by light microscopy, immunohistochemistry and in situ hybridization, exhibited mild inflammatory lesions and/or viral antigens/RNA in the squamous epithelia of the oral cavity, tongue, paws, skin, esophagus, gastric epithelium, salivary glands, lacrimal glands, central nervous system neurons, muscles (skeletal, cardiac and smooth muscles) and liver. Orally shed viruses were probably derived from infected oral mucosa and salivary glands, whereas fecal viruses may have derived from these sites as well as from esophageal and gastric epithelia. Asymptomatic seroconversion in exposed mother hamsters was demonstrated. Our hamster model should be useful in studying person-to-person EV-A71 transmission and how drugs and vaccines may interrupt transmission.

Pre-vaccination evolution of antibodies among infants 0, 3 and 6months of age: A longitudinal analysis of measles, enterovirus 71 and coxsackievirus 16

BACKGROUND

Due to waning levels of maternal antibodies (measles; enterovirus 71, EV71; and coxsackievirus A16, CoxA16), some infants may lose protection against infection prior to vaccination. Using a longitudinal design, we examine how maternal antibody levels evolve over time in infants prior to vaccination.

METHODS

In 2013-2014, we collected sera at ages 0, 3 and 6months from infants. We assayed for levels of measles IgG antibody (717, 233 and 75 sample sera tested at months 0, 3 and 6, respectively), and neutralizing antibodies for EV71 and CoxA16 (225, 217, and 72). Demographic and health information were collected, and a linear mixed model (LMM) was used to describe antibody levels over time.

RESULTS

Pre-vaccination monotonic antibody decreases were observed for measles (1410, 195 and 22mIU/ml, p<0.001), EV71 (1:19.9, 6.3 and 4.5, p<0.001) and CoxA16 (1:16.3, 5.9, and 4.5, p<0.001). At 6months of age, only 2.7% (95%CI, 0.6-8.3), 6.8% (95%CI, 2.7-14.4) and 5.6% (95%CI, 1.9-12.7) of infants were antibody positive for measles, EV71 and CoxA16, respectively. LMM findings indicated that infants with higher antibody titers at birth experienced a greater loss of antibody level. An infection rate of 1.3% (95%CI, 0.1-6.1) was reported for both EV71 and CoxA16.

CONCLUSIONS

Further modifications of vaccination strategies for measles, earlier vaccination for EV71 infection, and deployment of a CoxA16 vaccine need to be considered to limit infection among the very young.

Genetic characterization of enterovirus strains identified in Hand, Foot and Mouth Disease (HFMD): Emergence of B1c, C1 subgenotypes, E2 sublineage of CVA16, EV71 and CVA6 strains in India

Hand, Foot and Mouth disease (HFMD) is a common childhood disease and caused due to Enterovirus-A (EV-A), EV-B and EV-C species worldwide. Cases of HFMD were reported from, Ahmedabad (Gujarat, 2012) and Pune (Maharashtra, 2013-2014) in India. The present study highlights the identification of EV strains (CVA16, CVA6, CVA4 and Echo12), characterization of subgenotypes of CVA16, CVA6 strains during 2012-14 and CVA16, CVA6, EV71 strains reported from the earlier study (2009-10) in HFMD cases from India. A total 158 clinical specimens collected from 64 HFMD cases (2012-2014) were included in the study. EV detection was carried out by 5'NCR based RT-PCR, molecular typing and subgenotyping was by VP1/2A junction or VP1, full VP1 gene amplification respectively followed by phylogenetic analysis. The present study reports 63.92% (101/158) EV positivity by RT-PCR. Ninety four of the 101 (93.06%) EV positive strains were amplified by VP1/2A junction or VP1 regions. Sequence analysis revealed the presence of CVA16 (61.7%), CVA6 (34.04%), CVA4 and Echo12 (4.3%). A total of 114 EV positive strains were genotyped using full and partial VP1 region. All CVA16 Indian strains (n=70) clustered with rarely reported B1c subgenotype, CVA6 (n=43) and EV71 (n=1) strains clustered with sub-lineage E2 and C1 subgenotypes respectively. In summary, the study reports genetic characterization of CVA16, CVA6, CVA4 and Echo12 strains in HFMD cases from India. Circulation of B1c subgenotype of CVA16, E2 sub-lineage of CVA6 and C1 subgenotype of EV 71 strains in HFMD cases were reported for the first time from India. This study helps to understand the genotype distribution, genetic diversity of EV strains associated with HFMD from Eastern, Western and Southern regions in India.

Beta-Propiolactone Inactivation of Coxsackievirus A16 Induces Structural Alteration and Surface Modification of Viral Capsids

Beta-propiolactone (BPL) is an inactivating agent that is widely used in the vaccine industry. However, its effects on vaccine protein antigens and its mechanisms of action remain poorly understood. Here we present cryo-electron microscopy (cryo-EM) structures of BPL-treated coxsackievirus A16 (CVA16) mature virions and procapsids at resolutions of 3.9 Å and 6.5 Å, respectively. Notably, both particles were found to adopt an expanded conformation resembling the 135S-like uncoating intermediate, with characteristic features including an opened 2-fold channel, the externalization of the N terminus of VP1 capsid protein, and the absence of pocket factor. However, major neutralizing epitopes are very well preserved on these particles. Further biochemical analyses revealed that BPL treatment impairs the abilities of CVA16 particles to bind to the attachment receptor heparan sulfate and to a conformation-dependent monoclonal antibody in a BPL dose-dependent manner, indicating that BPL is able to modify surface-exposed amino acid residues. Taken together, our results demonstrate that BPL treatment may induce alteration of the overall structure and surface properties of a nonenveloped viral capsid, thus revealing a novel mode of action of BPL.IMPORTANCE Beta-propiolactone (BPL) is commonly used as an inactivating reagent to produce viral vaccines. It is recognized that BPL inactivates viral infectivity through modification of viral nucleic acids. However, its effect on viral proteins remains largely unknown. Here, we present high-resolution cryo-EM structures of BPL-treated coxsackievirus A16 (CVA16) mature virions and procapsids, which reveals an expanded overall conformation and characteristic features that are typical for the 135S-like uncoating intermediate. We further show that the BPL concentration affects the binding of inactivated CVA16 particles to their receptor/antibody. Thus, BPL treatment can alter the overall structure and surface properties of viral capsids, which may lead to antigenic and immunogenic variations. Our findings provide important information for future development of BPL-inactivated vaccines.

Transcriptome analysis reveals dynamic changes in coxsackievirus A16 infected HEK 293T cells

BACKGROUND

Coxsackievirus A16 (CVA16) and enterovirus 71 (EV71) are two of the major causes of hand, foot and mouth disease (HFMD) world-wide. Although many studies have focused on infection and pathogenic mechanisms, the transcriptome profile of the host cell upon CVA16 infection is still largely unknown.

RESULTS

In this study, we compared the mRNA and miRNA expression profiles of human embryonic kidney 293T cells infected and non-infected with CVA16. We highlighted that the transcription of SCARB2, a cellular receptor for both CVA16 and EV71, was up-regulated by nearly 10-fold in infected cells compared to non-infected cells. The up-regulation of SCARB2 transcription induced by CVA16 may increase the possibility of subsequent infection of CVA16/EV71, resulting in the co-infection with two viruses in a single cell. This explanation would partly account for the co-circulation and genetic recombination of a great number of EV71 and CVA16 viruses. Based on correlation analysis of miRNAs and genes, we speculated that the high expression of SCARB2 is modulated by down-regulation of miRNA has-miR-3605-5p. At the same time, we found that differentially expressed miRNA target genes were mainly reflected in the extracellular membrane (ECM)-receptor interaction and circadian rhythm pathways, which may be related to clinical symptoms of patients infected with CVA16, such as aphthous ulcers, cough, myocarditis, somnolence and potentially meningoencephalitis. The miRNAs hsa-miR-149-3p and hsa-miR-5001-5p may result in up-regulation of genes in these morbigenous pathways related to CVA16 and further cause clinical symptoms.

CONCLUSIONS

The present study elucidated the changes in 293T cells upon CVA16 infection at transcriptome level, containing highly up-regulated SCARB2 and genes in ECM-receptor interaction and circadian rhythm pathways, and key miRNAs in gene expression regulation. These results provided novel insight into the pathogenesis of HFMD induced by CVA16 infection.

Identification of Novel Rosavirus Species That Infects Diverse Rodent Species and Causes Multisystemic Dissemination in Mouse Model

While novel picornaviruses are being discovered in rodents, their host range and pathogenicity are largely unknown. We identified two novel picornaviruses, rosavirus B from the street rat, Norway rat, and rosavirus C from five different wild rat species (chestnut spiny rat, greater bandicoot rat, Indochinese forest rat, roof rat and Coxing's white-bellied rat) in China. Analysis of 13 complete genome sequences showed that “Rosavirus B” and “Rosavirus C” represent two potentially novel picornavirus species infecting different rodents. Though being most closely related to rosavirus A, rosavirus B and C possessed distinct protease cleavage sites and variations in Yn-Xm-AUG sequence in 5’UTR and myristylation site in VP4. Anti-rosavirus B VP1 antibodies were detected in Norway rats, whereas anti-rosavirus C VP1 and neutralizing antibodies were detected in Indochinese forest rats and Coxing's white-bellied rats. While the highest prevalence was observed in Coxing's white-bellied rats by RT-PCR, the detection of rosavirus C from different rat species suggests potential interspecies transmission. Rosavirus C isolated from 3T3 cells causes multisystemic diseases in a mouse model, with high viral loads and positive viral antigen expression in organs of infected mice after oral or intracerebral inoculation. Histological examination revealed alveolar fluid exudation, interstitial infiltration, alveolar fluid exudate and wall thickening in lungs, and hepatocyte degeneration and lymphocytic/monocytic inflammatory infiltrates with giant cell formation in liver sections of sacrificed mice. Since rosavirus A2 has been detected in fecal samples of children, further studies should elucidate the pathogenicity and emergence potential of different rosaviruses.

We identified two novel picornaviruses, rosavirus B and C, infecting street and wild rats respectively in China. While rosavirus B was detected from Norway rats, rosavirus C was detected from five different wild rat species (chestnut spiny rat, greater bandicoot rat, Indochinese forest rat, roof rat and Coxing's white-bellied rat) by RT-PCR. Anti-rosavirus B antibodies were detected in Norway rats, whereas anti-rosavirus C antibodies were detected in Indochinese forest rats and Coxing's white-bellied rats, supporting potential interspecies transmission of rosavirus C. Genome analysis supported the classification of rosavirus B and C as two novel picornavirus species, with genome features distinct from rosavirus A. Rosavirus C isolated from 3T3 cells causes multisystemic diseases in a mouse model, with viruses and pathologies detected in various organs of infected mice after oral or intracerebral inoculation. Our results extend our knowledge on the host range and pathogenicity of rodent picornaviruses.

Virus-Like Particles Produced in Pichia Pastoris Induce Protective Immune Responses Against Coxsackievirus A16 in Mice

BACKGROUND Coxsackievirus A16 (CA16) is one of the main causative agents of hand, foot, and mouth disease (HFMD), and the development of a safe and effective vaccine has been a top priority among CA16 researchers. MATERIAL AND METHODS In this study, we developed a Pichia pastoris yeast system for secretory expression of the virus-like particles (VLPs) for CA16 by co-expression of the P1 and 3CD proteins of CA16. SDS-PAGE, Western blot, and transmission electron microscopy (TEM) were performed to identify the formation of VLPs. Immunogenicity and vaccine efficacy of the CA16 VLPs were assessed in BABL/c mouse models. RESULTS Biochemical and biophysical analysis showed that the yeast-expressed CA16 VLPs were composed of VP0, VP1, and VP3 capsid subunit proteins, and present spherical particles with a diameter of 30 nm, similar to the parental infectious CA16 virus. Furthermore, CA16 VLPs elicited potent humoral and cellular immune responses, and VLPs-immunized sera conferred efficient protection to neonatal mice against lethal CA16 challenge. CONCLUSIONS Our results demonstrate that VLPs produced in Pichia pastoris represent a safe and effective vaccine strategy for CA16.

Molecular epidemiology of human enterovirus 71 at the origin of an epidemic of fatal hand, foot and mouth disease cases in Cambodia

Human enterovirus 71 (EV-A71) causes hand, foot and mouth disease (HFMD). EV-A71 circulates in many countries and has caused large epidemics, especially in the Asia-Pacific region, since 1997. In April 2012, an undiagnosed fatal disease with neurological involvement and respiratory distress occurred in young children admitted to the Kantha Bopha Children's Hospital in Phnom Penh, Cambodia. Most died within a day of hospital admission, causing public panic and international concern. In this study, we describe the enterovirus (EV) genotypes that were isolated during the outbreak in 2012 and the following year. From June 2012 to November 2013, 312 specimens were collected from hospitalized and ambulatory patients and tested by generic EV and specific EV-A71 reverse transcription PCR. EV-A71 was detected in 208 clinical specimens while other EVs were found in 32 patients. The VP1 gene and/or the complete genome were generated. Our phylogenetic sequencing analysis demonstrated that 80 EV-A71 strains belonged to the C4a subgenotype and 3 EV-A71 strains belonged to the B5 genotype. Furthermore, some lineages of EV-A71 were found to have appeared in Cambodia following separate introductions from neighboring countries. Nineteen EV A (CV-A6 and CV-A16), 9 EV B (EV-B83, CV-B3, CV-B2, CV-A9, E-31, E-2 and EV-B80) and 4 EV C (EV-C116, EV-C96, CV-A20 and Vaccine-related PV-3) strains were also detected. We found no molecular markers of disease severity. We report here that EV-A71 genotype C4 was the main etiological agent of a large outbreak of HFMD and particularly of severe forms associated with central nervous system infections. The role played by other EVs in the epidemic could not be clearly established.

Equine rhinitis B viruses in horse fecal samples from the Middle East

Background

Among all known picornaviruses, only two species, equine rhinitis A virus and equine rhinitis B virus (ERBV) are known to infect horses, causing respiratory infections. No reports have described the detection of ERBV in fecal samples of horses and no complete genome sequences of ERBV3 are available.

Methods

We performed a molecular epidemiology study to detect ERBVs in horses from Dubai and Hong Kong. Complete genome sequencing of the ERBVs as well as viral loads and genome, phylogenetic and evolutionary analysis were performed on the positive samples.

Results

ERBV was detected in four (13.8 %) of the 29 fecal samples in horses from Dubai, with viral loads 8.28 × 10³ to 5.83 × 10⁴ copies per ml, but none of the 47 fecal samples in horses from Hong Kong by RT-PCR. Complete genome sequencing and phylogenetic analysis showed that three of the four strains were ERBV3 and one was ERBV2. The major difference between the genomes of ERBV3 and those of ERBV1 and ERBV2 lied in the amino acid sequences of their VP1 proteins. The Ka/Ks ratios of all the coding regions in the ERBV3 genomes were all <0.1, suggesting that ERBV3 were stably evolving in horses. Using the uncorrelated lognormal distributed relaxed clock model on VP1 gene, the date of the most recent common ancestor (MRCA) of ERBV3 was estimated to be 1785 (HPDs, 1176 to 1937) and the MRCA dates of ERBV1 and ERBV2 were estimated to be 1848 (HPDs, 1466 to 1949) respectively.

Conclusions

Both acid stable (ERBV3) and acid labile (ERBV2) ERBVs could be found in fecal samples of horses. Detection of ERBVs in fecal samples would have implications for their transmission and potential role in gastrointestinal diseases as well as fecal sampling as an alternative method of identifying infected horses.

Enterovirus D68 Infections Associated with Severe Respiratory Illness in Elderly Patients and Emergence of a Novel Clade in Hong Kong

Despite the recent emergence of enterovirus D68 (EV-D68), its clinical impact on adult population is less well defined. To better define the epidemiology of EV-D68, 6,800 nasopharyngeal aspirates (NPAs) from 2010–2014 were subject to EV-D68 detection by RT-PCR and sequencing of 5′UTR and partial VP1. EV-D68 was detected in 30 (0.44%) NPAs from 22 children and 8 adults/elderlies. Sixteen patients (including five elderly) (53%) had pneumonia and 13 (43%) patients were complicated by small airway disease exacerbation. Phylogenetic analysis of VP1, 2C and 3D regions showed four distinct lineages of EV-D68, clade A1, A2, B1 and B3, with adults/elderlies exclusively infected by clade A2. The potentially new clade, B3, has emerged in 2014, while strains closely related to recently emerged B1 strains in the United States were also detected as early as 2011 in Hong Kong. The four lineages possessed distinct aa sequence patterns in BC and DE loops. Amino acid residues 97 and 140, within BC and DE-surface loops of VP1 respectively, were under potential positive selection. EV-D68 infections in Hong Kong usually peak in spring/summer, though with a delayed autumn/winter peak in 2011. This report suggests that EV-D68 may cause severe respiratory illness in adults/elderlies with underlying co-morbidities.

Molecular epidemiology of canine picornavirus in Hong Kong and Dubai and proposal of a novel genus in Picornaviridae

Previously, we reported the discovery of a novel canine picornavirus (CanPV) in the fecal sample of a dog. In this molecular epidemiology study, CanPV was detected in 15 (1.11%) of 1347 canine fecal samples from Hong Kong and one (0.76%) of 131 canine fecal samples from Dubai, with viral loads 1.06×10(3) to 6.64×10(6) copies/ml. Complete genome sequencing and phylogenetic analysis showed that CanPV was clustered with feline picornavirus (FePV), bat picornavirus (BatPV) 1 to 3, Ia io picornavirus 1 (IaioPV1) and bovine picornavirus (BoPV), and this cluster was most closely related to the genera Enterovirus and Sapelovirus. The Ka/Ks ratios of all the coding regions were <0.1. According to the definition of the Picornavirus Study Group of ICTV, CanPV, FePV, BatPV 1 to 3, IaioPV1 and BoPV should constitute a novel genus in Picornaviridae. BEAST analysis showed that this genus diverged from its most closely related genus, Sapelovirus, about 49 years ago.

Impact of Human Enterovirus 71 Genotypes in Meningoencephalitis in Iran

Background:

Since the importance of poliovirus has diminished, as a result of its elimination in the majority of countries, non-polioviruses are emerging as causative agents of severe central nervous system (CNS) involvement. Outbreaks of enterovirus 71 (EV71)-associated CNS infections have recently been reported in Asia, Australia, and Europe.

Objectives:

This is the first study on genotyping of EV71 in children with meningoencephalitis to be carried out in Iran, and it was conducted in order to obtain an improved understanding of the disease burden of this virus, particularly with regard to CNS involvement.

Patients and Methods:

Viral RNA was extracted from 170 cerebrospinal fluid samples obtained from children aged under 8 years with a primary diagnosis of aseptic meningitis. Specific EV71 PCR was conducted to identify the genotype of the detected EV71 viruses.

Results:

Human enteroviruses (HEVs) were detected in 89 patients (52.3%). EV71 infection was detected in 19 (21.3%) of the 89 EV71-positive patients, and the C genotype was identified in 15 isolates.

Conclusions:

The C genotype should be considered as the prevalent EV71 circulating genotype in Iran, particularly in cases of aseptic meningitis.

Complete genome sequence analysis of enterovirus 71 isolated from children with hand, foot, and mouth disease in Thailand, 2012-2014

The complete genomic sequences of 14 enterovirus 71 (EV71) strains isolated from children with hand, foot, and mouth disease in Thailand from 2012 to 2014 were determined and compared to enterovirus group A prototypes. Phylogenetic analysis revealed that 13 strains resembled the B5 subgroup, while one strain from a fatal case designated THA_1219 belonged to the C4 subgroup. Similarity plot and bootscan analyses suggested that THA_1219 underwent recombination in the P2 and P3 regions. Full-genome data from this work will contribute to the study of evolution dynamics of EV71.

Optimization and Characterization of Candidate Strain for Coxsackievirus A16 Inactivated Vaccine

Coxsackievirus A16 (CA16) and enterovirus 71 (EV71), both of which can cause hand, foot and mouth disease (HFMD), are responsible for large epidemics in Asian and Pacific areas. Although inactivated EV71 vaccines have completed testing in phase III clinical trials in Mainland China, CA16 vaccines are still under development. A Vero cell-based inactivated CA16 vaccine was developed by our group. Screening identified a CA16 vaccine strain (CC024) isolated from HFMD patients, which had broad cross-protective abilities and satisfied all requirements for vaccine production. Identification of the biological characteristics showed that the CA16CC024 strain had the highest titer (107.5 CCID50/mL) in Vero cells, which would benefit the development of an EV71/CA16 divalent vaccine. A potential vaccine manufacturing process was established, including the selection of optimal time for virus harvesting, membrane for diafiltration and concentration, gel-filtration chromatography for the down-stream virus purification and virus inactivation method. Altogether, the analyses suggested that the CC-16, a limiting dilution clone of the CC024 strain, with good genetic stability, high titer and broad-spectrum immunogenicity, would be the best candidate strain for a CA16 inactivated vaccine. Therefore, our study provides valuable information for the development of a Vero cell-based CA16 or EV71-CA16 divalent inactivated vaccine.

Enterovirus 71 infection in children with hand, foot, and mouth disease in Shanghai, China: epidemiology, clinical feature and diagnosis

BACKGROUND

In 2012 a large outbreak of hand, foot, and mouth disease (HFMD) widely spread over China, causing more than 2 million cases and 567 deaths. Our purpose was to characterize the major pathogens responsible for the 2012 HFMD outbreak and analyze the genetic characterization of the enterovirus 71 (EV71) strains in Shanghai; also, to analyze the dynamic patterns of neutralizing antibody (NAb) against EV71 and evaluate the diagnostic value of several methods for clinical detection of EV71.

METHODS

Clinical samples including stool, serum and CSF were collected from 396 enrolled HFMD inpatients during the peak seasons in 2012. We analyzed the molecular epidemiology, clinical feature, and diagnostic tests of EV71 infection.

RESULTS

EV71 was responsible for 60.35 % of HFMD inpatients and 88.46 % of severe cases. The circulating EV71 strains belonged to subgenogroup C4a. The nucleotide sequences of VP1 between severe cases and uncomplicated cases shared 99.2 ~ 100 % of homology. Among 218 cases with EV71 infection, 211 (96.79 %) serum samples showed NAb positive against EV71 and NAb titer reached higher level 3 days after disease onset. Of 92 cases with EV71-associated meningitis or encephalitis, 5 (5.43 %) of 92 had EV71 RNA detected in CSF samples. The blood anti-EV71 IgM assay showed a sensitivity of 93.30 % and a specificity of 50 %.

CONCLUSIONS

EV71 C4a remained the predominant subgenotype circulating in Shanghai. The severity of the EV71 infection is not associated with the virulence determinants in VP1. RT-PCR together with IgM detection can enhance the early diagnosis of severe EV71-associated HFMD.

A novel dromedary camel enterovirus in the family Picornaviridae from dromedaries in the Middle East

The recent emergence of Middle East respiratory syndrome coronavirus from the Middle East and the discovery of the virus from dromedary camels have boosted interest in the search for novel viruses in dromedaries. Whilst picornaviruses are known to infect various animals, their existence in dromedaries was unknown. We describe the discovery of a novel picornavirus, dromedary camel enterovirus (DcEV), from dromedaries in Dubai. Among 215 dromedaries, DcEV was detected in faecal samples of four (1.9 %) dromedaries [one (0.5 %) adult dromedary and three (25 %) dromedary calves] by reverse transcription PCR. Analysis of two DcEV genomes showed that DcEV was clustered with other species of the genus Enterovirus and was most closely related to and possessed highest amino acid identities to the species Enterovirus E and Enterovirus F found in cattle. The G+C content of DcEV was 45 mol%, which differed from that of Enterovirus E and Enterovirus F (49-50 mol%) by 4-5 %. Similar to other members of the genus Enterovirus, the 5' UTR of DcEV possessed a putative type I internal ribosome entry site. The low ratios of the number of nonsynonymous substitutions per non-synonymous site to the number of synonymous substitutions per synonymous site (Ka/Ks) of various coding regions suggested that dromedaries are the natural reservoir in which DcEV has been stably evolving. These results suggest that DcEV is a novel species of the genus Enterovirus in the family Picornaviridae. Western blot analysis using recombinant DcEV VP1 polypeptide showed a high seroprevalence of 52 % among serum samples from 172 dromedaries for IgG, concurring with its much higher infection rates in dromedary calves than in adults. Further studies are important to understand the pathogenicity, epidemiology and genetic evolution of DcEV in this unique group of animals.

Combination of intratypic and intertypic recombinant events in EV71: a novel evidence for the "triple-recombinant" strains of genotype A viruses in Mainland China from 2008 to 2010

The first Enterovirus 71 (EV71) strain isolated in 1969 was classified as genotype A. It is interesting that the genotype A disappeared nearly 40 years until its re-emergence in mainland China in 2008-2010. Few studies on genetic characterization of the re-emerged genotype A viruses have been reported. In this study, a series of analyses were performed on molecular epidemiology and genome recombination of genotype A viruses in China. Phylogenetic analysis indicated that except for 17 reported genotype A strains and 3 orphan strains (C0, C3 and B5), almost all EV71 strains in mainland China were belonging to subgenotype C4 during 1987-2011. The subgenotype C4 was further divided into 3 clades C4a1, C4a2, and C4b. The genotype A viruses co-circulated with the predominant clade C4a2 and the re-emerged clade C4b both in eastern and central China in 2008-2009. Moreover, comprehensive recombination analysis showed that the genotype A viruses were "triple-recombinant" by combination of intratypic and intertypic recombination. Intertypic recombination between the oldest C4b strain (SHZH98) and Coxsackievirus A5 (CVA5) and intratypic recombination between the SHZH98 and C1 strains both with one junction in 5'-UTR were observed for some specific C4a2 strains and the re-emerged C4b strain, respectively. And intratypic recombination between the re-emerged C4b strain and the specific C4a2 strains with one junction in 5'-UTR was observed for the Chinese genotype A viruses. Taken together, these results provided potential explanations for the genesis of Chinese genotype A viruses which were significant for preventing and controlling outbreaks.

Novel recombinant chimeric virus-like particle is immunogenic and protective against both enterovirus 71 and coxsackievirus A16 in mice

Hand-foot-and-mouth disease (HFMD) has been recognized as an important global public health issue, which is predominantly caused by enterovirus 71 (EV-A71) and coxsackievirus A16 (CVA16). There is no available vaccine against HFMD. An ideal HFMD vaccine should be bivalent against both EV-A71 and CVA16. Here, a novel strategy to produce bivalent HFMD vaccine based on chimeric EV-A71 virus-like particles (ChiEV-A71 VLPs) was proposed and illustrated. The neutralizing epitope SP70 within the capsid protein VP1 of EV-A71 was replaced with that of CVA16 in ChiEV-A71 VLPs. Structural modeling revealed that the replaced CVA16-SP70 epitope is well exposed on the surface of ChiEV-A71 VLPs. These VLPs produced in Saccharomyces cerevisiae exhibited similarity in both protein composition and morphology as naive EV-A71 VLPs. Immunization with ChiEV-A71 VLPs in mice elicited robust Th1/Th2 dependent immune responses against EV-A71 and CVA16. Furthermore, passive immunization with anti-ChiEV-A71 VLPs sera conferred full protection against lethal challenge of both EV-A71 and CVA16 infection in neonatal mice. These results suggested that this chimeric vaccine, ChiEV-A71 might have the potential to be further developed as a bivalent HFMD vaccine in the near future. Such chimeric enterovirus VLPs provide an alternative platform for bivalent HFMD vaccine development.

Recombination among human non-polio enteroviruses: implications for epidemiology and evolution

Human enteroviruses (EV) belong to the Picornaviridae family and are among the most common viruses infecting humans. They consist of up to 100 immunologically and genetically distinct types: polioviruses, coxsackieviruses A and B, echoviruses, and the more recently characterized 43 EV types. Frequent recombinations and mutations in enteroviruses have been recognized as the main mechanisms for the observed high rate of evolution, thus enabling them to rapidly respond and adapt to new environmental challenges. The first signs of genetic exchanges between enteroviruses came from polioviruses many years ago, and since then recombination has been recognized, along with mutations, as the main cause for reversion of vaccine strains to neurovirulence. More recently, non-polio enteroviruses became the focus of many studies, where recombination was recognized as a frequent event and was correlated with the appearance of new enterovirus lineages and types. The accumulation of multiple inter- and intra-typic recombination events could also explain the series of successive emergences and disappearances of specific enterovirus types that could in turn explain the epidemic profile of circulation of several types. This review focuses on recombination among human non-polio enteroviruses from all four species (EV-A, EV-B, EV-C, and EV-D) and discusses the recombination effects on enterovirus epidemiology and evolution.

Towards broadly protective polyvalent vaccines against hand, foot and mouth disease

Hand, foot, and mouth disease (HFMD) caused by multiple enterovirus infections is a serious health threat to children in the Asia-Pacific region. This article reviews progresses in the development of vaccines for HFMD and discusses the need for polyvalent HFMD vaccines for conferring broad-spectrum protection.

DA virus mutant H101 has altered CNS pathogenesis and causes immunosuppression

Viruses use various mechanisms to evade clearance by the host. Investigating how a few changes in the genome of a non-lethal virus can lead to altered disease, from survivable to immunosuppression/death, would provide valuable information into viral pathogenesis. The Daniels strain of Theiler's murine encephalomyelitis virus causes an asymptomatic infection or acute encephalitis followed by viral clearance. A mutant, H101, carries several alterations in the viral genome. H101 infection causes profound immunosuppression and death. Thus, a virus that is normally cleared by its natural host can become lethal due to just a few changes in the viral genome.

Epidemiology of human parechovirus, Aichi virus and salivirus in fecal samples from hospitalized children with gastroenteritis in Hong Kong

BACKGROUND

Emerging human picornaviruses, including human parechovirus (HPeV), Aichi virus (AiV) and salivirus (SalV) were found to be associated with gastroenteritis, but their roles in enteric infections are not fully understood. In addition, no report on the circulation of these viruses in Hong Kong is available. The objective of this study was to investigate the prevalence and genetic diversity of HPeV, AiV and SalV in fecal samples from hospitalized children with gastroenteritis in Hong Kong.

METHODS

Fecal samples from hospitalized children with gastroenteritis were subject to detection of HPeV, AiV and SalV by RT-PCR using consensus primers targeted to their 5'UTRs. Positive samples were subject to capsid and/or 3CD region analysis for genotype determination. The epidemiology of HPeV, AiV and SalV infections was analyzed.

RESULTS

Among 1,708 fecal samples subjected to RT-PCR using primers targeted to 5'UTR of HPeV, AiV and SalV, viruses were detected in 55 samples, with 50 positive for HPeV only, 3 positive for AiV only, 1 positive for both HPeV and AiV, and 1 positive for both HPeV and SalV. Phylogenetic analysis of the partial VP1 gene of the 33 HPeV strains revealed the presence of genotypes of HPeV- 1, 3, 4, 5, 7, 10, among which HPeV-1 was the predominant genotype circulating in our population. The peak activity of HPeV infection was in fall. Of the 3 children with AiV infection, the 3 AiV strains were found to belong to genotype A based on the phylogenetic analysis of their partial VP1 and 3CD regions. The genotype of a SalV strain detected in this study could not be determined. Co-detection of different pathogens was observed in 24 samples (43.6%) of 55 fecal samples positive for HPeV, AiV and SalV.

CONCLUSIONS

HPeV, AiV and SalV were detected in fecal samples of hospitalized children with gastroenteritis in Hong Kong, with the former having the highest prevalence. HPeV-1 was the predominant genotype among HPeVs, while genotype A was the predominant genotype among AiVs in this study.

Update on the development of enterovirus 71 vaccines

INTRODUCTION

Enterovirus 71 (EV71) is an etiological agent that causes severe neurological complications in children. EV71 outbreaks have occurred throughout the Asia-Pacific region, posing a severe global public health threat; however, no specific therapeutic strategy exists for treating EV71-infected children.

AREAS COVERED

Five manufacturers have produced inactivated EV71 whole virus vaccines in mainland China, Taiwan, and Singapore, which have completed Phase III (mainland China) and Phase I (Taiwan and Singapore) clinical trials. Various EV71 vaccine candidates are being researched in animal models, including live-attenuated virus vaccine, recombinant VP1 vaccine, VP1-based DNA vaccine, synthetic peptide vaccine and virus-like particle vaccine. In this review, the present situation is summarized, and feasible improvements to the EV71 vaccine are explored.

EXPERT OPINION

Although inactivated EV71 vaccines are safe, efficient and elicit strong immune responses to protect adults, children and infants against infection, the quality control of production is critical.

Identification of luteolin as enterovirus 71 and coxsackievirus A16 inhibitors through reporter viruses and cell viability-based screening

Hand, foot and mouth disease (HFMD) is a common pediatric illness mainly caused by infection with enterovirus 71 (EV71) and coxsackievirus A16 (CA16). The frequent HFMD outbreaks have become a serious public health problem. Currently, no vaccine or antiviral drug for EV71/CA16 infections has been approved. In this study, a two-step screening platform consisting of reporter virus-based assays and cell viability‑based assays was developed to identify potential inhibitors of EV71/CA16 infection. Two types of reporter viruses, a pseudovirus containing luciferase-encoding RNA replicons encapsidated by viral capsid proteins and a full-length reporter virus containing enhanced green fluorescent protein, were used for primary screening of 400 highly purified natural compounds. Thereafter, a cell viability-based secondary screen was performed for the identified hits to confirm their antiviral activities. Three compounds (luteolin, galangin, and quercetin) were identified, among which luteolin exhibited the most potent inhibition of viral infection. In the cell viability assay and plaque reduction assay, luteolin showed similar 50% effective concentration (EC₅₀) values of about 10 μM. Luteolin targeted the post-attachment stage of EV71 and CA16 infection by inhibiting viral RNA replication. This study suggests that luteolin may serve as a lead compound to develop potent anti-EV71 and CA16 drugs.

Chickens host diverse picornaviruses originated from potential interspecies transmission with recombination

While chickens are an important reservoir for emerging pathogens such as avian influenza viruses, little is known about the diversity of picornaviruses in poultry. We discovered a previously unknown diversity of picornaviruses in chickens in Hong Kong. Picornaviruses were detected in 87 cloacal and 7 tracheal samples from 93 of 900 chickens by reverse transcription-PCR, with their partial 3D(pol) gene sequences forming five distinct clades (I to V) among known picornaviruses. Analysis of eight genomes from different clades revealed seven different picornaviruses, including six novel picornavirus species (ChPV1 from clade I, ChPV2 and ChPV3 from clade II, ChPV4 and ChPV5 from clade III, ChGV1 from clade IV) and one existing species (Avian encephalomyelitis virus from clade V). The six novel chicken picornavirus genomes exhibited distinct phylogenetic positions and genome features different from related picornaviruses, supporting their classification as separate species. Moreover, ChPV1 may potentially belong to a novel genus, with low sequence homologies to related picornaviruses, especially in the P1 and P2 regions, including the predicted L and 2A proteins. Nevertheless, these novel picornaviruses were most closely related to picornaviruses of other avian species (ChPV1 related to Passerivirus A, ChPV2 and ChPV3 to Avisivirus A and Duck hepatitis A virus, ChPV4 and ChPV5 to Melegrivirus A, ChGV1 to Gallivirus A). Furthermore, ChPV5 represented a potential recombinant picornavirus, with its P2 and P3 regions possibly originating from Melegrivirus A. Chickens are an important reservoir for diverse picornaviruses that may cross avian species barriers through mutation or recombination.

Co-circulation and genomic recombination of coxsackievirus A16 and enterovirus 71 during a large outbreak of hand, foot, and mouth disease in Central China

A total of 1844 patients with hand, foot, and mouth disease (HFMD), most of them were children of age 1–3-year-old, in Central China were hospitalized from 2011 to 2012. Among them, 422 were infected with coxsackievirus A16 (CVA16), 334 were infected with enterovirus 71 (EV71), 38 were co-infected with EV71 and CVA16, and 35 were infected with other enteroviruses. Molecular epidemiology analysis revealed that EV71 and CVA16 were detected year-round, but EV71 circulated mainly in July and CVA16 circulated predominantly in November, and incidence of HFMD was reduced in January and February and increased in March. Clinical data showed that hyperglycemia and neurologic complications were significantly higher in EV71-infected patients, while upper respiratory tract infection and C-reactive protein were significantly higher in CVA16-associated patients. 124 EV71 and 80 CVA16 strains were isolated, among them 56 and 68 EV71 strains were C4a and C4b, while 25 and 55 CVA16 strains were B1a and B1b, respectively. Similarity plots and bootscan analyses based on entire genomic sequences revealed that the three C4a sub-genotype EV71 strains were recombinant with C4b sub-genotype EV71 in 2B–2C region, and the three CVA16 strains were recombinant with EV71 in 2A–2B region. Thus, CVA16 and EV71 were the major causative agents in a large HFMD outbreak in Central China. HFMD incidence was high for children among household contact and was detected year-round, but outbreak was seasonal dependent. CVA16 B1b and EV71 C4b reemerged and caused a large epidemic in China after a quiet period of many years. Moreover, EV71 and CVA16 were co-circulated during the outbreak, which may have contributed to the genomic recombination between the pathogens. It should gain more attention as there may be an upward trend in co-circulation of the two pathogens globally and the new role recombination plays in the emergence of new enterovirus variants.

Circulating HFMD-associated coxsackievirus A16 is genetically and phenotypically distinct from the prototype CV-A16

Human enteroviruses (HEV) have been linked to hand, foot, and mouth disease (HFMD) in the Pacific and Southeast Asia for decades. Many cases of HFMD have been attributed to coxsackievirus A16 (CV-A16, CA16), based on only partial viral genome determination. Viral phenotypes are also poorly defined. Herein, we have genetically and phenotypically characterized multiple circulating CV-A16 viruses from HFMD patients and determined multiple full-length sequences of these circulating viruses. We discovered that the circulating CV-A16 viruses from HFMD patients are genetically distinct from the proto-type CV-A16 G10. We have also isolated circulating CV-A16 viruses from hospitalized HFMD patients and compared their virological differences. Interestingly, circulating CV-A16 viruses are more pathogenic in a neonatal mouse model than is CV-A16 G10. Thus, we have found circulating recombinant forms of CV-A16 (CRF CV-A16) that are related to, but different from, the prototype CV-A16 G10 that have distinct biological phenotypes.

A combination vaccine comprising of inactivated enterovirus 71 and coxsackievirus A16 elicits balanced protective immunity against both viruses

Enterovirus 71 (EV71) and coxsackievirus A16 (CA16) are the two major causative agents of hand, foot and mouth disease (HFMD), which is an infectious disease frequently occurring in children. A bivalent vaccine against both EV71 and CA16 is highly desirable. In the present study, we compare monovalent inactivated EV71, monovalent inactivated CA16, and a combination vaccine candidate comprising of both inactivated EV71 and CA16, for their immunogenicity and in vivo protective efficacy. The two monovalent vaccines were found to elicit serum antibodies that potently neutralized the homologous virus but had no or weak neutralization activity against the heterologous one; in contrast, the bivalent vaccine immunized sera efficiently neutralized both EV71 and CA16. More importantly, passive immunization with the bivalent vaccine protected mice against either EV71 or CA16 lethal infections, whereas the monovalent vaccines only prevented the homologous but not the heterologous challenges. Together, our results demonstrate that the experimental bivalent vaccine comprising of inactivated EV71 and CA16 induces a balanced protective immunity against both EV71 and CA16, and thus provide proof-of-concept for further development of multivalent vaccines for broad protection against HFMD.

Development of enterovirus 71 vaccines: from the lab bench to Phase III clinical trials

The widespread epidemics of enterovirus 71 (EV71) seriously affected the Western Pacific Region. Young children, especially those younger than 3 years are the most susceptible population to the EV71-associated diseases. Several Asian countries have begun to focus on the research and development of EV71 vaccines. Five inactivated whole-virus EV71 candidate vaccines (three were manufactured in mainland China based on a C4 genotype strain, one in Taiwan based on a B4 genotype strain and one in Singapore based on a B2 genotype strain) have been assessed in clinical trials. Three candidate vaccines developed in mainland China have already completed Phase III clinical trials recently. The tested EV71 vaccine could provide good efficacy, satisfactory safety, and high immunogenicity. Thus, inactivated EV71 vaccines are expected to become the first available vaccines against EV71 in the near future.

An atypical winter outbreak of hand, foot, and mouth disease associated with human enterovirus 71, 2010

BACKGROUND

To analyze the epidemiological characteristics and pathogenic molecular characteristics of an hand, foot, and mouth disease (HFMD) outbreak caused by enterovirus 71 in Linyi City, Shandong Province, China during November 30 to December 28, 2010.

METHODS

One hundred and seventy three stool specimens and 40 throat samples were collected from 173 hospitalized cases. Epidemiologic and clinical investigations, laboratory testing, and genetic analyses were performed to identify the causal pathogen of the outbreak.

RESULTS

Among the 173 cases reported in December 2010, the male-female ratio was 1.88: 1; 23 cases (13.3%) were severe. The majority of patients were children aged < 5 years (95.4%). Some patients developed respiratory symptoms including runny nose (38.2%), cough (20.2%), and sore throat (14.5%). One hundred and thirty eight EV71 positive cases were identified based on real time reverse-transcription PCR detection and 107 isolates were sequenced with the VP1 region. Phylogenetic analysis of full-length VP1 sequences of 107 Linyi EV71 isolates showed that they belonged to the C4a cluster of the C4 subgenotype and were divided into 3 lineages (Lineage I, II and III). The two amino acid substitutions (Gly and Gln for Glu) at position 145 within the VP1 region are more likely to appear in EV71 isolates from severe cases (52.2%) than those recovered from mild cases (8.3%).

CONCLUSION

This outbreak of HMFD was caused by EV71 in an atypical winter. EV71 strains associated with this outbreak represented three separate chains of transmission. Substitution at amino acid position 145 of the VP1 region of EV71 might be an important virulence marker for severe cases. These findings suggest that continued surveillance for EV71 variants has the potential to greatly impact HFMD prevention and control.