Detection of recombination breakpoints in the genomes of human enterovirus 71 strains isolated in the Netherlands in epidemic and non-epidemic years, 1963–2010

A review of enterovirus-associated hand-foot and mouth disease: preventive strategies and the need for a global enterovirus surveillance network

Enterovirus (EV)-associated hand, foot, and mouth disease (HFMD) is a significant public health issue worldwide, commonly occurring in children five years of age or younger. The leading causes of most HFMD cases are EVs, which are members of the Picornaviridae family. The typical clinical manifestations of EV-associated HFMD are febrile presentations with mucosal herpangina, oral ulcerations, and skin rashes on the hands and feet. The majority of HFMD cases resolve without consequence; however, a subset progresses to severe neurological and cardiopulmonary complications, which can be fatal. In the past two decades, EV-associated HFMD has received significant attention. In this review, we organize published papers and provide updates on epidemiology, pathogenesis, surveillance, and vaccine developments for EV-associated HFMD. The impact of EV-associated HFMD is increasing globally. Developing efficacious vaccines has become a priority for preventing EV infections without adequate treatment. Simultaneously, emerging EV infections (including EV-D68, EV-A71, Coxsackieviruses, and echoviruses) are increasing, highlighting the need to create a vigilant surveillance system for EV infections worldwide.

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.

Genomic Epidemiology and Phylodynamic Analysis of Enterovirus A71 Reveal Its Transmission Dynamics in Asia

Enterovirus A71 (EV-A71) is one of the main pathogens causing hand, foot, and mouth disease (HFMD) outbreaks in Asian children under 5 years of age. In severe cases, it can cause neurological complications and be life-threatening. In this study, 200 newly sequenced EV-A71 whole-genome sequences were combined with 772 EV-A71 sequences from GenBank for large-scale analysis to investigate global EV-A71 epidemiology, phylogeny, and Bayesian phylodynamic characteristics. Based on the phylogenetic analysis of the EV-A71 3D^pol region, six new evolutionary lineages (lineages B, J, K, O, P, and Q) were found in this study, and the number of evolutionary lineages was expanded from 11 to 17. Temporal dynamics and recombination breakpoint analyses based on genotype C revealed that recombination of nonstructural protein-coding regions, including 3D^pol, is an important reason for the emergence of new lineages. The EV-A71 epidemic in the Asia-Pacific region is complex, and phylogeographic analysis found that Vietnam played a key role in the spread of subgenotypes B5 and C4. The origin of EV-A71 subgenotype C4 in China is East China, which is closely related to the prevalence of subgenotype C4 in the south and throughout China. Selection pressure analysis revealed that, in addition to VP1 amino acid residues VP1-98 and VP1-145, which are associated with EV-A71 pathogenicity, amino acid residues VP1-184 and VP1-249 were also positively selected, and their functions still need to be determined by biology and immunology. This study aimed to provide a solid theoretical basis for EV-A71-related disease surveillance and prevention, antiviral research, and vaccine development through a comprehensive analysis. IMPORTANCE EV-A71 is one of the most important pathogens causing HFMD outbreaks; however, large-scale studies of EV-A71 genomic epidemiology are currently lacking. In this study, 200 new EV-A71 whole-genome sequences were determined. Combining these with 772 EV-A71 whole-genome sequences in the GenBank database, the evolutionary and transmission characteristics of global and Asian EV-A71 were analyzed. Six new evolutionary lineages were identified in this study. We also found that recombination in nonstructural protein-coding regions, including 3D^pol, is an important cause for the emergence of new lineages. The results provided a solid theoretical basis for EV-A71-related disease surveillance and prevention, antiviral research, and vaccine development.

A novel subgenotype C6 Enterovirus A71 originating from the recombination between subgenotypes C4 and C2 strains in mainland China

Recombination plays important roles in the genetic diversity and evolution of Enterovirus A71 (EV-A71). The phylogenetics of EV-A71 in mainland China found that one strain DL71 formed a new subgenotype C6 with unknown origin. This study investigated the detailed genetic characteristics of the new variant. DL71 formed a distinct cluster within genotype C based on the genome and individual genes (5′UTR, VP4, VP1, 2A, 2B, 2C, 3D, and 3′UTR). The average genetic distances of the genome and individual genes (VP3, 2A, 2B, 2C, 3A, 3C, and 3D) between DL71 and reference strains were greater than 0.1. Nine recombination events involving smaller fragments along DL71 genome were detected. The strains Fuyang-0805a (C4) and Tainan/5746/98 (C2) were identified as the parental strains of DL71. In the non-recombination regions, DL71 had higher identities with Fuyang-0805a than Tainan/5746/98, and located in the cluster with C4 strains. However, in the recombination regions, DL71 had higher identities with Tainan/5746/98 than Fuyang-0805a, and located in the cluster with C2 strains. Thus, DL71 was a novel multiple inter-subgenotype recombinant derived from the dominant subgenotype C4 and the sporadic subgenotype C2 strains. Monitoring the emergence of new variants by the whole-genome sequencing remains essential for preventing disease outbreaks and developing new vaccines.

Genetic diversity and evolution of enterovirus A71 subgenogroup C1 from children with hand, foot, and mouth disease in Thailand

Enterovirus A71 (EV-A71) can cause hand, foot, and mouth disease (HFMD) in children and may be associated with severe neurological complications. There have been numerous reports of increased incidence of EV-A71 subgenogroup C1 (EV-A71 C1) infections associated with neurological diseases since the first occurrence in Germany in 2015. Here, we describe 11 full-length genome sequences of 2019 EV-A71 C1 strains isolated from HFMD patients in Thailand from 2019 to early 2020. The genetic evolution of 2019 EV-A71 C1 was traced in the outbreaks, and the emergence of multiple lineages was detected. Our results demonstrated that 2019 EV-A71 C1 from Thailand emerged through recombination between its nonstructural protein gene and those of other EV-A genotypes. Bayesian-based phylogenetic analysis showed that the 2019 EV-A71 C1 Thai strains share a common ancestor with variants in Europe (Denmark and France). The substitution rate for the 2019 EV-A71 C1 genome was estimated to be 4.38 × 10^-3 substitutions/(site∙year^-1) (95% highest posterior density interval: 3.84-4.94 × 10^-3 substitutions/[site∙year^-1]), approximating that observed between previous EV-A71 C1 outbreaks. These data are essential for understanding the evolution of EV-A C1 during the ongoing HFMD outbreak and may be relevant to disease outcomes in children worldwide.

Natural intertypic and intratypic recombinants of enterovirus 71 from mainland China during 2009-2018: a complete genome analysis

Surveillance of recombinant enterovirus 71 (EV71) and subgenotype replacement is vital for preventing and controlling hand, foot, and mouth disease (HFMD) outbreaks. Despite this, data on recombinant variants and phylogeny of circulating EV71 strains in mainland China are limited. In this study, recombinant variants of EV71 were identified in mainland China from 2009 to 2018. Phylogenetic analysis indicated that except for individual strains (CQ2014-86/CQ/CHN/2014 and EV71/Xiamen/2009 (B5)), almost all of the EV71 strains in mainland China belonged to the subgenotype C4a. Analysing complete genome sequences of 196 EV71 isolates, 3 intertypic recombination strains (VR1432, 30-2/2015/BJ, and Guangdong-2009) and 5 intratypic recombination strains (EV71/P1034/2013, VR1432, Henan-ZMD/CHN/2012, Hubei-WH/CHN/2012, and EV71/P868/2013/China) were identified among naturally circulating EV71. The breakpoints of these recombinant strains were located within the P1, P2, and P3 encoding regions. Notably, a double recombinant (VR1432) resulting from recombination between EV71 subgenotype C4a and C4b strain SHZH98 and a CA8 strain Donovan was identified. This study reports these specific intertypic and intratypic recombination events for the first time highlighting the importance of genetic recombination in the emergence of new enterovirus variants.

Genomic epidemiology of coxsackievirus A16 in mainland of China, 2000-18

Hand, foot, and mouth disease (HFMD), which is a frequently reported and concerning disease worldwide, is a severe burden on societies globally, especially in the countries of East and Southeast Asia. Coxsackievirus A16 (CV-A16) is one of the most important causes of HFMD and a severe threat to human health, especially in children under 5 years of age. To investigate the epidemiological characteristics, spread dynamics, recombinant forms (RFs), and other features of CV-A16, we leveraged the continuous surveillance data of CV-A16-related HFMD cases collected over an 18-year period. With the advent of the EV-A71 vaccine since 2016, which targeted the EV-A71-related HFMD cases, EV-A71-related HFMD cases decreased dramatically, whereas the CV-A16-related HFMD cases showed an upward trend from 2017 to October 2019. The CV-A16 strains observed in this study were genetically related and widely distributed in the mainland of China. Our results show that three clusters (B1a-B1c) existed in the mainland of China and that the cluster of B1b dominates the diffusion of CV-A16 in China. We found that eastern China played a decisive role in seeding the diffusion of CV-A16 in China, with a more complex and variant transmission trend. Although EV-A71 vaccine was launched in China in 2016, it did not affect the genetic diversity of CV-A16, and its genetic diversity did not decline, which confirmed the epidemiological surveillance trend of CV-A16. Two discontinuous clusters (2000-13 and 2014-18) were observed in the full-length genome and arranged along the time gradient, which revealed the reason why the relative genetic diversity of CV-A16 increased and experienced more complex fluctuation model after 2014. In addition, the switch from RFs B (RF-B) and RF-C co-circulation to RF-D contributes to the prevalence of B1b cluster in China after 2008. The correlation between genotype and RFs partially explained the current prevalence of B1b. This study provides unprecedented full-length genomic sequences of CV-A16 in China, with a wider geographic distribution and a long-term time scale. The study presents valuable information about CV-A16, aimed at developing effective control strategies, as well as a call for a more robust surveillance system, especially in the Asia-Pacific region.

Molecular characteristics of the VP1 region of enterovirus 71 strains in China

Background

Enterovirus 71 (EV71) is the most commonly implicated causative agent of severe outbreaks of paediatric hand, foot, and mouth disease (HFMD).VP1 protein, a capsid protein of EV71, is responsible for the genotype of the virus and is essential for vaccine development and effectiveness. However, the genotypes of EV71 isolates in China are still not completely clear.

Methods

The VP1 gene sequences of 3712 EV71 virus strains from China, excluding repetitive sequences and 30 known EV71 genotypes as reference strains, between 1986 and 2019 were obtained from GenBank. Phylogenetic tree, amino acid homology, genetic variation and genotype analyses of the EV71VP1 protein were performed with MEGA 6.0 software.

Results

The amino acid identity was found to be 88.33%–100% among the 3712 EV71 strains, 93.47%–100% compared with vaccine strain H07, and 93.04%–100% compared with vaccine strains FY7VP5 or FY-23 K-B. Since 2000, the prevalent strains of EV71 were mainly of the C4 genotype. Among these, the C4a subgenotype was predominant, followed by the C4b subgenotype; other subgenotypes appeared sporadically between 2005 and 2018 in mainland China. The B4 genotype was the main genotype in Taiwan, and the epidemic strains were constantly changing. Some amino acid variations in VP1 of EV71 occurred with high frequencies, including A289T (20.99%), H22Q (16.49%), A293S (15.95%), S283T (15.11%), V249I (7.76%), N31D (7.25%), and E98K (6.65%).

Conclusion

The C4 genotype of EV71 in China matches the vaccine and should effectively control EV71. However, the efficacy of the vaccine is partially affected by the continuous change in epidemic strains in Taiwan. These results suggest that the genetic characteristics of the EV71-VP1 region should be continuously monitored, which is critical for epidemic control and vaccine design to prevent EV71 infection in children.

Recombination Analysis of Non-Poliovirus Members of the Enterovirus C Species; Restriction of Recombination Events to Members of the Same 3DPol Cluster

Enteroviruses (EVs) are highly prevalent viruses worldwide. Recombination is known to occur frequently in EVs belonging to species Enterovirus A, Enterovirus B, and Enterovirus C. Although many recombinant vaccine-derived poliovirus (VDPV) strains have been reported, our knowledge on recombination in non-polio EVs in the species Enterovirus C is limited. Here, we combined a dataset consisting of 11 newly generated full-length Enterovirus C sequences and 180 publicly available sequences to study recombination dynamics in non-polio EVs. To identify recombination patterns, maximum likelihood phylogenetic trees of different genomic regions were constructed, and segregation analyses were performed. Recombination was observed between members of the same 3DPol cluster, but was rarely observed between members of different clusters. We hypothesize that this restriction may have arisen through their different compartmentalization in respiratory and enteric tracts related to differences in cellular tropisms so that the opportunity to recombine may not be available.

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.

High Permissiveness for Genetic Exchanges between Enteroviruses of Species A, including Enterovirus 71, Favors Evolution through Intertypic Recombination in Madagascar

Human enteroviruses of species A (EV-A) are the leading cause of hand-foot-and-mouth disease (HFMD). EV-A71 is frequently implicated in HFMD outbreaks and can also cause severe neurological manifestations. We investigated the molecular epidemiological processes at work and the contribution of genetic recombination to the evolutionary history of EV-A in Madagascar, focusing on the recently described EV-A71 genogroup F in particular. Twenty-three EV-A isolates, collected mostly in 2011 from healthy children living in various districts of Madagascar, were characterized by whole-genome sequencing. Eight different types were identified, highlighting the local circulation and diversity of EV-A. Comparative genome analysis revealed evidence of frequent recent intra- and intertypic genetic exchanges between the noncapsid sequences of Madagascan EV-A isolates. The three EV-A71 isolates had different evolutionary histories in terms of recombination, with one isolate displaying a mosaic genome resulting from recent genetic exchanges with Madagascan coxsackieviruses A7 and possibly A5 and A10 or common ancestors. The engineering and characterization of recombinants generated from progenitors belonging to different EV-A types or EV-A71 genogroups with distantly related nonstructural sequences indicated a high level of permissiveness for intertypic genetic exchange in EV-A. This permissiveness suggests that the primary viral functions associated with the nonstructural sequences have been highly conserved through the diversification and evolution of the EV-A species. No outbreak of disease due to EV-A has yet been reported in Madagascar, but the diversity, circulation, and evolution of these viruses justify surveillance of EV-A circulation and HFMD cases to prevent possible outbreaks due to emerging strains.IMPORTANCE Human enteroviruses of species A (EV-A), including EV-A71, are the leading cause of hand-foot-and-mouth disease (HFMD) and may also cause severe neurological manifestations. We investigated the circulation and molecular evolution of EV-A in Madagascar, focusing particularly on the recently described EV-A71 genogroup F. Eight different types, collected mostly in 2011, were identified, highlighting the local circulation and diversity of EV-A. Comparative genome analysis revealed evidence of frequent genetic exchanges between the different types of isolates. The three EV-A71 isolates had different evolutionary histories in terms of recombination. The engineering and characterization of recombinants involving progenitors belonging to different EV-A types indicated a high degree of permissiveness for genetic exchange in EV-A. No outbreak of disease due to EV-A has yet been reported in Madagascar, but the diversity, circulation, and evolution of these viruses justify the surveillance of EV-A circulation to prevent possible HFMD outbreaks due to emerging 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.

Hand, foot and mouth disease and herpangina caused by enterovirus A71 infections: a review of enterovirus A71 molecular epidemiology, pathogenesis, and current vaccine development

Enterovirus A71 (EV-A71) infections are one of the main etiological agents of hand, foot and mouth disease (HFMD) and herpangina worldwide. EV-A71 infection is a life-threatening communicable disease and there is an urgent global need for the development of vaccines for its prevention and control. The morbidity rate of EV-A71 infection differs between countries. The pathogen’s genetic lineages are undergoing rapid evolutionary changes. An association between the occurrence of EV-A71 infection and the circulation of different genetic strains of EV-A71 virus has been identified around the world. In this review, we present and discuss the molecular epidemiology and pathogenesis of the human disease caused by EV-A71 infection, as well as current prospects for the development of an EV-A71 vaccine.

Prediction of Protection against Asian Enterovirus 71 Outbreak Strains by Cross-neutralizing Capacity of Serum from Dutch Donors, The Netherlands

Herd immunity induced by locally circulating strains could provide protection against introduction of new strains.

Outbreaks of human enterovirus 71 (EV-71) in Asia are related to high illness and death rates among children. To gain insight into the potential threat for the population of Europe, we determined the neutralizing activity in intravenous immunoglobulin (IVIg) batches and individual serum samples from donors in the Netherlands against EV-71 strains isolated in Europe and in Asia. All IVIg batches and 41%, 79%, and 65% of serum samples from children ≤5 years of age, women of childbearing age, and HIV-positive men, respectively, showed high neutralizing activity against a Dutch C1 strain, confirming widespread circulation of EV-71 in the Netherlands. Asian B3–4 and C4 strains were efficiently cross-neutralized, predicting possible protection against extensive circulation and associated outbreaks of those types in Europe. However, C2 and C5 strains that had few mutations in the capsid region consistently escaped neutralization, emphasizing the importance of monitoring antigenic diversity among circulating EV-71 strains.

Human picornaviruses associated with neurological diseases and their neutralization by antibodies

Picornaviruses are the most commonly encountered infectious agents in mankind. They typically cause mild infections of the gastrointestinal or respiratory tract, but sometimes also invade the central nervous system. There, they can cause severe diseases with long-term sequelae and even be lethal. The most infamous picornavirus is poliovirus, for which significant epidemics of poliomyelitis were reported from the end of the nineteenth century. A successful vaccination campaign has brought poliovirus close to eradication, but neurological diseases caused by other picornaviruses have increasingly been reported since the late 1990s. In this review we focus on enterovirus 71, coxsackievirus A16, enterovirus 68 and human parechovirus 3, which have recently drawn attention because of their links to severe neurological diseases. We discuss the clinical relevance of these viruses and the primary role of humoral immunity in controlling them, and summarize current knowledge on the neutralization of such viruses by antibodies.

Intertypic recombination of human parechovirus 4 isolated from infants with sepsis-like disease

BACKGROUND

Human parechoviruses (HPeVs) (family Picornaviridae), are common pathogens in young children. Despite their high prevalence, research on their genetic identity, diversity and evolution have remained scarce.

OBJECTIVES

Complete coding regions of three previously reported HPeV-4 isolates from Finnish children with sepsis-like disease were sequenced in order to elucidate the phylogenetic relationships and potential recombination events during the evolution of these isolates.

STUDY DESIGN

The isolated viruses were sequenced and aligned with all HPeV complete genome sequences available in GenBank. Phylogenetic trees were constructed and similarity plot and bootscanning methods were used for recombination analysis.

RESULTS

The three HPeV-4 isolates had 99.8% nucleotide sequence similarity. The phylogenetic analysis indicated that capsid-encoding sequences of these HPeV-4 isolates were closely related to other HPeV-4 strains (80.7-94.7% nucleotide similarity), whereas their non-structural region genes 2A to 3C clustered together with several HPeV-1 and HPeV-3 strains, in addition to the HPeV-4 strain K251176-02 (isolated 2002 in the Netherlands), but not with other HPeV-4 strains. However, in 3D-encoding sequence the Finnish HPeV-4 isolates did not cluster with the strain HPeV-4/K251176-02, but instead, formed a distinct group together with several HPeV-1 and HPeV-3 strains. Similarity plot and Bootscan analyses further confirmed intertypic recombination events in the evolution of the Finnish HPeV-4 isolates.

CONCLUSION

Intertypic recombination event(s) have occurred during the evolution of HPeV-4 isolates from children with sepsis-like disease. However, due to the low number of parechovirus complete genomes available, the precise recombination partners could not be detected. The results suggest frequent intratypic recombination among parechoviruses.

Enterovirus-71 genotype C isolated in Peru between 2006 and 2009

Enterovirus-71 (EV71) was first isolated in California, United States in 1969, belongs to the genus Enterovirus, family Picornaviridae. Although infection normally causes mild, often undiagnosed illness, it can cause central nervous system infections that could turn fatal. Based on VP1 gene analysis, EV71 has been classified into six separate genotypes. Although the molecular epidemiology of EV71 has been well described via studies originating from Asia and Europe, it is mostly unknown in South America. From our study, four EV71 isolates from Peru were characterized using phylogenetic methods to determine their relationship with known reference strains. These four Peruvian EV71 isolates from between 2006 and 2009 were analyzed by RT-PCR using primers capable of amplifying the entire VP1 gene. Reference strains representing all six known genotypes were used to determine any recognizable phylogenetic relationships. In fact, all of our isolates clustered together within the genotype C1 lineage- separate from Asian, European, North American, and Australian strains. We present evidence that EV71 genotype C1 exists in Peru, and this is the first such report documenting EV71 genotype C1 circulating in South America. Gathering additional isolates will help elucidate a more complete global epidemiological picture of EV71 infections.

Epidemiological and genetic analysis of hand-foot-mouth disease by enterovirus A71 in Taizhou, P. R. China, between 2010 and 2013

Out of a population of 1,098 enteroviruses (EVs)-positive hand, foot, and mouth disease (HFMD) specimens, 352 were screened positive for EV-A71-accounting for 32.1% of all EV-positive specimens. This percentage denotes EV-A71 as the second major serotype of enteroviruse among HFMD suffers in Taizhou. An epidemic outbreak of EV-A71 among HFMD children was found in Taizhou in the second quarter of 2012. Phylogeny analysis based on the VP1 complete sequences leads us to find a sub-clade (designated TZ1-1) of EV-A71 circulating in Taizhou, whose emergence might be correlated with the epidemic outbreak. This correlation was further supported by the followed two analyses (namely skyline plot of population history and birth-death SIR simulation of epidemic history). And more importantly, at a positively selected site of VP1 caspid, a mutation of N31D was found to be a synapomorphy of TZ1-1 and its occurrence might be correlated with the epidemic outbreak. J. Med. Virol. 89:782-790, 2017. © 2016 Wiley Periodicals, Inc.

The Current Status of the Disease Caused by Enterovirus 71 Infections: Epidemiology, Pathogenesis, Molecular Epidemiology, and Vaccine Development

Enterovirus 71 (EV71) infections have a major public health impact in the Asia-Pacific region. We reviewed the epidemiology, pathogenesis, and molecular epidemiology of EV71 infection as well as EV71 vaccine development. Previous studies were found using the search terms "enterovirus 71" and "epidemiology" or "pathogenesis" or "molecular epidemiology" or "vaccine" in Medline and PubMed. Articles that were not published in the English language, manuscripts without an abstract, and opinion articles were excluded from the review. The reported epidemiology of cases caused by EV71 infection varied from country to country; seasonal variations in incidence were observed. Most cases of EV71 infection that resulted in hospitalization for complications occurred in children less than five years old. The brainstem was the most likely major target of EV71 infection. The emergence of the EV71 epidemic in the Asia-Pacific region has been associated with the circulation of different genetic lineages (genotypes B3, B4, C1, C2, and C4) that appear to be undergoing rapid evolutionary changes. The relationship between the gene structure of the EV71 virus and the factors that ensure its survival, circulation, and evasion of immunity is still unknown. EV71 infection has emerged as an important global public health problem. Vaccine development, including the development of inactivated whole-virus live attenuated, subviral particles, and DNA vaccines, has been progressing.

A Novel Recombinant Enterovirus Type EV-A89 with Low Epidemic Strength in Xinjiang, China

Enterovirus A89 (EV-A89) is a novel member of the EV-A species. To date, only one full-length genome sequence (the prototype strain) has been published. Here, we report the molecular identification and genomic characterization of a Chinese EV-A89 strain, KSYPH-TRMH22F/XJ/CHN/2011, isolated in 2011 from a contact of an acute flaccid paralysis (AFP) patient during AFP case surveillance in Xinjiang China. This was the first report of EV-A89 in China. The VP1 coding sequence of this strain demonstrated 93.2% nucleotide and 99.3% amino acid identity with the EV-A89 prototype strain. In the P2 and P3 regions, the Chinese EV-A89 strain demonstrated markedly higher identity than the prototype strains of EV-A76, EV-A90, and EV-A91, indicating that one or more recombination events between EV-A89 and these EV-A types might have occurred. Long-term evolution of these EV types originated from the same ancestor provides the spatial and temporal circumstances for recombination to occur. An antibody sero-prevalence survey against EV-A89 in two Xinjiang prefectures demonstrated low positive rates and low titres of EV-A89 neutralization antibody, suggesting limited range of transmission and exposure to the population. This study provides a solid foundation for further studies on the biological and pathogenic properties of EV-A89.

Mapping Enterovirus A71 Antigenic Determinants from Viral Evolution

Human enterovirus A71 (EV-A71) belongs to the Enterovirus A species in the Picornaviridae family. Several vaccines against EV-A71, a disease causing severe neurological complications or even death, are currently under development and being tested in clinical trials, and preventative vaccination programs are expected to start soon. To characterize the potential for antigenic change of EV-A71, we compared the sequences of two antigenically diverse genotype B4 and B5 strains of EV-A71 and identified substitutions at residues 98, 145, and 164 in the VP1 capsid protein as antigenic determinants. To examine the effects of these three substitutions on antigenicity, we constructed a series of recombinant viruses containing different mutation combinations at these three residues with a reverse genetics system and then investigated the molecular basis of antigenic changes with antigenic cartography. We found that a novel EV-A71 mutant, containing lysine, glutamine, and glutamic acid at the respective residues 98, 145, and 164 in the VP1 capsid protein, exhibited neutralization reduction against patients' antisera and substantially increased virus binding ability to human cells. These observations indicated that this low-neutralization-reactive EV-A71 VP1-98K/145Q/164E mutant potentially increases viral binding ability and that surveillance studies should look out for these mutants, which could compromise vaccine efficacy.

IMPORTANCE

Emerging and reemerging EV-A71 viruses can cause severe neurological etiology, primarily affecting children, especially around Asia-Pacific countries. We identified a set of mutations in EV-A71 that both reduced neutralization activity against humoral immunity in antisera of patients and healthy adults and greatly increased the viral binding ability to cells. These findings provide important insights for EV-A71 antigenic determinants and emphasize the importance of continuous surveillance, especially after EV-A71 vaccination programs begin.

Nuclear Protein Sam68 Interacts with the Enterovirus 71 Internal Ribosome Entry Site and Positively Regulates Viral Protein Translation

Enterovirus 71 (EV71) recruits various cellular factors to assist in the replication and translation of its genome. Identification of the host factors involved in the EV71 life cycle not only will enable a better understanding of the infection mechanism but also has the potential to be of use in the development of antiviral therapeutics. In this study, we demonstrated that the cellular factor 68-kDa Src-associated protein in mitosis (Sam68) acts as an internal ribosome entry site (IRES) trans-acting factor (ITAF) that binds specifically to the EV71 5' untranslated region (5'UTR). Interaction sites in both the viral IRES (stem-loops IV and V) and the heterogeneous nuclear ribonucleoprotein K homology (KH) domain of Sam68 protein were further mapped using an electrophoretic mobility shift assay (EMSA) and biotin RNA pulldown assay. More importantly, dual-luciferase (firefly) reporter analysis suggested that overexpression of Sam68 positively regulated IRES-dependent translation of virus proteins. In contrast, both IRES activity and viral protein translation significantly decreased in Sam68 knockdown cells compared with the negative-control cells treated with short hairpin RNA (shRNA). However, downregulation of Sam68 did not have a significant inhibitory effect on the accumulation of the EV71 genome. Moreover, Sam68 was redistributed from the nucleus to the cytoplasm and interacts with cellular factors, such as poly(rC)-binding protein 2 (PCBP2) and poly(A)-binding protein (PABP), during EV71 infection. The cytoplasmic relocalization of Sam68 in EV71-infected cells may be involved in the enhancement of EV71 IRES-mediated translation. Since Sam68 is known to be a RNA-binding protein, these results provide direct evidence that Sam68 is a novel ITAF that interacts with EV71 IRES and positively regulates viral protein translation.

IMPORTANCE

The nuclear protein Sam68 is found as an additional new host factor that interacts with the EV71 IRES during infection and could potentially enhance the translation of virus protein. To our knowledge, this is the first report that describes Sam68 actively participating in the life cycle of EV71 at a molecular level. These studies will not only improve our understanding of the replication of EV71 but also have the potential for aiding in developing a therapeutic strategy against EV71 infection.

Phylogenetic analysis of the major causative agents of hand, foot and mouth disease in Suzhou City, Jiangsu province, China, in 2012-2013

Hand, foot and mouth disease (HFMD) is a serious public health problem that has emerged over the past several decades. Pathogen detection by the Chinese national HFMD surveillance system has focused mainly on enterovirus 71 (EV71) and coxsackievirus A16 (CA16). Therefore, epidemiological information regarding the other causative enteroviruses is limited. To identify the pandemic enterovirus in Suzhou, Jiangsu province, China, clinical samples from patients with HFMD were collected from 2012 to 2013 and analyzed. The results revealed that CA16 was the most dominant HFMD pathogen in 2012, whereas CA6 and CA10 were the dominant pathogens in 2013. Phylogenetic analysis revealed that the C4a sub-genogroup of EV71 and the B1a and B1b sub-genogroups of CA16 continued to evolve and circulate in Suzhou. The CA6 strains were assigned to six genotypes (A–F) and the CA10 strains were assigned to seven genotypes (A–G), with clear geographical and temporal distributions. All of the CA6 strains in Suzhou belonged to genogroup F, and there were several lineages circulating in Suzhou. All of the CA10 strains in Suzhou belonged to genogroup G, and they had the same genetic origin. Co-infections of EV71/CA16 and CA6/CA10 were found in the samples, and bootscan analysis of 5′-untranslated regions (UTRs) revealed that some CA16 strains in Suzhou had genetic recombination with EV71. This property might allow CA16 to alter its evolvability and circulating ability. This study underscores the need for surveillance of CA6 and CA10 in the Yangtze River Delta and East China.

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.

Mutations in the non-structural protein region contribute to intra-genotypic evolution of enterovirus 71

Background

Clinical manifestations of enterovirus 71 (EV71) range from herpangina, hand-foot-and-mouth disease (HFMD), to severe neurological complications. Unlike the situation of switching genotypes seen in EV71 outbreaks during 1998–2008 in Taiwan, genotype B5 was responsible for two large outbreaks in 2008 and 2012, respectively. In China, by contrast, EV71 often persists as a single genotype in the population and causes frequent outbreaks. To investigate genetic changes in viral evolution, complete EV71 genome sequences were used to analyze the intra-genotypic evolution pattern in Taiwan, China, and the Netherlands.

Results

Genotype B5 was predominant in Taiwan’s 2008 outbreak and was re-emergent in 2012. EV71 strains from both outbreaks were phylogenetically segregated into two lineages containing fourteen non-synonymous substitutions predominantly in the non-structural protein coding region. In China, genotype C4 was first seen in 1998 and caused the latest large outbreak in 2008. Unlike shifting genotypes in Taiwan, genotype C4 persisted with progressive drift through time. A majority of non-synonymous mutations occurred in residues located in the non-structural coding region, showing annual increases. Interestingly, genotype B1/B2 in the Netherlands showed another stepwise evolution with dramatic EV71 activity increase in 1986. Phylogeny of the VP1 coding region in 1971–1986 exhibited similar lineage turnover with genotype C4 in China; however, phylogeny of the 3D-encoding region indicated separate lineage appearing after 1983, suggesting that the 3D-encoding region of genotype B2 was derived from an unidentified ancestor that contributed to intra-genotypic evolution in the Netherlands.

Conclusions

Unlike VP1 coding sequences long used for phylogenetic study of enteroviruses due to expected host immune escape, our study emphasizes a dominant role of non-synonymous mutations in non-structural protein regions that contribute to (re-)emergent genotypes in continuous stepwise evolution. Dozens of amino acid substitutions, especially in non-structural proteins, were identified via genetic changes driven through intra-genotypic evolution worldwide. These identified substitutions appeared to increase viral fitness in the population, affording valuable insights not only for viral evolution but also for prevention, control, and vaccine against EV71 infection.

Recombination in the evolution of enterovirus C species sub-group that contains types CVA-21, CVA-24, EV-C95, EV-C96 and EV-C99

Genetic recombination is considered to be a very frequent phenomenon among enteroviruses (Family Picornaviridae, Genus Enterovirus). However, the recombination patterns may differ between enterovirus species and between types within species. Enterovirus C (EV-C) species contains 21 types. In the capsid coding P1 region, the types of EV-C species cluster further into three sub-groups (designated here as A–C). In this study, the recombination pattern of EV-C species sub-group B that contains types CVA-21, CVA-24, EV-C95, EV-C96 and EV-C99 was determined using partial 5′UTR and VP1 sequences of enterovirus strains isolated during poliovirus surveillance and previously published complete genome sequences. Several inter-typic recombination events were detected. Furthermore, the analyses suggested that inter-typic recombination events have occurred mainly within the distinct sub-groups of EV-C species. Only sporadic recombination events between EV-C species sub-group B and other EV-C sub-groups were detected. In addition, strict recombination barriers were inferred for CVA-21 genotype C and CVA-24 variant strains. These results suggest that the frequency of inter-typic recombinations, even within species, may depend on the phylogenetic position of the given viruses.

Recombination strategies and evolutionary dynamics of the Human enterovirus A global gene pool

We analysed natural recombination in 79 Human enterovirus A strains representing 13 serotypes by sequencing of VP1, 2C and 3D genome regions. The half-life of a non-recombinant tree node in coxsackieviruses 2, 4 and 10 was only 3.5 years, and never more than 9 years. All coxsackieviruses that differed by more than 7 % of the nucleotide sequence in any genome region were recombinants relative to each other. Enterovirus 71 (EV71), on the contrary, displayed remarkable genetic stability. Three major EV71 clades were stable for 19-29 years, with a half-life of non-recombinant viruses between 13 and 18.5 years in different clades. Only five EV71 strains out of over 150 recently acquired non-structural genome regions from coxsackieviruses, while none of 80 contemporary coxsackieviruses had non-structural genes transferred from the three EV71 clades. In contrast to earlier observations, recombination between VP1 and 2C genome regions was not more frequent than between 2C and 3D regions.

Spatio-temporal analysis on enterovirus cases through integrated surveillance in Taiwan

Background

Severe epidemics of enterovirus have occurred frequently in Malaysia, Singapore, Taiwan, Cambodia, and China, involving cases of pulmonary edema, hemorrhage and encephalitis, and an effective vaccine has not been available. The specific aim of this study was to understand the epidemiological characteristics of mild and severe enterovirus cases through integrated surveillance data.

Methods

All enterovirus cases in Taiwan over almost ten years from three main databases, including national notifiable diseases surveillance, sentinel physician surveillance and laboratory surveillance programs from July 1, 1999 to December 31, 2008 were analyzed. The Pearson’s correlation coefficient was applied for measuring the consistency of the trends in the cases between different surveillance systems. Cross correlation analysis in a time series model was applied for examining the capability to predict severe enterovirus infections. Poisson temporal, spatial and space-time scan statistics were used for identifying the most likely clusters of severe enterovirus outbreaks. The directional distribution method with two standard deviations of ellipse was applied to measure the size and the movement of the epidemic.

Results

The secular trend showed that the number of severe EV cases peaked in 2008, and the number of mild EV cases was significantly correlated with that of severe ones occurring in the same week [r = 0.553, p < 0.01]. These severe EV cases showed significantly higher association with the weekly positive isolation rates of EV-71 than the mild cases [severe: 0.498, p < 0.01 vs. mild: 0.278, p < 0.01]. In a time series model, the increase of mild EV cases was the significant predictor for the occurrence of severe EV cases. The directional distribution showed that both the mild and severe EV cases spread extensively during the peak. Before the detected spatio-temporal clusters in June 2008, the mild cases had begun to rise since May 2008, and the outbreak spread from south to north.

Conclusions

Local public health professionals can monitor the temporal and spatial trends plus spatio-temporal clusters and isolation rate of EV-71 in mild and severe EV cases in a community when virus transmission is high, to provide early warning signals and to prevent subsequent severe epidemics.

Human enterovirus 71 epidemics: what's next?

Human enterovirus 71 (EV71) epidemics have affected various countries in the past 40 years. EV71 commonly causes hand, foot and mouth disease (HFMD) in children, but can result in neurological and cardiorespiratory complications in severe cases. Genotypic changes of EV71 have been observed in different places over time, with the emergence of novel genotypes or subgenotypes giving rise to serious outbreaks. Since the late 1990s, intra- and inter-typic recombination events in EV71 have been increasingly reported in the Asia-Pacific region. In particular, 'double-recombinant' EV71 strains belonging to a novel genotype D have been predominant in mainland China and Hong Kong over the last decade, though co-circulating with a minority of other EV71 subgenotypes and coxsackie A viruses. Continuous surveillance and genome studies are important to detect potential novel mutants or recombinants in the near future. Rapid and sensitive molecular detection of EV71 is of paramount importance in anticipating and combating EV71 outbreaks.

Multilocus sequence typing reveals evidence of homologous recombination linked to antibiotic resistance in the genus Salinispora

The three closely related species that currently comprise the genus Salinispora were analyzed using a multilocus sequence typing approach targeting 48 strains derived from four geographic locations. Phylogenetic congruence and a well-supported concatenated tree provide strong support for the delineation of the three species as currently described and the basal relationship of Salinispora arenicola to the more recently diverged sister taxa S. tropica and S. pacifica. The phylogeny of the initial region of the rpoB gene sequenced was atypical, placing the related genera Micromonospora and Verrucosispora within the Salinispora clade. This phylogenetic incongruence was subsequently ascribed to a homologous-recombination event in a portion of the gene associated with resistance to compounds in the rifamycin class, which target RpoB. All S. arenicola strains produced compounds in this class and possessed resistance-conferring amino acid changes in RpoB. The phylogeny of a region of the rpoB gene that is not associated with rifamycin resistance was congruent with the other housekeeping genes. The link between antibiotic resistance and homologous recombination suggests that incongruent phylogenies provide opportunities to identify the molecular targets of secondary metabolites, an observation with potential relevance for drug discovery efforts. Low ratios of interspecies recombination to mutation, even among cooccurring strains, coupled with high levels of within-species recombination suggest that the three species have been described in accordance with natural barriers to recombination.

What we are watching--five top global infectious disease threats, 2012: a perspective from CDC's Global Disease Detection Operations Center

Disease outbreaks of international public health importance continue to occur regularly; detecting and tracking significant new public health threats in countries that cannot or might not report such events to the global health community is a challenge. The Centers for Disease Control and Prevention's (CDC) Global Disease Detection (GDD) Operations Center, established in early 2007, monitors infectious and non-infectious public health events to identify new or unexplained global public health threats and better position CDC to respond, if public health assistance is requested or required. At any one time, the GDD Operations Center actively monitors approximately 30-40 such public health threats; here we provide our perspective on five of the top global infectious disease threats that we were watching in 2012: 1 avian influenza A (H5N1), 2 cholera, 3 wild poliovirus, 4 enterovirus-71, and 5 extensively drug-resistant tuberculosis11†Current address: Division of Integrated Biosurveillance, Armed Forces Health Surveillance Center, US Department of Defense, Silver Spring, MD, USA.

Specific primer amplification of the VP1 region directed by 5' UTR sequence analysis: enterovirus testing and identification in clinical samples from hand-foot-and-mouth disease patients

Many genotypes of the enterovirus (EV) pathogens can cause clinical hand-foot-and-mouth disease (HFMD). Therefore, rapid identification and monitoring of HFMD pathogens can be difficult, especially from the original clinical specimens. In this study, both universal pan-enterovirus and EV71/CA16 VP1-specific primer sets were designed and used to examine clinical specimens from HFMD patients. Based on the initial sequence analysis of the 5'-untanslated region (5'-UTR) and VP1 amplification products, additional primers for the VP1 region were redesigned for further genotyping of the remaining small portion non-EV71/non-CA16 specimens. With a known panel, it was possible to identify 15 out of 16 members using 5'-UTR sequence typing and VP1 typing, suggesting good detectability and genotyping of this method. One strain that was not typed by 5'-UTR was shown to be a recombinant virus. When this method was applied to examine clinical specimens from 44 suspected HFMD patients, 41 were detected as EV positive. In only one case, the VP1 sequence could not be identified. Four types of EVs, including CA16 (26/41, 63.4%), EV71-C4 (6/41, 14.6%), CA6 (5/41, 12.2%) and CA10 (3/41, 7.3%), were detected. In conclusion, 5' UTR amplification sequencing and subsequent VP1 specific primer amplification ensures a high detection rate and good genotyping accuracy in the examination of clinical samples. This detection strategy can be used for routine evaluation and monitoring of HFMD to follow local trends of EV infection.

Human enterovirus 71 strains in the background population and in hospital patients in Finland

BACKGROUND

Human enterovirus 71 (HEV71) is a common cause of severe outbreaks of hand-foot- and mouth disease, aseptic meningitis and encephalitis in Asian populations but has not caused such epidemics in all populations.

OBJECTIVES

To analyze the frequency of HEV71 in the background childhood population in Finland by screening in stool and serum samples and by measuring neutralizing antibodies against HEV71 in serum and to compare the genetic relationship of virus strains detected in asymptomatic children and those causing severe illness in Finland to the strains found in other countries.

STUDY DESIGN

4185 stool samples and 5686 serum samples were collected and clinical symptoms recorded from children who were observed from birth. Additional stool samples were available from four children hospitalized due to EV71 infection. Samples were screened for the presence of RNA of human enteroviruses using RT-PCR and HEV71 amplicons were identified by sequencing. Phylogenetic analyses were carried out to study genetic relationships between different virus strains. Neutralizing antibodies against HEV71 were screened from 522 children.

RESULTS

A total of 0.3% of stool samples and two serum samples from healthy children were positive for HEV71 genome. 1.6% of the children had neutralizing antibodies against HEV71. Most infections were asymptomatic or mild in contrast to the clear symptoms in the children hospitalized due to HEV71. All viruses were C strains.

CONCLUSIONS

HEV71 is circulating in Finland but it is rare. No clear difference was seen between strains circulating in the Finnish background population and those found in hospitalized patients or those causing severe outbreaks worldwide.

The Pathogenesis and Prevention of Encephalitis due to Human Enterovirus 71

Human enterovirus 71 (HEV71) has emerged as a major cause of viral encephalitis in Southeast Asia, with increased epidemic activity observed since 1997. This is reflected in a large increase in scientific publications relating directly to HEV71. New research is elucidating details of the viral life cycle, confirming similarities between HEV71 and other enteroviruses. Scavenger receptor B2 (SCARB2) is a receptor for HEV71, although other receptors are likely to be identified. Currently, the only strategies to prevent HEV71-associated disease are early diagnosis and aggressive supportive management of identified cases. As more information emerges regarding the molecular processes of HEV71 infection, further advances may lead to the development of effective antiviral treatments and ultimately a vaccine-protection strategy. The protective efficacies of several inactivated HEV71 vaccines have been confirmed in animal models, suggesting that an effective vaccine may become available in the next decade.

Recent advances in the molecular epidemiology and control of human enterovirus 71 infection

Human enterovirus 71 (HEV71) has emerged as an important cause of viral encephalitis in the Southeast Asia over the past 15 years. A pattern of increased epidemic activity and endemic circulation of HEV71 has been observed since 1997 and is associated with the regular emergence of new genetic lineages. Although the reason for this increase in HEV71 circulation remains unknown, evidence is accumulating that recombination events may drive the evolution of new genetic lineages. Prevention of HEV71 epidemics is likely to require the development of an effective vaccine. Fortunately, several candidate EV71 vaccines have recently been reported, several of which have been shown to be effective in animal models and commenced clinical trial in 2010. Furthermore, ongoing investigations into the molecular basis of HEV71 infection and virulence have pointed the way towards novel approaches to live attenuated vaccine development.

The association of recombination events in the founding and emergence of subgenogroup evolutionary lineages of human enterovirus 71

Enterovirus 71 (EV71) is responsible for frequent large-scale outbreaks of hand, foot, and mouth disease worldwide and represent a major etiological agent of severe, sometimes fatal neurological disease. EV71 variants have been classified into three genogroups (GgA, GgB, and GgC), and the latter two are further subdivided into subgenogroups B1 to B5 and C1 to C5. To investigate the dual roles of recombination and evolution in the epidemiology and transmission of EV71 worldwide, we performed a large-scale genetic analysis of isolates (n = 308) collected from 19 countries worldwide over a 40-year period. A series of recombination events occurred over this period, which have been identified through incongruities in sequence grouping between the VP1 and 3Dpol regions. Eleven 3Dpol clades were identified, each specific to EV71 and associated with specific subgenogroups but interspersed phylogenetically with clades of coxsackievirus A16 and other EV species A serotypes. The likelihood of recombination increased with VP1 sequence divergence; mean half-lives for EV71 recombinant forms (RFs) of 6 and 9 years for GgB and GgC overlapped with those observed for the EV-B serotypes, echovirus 9 (E9), E30, and E11, respectively (1.3 to 9.8 years). Furthermore, within genogroups, sporadic recombination events occurred, such as the linkage of two B4 variants to RF-W instead of RF-A and of two C4 variants to RF-H. Intriguingly, recombination events occurred as a founding event of most subgenogroups immediately preceding their lineage expansion and global emergence. The possibility that recombination contributed to their subsequent spread through improved fitness requires further biological and immunological characterization.