Molecular typing and characterization of a new serotype of human enterovirus (EV-B111) identified in China

Evolutionary Diversity of Coxsackievirus A6 Causing Severe Hand, Foot, and Mouth Disease - China, 2012-2023

Introduction

Coxsackievirus A6 (CVA6) has emerged as a significant pathogen responsible for severe cases of hand, foot, and mouth disease (HFMD). This study aims to delineate the demographic characteristics and analyze the viral evolution of severe HFMD associated with CVA6, thereby assisting in its surveillance and management.

Methods

In this investigation, 74 strains of CVA6 were isolated from samples collected from severe HFMD cases between 2012 and 2023. The VP1 gene sequences of CVA6 were amplified and analyzed to assess population historical dynamics and evolutionary characteristics using BEAST, DnaSP6, and PopART.

Results

A significant portion (94.4%) of severe CVA6-associated HFMD cases (51 out of 54, with 20 lacking age information) were children under 5 years old. Among the 74 CVA6 strains analyzed, 72 belonged to the D3a sub-genotype, while only two strains were D2 sub-genotype. The average genetic distance between VP1 sequences prior to 2015 was 0.027, which increased to 0.051 when compared to sequences post-2015. Historical population dynamics analysis indicated three significant population expansions of severe CVA6-associated HFMD during 2012-2013, 2013-2014, and 2019-2020, resulting in the formation of 65 distinct haplotypes. Consistent with the MCC tree findings, transitioning between regional haplotypes required multiple base substitutions, showcasing an increase in population diversity during the evolutionary process (from 14 haplotypes in 2013 to 55 haplotypes over the subsequent decade).

Conclusions

CVA6, associated with severe HFMD, is evolving and presents a risk of outbreak occurrence. Thus, enhanced surveillance of severe HFMD is imperative.

Genetic characterization and molecular epidemiological analysis of enterovirus C99 in China

Enterovirus C99 (EV-C99) is a newly identified EV serotype within the species Enterovirus C. Few studies on EV-C99 have been conducted globally. More information and research on EV-C99 are needed to assess its genetic characteristics, phylogenetic relationships, and associations with enteroviral diseases. Here, the phylogenetic characteristics of 11 Chinese EV-C99 strains have been reported. The full-length genomic sequences of these 11 strains show 79.4-80.5% nucleotide identity and 91.7-94.3% amino acid (aa) identity with the prototype EV-C99. A maximum likelihood phylogenetic tree constructed based on the entire VP1 coding region identified 13 genotypes (A-M), revealing a high degree of variation among the EV-C99 strains. Phylogeographic analysis showed that the Xinjiang Uygur Autonomous Region is an important source of EV-C99 epidemics in various regions of China. Recombination analysis revealed inter-serotype recombination events of 16 Chinese EV-C99 strains in 5' untranslated regions and 3D regions, resulting in the formation of a single recombination form. Additionally, the Chinese strain of genotype J showed rich aa diversity in the P1 region, indicating that the genotype J of EV-C99 is still going through variable dynamic changes. This study contributes to the global understanding of the EV-C99 genome sequence and holds substantial implications for the surveillance of EV-C99.

Molecular Characteristics and Genetic Evolution of Echovirus 33 in Mainland of China

Echovirus, a member of the Enterovirus B (EV-B) family, has led to numerous outbreaks and pandemics, causing a broad spectrum of diseases. Based on the national hand, foot, and mouth disease (HFMD) surveillance system, seven strains of echovirus 33 (E33) were isolated from Mainland of China between 2010 and 2018. The whole genomes of these strains were isolated and sequenced, and phylogenetic trees were constructed based on the gene sequences in different regions of the EV-B prototype strains. It was found that E33 may be recombined in the P2 and P3 regions. Five genotypes (A–E) were defined based on the entire VP1 region of E33, of which the C gene subtype was the dominant gene subtype at present. Recombinant analysis showed that genotype C strains likely recombined with EV-B80, EV-B85, E13, and CVA9 in the P2 and P3 regions, while genotype E had the possibility of recombination with CVB3, E3, E6, and E4. Results of Bayesian analysis indicated that E33 may have appeared around 1955 (95% confidence interval: 1945–1959), with a high evolutionary rate of 1.11 × 10⁻² substitution/site/year (95% highest posterior density (HPD): 8.17 × 10⁻³ to 1.4 × 10⁻² substitution/site/year). According to spatial transmission route analysis, two significant transmission routes were identified: from Australia to India and from Oman to Thailand, which the E33 strain in Mainland of China likely introduced from Mexico and India. In conclusion, our study fills the gaps in the evolutionary analysis of E33 and can provide important data for enterovirus surveillance.

A novel interspecies recombinant enterovirus (Enterovirus A120) isolated from a case of acute flaccid paralysis in China

EV-A120 is a recently identified serotype of the enterovirus A species. Only one full-length genomic sequence is currently available in GenBank, and very few studies have been conducted on EV-A120 globally. Thus, additional information and research on EV-A120 are needed to explore its genetic characteristics, phylogeny, and relationship with enteroviral disease. In this study, we report the phylogenetic characteristics of a EV-A120 strain (Q0082/XZ/CHN/2000) from Tibet, China. The amino acid sequence similarity and nucleotide sequence similarity of the full-length genomic sequence of this EV-A120 strain and the EV-A120 prototype strain were 96.3% and 79.9%, respectively, showing an evolutionary trend. Recombination analysis found intraspecies recombination in the 5′ -UTR, 2B, 2C, and 3D regions. Serum neutralization testing of the EV-A120 (Q0082) strain was also carried out. Low serum-positive rates and geometric mean titres (GMTs) indicated that the extent of EV-A120 transmission and exposure in the population was very limited compared with that in the outbreaks of EV-A71 and CV-A16 in China since 2008. The EV-A120 strain (Q0082) is non-temperature sensitive, indicating its potential to spread in the population. In summary, this study reports the full-length genomic sequence of EV-A120 and provides important information for its global molecular epidemiology.

Molecular Epidemiological, Serological, and Pathogenic Analysis of EV-B75 Associated With Acute Flaccid Paralysis Cases in Tibet, China

Enterovirus B75 (EV-B75) is a newly identified serotype of the enterovirus B species. To date, only 112 cases related to EV-B75 have been reported worldwide, and research on EV-B75 is still limited with only two full-length genome sequences available in GenBank. The present study reported seven EV-B75 sequences from a child with acute flaccid paralysis and six asymptomatic close contacts in Shigatse, Tibet. Phylogenetic analysis revealed that the Tibetan strain was possibly imported from neighboring India. Seroepidemiological analyses indicated that EV-B75 has not yet caused a large-scale epidemic in Tibet. Similarity plots and boot scanning analyses revealed frequent intertypic recombination in the non-structural region of all seven Tibet EV-B75 strains. All seven Tibetan strains were temperature-sensitive, suggesting their poor transmissibility in the environment. Overall, though the seven Tibetan strains did not cause large-scale infection, prevention and control of the novel enterovirus cannot be underestimated.

Epidemiology and Sequence-Based Evolutionary Analysis of Circulating Non-Polio Enteroviruses

Enteroviruses (EVs) are positive-sense RNA viruses, with over 50,000 nucleotide sequences publicly available. While most human infections are typically associated with mild respiratory symptoms, several different EV types have also been associated with severe human disease, especially acute flaccid paralysis (AFP), particularly with endemic members of the EV-B species and two pandemic types—EV-A71 and EV-D68—that appear to be responsible for recent widespread outbreaks. Here we review the recent literature on the prevalence, characteristics, and circulation dynamics of different enterovirus types and combine this with an analysis of the sequence coverage of different EV types in public databases (e.g., the Virus Pathogen Resource). This evaluation reveals temporal and geographic differences in EV circulation and sequence distribution, highlighting recent EV outbreaks and revealing gaps in sequence coverage. Phylogenetic analysis of the EV genus shows the relatedness of different EV types. Recombination analysis of the EV-A species provides evidence for recombination as a mechanism of genomic diversification. The absence of broadly protective vaccines and effective antivirals makes human enteroviruses important pathogens of public health concern.

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 typing and characterization of a novel genotype of EV-B93 isolated from Tibet, China

EV-B93 is a novel serotype within the Enterovirus B species and is uncommon worldwide. Currently, only one full-length genomic sequence (the prototype strain) has been deposited in the GenBank database. In this study, three EV-B93 were identified, including one from an acute flaccid paralysis (AFP) patient (named 99052/XZ/CHN/1999, hereafter XZ99052) and two from healthy children (named 99096/XZ/CHN/1999 and 99167/XZ/CHN/1999, hereafter XZ99096 and XZ99167, respectively) from Tibet in 1999 during the polio eradication program. The identity between the nucleotide and amino acid sequences of the Tibet EV-B93 strain and the EV-B93 prototype strain is 83.2%–83.4% and 96.8%–96.9%, respectively. The Tibet EV-B93 strain was found to have greater nucleotide sequence identity in the P3 region to another enterovirus EV-B107 as per a phylogenetic tree analysis, which revealed that recombination occurred. Seroepidemiology data showed that EV-B93 has not produced an epidemic in Tibet and there may be susceptible individuals. The three Tibet EV-B93 strains are temperature-resistant with prognosticative virulence, suggesting the possibility of a potential large-scale outbreak of EV-B93. The analyzed EV-B93 strains enrich our knowledge about this serotype and provide valuable information on global EV-B93 molecular epidemiology. What is more, they permit the appraisal of the serotype's potential public health impact and aid in understanding the role of recombination events in the evolution of enteroviruses.

A Large-Scale Outbreak of Echovirus 30 in Gansu Province of China in 2015 and Its Phylodynamic Characterization

Background

Echovirus 30 (E-30) has been investigated and reported worldwide and is closely associated with several infectious diseases, including encephalitis; myocarditis; and hand, foot, and mouth disease. Although many E-30 outbreaks associated with encephalitis have been reported around the world, it was not reported in northwest China until 2015.

Methods

The clinical samples, including the feces, serum, throat swabs, and cerebrospinal fluid, were collected for this study and were analyzed for diagnosis. E-30 was isolated and processed according to the standard procedures. The epidemiological and phylogenetic analysis were performed to indicate the characteristics of E-30 outbreaks and phylodynamics of E-30 in China.

Results

The E-30 outbreaks affected nine towns of Gansu Province in 2015, starting at a school of Nancha town and spreading to other towns within 1 month. The epidemiological features showed that children aged 6–15 years were more susceptible to E-30 infection. The genotypes B and C cocirculated in the world, whereas the latter dominated the circulation of E-30 in China. The genome sequences of this outbreak present 99.3–100% similarity among these strains, indicating a genetic-linked aggregate outbreak of E-30 in this study. Two larger genetic diversity expansions and three small fluctuations of E-30 were observed from 1987 to 2016 in China, which revealed the oscillating patterns of E-30 in China. In addition, the coastal provinces of China, such as Zhejiang, Fujian, and Shandong, were initially infected, followed by other parts of the country. The E-30 strains isolated from mainland of China may have originated from Taiwan of China in the last century.

Conclusion

The highly similar E-30 genomes in this outbreak showed an aggregate outbreak of E-30, with nine towns affected. Our results suggested that, although the genetic diversity of E-30 oscillates, the dominant lineages of E-30 in China has complex genetic transmission. The coastal provinces played an important role in E-30 spread, which implied further development of effective countermeasures. This study provides a further insight into the E-30 outbreak and transmission and illustrates the importance of valuable surveillance in the future.

Phylogenetic characteristics and molecular epidemiological analysis of novel enterovirus EV-B83 isolated from Tibet, China

Enterovirus B83 (EV-B83) is a new member of the enterovirus B group. Currently, there are only two full-length genomic sequences of EV-B83 in the GenBank database and few VP1 region sequences. The aetiology and epidemiology of EV-B83 is unclear. 24 stool specimens were collected from twelve AFP patients and 298 stool specimens were collected from 298 healthy children in support of polio eradication activities in Tibet in 1999. Two polioviruses (isolated by L20B cell) and one non-polio enterovirus (isolated by RD cell) were isolated from AFP patients and nine polioviruses (isolated by L20B cell) and 90 non-polio enteroviruses (isolated by RD cell) were isolated from health children. Through molecular typing, we confirmed that the six of non-polio enteroviruses belong to EV-B83. The sequence similarity between the VP1 region of the Tibet isolates and that of the EV-B83 prototype strain was 80%. The maximum-likelihood phylogenetic tree of the partial VP1 region in EV-B83 demonstrated that EV-B83 formed four genotypes globally during the evolution process. The six Tibet EV-B83 strains formed the D genotype alone. Recombination analysis of Tibet EV-B83 showed that CV-B4, CV-A9, EV-B80, and EV-B106 may act as recombinant donors in multiple regions. The serum neutralization test showed that the antibody-positive rate was 58.8% and GMT was 1:19.70, which was higher than the previously reported results of EV-B106 and EV-B80. Temperature sensitivity test results showed that the six Tibet EV-B83 strains were temperature-insensitive with stronger virulence and potential infectivity, which was consistent with the results of the serum neutralization test. This study enriched the genome-wide sequence, epidemiological characteristics, and provided basic data for the follow-up study of EV-B83.

Genetic characterization and molecular epidemiological analysis of novel enterovirus EV-B80 in China

Enterovirus B80 (EV-B80) is a newly identified serotype belonging to the enterovirus B species. To date, only two full-length genomic sequences of EV-B80 are available in GenBank, and few studies on EV-B80 have been conducted in China or worldwide. More information and research on EV-B80 is needed to assess its genetic characteristics, phylogenetic relationships, and association with enteroviral diseases. In this study, we report the phylogenetic characteristics of three Xinjiang EV-B80 strains and one Tibet EV-B80 strain in China. The full-length genomic sequences of four strains show 78.8-79% nucleotide identity and 94-94.2% amino acid identity with the prototype of EV-B80, indicating a tendency for evolution. Based on a maximum likelihood phylogenetic tree based on the entire VP1 region, three genotypes (A-C) were defined, revealing the possible origin of EV-B80 strains in the mainland of China. Recombination analysis revealed intraspecies recombinations in all four EV-B80 strains in nonstructural regions along with two recombination patterns. Due to the geographic factor, the coevolution of EV-B strains formed two different patterns of circulation. An antibody seroprevalence study against EV-B80 in two Xinjiang prefectures also showed that EV-B80 strains were widely prevalent in Xinjiang, China, compared to other studies on EV-B106 and EV-B89. All four EV-B80 strains are not temperature sensitive, showing a higher transmissibility in the population. In summary, this study reports the full-length genomic sequences of EV-B80 and provides valuable information on global EV-B80 molecular epidemiology.

Antigenic characteristics and genomic analysis of novel EV-A90 enteroviruses isolated in Xinjiang, China

Enterovirus A90 (EV-A90) is a novel serotype of enterovirus A species that is rarely reported. Here, we isolated five enteroviruses from patients with acute flaccid paralysis in Hotan and Kashgar cities in Xinjiang, China that were identified as EV-A90 by molecular typing. The VP1 sequences of these Xinjiang EV-A90 strains showed 88.4–89% nucleotide sequence identity to the prototype EV-A90 strain; however, genome analysis indicated complex recombination events in P2 and P3 regions. Next, the seroprevalence of EV-A90 was examined in 49 serum specimens collected in Hotan and Kashgar, and 37.5% were EV-A90 antibody positive (>1:8), with a geometric mean titre (GMT) of 1:10.47. The low positive rate and GMT suggest a low-level EV-A90 epidemic in Xinjiang. Two of the five Xinjiang EV-A90 strains were temperature sensitive, and three were temperature resistant, and a comparative genomics analysis suggested that an amino acid substitution (H1799Y) in the 3D^pol region was related to temperature sensitivity. Although the epidemic strength is low, some EV-A90 strains were temperature resistant, which is suggestive of strong virulence and transmission capacity. This study expanded the number of EV-A90 in GenBank and provided basic data that may be useful for studying the molecular epidemiology of EV-A90.

Molecular characterization of two novel echovirus 18 recombinants associated with hand-foot-mouth disease

Human echovirus 18 (E-18) is a member of the enterovirus B species. To date, sixteen full-length genome sequences of E-18 are available in the GenBank database. In this study, we describe the complete genomic characterization of two E-18 strains isolated in Yunnan, China. Pairwise comparisons of the nucleotide sequences and the deduced amino acid sequences revealed that the two Yunnan E-18 strains had 87.5% nucleotide identity and 96.3–96.5% amino acid identity with the Chinese strain. Phylogenetic and bootscanning analyses revealed the two E-18 strains had the highest identity with other several EV-B serotypes than the other E-18 strains in the P3 coding region, especially, 3B region of the Swine Vesicular disease virus (SVDV) strain HK70, indicated that frequent intertypic recombination might have occurred in the two Yunnan strains. This study contributes the complete genome sequences of E-18 to the GenBank database and provides valuable information on the molecular epidemiology of E-18 in China.

Preponderance of enterovirus C in RD-L20B-cell-culture-negative stool samples from children diagnosed with acute flaccid paralysis in Nigeria

Recently, a reverse transcriptase semi-nested polymerase chain reaction (RT-snPCR) assay was recommended by the WHO for direct detection of enteroviruses in clinical specimens. In this study, we use this assay and a modification thereof to screen acute flaccid paralysis (AFP) samples that had previously tested negative for enteroviruses by the RD-L20B algorithm. Thirty paired stool suspensions collected in 2015 as part of the national AFP surveillance program in different states of Nigeria were analyzed in this study. The samples had previously tested negative for enteroviruses in the polio laboratory in accordance with the WHO-recommended RD-L20B-cell-culture-based algorithm. Two samples that had previously been found to contain enteroviruses were included as positive controls. All samples were subjected to RNA extraction, the RT-snPCR assay and a modified version of the RT-snPCR. All amplicons were sequenced, and enteroviruses were identified using the enterovirus genotyping tool and phylogenetic analysis. Amplicons were recovered from the two controls and 50% (15/30) of the samples screened. Fourteen were successfully typed, of which, 7.1% (1/14), 21.4% (3/14), 64.3% (9/14) and 7.1% (1/14) were enterovirus (EV) -A, EV-B, EV-C and a mixture of EV-B and C (EV-C99 and E25), respectively. The two controls were identified as EV-C99 and coxsackievirus (CV) -A1, both of which belong to the species Enterovirus C. In one sample, poliovirus serotype 2 was detected and found to have the VP1 _ILE143 variation and was therefore identified as a vaccine strain. The results of this study showed that significant proportion of enterovirus infections (including some with Sabin PV2) are being missed by the RD-L20B-cell-culture-based algorithm, thus highlighting the value of the RT-snPCR assay and its modifications. The circulation and preponderance of EV-C in Nigeria was also confirmed.

Phylogenetic Characterizations of Highly Mutated EV-B106 Recombinants Showing Extensive Genetic Exchanges with Other EV-B in Xinjiang, China

Human enterovirus B106 (EV-B106) is a new member of the enterovirus B species. To date, only three nucleotide sequences of EV-B106 have been published, and only one full-length genome sequence (the Yunnan strain 148/YN/CHN/12) is available in the GenBank database. In this study, we conducted phylogenetic characterisation of four EV-B106 strains isolated in Xinjiang, China. Pairwise comparisons of the nucleotide sequences and the deduced amino acid sequences revealed that the four Xinjiang EV-B106 strains had only 80.5–80.8% nucleotide identity and 95.4–97.3% amino acid identity with the Yunnan EV-B106 strain, indicating high mutagenicity. Similarity plots and bootscanning analyses revealed that frequent intertypic recombination occurred in all four Xinjiang EV-B106 strains in the non-structural region. These four strains may share a donor sequence with the EV-B85 strain, which circulated in Xinjiang in 2011, indicating extensive genetic exchanges between these strains. All Xinjiang EV-B106 strains were temperature-sensitive. An antibody seroprevalence study against EV-B106 in two Xinjiang prefectures also showed low titres of neutralizing antibodies, suggesting limited exposure and transmission in the population. This study contributes the whole genome sequences of EV-B106 to the GenBank database and provides valuable information regarding the molecular epidemiology of EV-B106 in China.

Isolation and Characterization of a Highly Mutated Chinese Isolate of Enterovirus B84 from a Patient with Acute Flaccid Paralysis

Enterovirus B84 (EV-B84) is a newly identified serotype within the species Enterovirus B (EV-B). To date, only ten nucleotide sequences of EV-B84 are published and only one full-length genome sequence (the prototype strain) is available in the GenBank database. Here, a highly mutated EV-B84 (strain AFP452/GD/CHN/2004) was recovered from a patient with acute flaccid paralysis in the Guangdong province of China in 2004 making this the first report of EV-B84 in China. Sequence comparison and phylogenetic dendrogram analysis revealed high variation from the global EV-B84 strains (African and Indian strains) and frequent intertypic recombination in the non-structural protein region, suggesting high genetic diversity in EV-B84. The Chinese EV-B84 strain, apparently evolving independently of the other ten strains, strongly suggests that the EV-B84 strain has been circulating for many years. However, the extremely low isolation rate suggests that it is not a prevalent EV serotype in China or worldwide. This study provides valuable information about the molecular epidemiology of EV-B84 in China, and will be helpful in future studies to understand the association of EV-B84 with neurological disorders; it also helps expand the number of whole virus genome sequences of EV-B84 in the GenBank database.

Complete Genome Analysis of an Enterovirus EV-B83 Isolated in China

Enterovirus B83 (EV-B83) is a recently identified member of enterovirus species B. It is a rarely reported serotype and up to date, only the complete genome sequence of the prototype strain from the United States is available. In this study, we describe the complete genomic characterization of an EV-B83 strain 246/YN/CHN/08HC isolated from a healthy child living in border region of Yunnan Province, China in 2008. Compared with the prototype strain, it had 79.6% similarity in the complete genome and 78.9% similarity in the VP1 coding region, reflecting the great genetic divergence among them. VP1-coding region alignment revealed it had 77.2–91.3% with other EV-B83 sequences available in GenBank. Similarity plot analysis revealed it had higher identity with several other EV-B serotypes than the EV-B83 prototype strain in the P2 and P3 coding region, suggesting multiple recombination events might have occurred. The great genetic divergence with previously isolated strains and the extremely rare isolation suggest this serotype has circulated at a low epidemic strength for many years. This is the first report of complete genome of EV-B83 in China.

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.

Phylogenetic evidence for multiple intertypic recombinations in enterovirus B81 strains isolated in Tibet, China

Enterovirus B81 (EV-B81) is a newly identified serotype within the species enterovirus B (EV-B). To date, only eight nucleotide sequences of EV-B81 have been published and only one full-length genome sequence (the prototype strain) has been made available in the GenBank database. Here, we report the full-length genome sequences of two EV-B81 strains isolated in the Tibet Autonomous Region of China during acute flaccid paralysis surveillance activities, and we also conducted an antibody seroprevalence study in two prefectures of Tibet. The sequence comparison and phylogenetic dendrogram analysis revealed high variability among the global EV-B81 strains and frequent intertypic recombination in the non-structural protein region of EV-B serotypes, suggesting high genetic diversity of EV-B81. However, low positive rates and low titers of neutralizing antibodies against EV-B81 were detected. Nearly 68% of children under the age of five had no neutralizing antibodies against EV-B81. Hence, the extent of transmission and the exposure of the population to this EV type are very limited. Although little is known about the biological and pathogenic properties of EV-B81 because of few research in this field owing to the limited number of isolates, our study provides basic information for further studies of EV-B81.