What's new with enteroviral infections?

Low prevalence of invasive bacterial infection in febrile infants under 3 months of age with enterovirus infection

Infants under 3 months of age with fever without source (FWS) generally undergo a full, invasive septic evaluation to exclude invasive bacterial infection (IBI). Enterovirus (EV) infections are mostly banal and self-limiting and show a high prevalence rate at this age. We aimed to investigate the prevalence of IBI in EV-infected and uninfected infants under 3 months of age with FWS. This was a prospective observational cohort study of infants aged <90 days who were admitted because of FWS. As per protocol, blood and urine analysis and culture were obtained in all cases, and RNA EV from blood and/or cerebrospinal fluid samples was determined by real-time PCR. Three hundred and eighty-one previously healthy infants with FWS were included. EV infection was diagnosed in 64 children (16.8%; 95% confidence interval, 13.2-20.9%) and showed an uneventful evolution in all cases. Laboratory markers of infection were consistently lower in EV-infected patients; only one case of IBI (1.6%) was observed in an EV-infected patient as compared with 25.2% in EV-negative infants (p <0.001). Intravenous antibiotic use and length of stay were no different in EV-infected and uninfected patients. In our study, febrile infants (<90 days) diagnosed with EV infection showed a low risk of IBI when compared with uninfected patients. The systematic investigation of EV infection in young infants with FWS may allow a more conservative approach to the management of these patients. Further studies on this diagnostic approach are needed.

Pitfalls in the diagnosis of enteroviral infection in young children

BACKGROUND

Three infants with enteroviral infections were admitted to a neonatal intensive care unit (NICU). Investigation into the possible nosocomial spread of enterovirus identified 31 other infected infants. Only 1 of the 31 was truly positive; 30 were false-positive results.

METHODS

This was a retrospective observational study. Investigational laboratory studies were conducted to identify problems in diagnostic procedures.

RESULTS

Stool cultures were used to identify asymptomatic infections. Investigation identified several problems in the procedures in identification of enterovirus: (1) stool specimens were not properly filtered, (2) insufficient number of tissue culture cell types were used, (3) nonspecific toxicity due to stool and the presence of Clostridia difficile toxin was responsible for cytopathic effects in tissue culture, (4) the failure to block nonspecific fluorescent staining led to misidentification of enteroviruses.

CONCLUSIONS

The use of stool cultures to identify asymptomatic enteroviral infections in infants in an NICU can be fraught with problems because of high frequency of C. difficile toxin and the nonspecific toxic effects of stool on tissue culture cells. These problems can be rectified when proper procedures are followed.

A small interfering RNA targeting coxsackievirus B3 protects permissive HeLa cells from viral challenge

We examined the ability of small interfering RNAs (siRNAs) to disrupt infection by coxsackievirus B3 (CVB3). The incorporation of siRNAs dramatically decreased cell death in permissive HeLa cells in parallel with a reduction in viral replication. Three of four siRNAs had potent anti-CVB3 activity. The present study thus demonstrates that the antiviral effect is due to the downregulation of viral replication. In addition, an effective CVB3-specific siRNA had similar antiviral effects in other related enteroviruses possessing sequence homology in the targeted region. Because the CVB3-specific siRNA is effective against other enteroviruses, siRNAs have potential for a universal anti-enterovirus strategy.

Characterization of Nonpolio Enteroviruses Recovered from Patients with Aseptic Meningitis in Korea

OBJECTIVES

We attempted to characterize nonpolio enteroviruses recovered from Korean patients with aseptic meningitis.

METHODS

We performed RT-PCR on the 5'-nontranslated region using clinical specimens. Infectious clinical isolates were amplified by infecting Vero cells with RT-PCR-positive clinical specimens. We then investigated the direct effect in primary neuronal cells or cardiomyocytes following virus infection.

RESULTS

Total 12 clinical isolates were subtypically analyzed by both RT-PCR/sequencing comparison of the VP-1 region and neutralization assay. 43-2, 43-2S, 57 and 58 were found to be coxsackievirus B1 (CVB1), 312 to be CVB5, 14-2S and 327 to be echovirus 6, 165 to be echovirus 9, 337 to be echovirus 11, and 270 to be echovirus 30. All the clinical isolates tested showed profound cytotoxicity to various degrees in the primary neuronal cells within 24 h postinfection at 10 MOI. By contrast, a significant cytopathic effect was observed in the primary cardiomyocytes at 3-5 days postinfection at 50 MOI.

CONCLUSIONS

The present study suggests that the clinical isolates recovered from Korean patients belonged to different CVB or echovirus serotypes and that these viruses showed diversities in their virulence in primary neuronal cells and cardiomyocytes.

Susceptibility of mouse primary cortical neuronal cells to coxsackievirus B

Coxsackievirus B (CVB) is often associated with aseptic meningitis and encephalitis, but the six serotypes of CVB vary in their relative disease severity. To elucidate the detailed mechanisms of CVB-induced cytopathological effects, the morphological and biochemical characteristics caused by the CVB serotypes in mouse primary cortical neuronal cells were investigated. By 24 h post-infection, all CVB serotypes except CVB2 induced severe cytotoxic alterations, including a loss of neurites. Both fluorescence and transmission electron microscopy revealed CVB-induced morphological changes indicative of apoptosis, including heavily condensed nuclei, subsequent chromatin condensation into the periphery of the nuclei and oligonucleosomal DNA fragmentation. It was also found that infection with all six CVB serotypes led to productive virus replication, which was completed prior to an apoptotic signal. The caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone significantly inhibited nuclear changes associated with virus-induced apoptosis, but had less effect on virus-associated cytopathic effects and no effect on virus production. In contrast, the transcription inhibitor actinomycin D profoundly inhibited all three virus-induced events. Taken together, these findings demonstrate that all six CVB serotypes can efficiently replicate in mouse cortical neuronal cells and that productive replication of these CVBs, except for CVB2, induces multiple cytopathological effects, including apoptotic alterations.

Characteristics of apoptotic cell death induced by coxsackievirus B in permissive Vero cells

Coxsackievirus B (CVB) causes a wide spectrum of human diseases which are closely associated with direct destruction of infected cells. We investigated the morphological and biochemical characteristics of CPEs in permissive Vero cells caused by different CVB serotypes. Regardless of serotype, the infected cells experienced similar degrees of CPEs within 24 h postinfection (p.i.). Using both Hoechst 33342 staining and transmission electron microscopy, we consistently observed morphological properties of apoptosis, heavily condensed nuclei and subsequent chromatin condensation into the periphery of the nuclei within 12 h p.i. Moreover, we noticed typical oligonucleosomal DNA fragmentation, while productive CVB multiplication was accomplished within 6 h p.i. prior to an apoptotic signal. Caspase inhibitor significantly prohibited nuclear changes due to apoptosis with no influence on virus production and cell death, demonstrating that all the CVBs induced more than one type of pathological effect, including apoptotic alteration in permissive Vero cells.