Hepatitis E Virus Genotypes and Evolution: Emergence of Camel Hepatitis E Variants

Abstract

Hepatitis E virus (HEV) is a major cause of viral hepatitis globally. Zoonotic HEV is an important cause of chronic hepatitis in immunocompromised patients. The rapid identification of novel HEV variants and accumulating sequence information has prompted significant changes in taxonomy of the family Hepeviridae. This family includes two genera: Orthohepevirus, which infects terrestrial vertebrates, and Piscihepevirus, which infects fish. Within Orthohepevirus, there are four species, A–D, with widely differing host range. Orthohepevirus A contains the HEV variants infecting humans and its significance continues to expand with new clinical information. We now recognize eight genotypes within Orthohepevirus A: HEV1 and HEV2, restricted to humans; HEV3, which circulates among humans, swine, rabbits, deer and mongooses; HEV4, which circulates between humans and swine; HEV5 and HEV6, which are found in wild boars; and HEV7 and HEV8, which were recently identified in dromedary and Bactrian camels, respectively. HEV7 is an example of a novel genotype that was found to have significance to human health shortly after discovery. In this review, we summarize recent developments in HEV molecular taxonomy, epidemiology and evolution and describe the discovery of novel camel HEV genotypes as an illustrative example of the changes in this field.

Detection of Genotype 1a and 1f of Hepatitis E Virus in Patients Treated at Tertiary Care Hospitals in Central India

“…The subtyping based on complete genome sequences reveals that HEV is divided into 8 genotypes, of which 1 and 2 are mainly confined to humans and 3–8 are predominantly zoonotic in nature [4, 10, 24]. However, very limited sequence information on sequences of genotype 5–8 is available [10].…”

“…The subtyping based on complete genome sequences reveals that HEV is divided into 8 genotypes, of which 1 and 2 are mainly confined to humans and 3–8 are predominantly zoonotic in nature [4, 10, 24]. However, very limited sequence information on sequences of genotype 5–8 is available [10]. Genotypes 1 and 2 are mostly reported from endemic regions [3, 28], and genotype 1 is more frequently associated with large outbreaks than other genotypes [4, 22].…”

“…The genotype and subtype of an HEV virus can be determined by studying the regions under ORF1 and ORF2, or based on full genome sequences. The ORF 1 contains the most hypervariable region of the HEV genome, thereby it is preferred for genotyping and subtyping [10, 15, 16]. Genotypes 1a and 1c were reported to have been circulating in south, north, and west India [11, 15, 16].…”

“…Genotypes 1 and 2 have exclusively been found to cause infections in humans, whereas genotype 3 and 4 are zoonotic in nature and are more frequently detected in animals such as pigs, boars, and deer [11-13]. Genotypes 5–8 are detected in wild boar and camel, and limited sequences of these genotypes are available [10]. The circulation of genotype 1 has been observed in Africa and Asia; genotype 2 is found in Mexico and in some African countries; genotype 3 is distributed through out world and genotype 4 has also been detected in Asia [11-13].…”

“…The ORF1 encodes polyprotein predicted to have enzymatic activities of viral replication, ORF2 is responsible for the synthesis of capsid protein, and ORF3 expresses a small phosphoprotein [3]. The virus has a single serotype and based on nucleotide sequences, it is classified into 8 genotypes which are further classified into subtypes [10]. Genotypes 1 and 2 have exclusively been found to cause infections in humans, whereas genotype 3 and 4 are zoonotic in nature and are more frequently detected in animals such as pigs, boars, and deer [11-13].…”