Biology of coxsackie A viruses

Recent advances in anti-coxsackievirus A16 viral drug research

Hand, foot and mouth disease, a childhood disorder caused by enteroviruses, is intermittently endemic in the Asia-Pacific region and endangers the lives of many infants and young children. Coxsackievirus A16 (CV-A16) is one of the major pathogens causing hand, foot, and mouth disease on occasion, resulting in catastrophic neurological sequelae and patient death. Currently, no clinical interventions are available that completely block the CV-A16 infection. Therefore, research on anti-CV-A16 treatment continues to be a significant focus of interest. This report provides a detailed background on and an introduction to CV-A16; a description of the viral gene and protein structures and a summary of the current advances in pharmaceutical targets, drug research and other related areas.

Fulminant Type 1 Diabetes Mellitus Associated with Coxsackie Virus Type A2 Infection: A Case Report and Literature Review

A 65-year-old Japanese man presented to our hospital in June 2013 with a 6-day history of fever and fatigue, a 24-h history of thirst, and polyuria. His temperature was 37.8°C and he was alert. However, laboratory tests revealed severe hyperglycemia, undetectable C-peptide levels, and diabetic ketoacidosis. Serum antibody testing confirmed a Coxsackie virus A2 infection. A variety of viral infections are reported to be involved in the development of fulminant type 1 diabetes mellitus (FT1D). Our patient is the first reported case of FT1D associated with Coxsackie virus A2 infection and supports the etiological role of common viral infections in FT1D.

Human parechovirus genotypes -10, -13 and -15 in Pakistani children with acute dehydrating gastroenteritis

Human parechoviruses are known to cause asymptomatic to severe clinical illness predominantly respiratory and gastroenetric infections. Despite their global prevalence, epidemiological studies have not been performed in Pakistan. In this study, we retrospectively analyzed 110 fecal specimen and found 26 (24%) positive for viral RNA with HPeV-10 (n = 3, 23%), HPeV-13 (n = 4, 31%) and HPeV-15 (n = 6, 46%) genotypes. Clinical features of patients with different HPeV genotypes were compared. All HPeV positive children were aged ≤4 years (mean 13.92 months). The male-to-female ratio was 1: 1.17 (46.2 vs 53.8%) with significant association (p = .031) to HPeV infectivity. HPeV-10 and -13 were found during summer while HPeV-15 was only detected during late winter season. Disease symptoms were more severe in children infected with HPeV-10 and -13 as compared to HPeV-15. Fever and vomiting were observed in 100% cases of HPeV-10 and -13 while only 17% patients of HPeV-15 had these complaints. Phylogenetic analyses showed that HPeV-10, -13 and -15 strains found in this study have 9-13%, 16.8% and 21.8% nucleotide divergence respectively from the prototype strains and were clustered to distinct genetic lineages. This is the first report of HPeV-15 infection in humans although first identified in rhesus macaques. The arginine-glycine-aspartic acid (RGD) motif present at the C-terminal of VP1 responsible for the viral attachment to cellular integrins was not found in all of these strains. In conclusion, these findings enhance our knowledge related to the epidemiology and genetic diversity of the HPeV in Pakistan and support the need for continued laboratory based surveillance programs especially in infants and neonatal clinical settings. Further, the parechovirus pathogenesis, cross-species transmission and disease reservoirs must be ascertained to adopt better prevention measures.

Detection and molecular characterization of enteroviruses in Korean surface water by using integrated cell culture multiplex RT-PCR

OBJECTIVE

To identify waterborne enteric viruses in Korean surface water.

METHODS

Integrated cell culture (ICC)-multiplex reverse transcription-polymerase chain reaction (RT-PCR) was simultaneously designed to detect coxsackieviruses (CV), polioviruses (PV), and reoviruses (RV). ICC-multiplex RT-PCR and phylogenetic analysis were conducted using 21 total culturable virus assay (TCVA)-positive sample-inoculated cell cultures.

RESULTS

CV and RV were detected in 9 samples each, and 3 samples were positive for both CV and RV. PV was not detected in any sample. Molecular phylogenetic analysis of the VP1 gene sequences revealed that CV types B2 and B4 predominated in Korean surface water, and the nucleotide sequences of CV type B2 were clustered with those of CVs isolated from China and Japan. The results suggested that the evolution of these viruses occurred in a region-specific manner.

CONCLUSION

CV and RV are detectable in Korean surface water, with a predominance of CV type B2, and the evolution of CV type B2 occur in a region-specific manner.

A CpG oligodeoxynucleotide inducing anti-coxsackie B3 virus activity in human peripheral blood mononuclear cells

Coxsackie B3 virus (CVB3) is the most significant pathogen causing myocarditis in humans, and antiviral therapy would be most effective in the early stages of the disease. Here we provide evidence that BW001, a C-type CpG oligodeoxynucleotide, induces anti-CVB3 activity in human peripheral blood mononuclear cells (PBMCs). In parallel, we have demonstrated that BW001 induces human PBMCs to express mRNAs of multiple types of interferon (IFN), including IFN-alpha, IFN-beta, IFN-omega and IFN-gamma, and to express mRNAs of at least 11 subtypes of IFN-alpha. The induced IFNs may contribute to the anti-CVB3 activity. The results suggest that BW001 could be developed into a medication with the potential to treat CVB3 infectious diseases by inducing natural mixed IFNs.

The difficult-to-cultivate coxsackieviruses A can productively multiply in primary culture of mouse skeletal muscle

Coxsackieviruses A (CVA) are associated with several clinical manifestations such as aseptic meningitis and paralytic syndromes in humans. Most CVA are difficult-to-cultivate, which impedes their propagation and isolation from clinical material. Here, we tested the ability of cultivable (CVA-13, CVA-14), and difficult-to-cultivate (CVA-6, CVA-22) strains to infect primary cultures of skeletal muscle cells established from newborn mice. We found that such cultures sustained the multiplication of these CVA, as evidenced by the development of a cytopathic effect, already in the initial preparation or after passaging once. Cultures established for no more than 24h were sensitive to infection whereas older preparations were resistant. Using confocal microscopy after double-immunolabeling of the VP1 capsid protein and the muscle cell marker myosin, we demonstrated that only the myoblasts were infected, resulting in VP1 expression throughout their cytoplasm. Inoculation of infected cultures to suckling mice resulted in paralysis indicating that infection was productive. The nature of candidate receptors for virus entry in such cultures and the influence of cell culture conditions on the expression of these putative receptors are discussed. This work suggests that primary cultures of skeletal muscle cells could be used to propagate and isolate any CVA strain.

Recognition of coxsackievirus A by Enterovirus genus-specific immune and molecular markers in experimentally infected suckling mice

OBJECTIVE

Most of coxsackieviruses A (CV-A) are difficult to isolate in cell culture and are responsible for flask paralysis in suckling mice. The aim of the present work was to analyze the ability of immune and RT-PCR techniques to detect viral components of three different serotypes, CV-A6, CV-A13, and CV-A14, in skeletal muscles of experimentally infected suckling mice.

MATERIAL AND METHODS

The antigen detection was done by immunofluorescence technique on trypsinized muscular cells and by immunoperoxidase assay on frozen sections of skeletal muscle, using a monoclonal antibody directed towards a conserved epitope of the VP1 capsid protein among enteroviruses. The nested RT-PCR technique used primers located in the 5' non coding region of viral RNA.

RESULTS

The group antigen was present in muscle cells of suckling mice infected by the three serotypes of CV-A which were assayed. Similarly, the muscle specimens were positive by nested RT-PCR. A kinetic study performed with CV-A13 and CV-A14 showed that the RT-PCR assay was positive as soon as 24 h after infection whereas the detection of VP1 antigen and symptoms of flask paralysis were observed only 48 and 72 h after infection, respectively.

CONCLUSION

These results show that the tested serotypes of CV-A can be easily detected in muscle specimens of suckling mice by using antigenic and molecular techniques currently available for the diagnosis of enterovirus infections.

Advances in the diagnosis of respiratory virus infections

Background: Advances have been made in selecting sensitive cell lines for isolation, in early detection of respiratory virus growth in cells by rapid culture assays, in production of monoclonal antibodies to improve many tests such as immunofluorescence detection of virus antigens in nasopharyngeal aspirates, in highly sensitive antigen detections by time-resolved fluoroimmunoassays (TR-FIAs) and biotin-enzyme immunoassays (BIOTH-E), and, finally, in the polymerase chain reaction (PCR) detection of respiratory virus DNA or RNA in clinical specimens. All of these advances have contributed to new or improved possibilities for the diagnosis of respiratory virus infections.

Objectives and study design: This review summarizes our experiences during the last 15 years in the development of diagnostic tests for respiratory virus infections, and in use of these tests in daily diagnostic work and in epidemiological studies.

Results: Immunofluorescence tests based on monoclonal antibodies, all-monoclonal TR-FIAs, and biotin-enzyme immunoassays (EIAs) have about the same sensitivities and specificities. They compare well with the sensitivity of virus culture. PCR followed by liquid-phase hybridization is a sensitive method for detecting adenovirus DNA and enterovirus and rhinovirus RNA in clinical specimens. IgG EIA on paired acute and convalescent phase sera is the most sensitive serological test for respiratory virus infections and is a valuable reference method when evaluating the sensitivity of new diagnostic tests. The IgG avidity test can distinguish primary infections from re-infections at least in respiratory syncytial virus (RSV) infections. IgM antibody assays, on the other hand, had low sensitivities in our studies.

Conclusions: The choice of diagnostic methods for respiratory virus infections depends on the type and location of the laboratory, the number of specimens tested, and the previous experience of the laboratory. Virus culture, whenever possible, should be the basic diagnostic method; the results, including identification of the virus, should be available no more than 24 h later than the results of rapid diagnostic tests. In small laboratories, especially in hospitals where specimen transportation is well organized, immunofluorescence may be the best choice for antigen detection with the provision that an experienced microscopist and a good UV microscope are available. If the laboratory receives a large number of specimens and has previous experience with EIAs, then biotin-EIAs or TR-FIAs may be the most practical techniques. Their advantages include the stability of the antigens in clinical samples since intact, exfoliated epithelial cells are not required, treatment of specimens is practical, testing of large numbers of specimens is possible, and reading the printed test result is less subjective than reading fluorescence microscopy. The larger role of PCR in the diagnosis of respiratory virus infections depends on future developments such as practical methods to extract DNA or RNA and to purify the extracts from nonspecific inhibitors, plus further improvements to minimize cross-contamination. Group-specific detection of enteroviruses and rhinoviruses is an example of the potential for PCR technology. In experienced laboratories. EIA IgG antibody tests should be available. Recombinant antigens may be a useful part of such assays.

Molecular identification of enteroviruses responsible for an outbreak of aseptic meningitis; implications in clinical practice and epidemiology

An outbreak of aseptic meningitis was recorded in Greece during the year 2001. Detection of the clinical strains was achieved by performing reverse transcription-polymerase chain reaction (RT-PCR) on RNA isolated from cell cultures inoculated with treated faecal material from the patients. Serotypic identification of the isolates with mixed equine antisera pools followed and the RT-PCR amplicons were further studied by restriction fragment length polymorphism analysis and sequencing. Fifty-three clinical enterovirus strains were isolated from respective cases of suspected enterovirus infection, most of which showed the clinical symptoms of aseptic meningitis. Echovirus (ECV) 6 was the most frequently isolated serotype, followed by coxsackie B viruses, ECV13, poliovirus type 1 (PV1) vaccine strain and ECV30. Nucleotide sequence analysis showed the existence of different genetic groups on the basis of the 5'-untranslated region (5'-UTR) of the genome, which circulated in the population during the same time period. Different serotypes belonged to the same genetic group and vice versa. The 5'-UTR seems to be appropriate for the investigation of enterovirus evolution and epidemiology.

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.

Arginine-glycine-aspartic acid motif is critical for human parechovirus 1 entry

The human parechovirus 1 RGD motif in VP1 was studied by mutagenesis. An RGD-to-RGE change gave only revertant viruses with a restored RGD, while deletion of GD was lethal and nonrevertable. Mutations at the +1 and +2 positions had some effect on growth properties and a +1 M-to-P change was lethal. These studies indicate that the RGD motif plays a critical role in infectivity, presumably by interacting with integrins, and that downstream amino acids can have an influence on function.

The crystal structure of coxsackievirus A9: new insights into the uncoating mechanisms of enteroviruses

BACKGROUND

Coxsackievirus A9 (CAV9), a human pathogen causing symptoms ranging from common colds to fatal infections of the central nervous system, is an icosahedral single-stranded RNA virus that belongs to the genus Enterovirus of the family Picornaviridae. One of the four capsid proteins, VP1, includes the arginine-glycine-aspartate (RGD) motif within its C-terminal extension. This region binds to integrin alpha v beta 3, the only receptor for CAV9 to be conclusively identified to date.

RESULTS

The crystal structure of CAV9 in complex with the antiviral compound WIN 51711 has been solved to 2.9 A resolution. The structures of the four capsid proteins, VP1 to VP4, resemble those of other picornaviruses. The antiviral compound is bound in the VP1 hydrophobic pocket, and it is possible that the pocket entrance contains a second WIN 51711 molecule. Continuous electron density for the VP1 N terminus provides a complete picture of the structure close to the fivefold axis. The VP1 C-terminal portion is on the outer surface of the virus and becomes disordered five-residues N-terminal to the RGD motif.

CONCLUSIONS

The RGD motif is exposed and flexible in common with other known integrin ligands. Although CAV9 resembles coxsackie B viruses (CBVs), several substitutions in the areas implicated in CBV receptor attachment suggest it may recognise a different receptor. The structure along the fivefold axis provides new information on the uncoating mechanism of enteroviruses. CAV9 might bind a larger natural pocket factor than other picornaviruses, an observation of particular relevance to the design of new antiviral compounds.

An RNA tertiary structure in the 3' untranslated region of enteroviruses is necessary for efficient replication

RNA tertiary structures, such as pseudoknots, are known to be biologically significant in a number of virus systems. The 3' untranslated regions of the RNA genomes of all members of the Enterovirus genus of Picornaviridae exhibit a potential, pseudoknot-like, tertiary structure interaction of an unusual type. This is formed by base pairing between loop regions of two secondary structure domains. It is distinct from a potential, conventional pseudoknot, studied previously in poliovirus, which is less conserved phylogenetically. We have analyzed the tertiary structure feature in one enterovirus, coxsackievirus A9, using specific mutagenesis. A double mutant in which the potential interaction was destroyed was nonviable, and viability was restored by introducing compensating mutations, predicted to allow the interaction to reform. Phenotypic pseudorevertants of virus mutants, having mutations designed to disrupt the interaction, were all found to have acquired nucleotide changes which restored the potential interaction. Analysis of one mutant containing a single-base mutation indicated a greatly increased temperature sensitivity due to a step early in replication. The results show that, in addition to secondary structures, tertiary RNA structural interactions can play an important role in the biology of picornaviruses.

The coxsackievirus A9 RGD motif is not essential for virus viability

An RGD (arginine-glycine-aspartic acid) motif in coxsackievirus A9 has been implicated in internalization through an interaction with the integrin alpha v beta 3. We have produced a number of virus mutants, lacking the motif, which have a small-plaque phenotype in LLC-Mk2 and A-Vero cells and are phenotypically normal in RD cells. Substitution of flanking amino acids also affected plaque size. The results suggest that interaction between the RGD motif and alpha v beta 3 is not critical for virus viability in the cell lines tested and therefore that alternative regions of the CAV-9 capsid are involved in internalization.

Molecular epidemiology of enterovirus outbreaks in Canada during 1991-1992: identification of echovirus 30 and coxsackievirus B1 strains by amplicon sequencing

The relatedness of enteroviral isolates associated with two recent outbreaks in Canada was assessed using direct sequencing of amplicons derived from a large portion of the 5' nontranslated region (NTR) of the viral genome. The amplicons of 60 echovirus 30 isolates originating from seven different provinces in 1991 were found to share 99% or greater sequence identity. Recent coxsackievirus B1 isolates characterised in the same manner were identical to each other. When the 5' NTR sequence of these isolates was compared to prototype strains a difference of 11-15% in nucleotide composition was observed. These results indicate that the variability of nucleotide sequence found in 5' NTRs can be utilized to identify rapidly enteroviral strains associated with particular outbreaks and distinguish them from other strains and serotypes.