Replication and plaque formation of swine hemagglutinating encephalomyelitis virus (67N) in swine cell line, SK-K culture

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.

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.

Neurotropic virus tracing suggests a membranous-coating-mediated mechanism for transsynaptic communication

Swine hemagglutinating encephalomyelitis virus (HEV) has been shown to have a capability to propagate via neural circuits to the central nervous system after peripheral inoculation, resulting in acute deadly encephalomyelitis in natural host piglets as well as in experimental younger rodents. This study has systematically examined the assembly and dissemination of HEV 67N in the primary motor cortex of infected rats and provides additional evidence indicating that membranous‐coating‐mediated endo‐/exocytosis can be used by HEV for its transsynaptic transfer. In addition, our results suggested that this transsynaptic pathway could adapted for larger granular materials, such as viruses. These findings should help in understanding the mechanisms underlying coronavirus infections as well as the intercellular exchanges occurring at the synaptic junctions. J. Comp. Neurol. 521:203–212, 2013. © 2012 Wiley Periodicals, Inc.

Reverse transcription-loop-mediated isothermal amplification for the detection of rodent coronaviruses

Mouse hepatitis virus (MHV) is one of the most prevalent viruses detected in laboratory mouse colonies. Enterotropic strains predominate in natural infections, and molecular techniques for the detection of MHV shedding in feces are powerful enough to diagnose active infections. A reverse transcription-loop-mediated isothermal amplification (RT-LAMP) technique was developed for the detection of rodent coronaviruses within 90 min. The specificity of this technique was confirmed by its ability to detect all 17 different strains of MHV and 6 strains of rat coronaviruses as well as its failure to detect human, bovine, and porcine coronaviruses nonspecifically. The sensitivity of RT-LAMP was 3.2-fold higher than that of reverse transcription-polymerase chain reaction (RT-PCR) and 31.6-fold lower than that of nested RT-PCR. An evaluation of the diagnostic performance of RT-LAMP performed in duplicate using mouse fecal specimens showed that the sensitivity and specificity with respect to nested RT-PCR were 85.7% and 100%, respectively. RT-LAMP assays would be suitable for monitoring active MHV infection in mouse colonies.

Coronavirus infection of rat dorsal root ganglia: ultrastructural characterization of viral replication, transfer, and the early response of satellite cells

Swine hemagglutinating encephalomyelitis virus (HEV) has been shown to have a capability to gain access to the cell bodies of sensory neurons after peripheral inoculation, resulting in ganglionic infection. It is not clearly understood how this virus is replicated within and released from the sensory neurons, and it remains to know how satellite cells response to the HEV invasion. By ultrastructurally examining HEV-infected rat dorsal root ganglia, we found that HEV in the cell bodies of infected neurons budded from endoplasmic reticulum–Golgi intermediate compartments, and were assembled either individually within small vesicles or in groups within large vesicles. The progeny virions were released from the sensory neurons mainly by smooth-surfaced vesicle-mediated secretory pathway, which occurred predominantly at the perikaryal projections and infoldings of sensory neurons. Released HEV particles were subsequently taken up by the adjacent satellite cells. Almost all virus particles in the cytoplasm of satellite cells were contained in groups within vesicles and lysosome-like structures, suggesting that these glial cells may restrict the local diffusion of HEV. These observations give some insights into the pathogenesis of coronavirus infection and are thought to help understand the interactions between sensory neurons and their satellite cells.

Identification of NCAM that interacts with the PHE-CoV spike protein

BACKGROUND

The spike proteins of coronaviruses associate with cellular molecules to mediate infection of their target cells. The characterization of cellular proteins required for virus infection is essential for understanding viral life cycles and may provide cellular targets for antiviral therapies.

RESULTS

We identified Neural Cell Adhesion Molecule (NCAM) as a novel interacting partner of the PHE-CoV S protein. A T7 phage display cDNA library from N2a cells was constructed, and the library was screened with the soluble PHE-CoV S glycoproteins. We used a coimmunoprecipitation assay to show that only the NCAM was a binding partner of spike protein. We found that a soluble form of anti-NCAM antibody blocked association of the PHE-CoV with N2a cells. Furthermore, double-stranded siRNA targeted against NCAM inhibited PHE-CoV infection.

CONCLUSIONS

A novel interaction was identified between NCAM and spike protein and this association is critical during PHE-CoV infection.

Neurotropism of swine haemagglutinating encephalomyelitis virus (coronavirus) in mice depending upon host age and route of infection

Mice aged 1, 4 or 8 weeks were inoculated with haemagglutinating encephalomyelitis virus (HEV), strain 67N, by the intracerebral (i.c.), intranasal (i.n.), intraperitoneal (i.p.), subcutaneous (s.c.), intravenous (i.v.) or oral route, with different doses. In 1-week-old mice, mortality and mean time to death were mostly the same regardless of the inoculation route, except for the oral route, which appeared to be the least effective. The virus killed 4-week-old mice readily by all routes of inoculation except the oral, and 8-week-old mice by i.c., i.n. or s.c. inoculation. In descending order of efficacy, the routes of HEV infection were: i.c., i.n., s.c., i.p., i.v. and oral. To follow the spread of HEV from peripheral nerves to the central nervous system (CNS), the virus was inoculated subcutaneously into the right hind leg of 4-week-old mice. The virus was first detected in the spinal cord on day 2, and in the brain on day 3. The brain titres became higher than those of the spinal cord, reaching a maximum of 10⁷PFU/0.2 g when the animals were showing CNS signs. Viral antigen was first detected immunohistochemically in the lumbar spinal cord and the dorsal root ganglion ipsilateral to the inoculated leg; it was detected later in the pyramidal cells of the hippocampus and cerebral cortex, and in the Purkinje cells of the cerebellum but not in the ependymal cells, choroid plexus cells or other glial cells. The infected neurons showed no cytopathological changes.

Susceptibility of rats of different ages to inoculation with swine haemagglutinating encephalomyelitis virus (a coronavirus) by various routes

Haemagglutinating encephalomyelitis virus, strain 67N, was used to inoculate 1-, 2-, 4- and 8-week-old rats by the intracerebral (i.c.), intranasal (i.n.), intraperitoneal (i.p.), subcutaneous (s.c.), intravenous (i.v.) and oral routes with graded doses. The routes of infection, in descending order of efficacy, were: i.ci.ns.ci.pi.v. and oral. Rats aged 1 and 2 weeks were generally similar in terms of mortality and mean time to death, regardless of inoculation route, except for the oral route, which had little effect. In comparison with the 1- and 2-week-old rats, the 4-week-old rats were less susceptible to the virus by all routes. Eight-week-old rats inoculated by the i.ci.n. or s.c. routes died, but all those inoculated by other routes survived. To follow the spread of virus in the central nervous system, 4-week-old rats inoculated by the i.c. route were examined. The virus was first detected in the brain on day 1 and in the spinal cord on day 2. The viral titres in both tissues reached a plateau of 10(7) plaque-forming units (PFU)/0.2 g by day 4, at which time clinical signs had developed. By immunohistochemical analysis, virus-specific antigen was found first in the pyramidal cells of the hippocampus and cerebral cortex, and later in the large-sized neurons of the pons and spinal cord. Still later (day 4) immunolabelling was found in Purkinje cells of the cerebellum, but not in the ependymal cells, choroid plexus or other glial cells.

Spread of swine hemagglutinating encephalomyelitis virus from peripheral nerves to the CNS

Swine hemagglutinating encephalomyelitis virus (HEV) strain 67N was inoculated into the sciatic nerve or the right leg crural muscle of rats. In both cases, the virus was isolated first from the caudal half of the spinal cord on day 2 after inoculation, and from the rostral half of the spinal cord and the brain on day 3. The virus titers in the brain reached a maximum when the infected rats developed CNS symptoms on day 5. Using confocal laser scanning microscope, fluorescent positive cells were first found in the lumbar dorsal root ganglion (DRG) and spinal cord ipsilateral of the inoculated leg on day 3. Antigen positive neurons were found bilaterally in the lumbar DRG and spinal cord on day 4. On day 5 specific fluorescence was observed in the neurons of the cerebral cortex, hippocampus, brainstem and Purkinje cells in the cerebellum.

A serological survey of human coronavirus in pigs of the Tohoku District of Japan

A total of 2496 swine sera from 60 farms in the Tohoku District of Japan was examined for hemagglutination inhibiting (HI) antibodies to human coronavirus (HCV), swine hemagglutinating encephalomyelitis virus (HEV) and bovine coronavirus (BCV). HI antibodies to HCV OC43 strain and HEV 67N strain were highly prevalent with positivity rates of 91.4 and 82.1%, respectively, while the BCV Kakegawa strain was 44.2% positive. Farm D in Miyagi Prefecture showed the highest antibody titers to HCV OC43 strain with geometric mean titers (GMT) of 1:200. These results suggest that pigs might be infected with HCV or an antigenetically related virus as well as HEV.

The route of transmission of hemagglutinating encephalomyelitis virus (HEV) 67N strain in 4-week-old rats

Four-week-old Wistar rats were inoculated with HEV by different routes. Animals died of encephalitis after intraperitoneal (i.p.), subcutaneous (s.c.) and intravenous (i.v.) as well as intracerebral (i.c.) and intranasal (i.n.) inoculation. However when inoculated subcutaneously, rats died a few days earlier than those inoculated i.p. and i.v., suggesting that the virus might be transmitted to the central nervous system (CNS) by the neuronal route rather than by blood stream. Rats which were inoculated subcutaneously at the site of the neck (group A) began to die on day 4 p.i., a few days earlier than animals inoculated in the foot pad of the right leg (group B). On day 2 and 3 after inoculation, the virus titer in the brain was higher in group A, but group B animals showed higher virus titers in the lumber region of spinal cord than group A animals. In order to follow the virus spread from the peripheral nerve to the brain, the virus was inoculated into the sciatic nerve of rats. The inoculated rats developed clinical signs on day 4 and began to die on day 6. On day 2, virus was detected in the posterior half of the spinal cord and migrated toward the anterior half and in the brain where it was present on day 3. The highest virus titers in the brain were recorded on day 4 to 6, meanwhile the virus titers in the spinal cord tend to decrease. By immunohistochemical study, antigen positive neurons were found in the spinal cord and brain on day 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotropism of mouse-adapted haemagglutinating encephalomyelitis virus

The propagation of a mouse-adapted strain (67N) of haemagglutinating encephalomyelitis virus in infected mice and murine cells was examined by viral re-isolation and immunostaining. Viral propagation was strictly limited to the neurons and to an established line of neuroblastoma cells in in-vivo and in-vitro experiments. These results provide adequate evidence that this virus is neurotropic.