Evidence of Hepatitis E Virus Breaking Through the Blood–brain Barrier and Replicating in the Central Nervous System

R. Shi; M. H. Soomro; R. She; Y. Yang; T. Wang; Q. Wu; H. Li; W. Hao

Disclosures

J Viral Hepat. 2016;23(11):930-939. 

In This Article

Abstract and Introduction

Abstract

Neurologic dysfunctions such as Guillain–Barre' syndrome, encephalitis, meningitis and transverse myelitis occur frequently in patients with hepatitis E virus (HEV) infection, and this study was conducted to better characterize the role of HEV in the pathogenesis of neurologic disorders. Genotype 4 strain of swine HEV was used to inoculate Mongolian gerbils. Reverse transcription–nested polymerase chain reaction (RT-nPCR), ELISA, histopathology, ultrastructural pathology and enzyme immunohistochemistry method were conducted to investigate the replication and localization of HEV in the central nervous system (CNS) and the consequent pathological changes. Both positive- and negative-strand HEV RNA was detectable in brain and spinal cord from 7 to 28 dpi (days postinoculation) via RT-nPCR. Various pathological changes such as perineural invasion, neuron necrosis, microglia nodule, lymphocyte infiltration, perivascular cuff and myelin degeneration were observed in HEV-positive brains and spinal cords. Immunohistochemical (IHC) staining targeting on HEV ORF2 protein revealed positive signals concentrated mainly in the cytoplasm of neuron, ependymal epithelium and choroid plexus area. Positive area density of ZO-1 (zonula occludens-1) in brain of HEV-positive gerbils decreased, while the GFAP (glial fibrillary acidic protein) expression was upregulated compared with control groups. These results provide strong evidence that HEV is able to damage the blood–brain barrier (BBB), replicate in brain and spinal cord, and hammer the causative role of HEV in the pathogenesis of neurologic disorders.

Introduction

Hepatitis E virus (HEV) infection is an important public health problem and may lead to consequential morbidity and mortality, especially in developing countries. It is estimated that around 2 billion people are at risk of HEV infection given the fact that they live in epidemic areas.[1,2] HEV was known to be an enterically transmitted zoonotic pathogen, mostly associated with contaminated water and undercooked meat.[3,4] Nevertheless, recent literatures have been reporting cases of patients developing hepatitis E after undergoing blood transfusion or solid organ transplant like kidney.[5,6] Besides liver and intestine, recent reports showed that HEV may also invade a range of organs including spleen, kidney and placenta,[7,8,9,10] and the spectrum of disease caused by HEV is expanding, such as acute pancreatitis, nephropathy, pyomyositis and haematological problems.[11,12] Neurologic disorders including encephalitis, ataxia, acute transverse myelitis, Guillain–Barre' syndrome (GBS), inflammatory polyradiculopathy and brachial neuritis are also becoming an emerging extrahepatic manifestation of HEV infection, in both immunocompromised and immunocompetent patients.[13–16] These cases were reported in developing countries like Thailand, India and China, as well as industrialized countries such as UK, Germany and France.[17–19] It is described that among the patients with locally acquired hepatitis E in the United Kingdom, about 5% of them presented neurologic symptoms. While in Toulouse, France, the rate is around 6%.[20] It indicates a specific neurotropism for HEV.

In previous cases, the alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and γ-glutamyltransferase levels of most patients were much higher than reference value, and HEV infection was diagnosed through the detection of anti-HEV immunoglobulin(Ig)M and HEV RNA in serum and cerebrospinal fluid (CSF). In a specific case of GBS and encephalitis associated with HEV infection reported by Chen et al.,[21] the patient showed mild mental slowness and bilateral hippocampal damage on magnetic resonance imaging (MRI) and diffuse abnormalities in electroencephalogram. The cell level in CSF increased, in consistence with the similar cases presenting cerebellar ataxia reported by Deroux and Despierres.[22,23] However, in the absence of tissue samples, there has been no investigation regarding brain and spinal damages of the patients, and the mechanisms for neurological symptoms associated with HEV infection still remains unclear. The objectives of this study are to characterize the neuroinvasive features of HEV, investigate the replication and localization of HEV in the CNS of experimentally infected gerbils and determine the pathological changes and BBB permeability damage caused by HEV infection, to elucidate the relations between HEV per se and the onset of neurologic manifestations.

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