Enterovirus 71: pathogenesis, control and models of disease

Recent advances in enterovirus A71 pathogenesis: a focus on fatal human enterovirus A71 infection

Enterovirus A71 (EV-A71) is one of the major pathogens responsible for hand, foot, and mouth disease (HFMD). Many HFMD outbreaks have been reported throughout the world in the past decades. Compared with other viruses, EV-A71 infection is more frequently associated with severe neurological complications and even death in children. EV-A71 can also infect adults and cause severe complications and death, although such cases are very uncommon. Although fatal cases of EV-A71 infection have been reported, the underlying mechanisms of EV-A71 infection, especially the mode of viral spread into the central nervous system (CNS) and mechanisms of pulmonary edema, which is considered to be the direct cause of death, have not yet been fully clarified, and more studies are needed. Here, we first summarize the pathological findings in various systems of patients with fatal EV-A71 infections, focussing in detail on gross changes, histopathological examination, tissue distribution of viral antigens and nucleic acids, systemic inflammatory cell infiltration, and tissue distribution of viral receptors and their co-localization with viral antigens. We then present our conclusions about viral dissemination, neuropathogenesis, and the mechanism of pulmonary edema in EV-A71 infection, based on pathological findings.

Pathologic and molecular studies of enterovirus 71 infection in a fatal case from a recent epidemic in China: A case report

RATIONALE

Enterovirus 71 (EV71) is identified as the primary cause of hand, foot, and mouth disease (HFMD) and mainly infects the young infants. Though some fatal cases have been reported, the underlying mechanisms of EV71 infection remain elusive and more further pathologic and molecular studies of EV71 infection are needed.

PATIENT CONCERNS

A 26-month-old girl with a history of fever and lethargy for 3 days and intermittent seizures for 2 hours associated with rash on 4 limbs was brought to a hospital.

DIAGNOSES

The autopsy was performed to identify the cause of death for a medical dispute. The results of histologic examination, immunohistochemistry (IHC), nested reverse transcription polymerase chain reaction (RT-PCR), and viral isolation confirmed that this patient died of EV71 infection.

INTERVENTIONS

The patient was transferred to neonatal intensive care unit and was intubated and mechanically ventilated. The other treatment included cardiopulmonary resuscitation and intravenous injection of adrenaline.

OUTCOMES

The patient presented persistent coma and intermittent seizures and suddenly developed respiratory arrest and died 16 hours after admission.

LESSONS

Our results suggest that EV71 might invade into the central nervous system (CNS) through peripheral nerves which control the digestive tract in the early stage of infection. In addition, we successfully isolated one EV71 strain. Phylogenetic analysis showed that the isolated strain clustered in the C4a of C4 subgenotype. This case also highlights that rapid deterioration in HFMD cases is still a challenge to physicians and they must pay special attention to the infants with HFMD symptoms, particularly in EV71 epidemic areas for early diagnosis and treatment.

Antiviral effects of Retro-2cycl and Retro-2.1 against Enterovirus 71 in vitro and in vivo

Enterovirus 71 (EV71) is one of the causative pathogens of hand, foot and mouth disease (HFMD), especially the form associated with fatal neurological disorders. Sustained outbreaks of EV71 infections remain a serious health threat worldwide. However, no antiviral agent against EV71 for clinical therapy has been approved. Retro-2^cycl and Retro-2.1 are inhibitors of several pathogens specifically targeting the intracellular vesicle transport, which also participates in the EV71 lifecycle processes including progeny virus release. Here, we reported that Retro-2^cycl and Retro-2.1, respectively, could inhibit EV71 infection with 50% effective concentrations of 12.56 μM and 0.05 μM in a cytopathic effect inhibition assay and showed relatively low cytotoxicity with 50% cytotoxicity concentrations of more than 500 μM and 267.80 μM. Preliminary mechanism studies revealed that Retro-2^cycl and Retro-2.1 did not inhibit EV71 protein synthesis or RNA replication but could block progeny EV71 release specifically. Furthermore, administration of Retro-2^cycl at the dose of 10 mg/kg significantly protected 90% of newborn mice from lethal EV71 challenge. Consequently, our results for the first time identified Retro-2^cycl and Retro-2.1 as effective inhibitors of EV71 as well as lead compounds, which would contribute to anti-EV71 drug development. We also identified progeny virus release and the intracellular vesicle transport as antiviral targets for EV71.

Antiviral activity of Lactobacillus reuteri Protectis against Coxsackievirus A and Enterovirus 71 infection in human skeletal muscle and colon cell lines

Background

Recurrence of hand, foot and mouth disease (HFMD) pandemics continues to threaten public health. Despite increasing awareness and efforts, effective vaccine and drug treatment have yet to be available. Probiotics have gained recognition in the field of healthcare worldwide, and have been extensively prescribed to babies and young children to relieve gastrointestinal (GI) disturbances and diseases, associated or not with microbial infections. Since the faecal-oral axis represents the major route of HFMD transmission, transient persistence of probiotic bacteria in the GI tract may confer some protection against HFMD and limit transmission among children.

Methods

In this work, the antiviral activity of two commercially available probiotics, namely Lactobacillus reuteri Protectis (L. reuteri Protectis) and Lactobacillus casei Shirota (L. casei Shirota), was assayed against Coxsackieviruses and Enterovirus 71 (EV71), the main agents responsible for HFMD. In vitro infection set-ups using human skeletal muscle and colon cell lines were designed to assess the antiviral effect of the probiotic bacteria during entry and post-entry steps of the infection cycle.

Results

Our findings indicate that L. reuteri Protectis displays a significant dose-dependent antiviral activity against Coxsackievirus type A (CA) strain 6 (CA6), CA16 and EV71, but not against Coxsackievirus type B strain 2. Our data support that the antiviral effect is likely achieved through direct physical interaction between bacteria and virus particles, which impairs virus entry into its mammalian host cell. In contrast, no significant antiviral effect was observed with L. casei Shirota.

Conclusions

Should the antiviral activity of L. reuteri Protectis observed in vitro be translated in vivo, such probiotics-based therapeutic approach may have the potential to address the urgent need for a safe and effective means to protect against HFMD and limit its transmission among children.