Use of monoclonal antibodies to identify serotypes of enterovirus isolates

Seasonal Testing, Results, and Effect of the Pandemic on Coxsackievirus Serum Studies

Coxsackieviruses (CVs) are common causes of infections and can be life-threatening. Unfortunately, rigorous studies guiding the clinician in interpreting CV serum antibody titer testing is lacking. To explore the epidemiology of circulating CVs and the serological test utility in aiding diagnosis of CV infections in our community, we obtained results of CV immunologic diagnostic tests between 2018 and 2022 from a regional healthcare database. For CV type A, rare individuals had positive CF (complement fixation) tests whereas all 16 individuals with IFA testing showed at least one positive serotype. For CV type B CF testing, 52.2% of 222 patients had at least one serotype positive, with B5 being most common and also the most common with higher titers (14.8% with ≥1:32). We found a significant reduction in seropositivity rate during the pandemic in 2020 compared to 2018, which continued through 2022 (OR: 0.2, 95% CI: 0.08-0.49, p-value < 0.001). During the pandemic, the seasonal pattern of positive tests varied from the pre-pandemic pattern. Testing for CVs was increased after the first year of the pandemic. Overall, the variability by month and seasonal change in our data support that CF testing can be used to identify recent CVB infection.

Virus Shedding in Patients With Hand, Foot and Mouth Disease Induced by EV71, CA16 or CA6: Systematic Review and Meta-analysis

BACKGROUND

As the highly contagious hand, foot and mouth disease (HFMD) spreads rapidly among children, isolation is the most effective way to control its spread. However, studies on the duration of virus shedding of the HFMD-related enterovirus and a reasonable quarantine period for HFMD patients are inconsistent.

METHODS

We undertook a systematic review and meta-analysis evaluating the viral shedding of patients with HFMD caused by Enterovirus 71 (EV71) and coxsackievirus A16 (CVA16) and coxsackievirus A6.

RESULTS

A total of 17 observational studies evaluating 626 participants were included. In the first 5 weeks after onset, the pooled virus positive rate in specimens of EV71-related patients decreased from 0.79 (P < 0.001 for heterogeneity) to 0.38 (P < 0.001 for heterogeneity). The positive rate of CVA16 was reduced from 0.91 (P < 0.001 for heterogeneity) to 0.29 (P < 0.001 for heterogeneity). The positive rates of CVA16 and coxsackievirus A6 were approximately 50% in the third week after onset, while a 50% positive rate appeared in the fourth week in EV71 related cases.

CONCLUSIONS

We found the positive rates of virus shedding were still high among the patients released from quarantine, and the duration of viral shedding was inconsistent among HFMD patients caused by different serotypes. Our findings provide comprehensive evidence for a possible flexible quarantine period according to the serotype.

The History of Enterovirus A71 Outbreaks and Molecular Epidemiology in the Asia-Pacific Region

Enterovirus A71 (EV-A71) is one of the common causative pathogens for hand foot and mouth disease (HFMD) affecting young children. HFMD outbreak can result in a substantial pediatric hospitalization and burden the healthcare services, especially in less-developed countries. Since the initial epidemic of predominantly EV-A71 in California in 1969, the high prevalence of HFMD in the Asia-pacific region and elsewhere around the world represents a significant morbidity in this age group. With the advent of rapid and accurate diagnostic tools, there has been a dramatic increase in the number of laboratory-confirmed EV-A71 infection over the past two decades. The population, cultural, and socioeconomic diversity among countries in the Asia-Pacific region all influence the transmission and morbidity associated with HFMD. This review summarizes the current state of epidemiology of EV-A71 in Asia-Pacific countries based on the most recent epidemiological data and available information on the prevalence and disease burden. This knowledge is important in guiding the prevention, control and future research on vaccine development of this highly contagious disease of significant socioeconomic implications in public health.

[Detection of herpes virus and human enterovirus in pathology samples using low-density arrays]

Despite the frequency of infections with herpesviridae family, only eight subtypes affect humans (Herpex Simplex Virus types 1 and 2, Varicella Zoster Virus, Epstein-Barr Virus, Citomegalovirus and Human Herpes Virus types 6, 7 and 8). Amongst enteroviruses infections, the most important are Poliovirus, Coxackievirus and Echovirus. Symptoms can vary from mild to severe and early diagnosis is of upmost importance. Nowadays, low-density arrays can detect different types of viruses in a single assay using DNA extracted from biological samples. We analyzed 70 samples of formalin-fixed and paraffin-embedded tissue, searching for viruses (HSV-1, HSV-2, VZV, CMV, EBV, HHV-6, HHV-7 y HHV-8, Poliovirus, Echovirus and Coxsackievirus) using the kit CLART^® ENTHERPEX. Out of the total of 70 samples, 29 were positive for viral infection (41.43%), and only 4 of them showed cytopathic effect (100% correlation between histology and the test). 47.6% of GVHD samples were positive for virus; 68.75% of IBD analyzed showed positivity for viral infection; in colitis with ulcers (neither GVHD nor IBD), the test was positive in 50% of the samples and was also positive in 50% of ischemic lesions. The high sensitivity of the technique makes it a useful tool for the pathologist in addition to conventional histology-based diagnosis, as a viral infection may affect treatment.

Traditional and Modern Cell Culture in Virus Diagnosis

Cell cultures are developed from tissue samples and then disaggregated by mechanical, chemical, and enzymatic methods to extract cells suitable for isolation of viruses. With the recent advances in technology, cell culture is considered a gold standard for virus isolation. This paper reviews the evolution of cell culture methods and demonstrates why cell culture is a preferred method for identification of viruses. In addition, the advantages and disadvantages of both traditional and modern cell culture methods for diagnosis of each type of virus are discussed. Detection of viruses by the novel cell culture methods is considered more accurate and sensitive. However, there is a need to include some more accurate methods such as molecular methods in cell culture for precise identification of viruses.

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry applied to virus identification

Virus detection and/or identification traditionally rely on methods based on cell culture, electron microscopy and antigen or nucleic acid detection. These techniques are good, but often expensive and/or time-consuming; furthermore, they not always lead to virus identification at the species and/or type level. In this study, Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) was tested as an innovative tool to identify human polioviruses and to identify specific viral protein biomarkers in infected cells. The results revealed MALDI-TOF MS to be an effective and inexpensive tool for the identification of the three poliovirus serotypes. The method was firstly applied to Sabin reference strains, and then to isolates from different clinical samples, highlighting its value as a time-saving, sensitive and specific technique when compared to the gold standard neutralization assay and casting new light on its possible application to virus detection and/or identification.

Expression of enterovirus 71 capsid protein VP1 in Escherichia coli and its clinical application

The VPl gene of enterovirus 71 (EV71) was synthesized, construct a recombinant plasmid pET15b/VP1 and expressed in E. coli BL21. The recombinant VP1 protein could specifically react with EV71-infected patient sera without the cross-reaction with serum antibodies of coxsackievirus A16 (CA16), A4, A5, B3 and B5 as well as echovirus 6. In acute and convalescent phases, IgM and IgG antibodies of 182 serum samples were detected by ELISA with recombinant VP1 protein as a coated antigen. The results showed that the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of IgM antibodies in serum samples for the diagnosis of EV71 infection were 90.1, 98.4, 98.8 and 88.7%, respectively; similarly, those of IgG antibodies in serum samples were 82.4, 89.1, 91.5 and 78.1%, respectively. Five of 80 samples (6.25%) from CA16-infected patients were detected positive by ELISA with recombinant VP1 protein in which indicated the cross reactions and 0 of 5 samples from patients infected with other enteroviruses including CA4, CA5, CB3, CB5 and echovirus 6. Therefore, the recombinant VP1 protein of EV7l may provide a theoretical reference for establishing an effective antibody screening of IgM for EV71-infected patients with clinically suspected hand, foot, and mouth disease (HFMD).

Identification and characterization of a monoclonal antibody recognizing the linear epitope RVADVI on VP1 protein of enterovirus 71

Several large outbreaks of hand-foot-mouth disease (HFMD) have occurred in the Asian-Pacific region since 1997, with Enterovirus 71 (EV71) and/or Coxsackievirus A16 (CAV16) as the main causative agents. Despite the close genetic relationship between the two viruses, only EV71 is associated with severe clinical manifestations and deaths. Effective antiviral treatment and vaccines are not available. High-quality monoclonal antibodies (mAbs) are necessary to improve the accuracy of the diagnosis of EV71. In this study, a mAb (designated 1D9) was generated using EV71 C5 strain virus particles as immunogens. Examined by indirect immunofluorescence assay (IFA) and Western blotting, 1D9 detected successfully all 11 subgenotypes of EV71 and showed no cross-reactivity to the four selected subgenogroups of Coxsackieviruses CAV4, CAV6, CAV10, and CAV16. A linear motif, R(3) VADVI(8), which is located at the N-terminus of the EV71 VP1 protein, was identified as the minimal binding region of 1D9. Alignment and comparison of the 1D9-defined epitope sequence against the listed sequences in the NCBI EV71 database indicated that this epitope R(3) VADVI(8) was highly conserved among EV71 strains, while no significant similarity was observed when blasted against the Coxsackieviruses. This suggests that the mAb 1D9 may be useful for the development of a cost-effective and accurate method for surveillance and early differentiation of EV71 from CAV16 infection.

Simultaneously typing nine serotypes of enteroviruses associated with hand, foot, and mouth disease by a GeXP analyzer-based multiplex reverse transcription-PCR assay

Hand, foot, and mouth disease (HFMD) is a contagious enteroviral disease occurring primarily in young children and caused by enterovirus 71 (EV71), coxsackievirus A16 (CVA16), and other serotypes of coxsackievirus and echovirus. In this study, a GeXP analyzer-based multiplex reverse transcription (RT)-PCR assay (GeXP assay) consisting of chimeric primer-based PCR amplification with fluorescent labeling and capillary electrophoresis separation was developed to simultaneously identify nine serotypes of enteroviruses associated with HFMD in China, including EV71, CVA16, CVA4, -5, -9, and -10, and CVB1, -3, and -5. The RNAs extracted from cell cultures of viral isolates and synthetic RNAs via in vitro transcription were used to analyze the specificity and sensitivity of the assay. The GeXP assay detected as little as 0.03 tissue culture infective dose (TCID(50)) of EV71 and CVA16, 10 copies of panenterovirus, EV71, CVA16, CVB1, and CVB5, and 100 copies of 10 (including panenterovirus) premixed RNA templates. A total of 180 stool specimens collected from HFMD patients and persons suspected of having HFMD were used to evaluate the clinical performance of this assay. In comparison with the results of conventional methods, the sensitivities of the GeXP assay for detection of panenterovirus, EV71, and CVA16 were 98.79% (163/165), 91.67% (44/48), and 91.67% (33/36), respectively, and the specificities were 80.00% (12/15), 98.48% (130/132), and 100% (144/144), respectively. The concordance of typing seven other serotypes of enteroviruses with the results of conventional methods was 92.59% (25/27). In conclusion, the GeXP assay is a rapid, cost-effective, and high-throughput method for typing nine serotypes of HFMD-associated enteroviruses.

Etiologies of rash and fever illnesses in Campinas, Brazil

BACKGROUND

Few population-based studies of infectious etiologies of fever-rash illnesses have been conducted. This study reports on enhanced febrile-rash illness surveillance in Campinas, Brazil, a setting of low measles and rubella virus transmission.

METHODS

Cases of febrile-rash illnesses in individuals aged <40 years that occurred during the period 1 May 2003-30 May 2004 were reported. Blood samples were collected for laboratory diagnostic confirmation, which included testing for adenovirus, dengue virus, Epstein-Barr virus (EBV), enterovirus, human herpes virus 6 (HHV6), measles virus, parvovirus-B19, Rickettsia rickettsii, rubella virus, and group A streptococci (GAS) infections. Notification rates were compared with the prestudy period.

RESULTS

A total of 1248 cases were notified, of which 519 (42%) had laboratory diagnosis. Of these, HHV-6 (312 cases), EBV (66 cases), parvovirus (30 cases), rubella virus (30 cases), and GAS (30 cases) were the most frequent causes of infection. Only 10 rubella cases met the rubella clinical case definition currently in use. Notification rates were higher during the study than in the prestudy period (181 vs 52.3 cases per 100,000 population aged <40 years).

CONCLUSIONS

Stimulating a passive surveillance system enhanced its sensitivity and resulted in additional rubella cases detected. In settings with rubella elimination goals, rubella testing may be considered for all cases of febrile-rash illness, regardless of suspected clinical diagnosis.

Methods to detect infectious human enteric viruses in environmental water samples

Currently, a wide range of analytical methods is available for virus detection in environmental water samples. Molecular methods such as polymerase chain reaction (PCR) and quantitative real time PCR (qPCR) have the highest sensitivity and specificity to investigate virus contamination in water, so they are the most commonly used in environmental virology. Despite great sensitivity of PCR, the main limitation is the lack of the correlation between the detected viral genome and viral infectivity, which limits conclusions regarding the significance for public health. To provide information about the infectivity of the detected viruses, cultivation on animal cell culture is the gold standard. However, cell culture infectivity assays are laborious, time consuming and costly. Also, not all viruses are able to produce cytopathic effect and viruses such as human noroviruses have no available cell line for propagation. In this brief review, we present a summary and critical evaluation of different approaches that have been recently proposed to overcome limitations of the traditional cell culture assay and PCR assay such as integrated cell culture-PCR, detection of genome integrity, detection of capsid integrity, and measurement of oxidative damages on viral capsid protein. Techniques for rapid detection of infectious viruses such as fluorescence microscopy and automated flow cytometry have also been suggested to assess virus infectivity in water samples.

Spatiotemporal phylogenetic analysis and molecular characterization of coxsackievirus A4

Coxsackievirus A4 outbreaks occurred in Taiwan in 2004 and 2006. The spatiotemporal transmission of this error-prone RNA virus involves a continuous interaction between rapid sequence variation and natural selection. To elucidate the molecular characteristics of CV-A4 and the spatiotemporal dynamic changes in CV-A4 transmission, worldwide sequences of the 3' VP1 region (420 nt) obtained from GenBank were analyzed together with sequences isolated in Taiwan from 2002 to 2009. Sequences were characterized in terms of recombination, variability, and selection. Phylogenetic trees were constructed using neighbor-joining, maximum likelihood and Monte Carlo Markov Chain methods. Spatiotemporal dynamics of CV-A4 transmission were further estimated by a Bayesian statistical inference framework. No recombination was detected in the 420 nt region. The estimated evolution rate of CV-A4 was 8.65 × 10(-3) substitutions/site/year, and a purifying selection (d(N)/d(S)=0.032) was noted over the 3' VP1 region. All trees had similar topology: two genotypes (GI and GII), each including two subgenotypes (A and B), with the prototype and a Kenyan strain in separate branches. The results revealed that the virus first appeared in USA in 1950. Since 1998, it has evolved into the Kenya, GI-A (Asia) and GII-A (Asia and Europe) strains. Since 2004, GI-B and GII-B have evolved continuously and have remained prevalent. The co-existence of several positive selection lineages of GI-B in 2006 indicates that the subgenotype might have survived lineage extinction. This study revealed rapid lineage turnover of CV-A4 and the replacement of previously circulating strains by a new dominant variant. Therefore, continuous surveillance for further CV-A4 transmission is essential.

Detection and quantitation of infectious human adenoviruses and JC polyomaviruses in water by immunofluorescence assay

Human adenoviruses (HAdV) and JC polyomaviruses (JCPyV) have been proposed as markers of fecal/urine contamination of human origin. An indirect immunofluorescence assay has been developed to quantify infectious human adenoviruses types 2 and 41 and JC polyomaviruses strain Mad-4 in water samples. The immunofluorescence assay was compared with other quantitative techniques used commonly such as plaque assay, tissue culture infectious dose-50 and quantitative PCR (qPCR). The immunofluorescence assays showed to be specific for the detection of infectious viruses, obtaining negative results when UV or heat-inactivated viruses were analyzed. The assays required less time and showed higher sensitivity for the detection of infectious viral particles than other cell culture techniques (1 log(10) more) evaluated. River water samples spiked previously with human adenoviruses and raw sewage samples were also analyzed using the proposed immunofluorescence assay as well as by qPCR. The results show quantitations with 2 log(10) reduction in the numbers of infectious viruses compared with the number of genome copies detected by qPCR. The immunofluorescence assay developed is fast, sensitive, specific, and a standardizable technique for the quantitation and detection of infectious viruses in water samples.

Molecular identification and analysis of nonserotypeable human enteroviruses

Conventional approaches to characterizing human enteroviruses (HEVs) are based on viral isolation and neutralization. Molecular typing methods depend largely on reverse transcription-PCR (RT-PCR) and nucleotide sequencing of the entire or partial VP1 gene. A modified RT-PCR-based reverse line blot (RLB) hybridization assay was developed as a rapid and efficient way to characterize common and nonserotypeable (by neutralization) HEVs. Twenty HEV serotypes accounted for 87.1% of all HEVs isolated at a reference laboratory from 1979 to 2007; these common serotypes were identified using one sense and three antisense primers and a set of 80 serotype-specific probes in VP1 (F. Zhou et al., J. Clin. Microbiol. 47:2737-2743, 2009). In this study, one HEV-specific primer pair, two probes in the 5' untranslated region (UTR), and a new set of 80 serotype-specific probes in VP1 were designed. First, we successfully applied the modified RT-PCR-RLB (using two HEV-specific probes and two sets of serotype-specific probes) to synchronously detect the 5' UTR and VP1 regions of 131/132 isolates previously studied (F. Zhou et al., J. Clin. Microbiol. 47:2737-2743, 2009). Then, this method was used to identify 73/92 nonserotypeable HEV isolates; 19 nonserotypeable isolates were hybridized only with HEV-specific probes. The VP1 region of 92 nonserotypeable HEV isolates was sequenced; 73 sequences corresponded with one or both RLB results and 19 (not belonging to the 20 most common genotypes) were identified only by sequencing. Two sets of serotype-specific probes can capture the majority of strains belonging to the 20 most common serotypes/genotypes simultaneously or complementarily. Synchronous detection of the 5' UTR and VP1 region by RT-PCR-RLB will facilitate the identification of HEVs, especially nonserotypeable isolates.

Monoclonal antibodies to VP1 recognize a broad range of enteroviruses

Enteroviruses (EVs) are common seasonal viruses that are associated with a variety of diseases. High-quality monoclonal antibodies (MAbs) are needed to improve the accuracy of EV diagnosis in clinical laboratories. In the present study, the full-length VP1 genes of poliovirus 1 (Polio 1) and coxsackievirus B3 (Cox B3) were cloned, and the encoded proteins were expressed and used as antigens in an attempt to raise broad-spectrum MAbs to EVs. Two pan-EV MAbs were isolated: one raised against Polio 1 VP1 and the other against Cox B3 VP1. The binding sites of both pan-EV MAbs were mapped to an amino acid sequence within a conserved region in the N terminus of Polio 1 VP1 by peptide and competition enzyme-linked immunosorbent assay. Two additional MAbs, an EV70-specific MAb and an EV71/Cox A16-bispecific MAb, developed against EV70 and 71 VP1 proteins, were pooled with the two pan-EV MAbs (pan-EV MAb mix) and tested for their sensitivity and specificity in the staining of various virus-infected cells. The pan-EV MAb mix detected all 40 prototype EVs tested and showed no cross-reactivity to 18 different non-EV human viruses. Compared with two commercially available EV tests, the pan-EV MAb mix exhibited higher specificity than one test and broader spectrum reactivity than the other. Thus, our study demonstrates that full-length Polio 1 VP1 and Cox B3 VP1 can serve as effective antigens for developing a pan-EV MAb and that the pan-EV MAb mix can be used for the laboratory diagnosis of a wide range of EV infections.

An algorithm for the typing of enteroviruses and correlation to serotyping by viral neutralization

BACKGROUND

Human enteroviruses (HEVs) are common pathogens which cause a broad spectrum of illnesses ranging from asymptomatic infection to acute myocarditis and aseptic meningitis. The neutralization assay for serotype determination is labor-intensive and time-consuming. There is a need for a methodology that is more rapid and widely accessible.

OBJECTIVES

Our goals were to develop an algorithm to type enteroviruses which combines both serologic typing, based on indirect immunofluorescence assay (IFA) using type-specific monoclonal antibodies (mAbs) and genotyping, by DNA sequence analysis and to assess the correlation of both IFA and genotyping to traditional viral neutralization by type-specific antisera.

STUDY DESIGN

Clinical specimens initially determined to be enterovirus positive by nucleic acid detection were grown in cell culture and typed using mAbs. Specimens that could not be typed by mAbs were subject to molecular analysis. Genotyping was performed by a combination of either a primary or semi-nested RT-PCR for a region within VP3/VP1 and followed by direct DNA sequencing of PCR products. Database homology comparisons and phylogenetic analysis were performed based on a defined region (303 nt) within the VP1 gene.

RESULTS

We inoculated 134 enterovirus nucleic acid amplification-positive specimens into culture and 115 (86%) of these isolates were successfully typed by this algorithm. We have demonstrated a strong correlation between serotyping by viral neutralization to both IFA by type-specific mAbs and genotyping.

CONCLUSIONS

Typing of human enteroviruses can be effectively performed using an integration of antibody-based and molecular methods.

Simultaneous detection of human enterovirus 71 and coxsackievirus A16 in clinical specimens by multiplex real-time PCR with an internal amplification control

The recent and continuing HFMD outbreak caused by EV71 in several provinces of China since March 2008 has affected thousands of children and resulted in nearly 50 deaths. In this study, a sensitive and specific multiplex real-time RT-PCR assay has been developed for the rapid detection of EV71 and CV-A16. By using an internal amplification control, the real-time assay achieves detection of samples containing inhibitors and avoids false negatives. It should prove useful for clinical diagnosis of EV71 or CV-A16 infections.

[Diagnosis of non Poliovirus enteroviruses in Abidjan from 1996 to 2004]

Non Poliovirus enteroviruses (NPEV) are infectious agents which can determine various infections. They are more and more isolated within the context of the surveillance of acute flaccid paralysis (AFP) and raise a problem of antigenic identification. In Côte d'Ivoire the serotypes of NPEV circulating are unknown. In order to determine the epidemiological and virology characteristics of human (NPEV) stemming from virology investigations from 1996 to 2004, enteroviruses strains isolated from stools and from cerebrospinal fluid have been analysed. The biological products have been tested according to the procedures recommended by the World Health Organisation (WHO) within the context of the virology surveillance of acute flaccid paralysis and the antigenic identification by seroneutralization and serotyping has been done. Out of 144 isolates obtained from 10187 specimens, 637 were Poliovirus strains and 807 NPEV strains (7.9%). Among them 16.3% have been isolated during carrier studies and 83.7% were associated with cases of AFFP Out of the 807 strains of NPE, 218 strains have been tested by serotyping and the serotype of 77 strains (35.32%) has been determined: Coxsackievirus B (41.6%) and different serotypes of Echovirus (58.4%). The proportion of untypable strains (62.3%) confirms the difficulties to identify NPEV with the conventional available reagents. The molecular diagnosis is becoming necessary in order to establish a list of the serotypes of NPEV circulating and associated with clinical features in the country

Rapid and highly sensitive coxsackievirus a indirect immunofluorescence assay typing kit for enterovirus serotyping

We describe the development and evaluation of an indirect immunofluorescence assay (IFA) kit for rapid and sensitive detection of coxsackievirus A2, -4, -5, -6, and -10. This IFA kit was determined to have 95.9 to 100% sensitivity and 95.8 to 97.2% specificity. It also proved to be beneficial in reducing the number of enteroviruses that are untypeable in the clinical virology laboratory.

Basic rationale, current methods and future directions for molecular typing of human enterovirus

Enterovirus is a genus of the Picornaviridae family including more than 80 serotypes belonging to four species designed Human enterovirus A to D. The antigens of the structural proteins support the subdivision of enteroviruses into multiple serotypes. Comparative phylogeny based on molecular typing methods has been of great help to classify former and new types of enterovirus, and to investigate the diversity of enteroviruses and the evolutionary mechanisms involved in their diversity. By now, molecular typing methods of enterovirus rely mainly on the sequencing of an amplicon targeting a variable part of the region coding for the capsid proteins (VP1 and, alternatively, VP2 or VP4), either from a strain recovered by cell culture or, more recently, by direct amplification of a clinical or environmental specimen. In the future, microarrays are thought to play a major role in enterovirus typing and in the analysis of the determinants of virulence that support the puzzling diversity of the pathological conditions associated with human infection by these viruses.

Epidemiologic aspects and laboratory features of enterovirus infections in Western Germany, 2000–2005

From 2000 to 2005, a total of 1,096 enterovirus infections were diagnosed either by isolation of virus from cell culture or by RT-PCR (5'non-coding region (NCR)). Typing of viruses (n = 674) was carried out by immunofluorescence with monoclonal antibodies, neutralization test or molecular methods. Seasons with high enterovirus activity were characterized by high prevalence of echovirus 30 (62.2% in 2000, 25.5% in 2001) and echovirus 13 (34.5% in 2001). In contrast, in the 2003 season, which had very low enterovirus activity, these types were rare. During this season, cell culture sensitivity (human colonic carcinoma cells and human embryonic lung fibroblasts (HEL)) was exceptionally low. In order to determine the type of "non-cultivable" enteroviruses, purified RNA from selected stool samples was subjected to direct molecular typing. VP1/2A-specific fragments were amplified by RT-PCR, cloned and sequenced. The predominant virus identified was coxsackie A. Consequently, rhabdomyosarcom cells were introduced into the daily routine, which improved the isolation of enteroviruses. Echovirus 30 was again most commonly isolated during seasons 2004 and 2005 with increasing enterovirus activity. In conclusion, high prevalence of echovirus 30 and 13 is indicative of seasons with high enterovirus activity. The type of circulating enteroviruses may influence isolation of enterovirus from cell culture. RT-PCR (VP1/2A) combined with cloning and sequencing of amplicons is a useful tool for viral typing directly from stool samples. In cases of severe enterovirus infection, virological diagnosis should not solely rely on virus isolation from cell culture.

Role of cell culture for virus detection in the age of technology

Viral disease diagnosis has traditionally relied on the isolation of viral pathogens in cell cultures. Although this approach is often slow and requires considerable technical expertise, it has been regarded for decades as the "gold standard" for the laboratory diagnosis of viral disease. With the development of nonculture methods for the rapid detection of viral antigens and/or nucleic acids, the usefulness of viral culture has been questioned. This review describes advances in cell culture-based viral diagnostic products and techniques, including the use of newer cell culture formats, cryopreserved cell cultures, centrifugation-enhanced inoculation, precytopathogenic effect detection, cocultivated cell cultures, and transgenic cell lines. All of these contribute to more efficient and less technically demanding viral detection in cell culture. Although most laboratories combine various culture and nonculture approaches to optimize viral disease diagnosis, virus isolation in cell culture remains a useful approach, especially when a viable isolate is needed, if viable and nonviable virus must be differentiated, when infection is not characteristic of any single virus (i.e., when testing for only one virus is not sufficient), and when available culture-based methods can provide a result in a more timely fashion than molecular methods.

Combining multiplex reverse transcription-PCR and a diagnostic microarray to detect and differentiate enterovirus 71 and coxsackievirus A16

Cluster A enteroviruses, including enterovirus 71 (EV71) and coxsackievirus A16 (CA16), are known to cause hand-foot-and-mouth disease (HFMD). Despite the close genetic relationship between these two viruses, EV71 is generally known to be a more perpetuating pathogen involved in severe clinical manifestations and deaths. While the serotyping of enteroviruses is mostly done by conventional immunological methods, many clinical isolates remain unclassifiable due to the limited number of antibodies against enterovirus surface proteins. Array-based assays are able to detect several serotypes with high accuracy. We combined an enterovirus microarray with multiplex reverse transcription-PCR to try to develop a method of sensitively and accurately detecting and differentiating EV71 and CA16. In an effort to design serotype-specific probes for detection of the virus, we first did an elaborate bioinformatic analysis of the sequence database derived from different enterovirus serotypes. We then constructed a microarray using 60-mer degenerate oligonucleotide probes covalently bound to array slides. Using this enterovirus microarray to study 144 clinical specimens from patients infected with HFMD or suspected to have HFMD, we found that it had a diagnostic accuracy of 92.0% for EV71 and 95.8% for CA16. Diagnostic accuracy for other enteroviruses (non-EV71 or -CA16) was 92.0%. All specimens were analyzed in parallel by real-time PCR and subsequently confirmed by neutralization tests. This highly sensitive array-based assay may become a useful alternative in clinical diagnostics of EV71 and CA16.

A comparative amplification of five different genomic regions on Coxsackie A and B viruses. Implications in clinical diagnostics

Modern molecular approaches in Human Enterovirus detection rely on the designing of generic and often degenerate primers in order to amplify specific sequences within the enterovirus genome. In the present study a comparative application of primer sets targeting 5'UTR, the VP1 region, the 3D region as well as a long genomic fragment including the 3'end of VP1, the full length of 2A and 2B, and the 5' moiety of the 2C-coding region was attempted, in order to evaluate their specificity and suitability. The best amplification results from the investigation of 21 CAV reference strains, all six CBV reference strains and 44 clinical strains varying in origin and time of isolation, arose using primer sets 292-222 and UC53-UG52. Based on the above results we conclude that some of the published protocols need to be improved so as to fulfill the demands of an accurate detection and typing of Coxsackie A and B viruses. Contrarily, two of the protocols applied were proved to be more accurate in terms of specificity and general applicability, suggesting that RT-PCR followed by a simple RFLP assay in the case of primer pair UC53-UG52 or by sequencing and sequence analysis in the case of primer set 292-222 should constitute alternative means of modern typing and diagnostics against conventional immunological classification methods.

A highly effective method for removing suspended poliovirus from water using a positively-charged carbon felt electrode

We developed an effective system to eliminate poliovirus from modified tap water using a positively-charged carbon felt electrode. The zeta potential of polioviruses was measured using laser microscopic electrophoresis. Poliovirus adsorption to the electrode was examined by indirect immunofluorescence. The tissue culture infective dose (TCID) of poliovirus type 2 (Sabin strain) was determined using human rhabdomyosarcoma cells (RD cells). Poliovirus VP2 gene copy numbers were assessed by reverse transcription followed by a quantitative real-time polymerase chain reaction. The mean zeta potential of the viruses was -20 mV. Relatively large numbers of polioviruses (10(3) or 4 x 10(3) TCID(50)/0.1 ml) could be removed by adsorption to the electrode, drastically decreasing TCID and copy numbers of poliovirus genome in the water. Virus elimination was dependent on electric current and time. Thus, the positively-charged carbon felt electrode effectively adsorbed polioviruses. The system may prove applicable to the elimination of certain viruses from water.

Molecular identification and typing of enteroviruses isolated from clinical specimens

Enterovirus characterization and typing require an integrated technological approach, using both immunological and molecular methods. The seventy-nine enteroviruses included in this study were isolated from cell cultures and classified as enteroviruses on the basis of an indirect immunofluorescence assay (IFA) against common enterovirus antigens and a neutralization test based on the Lim Benyesh-Melnick (LBM) pool. The final identification was carried out using a number of different molecular approaches, including reverse transcription (RT)-PCR, restriction fragment length polymorphism (RFLP) analysis, and nucleotide sequence analysis of amplicons from various regions of the genome. Twenty-seven poliovirus strains (set A) were identified using LBM pool analysis, RFLP analysis, and IFA. Use of the LBM pool method showed that 35 out of 79 strains were nonpoliovirus (set B), while 17 specimens tested negative (set C). Sets B and C were further investigated. Twenty-five specimens from set B and 8 from set C were identified by IFA. Six specimens from set B and five from set C were identified by RFLP analysis. Specimens in sets B and C were treated using RT-PCR; the resulting amplicons were subjected to nucleotide sequence analysis. The VP1 region was analyzed using two sets of deoxyinosine degenerate primers. Where the VP1 test gave no signal, the VP4-VP2 region was analyzed. Where both tests were negative, a 5' noncoding region analysis was performed. Interestingly, analysis of the VP1 region showed that two specimens from set C were strains of enterovirus 71, whose presence was unexpected in Italy. As in other European epidemiological studies, the strain found most frequently was echovirus 30.

Rapid methods for identification of poliovirus isolates and determination of polio neutralizing antibody titers in human sera

A new rapid method for identification and determination of the titer of polioviruses and other enteroviruses in cell monolayers grown in microtiter plates is described. The method is based on immunoperoxidase staining of infected cells with commercial monoclonal antibodies (MAb) and biotin-labeled secondary antibody. The presence of poliovirus or other enteroviruses was established as the appearance of at least one focus of cells with stained cytoplasm 6 h post-infection. Viral titers determined by this method were expressed as focus forming unit (FFU) per ml which was found to correspond approximately to 10 TCID(50)/ml. The suitability of this technique to determine poliovirus antibody titers in human sera was also tested comparing the immunocytochemical neutralization assay with a conventional neutralization in microtiter plates. The test was standardized using reference human sera in order to produce antibody titers expressed in international units (IU). In addition to high reproducibility, the new neutralization test appears to be sensitive, specific and rapid, and might thus represent a useful tool for the diagnosis of polio and other enterovirus infections.

Variability in molecular typing of Coxsackie A viruses by RFLP analysis and sequencing

The aim of the present study was to develop an assay capable of classifying the Coxsackie A virus (CAV) prototype strains on the basis of restriction fragment length polymorphism (RFLP) analysis of 5'-UTR-derived reverse transcription polymerase chain reaction (RT-PCR) amplicons, and to determine how these data could be used for typing wild-type CAV isolates. Moreover, sequencing of the amplified genomic fragments of the clinical isolates, and comparison with all the published sequences of the respective genomic region of enterovirus reference and wild-type strains were attempted for typing of the isolates. Twenty-four prototype CAV strains from the 23 currently recognized serotypes were studied; most of them were successfully differentiated with the aid of four restriction endonucleases: HaeIII, HpaII, DdeI, and StyI. It was not possible to differentiate between CAV5, 7, and 16, or between CAV15 and 18 in this way, but the members of each of these two groups were satisfactorily differentiated with the aid of single-strand conformational polymorphism (SSCP) analysis of their RT-PCR amplicons. Fifteen clinical isolates, 13 of them of known CAV serotype, were also studied with the same four endonucleases and the results were compared with the data obtained from the RFLP analysis of the reference strains. The experimental results showed that only two clinical samples of previously known identity had an identical restriction pattern with the respective prototype strains. The sequences of the amplicons of the clinical isolates had the greatest percentage of alignment with enterovirus strains of a different serotype, indicating variability in the 5'-UTR and the inability to use the whole sequence of the amplicons for typing CAVs. The significance of the findings in relation to the possible usefulness of the RFLP-based method is discussed.

Molecular detection and identification of an enterovirus during an outbreak of aseptic meningitis

Stool samples from sixteen cases of children with meningitis originating from four different and geographically isolated parts of Greece were investigated for enteroviruses. The conventional method of cell culture in four different cell lines was initially used for the isolation of enteroviruses. The results showed a cytopathic effect (CPE) in all cases after two, or even more successive passages in only one cell line (RD), although a less-than-satisfactory CPE was obtained in many cases. Seroneutralization with RIVM mixed hyperimmune antisera followed and the isolates were typed as Coxsackie B viruses. The method of RT-PCR with enterovirus-specific primers targeted to the highly conserved 5'-UTR of the genome was initially used for the detection of enteroviruses from the inoculated cell cultures. A positive RT-PCR result was obtained for all of the clinical samples rapidly and accurately and the isolates were further characterized with the aid of Restriction Fragment Length Polymorphism (RFLP) analysis and Single Strand Conformation Polymorphism analysis (SSCP) of the amplicons. The RFLP analysis showed first of all that the isolates had an identical restriction pattern with Coxsackie B5 Faulkner reference strain with 4 out of 5 restriction enzymes and secondly, both RFLP and SSCP analysis indicated the epidemiological association of the isolates. The speed of the molecular methodology that was used in comparison with the conventional methods and its possible significance for the description of virus evolution and circulation in the populations is discussed.