Detection by Reverse Transcription-PCR and Genetic Characterization of Field Isolates of Swine Hepatitis E Virus from Pigs in Different Geographic Regions of the United States

Abstract

Hepatitis E virus (HEV) is an important public health concern in many developing countries. HEV is also endemic in some industrialized counties, including the United States. With our recent discovery of swine HEV in pigs that is genetically closely related to human HEV, hepatitis E is now considered a zoonotic disease. Human strains of HEV are genetically heterogenic. So far in the United States, only one strain of swine HEV has been identified and characterized from a pig. To determine the extent of genetic variations and the nature of swine HEV infections in U.S. pigs, we developed a universal reverse transcription-PCR (RT-PCR) assay that is capable of detecting genetically divergent strains of HEV. By using this universal RT-PCR assay, we tested fecal and serum samples of pigs of 2 to 4 months of age from 37 different U.S. swine farms for the presence of swine HEV RNA. Thirty-four of the 96 pigs (35%) and 20 of the 37 swine herds (54%) tested were positive for swine HEV RNA. The sequences of a 348-bp region within the ORF2 gene of 27 swine HEV isolates from different geographic regions were determined. Sequence analyses revealed that the 27 U.S. swine HEV isolates shared 88 to 100% nucleotide sequence identities with each other and 89 to 98% identities with the prototype U.S. strain of swine HEV. These U.S. swine HEV isolates are only distantly related to the Taiwanese strains of swine HEV, with about 74 to 78% nucleotide sequence identities; to most known human strains of HEV worldwide, with <79% sequence identities; and to avian HEV, with 54 to 56% sequence identities. Phylogenetic analysis showed that all the U.S. swine HEV isolates identified in this study clustered in the same genotype with the prototype U.S. swine HEV and the two U.S. strains of human HEV. The data from this study indicated that swine HEV is widespread and enzoonotic in U.S. swine herds and that, as is with human HEV, swine HEV isolates from different geographic regions of the world are also genetically heterogenic. These data further raise potential concerns for zoonosis, xenozoonosis, and food safety.

Determination of Fecal Shedding Rates and Genotypes of Swine Hepatitis E Virus (HEV) in Korea

“…Seroprevalence studies indicated that about 15-70% of pigs were infected with HEV in several countries [3,4,12,25]. The infection rate of pigs measured by detecting HEV RNA in the fecal specimens showed approximately 40% of pigs in the U.S.A. were infected by HEV [7]. A few studies were conducted in Korea to determine HEV infection rates with swine sera or liver tissues [4,8].…”

Detection of Hepatitis E Virus Shedding in Feces of Pigs at Different Stages of Production Using Reverse Transcription-Polymerase Chain Reaction

“…5 In the USA 25 (26.3%) 2-to 4-month-old pigs out of 95 were reported to be shedding the virus. 7 It takes between 2 and 3 weeks from initial infection to the time when HEV is excreted in feces, 11 and the viral shedding can last up to 7 weeks. Considering the fact that the maximum prevalence recorded in this work was found in the first month of feeding (around 13 to 16 weeks of age), it is reasonable to extrapolate that the majority of animals were infected at 3 to 6 weeks of age from contact with the sows.…”

“…Two pairs of degenerated oligonucleotide primers were used to amplify a 348-basepair (bp) fragment of open reading frame 2 (ORF-2) of HEV using an RT-nested PCR. 7 These primers were based on 18 human HEV sequences and the swine HEV prototype strain from USA. A positive control from a naturally infected pig (GenBank accesion number AY323506) was included in each procedure.…”

Distribution and Propagation of Hepatitis E Virus in Experimentally Infected Swine

“…Pigs are supposed to be infected with HEV via the fecal-oral route continuously, since pigs habitually eat feces naturally. Several epidemiological studies reported HEV shedding in up to 17-week-old pigs [23,[30][31][32]. An opportunity to come in contact with contaminated feces increases the intake of virus by pigs.…”