Neonatal rhesus monkey is a potential animal model for studying pathogenesis of EV71 infection

Necrotizing myositis causes restrictive hypoventilation in a mouse model for human enterovirus 71 infection

BACKGROUND

Enterovirus 71 (EV71) infections are associated with a high prevalence of hand, foot and mouth disease (HFMD) in children and occasionally cause lethal complications. Most infections are self-limiting. However, resulting complications, including aseptic meningitis, encephalitis, poliomyelitis-like acute flaccid paralysis, and neurological pulmonary edema or hemorrhage, are responsible for the lethal symptoms of EV71 infection, the pathogenesis of which remain to be clarified.

RESULTS

In the present study, 2-week-old Institute of Cancer Research (ICR) mice were infected with a mouse-adapted EV71 strain. These infected mice demonstrated progressive paralysis and died within 12 days post infection (d.p.i.). EV71, which mainly replicates in skeletal muscle tissues, caused severe necrotizing myositis. Lesions in the central nervous system (CNS) and other tissues were not observed.

CONCLUSIONS

Necrotizing myositis of respiratory-related muscles caused severe restrictive hypoventilation and subsequent hypoxia, which could explain the fatality of EV71-infected mice. This finding suggests that, in addition to CNS injury, necrotic myositis may also be responsible for the paralysis and death observed in EV71-infected mice.

Study of the integrated immune response induced by an inactivated EV71 vaccine

Enterovirus 71 (EV71), a major causative agent of hand-foot-and-mouth disease (HFMD), causes outbreaks among children in the Asia-Pacific region. A vaccine is urgently needed. Based on successful pre-clinical work, phase I and II clinical trials of an inactivated EV71 vaccine, which included the participants of 288 and 660 respectively, have been conducted. In the present study, the immune response and the correlated modulation of gene expression in the peripheral blood mononuclear cells (PBMCs) of 30 infants (6 to 11 months) immunized with this vaccine or placebo and consented to join this study in the phase II clinical trial were analyzed. The results showed significantly greater neutralizing antibody and specific T cell responses in vaccine group after two inoculations on days 0 and 28. Additionally, more than 600 functional genes that were up- or down-regulated in PBMCs were identified by the microarray assay, and these genes included 68 genes associated with the immune response in vaccine group. These results emphasize the gene expression profile of the immune system in response to an inactivated EV71 vaccine in humans and confirmed that such an immune response was generated as the result of the positive mobilization of the immune system. Furthermore, the immune response was not accompanied by the development of a remarkable inflammatory response.

Clinical Trial Registration: NCT01391494 and NCT01512706.

Progress on the research and development of human enterovirus 71 (EV71) vaccines

Enterovirus 71 (EV71) infections, which can cause severe complications, have become one of the serious public health issues in the Western Pacific region and China. To date, a number of pharmaceutical companies and institutes have initiated the research and development of EV71 vaccines as a countermeasure. As is the case with innovative vaccine development, there are several critical bottlenecks in EV71 vaccine development that must be overcome before the clinical trials, including the selection of vaccine strain, standardization of the procedure for quantifying neutralizing antibody (NTAb) and antigen, establishment and application of a reference standard and biological standards, development of animal models for the evaluation of protective efficacy, and identification of the target patient population. To tackle these technical obstacles, researchers in Mainland of China have conducted a series of studies concerning the screening of vaccine strains and the establishment of criteria, biological standards and detection methods, thereby advancing EV71 vaccine development. This review summarizes recent worldwide progress on the quality control and evaluation of EV71 vaccines.

Enterovirus 71: pathogenesis, control and models of disease

Enterovirus 71 (EV71) is one of the major agents responsible for hand, foot and mouth disease. The increasing incidence of hand, foot and mouth disease outbreaks, epidemics due to EV71 infection in South East Asia and the propensity of EV71 strains to cause severe neurological complications in young children underscore the need to further our knowledge and understanding of the mechanisms involved in EV71 pathogenesis; such knowledge could then be translated to the identification of biomarkers of disease severity, and the development of effective therapeutics and vaccines. This article reviews the current knowledge of EV71 pathogenesis, control measures and models of infection.

The effect of enterovirus 71 immunization on neuropathogenesis and protein expression profiles in the thalamus of infected rhesus neonates

Enterovirus 71 (EV71) is a major pathogen that causes hand-foot-mouth disease (HFMD). Our previous studies have demonstrated that the complete process of pathogenesis, which may include tissue damage induced by host inflammatory responses and direct tissue damage caused by viral infection, can be observed in the central nervous system (CNS) of animals infected in the laboratory with EV71. Based on these observations, the neuropathogenesis and protein expression profiles in the thalamic tissues of EV71-infected animals were further analyzed in the present study. Changes in protein expression profiles following immunization with the inactivated EV71 vaccine followed by virus challenge were observed and evaluated, and their physiological roles in viral pathogenesis are discussed. Taken together, the results of these experiments provide evidence regarding the neuropathogenesis and molecular mechanisms associated with EV71 infection and identify several protein indicators of pathogenic changes during viral infection.

A non-mouse-adapted enterovirus 71 (EV71) strain exhibits neurotropism, causing neurological manifestations in a novel mouse model of EV71 infection

Enterovirus 71 (EV71) is a neurotropic pathogen that has been consistently associated with the severe neurological forms of hand, foot, and mouth disease. The lack of a relevant animal model has hampered our understanding of EV71 pathogenesis, in particular the route and mode of viral dissemination. It has also hindered the development of effective prophylactic and therapeutic approaches, making EV71 one of the most pressing public health concerns in Southeast Asia. Here we report a novel mouse model of EV71 infection. We demonstrate that 2-week-old and younger immunodeficient AG129 mice, which lack type I and II interferon receptors, are susceptible to infection with a non-mouse-adapted EV71 strain via both the intraperitoneal (i.p.) and oral routes of inoculation. The infected mice displayed progressive limb paralysis prior to death. The dissemination of the virus was dependent on the route of inoculation but eventually resulted in virus accumulation in the central nervous systems of both animal groups, indicating a clear neurotropism of the virus. Histopathological examination revealed massive damage in the limb muscles, brainstem, and anterior horn areas. However, the minute amount of infectious viral particles in the limbs from orally infected animals argues against a direct viral cytopathic effect in this tissue and suggests that limb paralysis is a consequence of EV71 neuroinvasion. Together, our observations support that young AG129 mice display polio-like neuropathogenesis upon infection with a non-mouse-adapted EV71 strain, making this mouse model relevant for EV71 pathogenesis studies and an attractive platform for EV71 vaccine and drug testing.

Immunoprotection elicited by an enterovirus type 71 experimental inactivated vaccine in mice and rhesus monkeys

A number of commonly recognized public health issues are associated with EV71 infection, including the induction of severe cases of hand-foot-and-mouth disease (HFMD). Because of such issues, research and development of EV71 vaccine candidates is of growing importance. In the present study, an experimental EV71 inactivated vaccine was prepared, and its corresponding immunogenicity was analyzed. The immune responses and immunoprotective effect induced by the vaccine in mice and rhesus monkeys are described, and the two animal models are compared to evaluate the potential of assessing the inactivated vaccine's immunogenicity in these two species. In addition to assessing the vaccine's efficacy in mice, our data further elucidate the significance and value of assessing the immunogenicity and immunoprotection of vaccine candidates in rhesus monkeys by relying on a range of analyses, including pathological, etiological and lethal challenge analyses.