HIGHLIGHTS
1 ǀ INTRODUCTION
Hepatitis E virus (HEV) infection, the cause of acute viral hepatitis worldwide, poses a significant public health concern with high prevalence in low-income countries. It is long-neglected although has now also emerged as an important virus in the developed countries.1-4 In areas with heavy seasonal rainfall, high evaporation rates, and high population density the HEV can cause outbreaks of acute hepatitis.5-7 According to the World Health Organization (WHO), approximately 20 million cases of HEV have been reported every year globally. Of the total reported cases, an estimated 3.3 million infections are leading to asymptomatic hepatitis. In 2015, according to the WHO estimates, approximately 44,000 deaths due to HEV have been reported worldwide.8 HEV mortality rate among pregnant women especially in the third trimester can reach up to 30%.9-12
HEV is a small (approximately 27–34 nm in diameter) non-enveloped single-stranded positive-sense RNA virus belonging to the familyHepeviridae , which consists of two genera namedOrthohepevirus (infect birds and mammals) andPiscihepevirus (infect fish). The genus Orthohepevirus is further classified into four species known as Orthohepevirus A, B, C, and D. Furthermore, the species Orthohepevirus A includes at least eight distinct genotypes (HEV-1-8) infecting both humans and animals.13-15 Genotype 1 and 2 are responsible for large-scale water-borne epidemics in developing countries, while genotypes 3 and 4 are responsible for small outbreaks in industrialized countries.1,6
The species causing HEV infection in swine belongs to the Orthohepevirus A.14 The genotype 1 and 2 are constrained to humans; genotype 3 circulates in humans, deer, rabbits, mongooses, and swine; genotype 4 circulates in human, pig, wild boar, cattle, cow, sheep, goat, and yak; genotype 5 and 6 are found in wild boars; genotype 7 has been identified in dromedary; and genotype 8 has been isolated recently in Bactrian camels.15-17 Figure 1 demonstrates different HEV genotypes circulate in humans and animals.