healthcare Review Towards the Improved Accuracy of Hepatitis E Diagnosis in Vulnerable and Target Groups: A Global Perspective on the Current State of Knowledge and the Implications for Practice Jasminka Talapko 1 , Tomislav Meštrovi´c 2,3, Emina Pustijanac 4 and Ivana Škrlec 1,* 1 Faculty of Dental Medicine and Health, Josip Juraj Strossmayer University of Osijek, HR-31000 Osijek, Croatia; [email protected] 2 University Centre Varaždin, University North, HR-42000 Varaždin, Croatia; [email protected] 3 Clinical Microbiology and Parasitology Unit, Dr. Zora Profozi´cPolyclinic, HR-10000 Zagreb, Croatia 4 Faculty of Natural Sciences, Juraj Dobrila University of Pula, HR-52100 Pula, Croatia; [email protected] * Correspondence: [email protected] Abstract: The hepatitis E virus (HEV) is a positive single-stranded, icosahedral, quasi-enveloped RNA virus in the genus Orthohepevirus of the family Hepeviridae. Orthohepevirus A is the most numerous species of the genus Orthohepevirus and consists of eight different HEV genotypes that can cause infection in humans. HEV is a pathogen transmitted via the fecal–oral route, most commonly by consuming fecally contaminated water. A particular danger is the HEV-1 genotype, which poses a very high risk of vertical transmission from the mother to the fetus. Several outbreaks caused by this genotype have been reported, resulting in many premature births, abortions, and also neonatal Citation: Talapko, J.; Meštrovi´c,T.; and maternal deaths. Genotype 3 is more prevalent in Europe; however, due to the openness of Pustijanac, E.; Škrlec, I. Towards the the market, i.e., trade-in animals which represent a natural reservoir of HEV (such as pigs), there is Improved Accuracy of Hepatitis E a possibility of spreading HEV infections outside endemic areas. This problem is indeed global Diagnosis in Vulnerable and Target and requires increased hygiene measures in endemic areas, which entails special care for pregnant Groups: A Global Perspective on the women in both endemic and non-endemic regions. As already highlighted, pregnant women could Current State of Knowledge and the have significant health consequences due to the untimely diagnosis of HEV infection; hence, this is Implications for Practice. Healthcare a population that should be targeted with a specific combination of testing approaches to ensure 2021, 9, 133. https://doi.org/ optimal specificity and sensitivity. Until we advance from predominantly supportive treatment in 10.3390/healthcare9020133 pregnancy and appraise the safety and efficacy of a HEV vaccine in this population, such screening Academic Editor: approaches represent the mainstay of our public health endeavors. Abdel-Latif Mohamed Received: 21 December 2020 Keywords: hepatitis E; hepatitis E virus; pregnancy; diagnosis Accepted: 26 January 2021 Published: 29 January 2021 Publisher’s Note: MDPI stays neutral 1. Introduction with regard to jurisdictional claims in Hepatitis E virus (HEV) is a positive single-stranded, small, quasi-enveloped RNA published maps and institutional affil- virus. It is the only member of the genus Orthohepevirus of the family Hepeviridae [1,2]. iations. Orthohepevirus A is the largest species of the genus Orthohepevirus and consists of eight different genotypes of HEV that can cause infection in humans (HEV-1, 2, 3, 4, and 7), rabbits (HEV-3), pigs (HEV-3 and 4), boars (HEV-3, 4, 5, and 6), deer (HEV-3), mongoose (HEV-3), camel (HEV-7 and HEV-8), and yak (HEV-4) [3,4], as shown in Table1. Copyright: © 2021 by the authors. In northern India, during the 1978 hepatitis epidemic, the hepatitis E virus was first Licensee MDPI, Basel, Switzerland. identified in the Kashmir Valley. In that specific outbreak there were 5200 cases of hepatitis, This article is an open access article resulting in 17,000 deaths [5]. distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Healthcare 2021, 9, 133. https://doi.org/10.3390/healthcare9020133 https://www.mdpi.com/journal/healthcare Healthcare 2021, 9, 133 2 of 14 Table 1. Classification of hepatitis E virus (HEV). Genus Orthohepevirus Healthcare 2021, 9, x FOR PEER REVIEW 2 of 14 Family Hepeviridae Species A, B, C, D Table 1. Classification of hepatitis E virus (HEV). Genotypes 1,2,3,4,5,6,7,8 Genus VirionOrthohepevirus 32–34 nm, icosahedral Family Hepeviridae Species EnvelopeA, B, C, D quasi-enveloped Genotypes Genome1,2,3,4,5,6,7,8 single-stranded, positive-sense, linear RNA Virion 32–34 nm, icosahedral Genome size 7.2 kb Envelope quasi-enveloped ◦ Genome Sensitivitysingle-stranded, positive-sense, Inactivation at linear temperatures RNA above 70 C Genome size 7.2 kb Sensitivity Inactivation at temperatures above 70 °C The structure of the HEV genome was thoroughly studied in 1991. The RNA molecule consistsThe of structure 7200 positively of the HEV directed genome nucleotides was thoroughly [6]. There studied are in three 1991. mainThe RNA coding mole- regions whosecule consists protein of products 7200 positively have not directed been nucl thoroughlyeotides [6]. studied. There are It wasthree alsomain found coding that re- there is agions fourth whose coding protein region products characteristic have not ofbeen the thoroughly HEV-1 genotype studied. [It6 –was8]. Thealso heparanfound that sulfate proteoglycan,there is a fourth HSC70 coding (heat region shock characteristic cognate70 of kDa),the HEV-1 allows genotype HEV to[6–8]. enter The the heparan cell. Other specific,sulfate but proteoglycan, insufficiently HSC70 studied, (heat shock receptors cognat ande 70 co-receptors kDa), allows are HEV also to crucialenter the for cell. entering theOther cell. Thespecific, process but insufficiently of releasing, studied, transcribing, receptors and and translating co-receptors HEV are RNA,also crucial as well for as the assemblageentering the of cell. new The virions, process occurs of releasing, in the transcribing, cytoplasm [and6,9, 10translating]. HEV RNA, as well as the assemblage of new virions, occurs in the cytoplasm [6,9,10]. 2. Molecular Biology of the Hepatitis E Virus 2. Molecular Biology of the Hepatitis E Virus The hepatitis E virus genome is a single-stranded positive linear RNA 7.2 kb in length [The11– hepatitis13]. HEV E virus RNA genome consists is a of single-stranded four open reading positive frames linear RNA (ORF) 7.2 and kb in untranslated length [11–13]. HEV RNA consists of four open reading frames (ORF) and untranslated regions regions at the 5’ and 3’ ends. At the 5’ end is a 7-methylguanosine cap and at the 3’ end is at the 5’ and 3’ ends. At the 5’ end is a 7-methylguanosine cap and at the 3’ end is a poly- a polyadenylated tail, just like eukaryotic messenger RNA (mRNA) [14,15], as shown in adenylated tail, just like eukaryotic messenger RNA (mRNA) [14,15], as shown in Figure Figure1. During1. During viral viralreplication replication two viral two RNA viral are RNA generated: are generated: a full-length a full-length RNA of 7.2 RNA kb and of 7.2 kb andsubgenomic subgenomic RNA RNA of 2.2 of kb 2.2 [13,14]. kb [13 ,14]. FigureFigure 1. Hepatitis 1. Hepatitis E virus E virus genome genome organization. organization. The The genomegenome is 7.2 7.2 kb kb positive-strand positive-strand RNA RNA with with a 5′ 7-methylguanosine a 50 7-methylguanosine cap (7 mG cap) and a 3′ polyadenylated tail (polyA). It harbors four open reading frames (ORF). ORF1 codes nonstructural cap (7 mG cap) and a 30 polyadenylated tail (polyA). It harbors four open reading frames (ORF). ORF1 codes nonstructural proteins, including a methyltransferase (MET), an RNA helicase (Hel), and an RNA-dependent RNA polymerase (RdRp), proteins,as well including as less well-characterized a methyltransferase domain (MET),s, such an as RNA the Y helicase domain, (Hel), a papain-like and an RNA-dependentcysteine protease (PCP), RNA a polymerase hypervariable (RdRp), as wellregion as less (HVR), well-characterized and the X domain. domains, ORF2 and such ORF3 as encode the Y domain, the viral capsid a papain-like and a small cysteine protein protease involved (PCP), in virus a secretion, hypervariable regionrespectively, (HVR), and translated the X domain. from a 2.2 ORF2 kb su andbgenomic ORF3 encodeRNA generated the viral during capsid viral and replication. a small protein The ORF4 involved is found in in virusthe HEV- secretion, 1 genotype and codes protein enhanced viral replication. respectively, translated from a 2.2 kb subgenomic RNA generated during viral replication. The ORF4 is found in the HEV-1 genotype and codes protein enhancedORF1 viral occupies replication. about 2/3 of the genome and codes nonstructural proteins included in viral RNA replication. These are methyltransferase (MET), X domain, helicase (Hel), ORF1 occupies about 2/3 of the genome and codes nonstructural proteins included and RNA-dependent RNA polymerase (RdRp). The function of other domains such as the in viralY domain, RNA papain-like replication. cysteine These protease are methyltransferase (PCP), and hypervariable (MET), X region domain, (HVR) helicase is still (Hel), andundetermined RNA-dependent [16,17]. RNA polymerase (RdRp). The function of other domains such as Healthcare 2021, 9, 133 3 of 14 the Y domain, papain-like cysteine protease (PCP), and hypervariable region (HVR) is still undetermined [16,17]. ORF2 encodes for the capsid protein and has its role in HEV infection diagnostics and vaccine development. It is a 72 kDa protein that is N-glycosylated in mammalian cells [17,18]. ORF3 codes a small phosphoprotein (VP13) of 13 kDa and is phosphorylated at serine residue [16,18]. The ORF2 and ORF3 proteins are the results of subgenomic RNA translation [19]. ORF4 is unique to the HEV-1 genotype. It is entirely within ORF1 and overlaps with the X domain and helicase.