Assessment of twelve echovirus virus-neutralisation assays in Europe: recommendations for harmonisation of non-polio enterovirus sero-surveillance studies.

Non-polio enteroviruses (NPEV) cause significant disease worldwide. Population-based sero-surveillance, by measuring antibodies against specific NPEV types, provides additional information on past circulation and the prediction for future upsurges. Virus neutralisation assays (VNA), the current method of choice for measuring NPEV type specific antibodies, are not entirely standardised. Via the European Non-Polio Enterovirus Network, we organised a VNA quality assessment in which twelve laboratories participated. We provided five echovirus (E) types (E1, E18, E30 G2, E30 G6 and E6) and intravenous immunoglobulins (IVIG) as a sample for the NPEV VNA quality assessment. Differences in VNA protocols and neutralising Ab (nAb) titres were found between the participating laboratories with geometric coefficients of variation ranging from 10.3-62.9 %. Mixed-effects regression analysis indicated a small but significant effect of type of cell line used. Harmonisation of cell line passage number, however, did not improve variation between laboratories. Calibration by making use of a reference sample, reduced variation between laboratories but differences in nAb titres remained higher than two log2 dilution steps. In conclusion, sero-surveillance data from different laboratories should be compared with caution and standardised protocols are needed.

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

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

Genetic variation of hepatitis B surface antigen among acute and chronic hepatitis B virus infections in The Netherlands.

Genetic variation within hepatitis B surface antigen (HBsAg), in particular within the major hydrophobic region (MHR), is related to immune/vaccine and test failures and can have a significant impact on the vaccination and diagnosis of acute infection. This study shows, for the first time, variation among acute cases and compares the amino acid variation within the HBsAg between acute and chronic infections. We analyzed the virus isolated from 1231 acute and 585 chronic cases reported to an anonymized public health surveillance database between 2004 and 2014 in The Netherlands. HBsAg analysis revealed the circulation of 6 genotypes (Gt); GtA was the dominant genotype followed by GtD among both acute (68.2% and 17.4%, respectively) and chronic (34.9% and 34.2%, respectively) cases. Variation was the highest among chronic strains compared to that among acute strains. Both acute and chronic GtD showed the highest variation compared to that of other genotypes (P < .01). Substitutions within the MHR were found in 8.5% of the acute strains and 18.6% of the chronic strains. Specific MHR substitutions described to have an impact on vaccine/immune escape and/or HBsAg test failure were found among 4.1% of the acute strains and 7.0% of the chronic strains. In conclusion, we show a high variation of HBsAg among acute and chronic hepatitis B virus-infected cases in The Netherlands, in particular among those infected with GtD, and compare, for the first time, variation in frequencies between acute and chronic cases. Additional studies on the impact of these variations on vaccination and test failure need to be conducted, as well as whether HBsAg false-negative variants have been missed.

Polio and Measles Down the Drain: Environmental Enterovirus Surveillance in the Netherlands, 2005 to 2015.

Polioviruses (PVs) are members of the genus Enterovirus In the Netherlands, the exclusion of PV circulation is based on clinical enterovirus (EV) surveillance (CEVS) of EV-positive cases and routine environmental EV surveillance (EEVS) conducted on sewage samples collected in the region of the Netherlands where vaccination coverage is low due to religious reasons. We compared the EEVS data to those of the CEVS to gain insight into the relevance of EEVS for poliovirus and nonpolio enterovirus surveillance. Following the polio outbreak in Syria, EEVS was performed at the primary refugee center in Ter Apel in the Netherlands, and data were compared to those of CEVS and EEVS. Furthermore, we assessed the feasibility of poliovirus detection by EEVS using measles virus detection in sewage during a measles outbreak as a proxy. Two Sabin-like PVs were found in routine EEVS, 11 Sabin-like PVs were detected in the CEVS, and one Sabin-like PV was found in the Ter Apel sewage. We observed significant differences between the three programs regarding which EVs were found. In 6 sewage samples collected during the measles outbreak in 2013, measles virus RNA was detected in regions where measles cases were identified. In conclusion, we detected PVs, nonpolio EVs, and measles virus in sewage and showed that environmental surveillance is useful for poliovirus detection in the Netherlands, where live oral poliovirus vaccine is not used and communities with lower vaccination coverage exist. EEVS led to the detection of EV types not seen in the CEVS, showing that EEVS is complementary to CEVS.IMPORTANCE We show that environmental enterovirus surveillance complements clinical enterovirus surveillance for poliovirus detection, or exclusion, and for nonpolio enterovirus surveillance. Even in the presence of adequate surveillance, only a very limited number of Sabin-like poliovirus strains were detected in a 10-year period, and no signs of transmission of oral polio vaccine (OPV) strains were found in a country using exclusively inactivated polio vaccine (IPV). Measles viruses can be detected during an outbreak in sewage samples collected and concentrated following procedures used for environmental enterovirus surveillance.

VIRO-TypeNed, systematic molecular surveillance of enteroviruses in the Netherlands between 2010 and 2014.

VIRO-TypeNed is a collaborative molecular surveillance platform facilitated through a web-based database. Genetic data in combination with epidemiological, clinical and patient data are shared between clinical and public health laboratories, as part of the surveillance underpinning poliovirus eradication. We analysed the combination of data submitted from 2010 to 2014 to understand circulation patterns of non-polio enteroviruses (NPEV) of public health relevance. Two epidemiological patterns were observed based on VIRO-TypeNed data and classical surveillance data dating back to 1996: (i) endemic cyclic, characterised by predictable upsurges/outbreaks every two to four years, and (ii) epidemic, where rare virus types caused upsurges/outbreaks. Genetic analysis suggests continuous temporal displacement of virus lineages due to the accumulation of (silent) genetic changes. Non-synonymous changes in the antigenic B/C loop suggest antigenic diversification, which may affect population susceptibility. Infections were frequently detected at an age under three months and at an older, parenting age (25-49 years) pointing to a distinct role of immunity in the circulation patterns. Upsurges were detected in the summer and winter which can promote increased transmissibility underlying new (cyclic) upsurges and requires close monitoring. The combination of data provide a better understanding of NPEV circulation required to control and curtail upsurges and outbreaks.

Growth characteristics of human parechovirus 1 to 6 on different cell lines and cross- neutralization of human parechovirus antibodies: a comparison of the cytopathic effect and real time PCR.

BACKGROUND: Human parechoviruses (HPeVs) are among the most frequently detected picornaviruses in humans. HPeVs are usually associated with mild gastrointestinal and respiratory symptoms with the exception of HPeV3 which causes neonatal sepsis and CNS infection. Previous studies showed various results in culturing different HPeV genotypes, inducing only a low cytopathic effect (CPE). METHODS: In vitro growth characteristics of the different HPeV genotypes in a range of 10 different cell lines are scored with CPE and measured in the supernatant by real time PCR. In the optimal cell line for each genotype a standard neutralization assay with the available HPeV antibodies (Abs) was performed and scored by CPE and measured by real time PCR. RESULTS: All six HPeV types were able to replicate on the RD99, A549, and Vero cell lines. HPeV1 was the only genotype able to replicate on all cell lines. Most efficient growth of HPeV1, 2, 4, 5, and 6 was shown on the HT29 cell line, while HPeV3 was unable to replicate on HT29. In all cases viral replication could be measured by real time PCR before CPE appeared. The polyclonal Abs available against HPeV1, 2, 4 and 5 all showed neutralization of their respective genotype after 7 days with inhibition of >60% in real time PCR and full inhibition of CPE, although cross-neutralization is shown. Replication of HPeV3 could only be inhibited by 12% by the anti-HPeV3 (aHPeV3) Ab and no inhibition of CPE was shown after 7 days. CONCLUSION: When replication is monitored by PCR, growth of HPeV genotypes 1 to 6 is supported by most of the cell lines tested, where viral replication is measured before appearance of CPE. A combination of HT29 and Vero cells would therefore support replication of all culturable HPeV types, so viral replication could be detected by PCR within 3 days for all genotypes.In addition, we showed efficient neutralization for HPeV1, 2, 4, 5, while cross- neutralization was shown between these types, indicating possible common neutralizing epitopes. For HPeV3 no efficient (cross-) neutralization was shown, indicating different neutralizing epitopes for HPeV3 compared to the other HPeV genotypes.

Wastewater Surveillance in Europe for Non-Polio Enteroviruses and Beyond.

Wastewater surveillance (WWS) was developed in the early 1960s for the detection of poliovirus (PV) circulation in the population. It has been used to monitor several pathogens, including non-polio enteroviruses (NPEVs), which are increasingly recognised as causes of morbidity in children. However, when applying WWS to a new pathogen, it is important to consider the purpose of such a study as well as the suitability of the chosen methodology. With this purpose, the European Non-Polio Enterovirus Network (ENPEN) organised an expert webinar to discuss its history, methods, and applications; its evolution from a culture-based method to molecular detection; and future implementation of next generation sequencing (NGS). The first simulation experiments with PV calculated that a 400 mL sewage sample is sufficient for the detection of viral particles if 1:10,000 people excrete poliovirus in a population of 700,000 people. If the method is applied correctly, several NPEV types are detected. Despite culture-based methods remaining the gold standard for WWS, direct methods followed by molecular-based and sequence-based assays have been developed, not only for enterovirus but for several pathogens. Along with case-based sentinel and/or syndromic surveillance, WWS for NPEV and other pathogens represents an inexpensive, flexible, anonymised, reliable, population-based tool for monitoring outbreaks and the (re)emergence of these virus types/strains within the general population.

Pediatric acute flaccid myelitis: Evaluation of diagnostic criteria and differentiation from other causes of acute flaccid paralysis.

BACKGROUND: Acute flaccid paralysis (AFP) is characterized by rapidly progressive limb weakness with low muscle tone. It has a broad differential diagnosis, which includes acute flaccid myelitis (AFM), a rare polio-like condition that mainly affects young children. Differentiation between AFM and other causes of AFP may be difficult, particularly at onset of disease. Here, we evaluate the diagnostic criteria for AFM and compare AFM to other causes of acute weakness in children, aiming to identify differentiating clinical and diagnostic features. METHODS: The diagnostic criteria for AFM were applied to a cohort of children with acute onset of limb weakness. An initial classification based on positive diagnostic criteria was compared to the final classification, based on application of features suggestive for an alternative diagnosis and discussion with expert neurologists. Cases classified as definite, probable, or possible AFM or uncertain, were compared to cases with an alternative diagnosis. RESULTS: Of 141 patients, seven out of nine patients initially classified as definite AFM, retained this label after further classification. For probable AFM, this was 3/11, for possible AFM 3/14 and for uncertain 11/43. Patients initially classified as probable or possible AFM were most commonly diagnosed with transverse myelitis (16/25). If the initial classification was uncertain, Guillain-Barré syndrome was the most common diagnosis (31/43). Clinical and diagnostic features not included in the diagnostic criteria, were often used for the final classification. CONCLUSION: The current diagnostic criteria for AFM usually perform well, but additional features are sometimes required to distinguish AFM from other conditions.

Specific cell tropism and neutralization of human parechovirus types 1 and 3: implications for pathogenesis and therapy development.

Human parechoviruses (HPeVs) are picornaviruses frequently infecting humans. While HPeV1 is associated with mild disease, HPeV3 is the cause of neonatal sepsis and meningitis. To test whether in vitro replication kinetics of HPeV1 and HPeV3 could be related to pathogenicity, HPeV1 and HPeV3 strains isolated from patients were cultured on cell lines of gastrointestinal, respiratory and neural origin, and replication kinetics were measured by real-time PCR. No relationship was found between clinical symptoms and in vitro replication of the HPeV1 strains. In contrast, the HPeV3 strains showed faster replication in neural cells and there was a relationship between higher in vitro replication kinetics and neuropathogenicity in the patient. Furthermore, HPeV1 could be neutralized efficiently by its specific antibody and by intravenous immunoglobulins (IVIG), while most HPeV3 strains could not be neutralized. In IVIG, very low neutralizing antibody (nAb) titres against HPeV3 were found. Additionally, very low nAb titres were observed in sera of two HPeV3-infected donors, while high nAb titres against HPeV1 could be detected. Our data suggest that the mild clinical course of HPeV1 infection is primarily influenced by strong nAb responses, while HPeV3 might be difficult to neutralize in vivo and therefore the course of infection will mainly be determined by in vivo cell tropism.

European Non-Polio Enterovirus Network: Introduction of Hospital-Based Surveillance Network to Understand the True Disease Burden of Non-Polio Enterovirus and Parechovirus Infections in Europe.

BACKGROUND: Non-polio enteroviruses (EVs) and human parechoviruses (PeVs) cause a wide range of human infections. Limited data on their true disease burden exist as standardized European-wide surveillance is lacking. AIMS: Our aim is to estimate the disease burden of EV and PeV infections in Europe via establishment of standardized surveillance for hand, foot and mouth disease (HFMD) and respiratory and neurological infections caused by these viruses. We will also assess the sensitivity of assays implemented in the network of participating laboratories so that all EV and PeV types are adequately detected. Plan. The European Non-Polio Enterovirus Network (ENPEN) has developed standardized protocols for a prospective, multi-center and cross-sectional hospital-based pilot study. Protocols include guidance for diagnosis, case definition, detection, characterization and reporting of EV and PeV infections associated with HFMD and respiratory and neurological diseases. Over 30 sites from 17 European countries have already registered to this one pilot study, likely to be commenced in 2022. BENEFITS: This surveillance will allow European-wide comparison of data on EV and PeV infection. These data will also be used to determine the burden of EV and PeV infections, which is needed to guide the further prevention measures and policies.

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.

Human parechoviruses as an important viral cause of sepsislike illness and meningitis in young children.

BACKGROUND: Enteroviruses (EVs) belong to the family Picornaviridae and are a well-known cause of neonatal sepsis and viral meningitis. Human parechoviruses (HPeVs) type 1 and 2, previously named echovirus 22 and 23, have been associated with mild gastrointestinal or respiratory symptoms in young children. Six HPeV genotypes are currently known, of which HPeV3 is associated with neonatal sepsis and meningitis. METHODS: Cerebrospinal fluid samples from children aged <5 years previously tested by EV-specific polymerase chain reaction (PCR) during 2004-2006 were selected (N= 761). Samples from 716 of those children were available for retrospective testing by HPeV-specific real-time PCR. The prevalence of EV and HPeV in these samples was compared. Data on clinical presentation of children infected with HPeV were retrospectively documented. RESULTS: HPeV was found in cerebrospinal fluid samples from 33 (4.6%) of the children. Yearly prevalence of HPeV in cerebrospinal fluid varied remarkably: 8.2% in 2004, 0.4% in 2005, and 5.7% in 2006. EV was detected in 14% (108 of 761 samples), with no variation in yearly prevalence. Children with HPeV in cerebrospinal fluid presented with clinical symptoms of sepsislike illness and meningitis, which led to hospitalization and antibiotic treatment. CONCLUSION: EV-specific PCRs do not detect HPeVs. The addition of an HPeV-specific PCR has led to a 31% increase in detection of a viral cause of neonatal sepsis or central nervous system symptoms in children aged <5 years. HPeV can be considered to be the second cause of viral sepsis and meningitis in young children, and rapid identification of HPeV by PCR could contribute to shorter duration of both antibiotic use and hospital stay.

Human Parechovirus 1, 3 and 4 Neutralizing Antibodies in Dutch Mothers and Infants and Their Role in Protection Against Disease.

BACKGROUND: Human parechoviruses (HPeVs) are common pathogens in young children, and in the Netherlands, HPeV1, HPeV3 and HPeV4 are the most frequently detected genotypes. HPeV3 in particular has been associated with severe disease in young infants below 3 months of age while the other genotypes more often infect older children and elicit mild symptoms. We investigated if maternal neutralizing antibodies (nAbs) against HPeV1, HPeV3 and HPeV4 protect young Dutch infants from severe disease related to HPeV infection. METHODS: We conducted a prospective case-control study of Dutch mother-infant pairs. Thirty-eight HPeV-infected infants and their mothers were included as cases, and 65 HPeV-negative children and their mothers as controls. RESULTS: In control infants, we observed nAb seropositivity rates of 41.4%, 33.3% and 27.6%, with median nAb titers of 1:16, 1:12 and 1:8, against HPeV1, HPeV3 and HPeV4, respectively. In control mothers, nAb seropositivity rates were 84.6%, 55.4% and 60.0% with median nAb titers of 1:128, 1:32 and 1:45 against HPeV1, HPeV3 and HPeV4, respectively. The HPeV3 nAb seroprevalence was significantly lower in HPeV3-infected infants and their mothers (0.0% with P < 0.05 and 10.0% with P < 0.001, respectively). In contrast, no differences in nAb seroprevalence against HPeV1 or HPeV4 could be detected between case and control infants or mothers. CONCLUSIONS: Our results suggest that young Dutch infants are protected against severe disease related to HPeV1 and HPeV4 by maternal nAbs, but less so against HPeV3 explaining the distinct age distributions and disease severity profiles of children infected with these HPeV genotypes.

Prolonged Shedding of Human Parechovirus in Feces of Young Children after Symptomatic Infection.

After symptomatic human parechovirus (HPeV) infection in infants, the duration of (mostly asymptomatic) shedding in feces was 2-24 weeks (median 58 days). HPeV cycle threshold value could neither differentiate between symptomatic disease and asymptomatic shedding nor between severe and mild disease as high cycle threshold values (indicating low viral loads) were observed in HPeV3-infected children with severe disease.

Antivirals against enteroviruses: a critical review from a public-health perspective.

The enteroviruses (EVs) of the Picornaviridae family are the most common viral pathogens known. Most EV infections are mild and self-limiting but manifestations can be severe in children and immunodeficient individuals. Antiviral development is actively pursued to benefit these high-risk patients and, given the alarming problem of antimicrobial drug resistance, antiviral drug resistance is a public-health concern. Picornavirus antivirals can be used off-label or as part of outbreak control measures. They may be used in the final stages of poliovirus eradication and to mitigate EV-A71 outbreaks. We review the potential emergence of drug-resistant strains and their impact on EV transmission and endemic circulation. We include non-picornavirus antivirals that inhibit EV replication, for example, ribavirin, a treatment for infection with HCV, and amantadine, a treatment for influenza A. They may have spurred resistance emergence in HCV or influenza A patients who are unknowingly coinfected with EV. The public-health challenge is always to find a balance between individual benefit and the long-term health of the larger population.

September through October 2010 multi-centre study in the Netherlands examining laboratory ability to detect enterovirus 68, an emerging respiratory pathogen.

During September and October 2010, the Dutch Public Health Institute detected an enterovirus (EV) 68 (EV68) epidemic in the Netherlands through general practitioner-based surveillance of acute respiratory infections. EV68 shares phenotypic and genotypic properties with human rhinovirus (HRV). Despite increased EV and HRV detections, Dutch clinical laboratories did not identify EV68. To assess the capability of Dutch clinical laboratories to detect EV68, ten laboratories with more than eight detected EV and HRV cases in September and October 2010 provided information about their detection algorithms and testing results for a 2010 Dutch EV68 strain. For EV detection mostly stool specimens (median 49%), respiratory specimens (median 27%) and cerebrospinal fluid (median 22%) were used. For HRV detection only respiratory specimens were used. Except for the Seeplex® RV15ACE EV-specific assay, all EV and 73% of HRV assays, including those of the Public Health Institute, were able to detect EV68. Two-step EV RT-PCR protocols were the most sensitive. Thus, laboratories might have misidentified EV68 as HRV. In addition, EV68 cases might have also been missed because patients with respiratory diseases are usually not tested for EV infection. Therefore, clinical laboratories should include EV detection in the differential diagnosis of patients presenting with respiratory symptoms.

Pleconaril revisited: clinical course of chronic enteroviral meningoencephalitis after treatment correlates with in vitro susceptibility.

BACKGROUND: Human enteroviruses (HEVs) can cause severe infections, especially in patients with a deficient humoral immune response, such as X-linked agammaglobulinemia. In this patient group, chronic enteroviral meningitis (CEMA) is feared because of extensive morbidity and high fatality rate. Treatment options consist of intravenous immunoglobulin (IVIG), with various outcomes. Pleconaril is an antiviral agent with in vitro activity against HEVs that has been used in the treatment of HEV infections. METHODS: The efficacy of pleconaril and IVIG against HEV isolated from the patients was assessed in vitro in two patients with CEMA. RESULTS: Echovirus 11 was found in the cerebrospinal fluid (CSF) of case 1. Treatment with high-dose IVIG and pleconaril did not provide any clinical improvement and HEV PCR in CSF remained positive. Case 2 (echovirus 13 positive in CSF) was also treated with IVIG and pleconaril. The patient recovered completely and HEV PCR in CSF became negative. Recent IVIG batches contained low titres of neutralizing antibodies against the patient strains. Echovirus 11 (case 1) was resistant to pleconaril in vitro, whereas echovirus 13 (case 2) was susceptible, in accordance with virological response after treatment and subsequent clinical results. CONCLUSIONS: This is the first report that evaluates efficacy of antiviral treatment in CEMA patients in relation to in vitro susceptibility of clinical virus isolates. Since pleconaril is no longer available for compassionate use we strongly propagate that new drugs should be developed against these potential life threatening HEV infections.

Clinical characteristics of human parechoviruses 4-6 infections in young children.

BACKGROUND: Human parechoviruses (HPeVs) and enteroviruses (EVs) belong to the family Picornaviridae. EVs are known to cause a wide range of disease such as meningitis, encephalitis, and sepsis. HPeV1 and 2 have been associated with mild gastrointestinal or respiratory symptoms in young children. HPeV3 is associated with more severe neonatal infection. Little is known about the epidemiology and pathology of HPeV4-6 in children. METHODS: We evaluated the clinical symptoms of the children with an HPeV 4, 5, or 6 infection. The patients with positive HPeV4-6 in stool samples were selected and available plasma or cerebrospinal fluid samples from these patients were tested for HPeV. Data on clinical symptoms, diagnosis, presence and duration of fever, medical history, mean age, use of antibiotics of the children infected with HPeV4-6 were retrospectively documented. RESULTS: HPeV4-6 were found in 31 of the 277 HPeV positive children (11%). Coinfection with EV was seen in 8 patients. Fever was seen in 13 (42%) patients. Of the HPeV4-6 positive patients, 20 of the 31 children (64%) presented with gastrointestinal complaints and 18 of 31 (58%) patients had respiratory symptoms. The mean age was 14 months, 58% of the patients had an underlying disorder such as bronchomalacia or a cardiac disorder. CONCLUSIONS: Symptomatic HPeV4-6 infections are seen in relative young children and are associated with respiratory and/or gastrointestinal symptoms. HPeV type 4 was detected more frequently than HPeV types 5 and 6.

Fourth human parechovirus serotype.

We identified a novel human parechovirus (HPeV) type (K251176-02) from a neonate with fever. Analysis of the complete genome showed K251176-02 to be a new HPeV genotype. Since K251176-02 could not be neutralized with antibodies against known HPeV serotypes 1-3, it should be classified as a fourth HPeV serotype.