Detection and genetic analysis of porcine hemagglutinating encephalomyelitis virus in South Korea

Dipeptidyl peptidase 4 interacts with porcine coronavirus PHEV spikes and mediates host range expansion

Porcine hemagglutinating encephalomyelitis virus (PHEV), a neurotropic betacoronavirus, is prevalent in natural reservoir pigs and infects mice. This raises concerns about host jumping or spillover, but little is known about the cause of occurrence. Here, we revealed that dipeptidyl peptidase 4 (DPP4) is a candidate binding target of PHEV spikes and works as a broad barrier to overcome. Investigations of the host breadth of PHEV confirmed that cells derived from pigs and mice are permissive to virus propagation. Both porcine DPP4 and murine DPP4 have high affinity for the viral spike receptor-binding domain (RBD), independent of their catalytic activity. Loss of DPP4 expression results in limited PHEV infection. Structurally, PHEV spike protein binds to the outer surface of blades IV and V of the DPP4 β-propeller domain, and the DPP4 residues N229 and N321 (relative to human DPP4 numbering) participate in RBD binding via its linked carbohydrate entities. Removal of these N-glycosylations profoundly enhanced the RBD-DPP4 interaction and viral invasion, suggesting they act as shielding in PHEV infection. Furthermore, we found that glycosylation, rather than structural differences or surface charges, is more responsible for DPP4 recognition and species barrier formation. Overall, our findings shed light on virus-receptor interactions and highlight that PHEV tolerance to DPP4 orthologs is a putative determinant of its cross-species transmission or host range expansion.IMPORTANCEPHEV is a neurotropic betacoronavirus that is circulating worldwide and has raised veterinary and economic concerns. In addition to being a reservoir species of pigs, PHEV can also infect wild-type mice, suggesting a "host jump" event. Understanding cross-species transmission is crucial for disease prevention and control but remains to be addressed. Herein, we show that the multifunctional receptor DPP4 plays a pivotal role in the host tropism of PHEV and identifies the conserved glycosylation sites in DPP4 responsible for this restriction. These findings highlight that the ability of PHEV to utilize DPP4 orthologs potentially affects its natural host expansion.

Hidden evolutionary constraints dictate the retention of coronavirus accessory genes

Coronaviruses exhibit many mechanisms of genetic innovation (1-5), including the acquisition of accessory genes that originate by capture of cellular genes or through duplication of existing viral genes (6,7). Accessory genes influence viral host range and cellular tropism, but little is known about how selection acts on these variable regions of virus genomes. We used experimental evolution of mouse hepatitis virus (MHV) encoding a cellular AKAP7 phosphodiesterase and an inactive native phosphodiesterase, NS2 (ref 8) to simulate the capture of a host gene and analyze its evolution. After courses of serial infection, the gene encoding inactive NS2, ORF2, unexpectedly remained intact, suggesting it is under cryptic constraint uncoupled from the function of NS2. In contrast, AKAP7 was retained under strong selection but rapidly lost under relaxed selection. Guided by the retention of ORF2 and similar patterns in related betacoronaviruses, we analyzed ORF8 of SARS-CoV-2, which arose via gene duplication6 and contains premature stop codons in several globally successful lineages. As with MHV ORF2, the coding-defective SARS-CoV-2 ORF8 gene remains largely intact, mirroring patterns observed during MHV experimental evolution, challenging assumptions on the dynamics of gene loss in virus genomes and extending these findings to viruses currently adapting to humans.

Development of a quadruplex real-time quantitative RT-PCR for detection and differentiation of PHEV, PRV, CSFV, and JEV

Porcine hemagglutinating encephalomyelitis virus (PHEV), porcine pseudorabies virus (PRV), classical swine fever virus (CSFV), and Japanese encephalitis virus (JEV) cause similar neurological symptoms in the infected pigs, and their differential diagnosis depends on laboratory testing. Four pairs of specific primers and probes were designed targeting the PHEV N gene, PRV gB gene, CSFV 5' untranslated region (5'UTR), and JEV NS1 gene, respectively, and a quadruplex real-time quantitative RT-PCR (qRT-PCR) was developed to detect and differentiate PHEV, PRV, CSFV, and JEV. The assay showed high sensitivity, with the limit of detection (LOD) of 1.5 × 101 copies/μL for each pathogen. The assay specifically detected only PHEV, PRV, CSFV, and JEV, without cross-reaction with other swine viruses. The coefficients of variation (CVs) of the intra-assay and the inter-assay were less than 1.84%, with great repeatability. A total of 1,977 clinical samples, including tissue samples, and whole blood samples collected from Guangxi province in China, were tested by the developed quadruplex qRT-PCR, and the positivity rates of PHEV, PRV, CSFV, and JEV were 1.57% (31/1,977), 0.35% (7/1,977), 1.06% (21/1,977), and 0.10% (2/1,977), respectively. These 1,977 samples were also tested by the previously reported qRT-PCR assays, and the coincidence rates of these methods were more than 99.90%. The developed assay is demonstrated to be rapid, sensitive, and accurate for detection and differentiation of PHEV, PRV, CSFV, and JEV.

Newly identified lineages of porcine hemagglutinating encephalomyelitis virus exhibit respiratory phenotype

Swine pathogens have a long history of zoonotic transmission to humans, occasionally leading to sustained outbreaks or pandemics. Through a retrospective epidemiological study of swine populations in China, we describe novel lineages of porcine hemagglutinating encephalomyelitis virus (PHEV) complex coronaviruses (CoVs) that cause exclusively respiratory symptoms with no signs of the neurological symptoms typically associated with classical PHEV infection. Through large-scale epidemiological surveillance, we show that these novel lineages have circulated in at least eight provinces in southeastern China. Phylogenetic and recombination analyses of twenty-four genomes identified two major viral lineages causing respiratory symptoms with extensive recombination within them, between them, and between classical PHEV and the novel respiratory variant PHEV (rvPHEV) lineages. Divergence times among the sampled lineages in the PHEV virus complex date back to 1886-1958 (mean estimate 1928), with the two major rvPHEV lineages separating approximately 20 years later. Many rvPHEV viruses show amino acid substitutions at the carbohydrate-binding site of hemagglutinin esterase (HE) and/or have lost the cysteine required for HE dimerization. This resembles the early adaptation of human CoVs, where HE lost its hemagglutination ability to adapt to growth in the human respiratory tract. Our study represents the first report of the evolutionary history of rvPHEV circulating in swine and highlights the importance of characterizing CoV diversity and recombination in swine to identify pathogens with outbreak potential that could threaten swine farming.

Complete genome sequence of a novel porcine hemagglutinating encephalomyelitis virus strain identified in South Korea

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a member of the subgenus Embecovirus of the genus Betacoronavirus, and it is ubiquitously distributed in most pig-farming countries worldwide with low clinical incidence. Here, we report the full-length genome sequence and molecular characterization of a novel PHEV strain identified in diarrheic neonates in South Korea. The complete genome of the Korean PHEV strain GNU-2113 was sequenced and analyzed to characterize PHEV circulating in South Korea. The GNU-2113 genome was determined to be 29,982 nucleotides in length, with large unique deletions in the regions encoding nonstructural protein 3 and NS2. It was found to share 95.1–96.9% sequence identity with other global strains. Genetic and phylogenetic analysis indicated that the GNU-2113 strain is distantly related to the existing PHEV genotypes, implying that the virus appears to undergo substantial evolution under endemic pressure. This study provides important information about the genetic diversity of PHEV circulating subclinically in swine herds, which may ensure viral fitness in the enzootic environment.

Genetic Characteristics of Porcine Hemagglutinating Encephalomyelitis Coronavirus: Identification of Naturally Occurring Mutations Between 1970 and 2015

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a Betacoronavirus characterized by neurological symptoms and a worldwide prevalence. Although PHEV is one of the earliest discovered porcine coronaviruses, it remains poorly studied. The full-length genome of the earliest PHEV strain collected in 1970 in the United States (PHEV/67 N/US/1970) was determined in October 2020. Using this virus as a prototype, we comparatively analyzed all available PHEV full-length sequences during 1970–2015. In phylogenetic trees based on PHEV full-length or spike glycoprotein open reading frame genomic sequences, PHEV/67 N/US/1970 was sorted into a clade different from that of viruses isolated in the United States in 2015. Intriguingly, United States and Belgium viruses isolated in 2015 and 2005, respectively, revealed multiple deletion mutation patterns compared to the strain PHEV/67 N/US/1970, leading to a truncated or a non-functional NS2A coding region. In addition, the genomic similarity analysis showed a hypervariability of the spike glycoprotein coding region, which can affect at least eight potential linear B cell epitopes located in the spike glycoprotein. This report indicates that PHEVs in the United States underwent a significant genetic drift, which might influence PHEV surveillance in other countries.

Coronaviruses in farm animals: Epidemiology and public health implications

Coronaviruses (CoVs) are documented in a wide range of animal species, including terrestrial and aquatic, domestic and wild. The geographic distribution of animal CoVs is worldwide and prevalences were reported in several countries across the five continents. The viruses are known to cause mainly gastrointestinal and respiratory diseases with different severity levels. In certain cases, CoV infections are responsible of huge economic losses associated or not to highly public health impact. Despite being enveloped, CoVs are relatively resistant pathogens in the environment. Coronaviruses are characterized by a high mutation and recombination rate, which makes host jumping and cross-species transmission easy. In fact, increasing contact between different animal species fosters cross-species transmission, while agriculture intensification, animal trade and herd management are key drivers at the human-animal interface. If contacts with wild animals are still limited, humans have much more contact with farm animals, during breeding, transport, slaughter and food process, making CoVs a persistent threat to both humans and animals. A global network should be established for the surveillance and monitoring of animal CoVs.

Development of an indirect ELISA based on soluble antigen produced from virus-infected cells for detection of porcine hemagglutinating encephalomyelitis virus

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a member of the genus Betacoronavirus and is the etiologic agent of encephalomyelitis or vomiting and wasting disease in neonatal pigs. Although there are only a few epidemiological studies that document the seroprevalence of PHEV infection, there are reports of sporadic outbreaks, including recent documentation of an influenza-like respiratory disease associated with PHEV in the United States. To address this issue, we have developed a new indirect enzyme linked immunosorbent assay (ELISA) for use in sero-epidemiological research of PHEV infection. One hundred and fifty porcine serum samples that were determined as antibody-positive or antibody-negative in virus neutralization (VN) tests were used in conjunction with PHEV-specific antigen extracted from virus-infected FS-L3 cells using RBS buffer containing 0.2 % NP-40 to develop this assay. The ELISA showed a high sensitivity (95.35 %) and specificity (96.88 %) by receiver operating characteristic (ROC) analysis, with an area under the curve (AUC) of 0.996 attesting to its accuracy. Our results revealed a strong correlation between the results of the indirect ELISA and VN test (R = 0.850, P < 0.05), with near-perfect agreement (kappa value = 0.932). These results indicate that this new indirect ELISA might be useful for diagnosis and sero-epidemiological tracking of PHEV infection.

Detecting and Monitoring Porcine Hemagglutinating Encephalomyelitis Virus, an Underresearched Betacoronavirus

There is a paucity of information concerning the ecology of porcine hemagglutinating encephalomyelitis virus (PHEV) in commercial swine herds. This study provided evidence that PHEV infection is endemic and highly prevalent in U.S. swine herds. These results raised questions for future studies regarding the impact of endemic PHEV on swine health and the mechanisms by which this virus circulates in endemically infected populations. Regardless, the availability of the validated PHEV S1 enzyme-linked immunosorbent assay (ELISA) provides the means for swine producers to detect and monitor PHEV infections, confirm prior exposure to the virus, and to evaluate the immune status of breeding herds.

Members of family Coronaviridae cause a variety of diseases in birds and mammals. Porcine hemagglutinating encephalomyelitis virus (PHEV), a lesser-researched coronavirus, can infect naive pigs of any age, but clinical disease is observed in pigs ≤4 weeks of age. No commercial PHEV vaccines are available, and neonatal protection from PHEV-associated disease is presumably dependent on lactogenic immunity. Although subclinical PHEV infections are thought to be common, PHEV ecology in commercial swine herds is unknown. To begin to address this gap in knowledge, a serum IgG antibody enzyme-linked immunosorbent assay (ELISA) based on the S1 protein was developed and evaluated on known-status samples and then used to estimate PHEV seroprevalence in U.S. sow herds. Assessment of the diagnostic performance of the PHEV S1 ELISA using serum samples (n = 924) collected from 7-week-old pigs (n = 84; 12 pigs per group) inoculated with PHEV, porcine epidemic diarrhea virus, transmissible gastroenteritis virus, porcine respiratory coronavirus, or porcine deltacoronavirus showed that a sample-to-positive cutoff value of ≥0.6 was both sensitive and specific, i.e., all PHEV-inoculated pigs were seropositive from days postinoculation 10 to 42, and no cross-reactivity was observed in samples from other groups. The PHEV S1 ELISA was then used to estimate PHEV seroprevalence in U.S. sow herds (19 states) using 2,756 serum samples from breeding females (>28 weeks old) on commercial farms (n = 104) with no history of PHEV-associated disease. The overall seroprevalence was 53.35% (confidence interval [CI], ±1.86%) and herd seroprevalence was 96.15% (CI, ±3.70%).

IMPORTANCE There is a paucity of information concerning the ecology of porcine hemagglutinating encephalomyelitis virus (PHEV) in commercial swine herds. This study provided evidence that PHEV infection is endemic and highly prevalent in U.S. swine herds. These results raised questions for future studies regarding the impact of endemic PHEV on swine health and the mechanisms by which this virus circulates in endemically infected populations. Regardless, the availability of the validated PHEV S1 enzyme-linked immunosorbent assay (ELISA) provides the means for swine producers to detect and monitor PHEV infections, confirm prior exposure to the virus, and to evaluate the immune status of breeding herds.

MiR-10a-5p-Mediated Syndecan 1 Suppression Restricts Porcine Hemagglutinating Encephalomyelitis Virus Replication

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a single-stranded RNA coronavirus that causes nervous dysfunction in the infected hosts and leads to widespread alterations in the host transcriptome by modulating specific microRNA (miRNA) levels. MiRNAs contribute to RNA virus pathogenesis by promoting antiviral immune response, enhancing viral replication, or altering miRNA-mediated host gene regulation. Thus, exploration of the virus-miRNA interactions occurring in PHEV-infected host may lead to the identification of novel mechanisms combating the virus life cycle or pathogenesis. Here, we discovered that the expression of miR-10a-5p was constitutively up-regulated by PHEV in both the N2a cells in vitro and mice brain in vivo. Treatment with miR-10a-5p mimics allowed miR-10a-5p enrichment and resulted in a significant restriction in PHEV replication, suggesting widespread negative regulation of the RNA virus infection by miR-10a-5p. The outcomes were also evidenced by miR-10a-5p inhibitor over-expression. Luciferase reporter, quantitative real-time PCR (qRT-PCR), and western blotting analysis further showed that Syndecan 1 (SDC1), a cell surface proteoglycan associated with host defense mechanisms, acts as a target gene of miR-10a-5p during PHEV infection. Naturally, siRNA-mediated knockdown of SDC1 leads to a reduction in viral replication, implying that SDC1 expression is likely a favorable condition for viral replication. Together, the findings demonstrated that the abundant miR-10a-5p leads to downstream suppression of SDC1, and it functions as an antiviral mechanism in the PHEV-induced disease, providing a potential strategy for the prevention and treatment of PHEV infection in the future work.

Development of a triplex real-time RT-PCR assay for detection and differentiation of three US genotypes of porcine hemagglutinating encephalomyelitis virus

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a single-stranded, positive-sense RNA virus. PHEV mainly causes two types of clinical manifestations representing vomiting and wasting and encephalomyelitis in piglets. However, our recent findings provide strong evidence that PHEV can also cause respiratory disease in older pigs. Genomic analysis of new PHEV strains identified in our former study further classifies PHEV into three genotypes. Detection and differentiation of these new mutants are critical in monitoring PHEV evolution in the field. In the present study, we report the development of a triplex real-time RT-PCR assay for detection and differentiation of three PHEV genotypes, 1, 2, and 3. Three sets of primers and probes were designed; one set of primers and probe targeting the conserved regions of the 3' end nucleocapsid for detection of all three genotypes and another two sets of primers and probes targeting the regions of NS2 with different patterns of deletions for detection of both genotypes 1 and 3, or genotype 3 only. Genotype 1 was positive when two probe dyes showed signals, genotype 2 was positive when only one probe dye showed a signal, and genotype 3 was positive when all three probes showed signals. The detection limit of the developed triplex real-time RT-PCR was as low as 8 or 9 DNA copies for three sets of primers and probes. The specificity test showed no cross reaction with other porcine viruses. Positive field-samples were correctly typed by this new assay, which was further confirmed by DNA sequencing. The triplex real-time RT-PCR provides a rapid and sensitive method to detect and differentiate all three US genotypes of PHEV from clinical samples.

Porcine Hemagglutinating Encephalomyelitis Virus: A Review

The porcine hemagglutinating encephalomyelitis virus (PHEV) is classified as a member of genus Betacoronavirus, family Coronaviridae, sub-family Cornavirinae, and order Nidovirales. PHEV shares the same genomic organization, replication strategy, and expression of viral proteins as other nidoviruses. PHEV produces vomiting and wasting disease (VWD) and/or encephalomyelitis, being the only known neurotropic coronavirus affecting pigs. First clinical outbreak was reported in 1957 in Ontario, Canada. Although pigs are the only species susceptible to natural PHEV infections, the virus displays neurotropism in mice and Wistar rats. Clinical disease, morbidity, and mortality is age-dependent and generally reported only in piglets under 4 weeks old. The primary site of replication of PHEV in pigs is the respiratory tract, and it can be further spread to the central nervous system through the peripheral nervous system via different pathways. The diagnosis of PHEV can be made using a combination of direct and indirect detection methods. The virus can be isolated from different tissues within the acute phase of the clinical signs using primary and secondary pig-derived cell lines. PHEV agglutinates the erythrocytes of mice, rats, chickens, and several other animals. PCR-based methods are useful to identify and subsequently isolate animals that are actively shedding the virus. The ability to detect antibodies allows producers to know the status of first-litter gilts and evaluate their risk of tier offspring to infection. PHEV is highly prevalent and circulates subclinically in most swine herds worldwide. PHEV-related disease is not clinically relevant in most of the swine-producing countries, most likely because of dams are immune to PHEV which may confer passive immunity to their offspring. However, PHEV should be considered a major source of economic loss because of the high mortality on farms with high gilt replacement rates, specific pathogen-free animals, and gnotobiotic swine herds. Thus, in the absence of current PHEV vaccines, promoting virus circulation on farms with early exposure to gilts and young sows could induce maternal immunity and prevent disease in piglets.

Genomic characterization and pathogenicity of a porcine hemagglutinating encephalomyelitis virus strain isolated in China

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a member of the genus betacoronavirus within the family coronaviridae, which invades the central nervous system (CNS) via peripheral nervous system and causes encephalomyelitis or vomiting and wasting disease (VWD) in sucking piglets. Up to now, although few complete nucleotide sequences of PHEV have been reported, they are not annotated. This study aimed to illuminate genome characterization, phylogenesis and pathogenicity of the PHEV/2008 strain. The full length of the PHEV/2008 strain genome was 30,684 bp, with a G + C content of 37.27%. The genome included at a minimum of 11 predicted open reading frames (ORFs) flanked by 5' and 3' untranslated regions (UTR) of 211 and 289 nucleotides. The replicase polyproteins pp1a and pp1ab, which had 4382 and 7094 amino acid residues, respectively, were predicted to be cleaved into 16 subunits by two viral proteinases. Phylogenetic analysis based on the complete genome sequence revealed that PHEV/2008 strain was genetically different from other known PHEV types, which represented a novel genotype (GI-1). In addition, we found that PHEV/2008 was neurotropic and highly pathogenic to 4-week-old BALB/c mice. Taken together, this is the first detailed annotated, complete genomic sequence of a new genotype PHEV strain in China.

Newly emerged porcine enteric alphacoronavirus in southern China: Identification, origin and evolutionary history analysis

Coronaviruses have a wide host range and can cause a variety of diseases with varying severity in different animals. Several enteric coronaviruses have been identified that are associated with diarrhea in swine and that have caused substantial economic losses. In this study, a newly emerged porcine enteric alphacoronavirus (PEAV), PEAV-GD-CH/2017, was identified from suckling piglets with diarrhea in southern China, and a full-length genome sequence of PEAV was obtained for systematic analysis. The novel PEAV sequence was most identical to that of bat-HKU2, and the differences between them were comprehensively compared, especially the uniform features of the S protein, which was shown to have a close relationship with betacoronaviruses and to perhaps represent unrecognized betacoronaviruses. In addition, Bayesian analysis was conducted to address the origin of PEAV, and the divergence time between PEAV and bat-HKU2 was estimated at 1926, which indicates that PEAV is not newly emerged and may have circulated in swine herds for several decades since the interspecies transmission of this coronavirus from bat to swine. The evolutionary rate of coronaviruses was estimated to be 1.93 × 10⁻⁴ substitutions per site per year for the RdRp gene in our analysis. For the origin of PEAV, we suspect that it is the result of the interspecies transmission of bat-HKU2 from bat to swine. Our results provide valuable information about the uniform features, origin and evolution of the novel PEAV, which will facilitate further investigations of this newly emerged pathogen.

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Identify and sequence a PEAV strain from suckling piglets with diarrhea

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The S protein of PEAV may recombination from unrecognized beta-CoV.

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The novel PEAV was emerged approximately at 1926 based on Bayesian analysis.

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PEAV origin from the interspecies transmission of bat-HKU2 from bat to swine

Porcine Hemagglutinating Encephalomyelitis Virus Enters Neuro-2a Cells via Clathrin-Mediated Endocytosis in a Rab5-, Cholesterol-, and pH-Dependent Manner

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a highly neurovirulent coronavirus that invades the central nervous system (CNS) in piglets. Although important progress has been made toward understanding the biology of PHEV, many aspects of its life cycle remain obscure. Here we dissected the molecular mechanism underlying cellular entry and intracellular trafficking of PHEV in mouse neuroblastoma (Neuro-2a) cells. We first performed a thin-section transmission electron microscopy (TEM) assay to characterize the kinetics of PHEV, and we found that viral entry and transfer occur via membranous coating-mediated endo- and exocytosis. To verify the roles of distinct endocytic pathways, systematic approaches were used, including pharmacological inhibition, RNA interference, confocal microscopy analysis, use of fluorescently labeled virus particles, and overexpression of a dominant negative (DN) mutant. Quantification of infected cells showed that PHEV enters cells by clathrin-mediated endocytosis (CME) and that low pH, dynamin, cholesterol, and Eps15 are indispensably involved in this process. Intriguingly, PHEV invasion leads to rapid actin rearrangement, suggesting that the intactness and dynamics of the actin cytoskeleton are positively correlated with viral endocytosis. We next investigated the trafficking of internalized PHEV and found that Rab5- and Rab7-dependent pathways are required for the initiation of a productive infection. Furthermore, a GTPase activation assay suggested that endogenous Rab5 is activated by PHEV and is crucial for viral progression. Our findings demonstrate that PHEV hijacks the CME and endosomal system of the host to enter and traffic within neural cells, providing new insights into PHEV pathogenesis and guidance for antiviral drug design.

IMPORTANCE Porcine hemagglutinating encephalomyelitis virus (PHEV), a nonsegmented, positive-sense, single-stranded RNA coronavirus, invades the central nervous system (CNS) and causes neurological dysfunction. Neural cells are its targets for viral progression. However, the detailed mechanism underlying PHEV entry and trafficking remains unknown. PHEV is the etiological agent of porcine hemagglutinating encephalomyelitis, which is an acute and highly contagious disease that causes numerous deaths in suckling piglets and enormous economic losses in China. Understanding the viral entry pathway will not only advance our knowledge of PHEV infection and pathogenesis but also open new approaches to the development of novel therapeutic strategies. Therefore, we employed systematic approaches to dissect the internalization and intracellular trafficking mechanism of PHEV in Neuro-2a cells. This is the first report to describe the process of PHEV entry into nerve cells via clathrin-mediated endocytosis in a dynamin-, cholesterol-, and pH-dependent manner that requires Rab5 and Rab7.

The evidence of porcine hemagglutinating encephalomyelitis virus induced nonsuppurative encephalitis as the cause of death in piglets

An acute outbreak of porcine hemagglutinating encephalomyelitis virus (PHEV) infection in piglets, characterized with neurological symptoms, vomiting, diarrhea, and wasting, occurred in China. Coronavirus-like particles were observed in the homogenized tissue suspensions of the brain of dead piglets by electron microscopy, and a wild PHEV strain was isolated, characterized, and designated as PHEV-CC14. Histopathologic examinations of the dead piglets showed characteristics of non-suppurative encephalitis, and some neurons in the cerebral cortex were degenerated and necrotic, and neuronophagia. Similarly, mice inoculated with PHEV-CC14 were found to have central nervous system (CNS) dysfunction, with symptoms of depression, arched waists, standing and vellicating front claws. Furthmore, PHEV-positive labeling of neurons in cortices of dead piglets and infected mice supported the viral infections of the nervous system. Then, the major structural genes of PHEV-CC14 were sequenced and phylogenetically analyzed, and the strain shared 95%–99.2% nt identity with the other PHEV strains available in GenBank. Phylogenetic analysis clearly proved that the wild strain clustered into a subclass with a HEV-JT06 strain. These findings suggested that the virus had a strong tropism for CNS, in this way, inducing nonsuppurative encephalitis as the cause of death in piglets. Simultaneously, the predicted risk of widespread transmission showed a certain variation among the PHEV strains currently circulating around the world. Above all, the information presented in this study can not only provide good reference for the experimental diagnosis of PHEV infection for pig breeding, but also promote its new effective vaccine development.

A small region of porcine hemagglutinating encephalomyelitis virus spike protein interacts with the neural cell adhesion molecule

Objective

The spike (S) protein of porcine hemagglutinating encephalomyelitis virus (PHEV) may mediate infection by binding to a cellular neural cell adhesion molecule (NCAM). This study aimed to identify the crucial domain of the S1 subunit of the S protein that interacts with NCAM.

Methods

Three truncated segments (S_1-291, S_277-794 and S_548-868) of the S gene of PHEV and the NCAM gene were cloned individually into the Escherichia coli expression vectors and yeast two-hybrid expression vectors. The interaction between S_1-291, S_277-794, S_548-868 and NCAM were detected by a GST pull-down experiment and yeast two-hybrid assay.

Results

Three fusion proteins (S_1-291, S_277-794 and S_548-868) were screened for their interactions with NCAM by protein-protein interaction assays. The results of these assays clarified that S_277-794 interacted with NCAM, while S_1-291 and S_548-868 did not.

Conclusions

A small fragment (258-amino-acid fragment, residues 291-548) on the PHEV S protein was posited to be the minimum number of amino acids necessary to interact with NCAM. This fragment may be the receptor-binding domain that mediates PHEV binding to NCAM.

Microbiological safety of the first clinical pig islet xenotransplantation trial in New Zealand

BACKGROUND

Xenotransplantation using pig cells, tissues, or organs may be associated with the transmission of porcine microorganisms and the development of zoonoses. Among all porcine microorganisms porcine endogenous retroviruses (PERVs) represent a special risk because they are integrated in the genome of all pigs and able to infect human cells. In previous preclinical and retrospective clinical trials of xenotransplantation, no transmission of PERV was observed. The first clinical trial of (alginate-encapsulated) porcine islet cell transplantation in New Zealand, which was approved by the New Zealand Government as an open-label phase I/IIa safety/efficacy trial, offers the possibility to analyze microbiological safety in a prospective clinical study.

METHODS

Before the trial started, a multilevel testing strategy was used to screen for 26 microorganisms in donor pigs of the Auckland Island strain and the islet cell preparations used for treatment. Donor testing was performed using molecular methods including multiplex real-time PCR. Blood samples from 14 pig islet cell recipients were also investigated by molecular biological methods at weeks 1, 4, 8, 12, 24, and 52 post-transplant for the transmission of porcine microorganisms. Sera were also monitored at these time points for antibodies against PERVs.

RESULTS

Beginning in 2009, fourteen patients with severe unaware hypoglycemia were treated with one of four different dosages of alginate-encapsulated porcine islets ranging from 5000-20,000 islet equivalents delivered in a single dose. No transmission of either PERVs or other porcine microorganisms was detected by PCR and immunological methods.

CONCLUSION

These findings support previous results and strongly indicate the safety of xenotransplantation as performed here.

Identification and genetic characterization of porcine hemagglutinating encephalomyelitis virus from domestic piglets in China

In this study, we investigated an acute outbreak of porcine hemagglutinating encephalomyelitis on a farm of 127 pigs in Jilin province, China. Porcine hemagglutinating encephalomyelitis virus (PHEV) was detected in suckling and weaning pigs by RT-PCR assays. Coronavirus-like particles were observed by electron microscopy. The virus isolate was designated PHEV-JT06. The clinical signs, nervous symptoms and positive labeling of neurons in the cerebral cortex with an immunohistochemical stain in PHEV-JT06-infected BALB/c mice supported the diagnosis of PHEV infection. The five full-length PHEV-JT06 structural genes were cloned, sequenced and analyzed. Phylogenetic studies based on the nucleotide and amino acid sequences of the five genes in the outbreak showed that PHEV remained genetically stable. PHEV shares 95.3-99.3 % amino acid sequence identity with American strains (AY078417), suggesting that the Chinese isolate is most likely derived from the North American strain. Additionally, PHEV, HCoV-OC43 and BCoV were genetically close. These results may provide some insights into the genotype of the etiological agent responsible for the porcine hemagglutinating encephalomyelitis outbreak and could also provide a comparative view of the genomics of the five structural proteins of PHEV.

Porcine hemagglutinating encephalomyelitis virus induces apoptosis in a porcine kidney cell line via caspase-dependent pathways

Porcine hemagglutinating encephalomyelitis is an acute, highly contagious disease in piglets that is caused by the porcine hemagglutinating encephalomyelitis virus (PHEV). However, the pathogenesis of PHEV and the relationship between PHEV and the host cells are not fully understood. In this study, we investigated whether the PHEV-induced cytopathic effect (CPE) was caused by apoptosis. Replication of PHEV in a porcine kidney-derived cell line (PK-15 cells) caused an extensive CPE, leading to the destruction of the entire monolayer and the death of the infected cells. Staining with Hoechst 33,342 revealed morphological changes in the nuclei and chromatin fragmentation. In addition, PHEV caused DNA fragmentation detectable by agarose gel electrophoresis 48h post-infection, increasing with the incubation time. The percentage of apoptotic cells increased with the incubation time and reached a maximum at 96h post-infection, as determined using flow cytometry and fluorescence microscopy of cells that were stained with annexin V-FITC and propidium iodide (PI). Moreover, as is commonly observed for coronavirus infections of other animals, the activities of the effecter caspase, caspase-3, and the initiator caspases, caspase-8 and caspase-9, which are representative factors in the death receptor-mediated apoptotic pathway and the mitochondrial apoptotic pathway, respectively, were increased in PHEV-infected PK-15 cells. Moreover, the tripeptide pan-ICE (caspase) inhibitor Z-VAD-FMK blocked PHEV-induced apoptosis but did not have an effect on virus production by 96h post-infection. These results suggested that PHEV induces apoptosis in PK-15 cells via a caspase-dependent pathway. Apoptotic death of infected cells is detrimental to animals because it causes cell and tissue destruction. Although the pathological characteristics of PHEV are largely unknown, apoptosis may be the pathological basis of the lesions resulting from PHEV infection.

Inhibition of porcine hemagglutinating encephalomyelitis virus replication by short hairpin RNAs targeting of the nucleocapsid gene in a porcine kidney cell line

Porcine hemagglutinating encephalomyelitis virus (PHEV), which causes porcine encephalomyelitis and is widespread among swine worldwide. RNA interference (RNAi) pathways have emerged as important regulators of virus-host cell interactions. In this study, two siRNA expression plasmids (shN1 and shN2) were generated to target two different coding regions of the nucleocapsid protein (N) of PHEV. The shRNAs were transiently transfected into a porcine kidney cell line, PK-15, to determine whether these constructs inhibited PHEV production. Our results revealed that both shRNAs were highly capable of inhibiting viral RNA genome replication, especially shN2. Next, stable transfection of shN2 was used to produce two siRNA stably expressing PK-15 cell clones (shN2-1 and shN2-2), and these two lines were infected with PHEV. The analysis of cytopathic effects (CPE) demonstrated that shN2-1 and shN2-2 were capable of protecting cells against PHEV infection with high specificity and efficiency. Furthermore, effective inhibition of viral replication persisted for up to 120 h by a TCID(50) assay. These results indicated that RNAi targeting of the N gene could facilitate studies of the specific function of viral genes associated with PHEV replication and may have potential therapeutic applications.