Effect of a single point mutation on equine herpes virus 9 (EHV-9) neuropathogenicity after intranasal inoculation in a hamster model

Characterizing the Pathogenesis and Immune Response of Equine Herpesvirus 8 Infection in Lung of Mice

Simple Summary

Equine herpesvirus 8 (EHV-8) is an important pathogen primarily affecting the horse and donkey industry, but there is little information about the pathogenicity and immune response of EHV-8 in a mouse model. We aim to investigate the pathogenicity and immune response in the lung during EHV-8 infection in BALB/c mice. The results showed that EHV-8 could effectively replicate and elicits a strong proinflammatory response in the lung tissues of a mouse model. The mouse model of viral respiratory disease proposed here will also be useful for studying the underlying mechanisms of the pathology of respiration.

Abstract

Equine herpesvirus type 8 (EHV-8), associated with abortion and severe respiratory disease in donkeys and horses, causes significant economic losses in the global equine industry. However, the pathogenicity of EHV-8 is still unknown. Mice are widely used as an animal model to evaluate virus replication and virulence. The present study aimed to evaluate the pathogenicity of the EHV-8 SDLC66 strain in BALB/c mice. Mice were used to test for infection-associated parameters (such as clinical signs, body weights, virus replication in tissues, viremia, and cytokines) and sacrificed at 0, 2, 4, and 6 days post-infection (dpi). The mice inoculated with EHV-8 exhibited lethargy, dyspnea signs, loss in body weight, and viremia. EHV-8 was detected in the liver, spleen, brain, and lung by PCR at 4 dpi and 6 dpi, effectively replicating these tissues detected by TCID₅₀ at 6 dpi. Proinflammatory cytokines, including IL-6, IL-1β, and TNF-α, were significantly increased at the 4 dpi and 6 dpi in the lung than in the control group. However, IFN-γ was only increased at 6 dpi in the EHV-8-infected group. These data showed that EHV-8 could enter the lungs of mice and cause respiratory disease in the mouse model, which helps reveal the pathogenicity of EHV-8.

The Emergence of Viral Encephalitis in Donkeys by Equid Herpesvirus 8 in China

The equine herpesvirus type 8 (EHV-8) can cause significant economic losses in the global horses and donkey industry. The disease has been associated with abortion and respiratory symptoms. However, it is rare for a study to be reported about donkeys with neurological diseases induced by EHV-8 infection. In the present study, one 2-year-old male donkey, from a large-scale donkey farm in China, died with a severe neurological disorder. The causative agent, donkey/Shandong/10/2021 (GenBank accession: OL856098), was identified and isolated from the brain tissue of the dead donkey. Meanwhile, BALB/c mice were used as an animal model to evaluate the pathogenicity of the EHV-8 isolate. Our data showed that EHV-8 was positive in brains by PCR and immunohistochemistry, which induced typical viral encephalitis lesions in both donkey and mice consistent with clinical signs. For the first time, we reported that EHV-8 had been isolated from donkeys with a neurological illness in China, which is helpful to reveal the pathogenicity of EHV-8 in the donkey.

Histopathology of brain functional areas in pigs infected by porcine pseudorabies virus

Porcine pseudorabies virus (PRV) infection is a major disease in swine. It is challenging to eradicate the virus entirely after it has invaded Chinese farms, resulting in significant economic losses. This study aimed to explore the histopathological correlation of brain regions in PRV-infected pigs. Twenty pigs were randomly divided into two experimental groups (the PRV-infected and sham-inoculated groups; n = 10 per group). The pigs were then observed for clinical signs at specified time points. Brain tissue samples were collected for histopathological examination on days 3, 10, and 14. The correlation analysis was based on clinical observation, lesion characterization, and pathogen location. Clinical observation showed that the severity of clinical neurological signs increased with time. Pathological dissection and microscopic observation revealed gross pathological changes such as degeneration and necrosis of nerve cells, increase in microglia, eosinophilic inclusion body, lymphocyte infiltration, and loose cortical tissue structure. Immunohistochemistry showed that the virus was mainly localized in neurons, microglia, nerve fibers, cerebellar granular layer, and Purkinje cell layer. The virus invasion route was from the cerebrum to the cerebellum and eventually to the brainstem, and the severity of brain damage increased with time. The route of virus infection was from the olfactory bulb to the hippocampus and eventually to the medulla oblongata, and the viral expression increased with time. Of note, brain injury, viral expression, and clinical neurological signs were positively correlated with the infection period; similarly, the severity and degrees of their changes were positively correlated.

Correlation of Immunomodulatory Cytokine Expression with Histopathological Changes and Viral Antigen in a Hamster Model of Equine Herpesvirus-9 Encephalitis

A group of hamsters (n = 25) was intranasally infected with equine herpesvirus-9 (EHV-9) and mRNA transcription levels of several proinflammatory (IFN-γ, TNF-α and IL-6) and anti-inflammatory (IL-4, IL-10 and TGF-β) cytokines were investigated in brain tissue using RT-qPCR. These levels were correlated with the severity of sequential histopathological changes and intensity of immunohistochemical labelling of virus antigen in brain. Early and progressive upregulation of all the proinflammatory and anti-inflammatory cytokines investigated (P < 0.05) was correlated with increasing severity of encephalitis and viral antigen expression from 2 days post infection (dpi) with a peak at 4-5 dpi (P <0.05).

Comparative Neuropathogenesis of Equine Herpesvirus 9 and its Mutant Clone (SP21) Inoculated Intranasally in a Hamster Model

The neuropathogenesis of equine herpesvirus 9 (EHV-9), a neurotropic herpesvirus, and its mutant clone (SP21) was studied experimentally in a hamster model. EHV-9-infected hamsters showed clinical signs of infection at 3 days post infection (dpi), while infection with SP21 resulted in clinical signs at 4 dpi. Clinical signs were more severe in the EHV-9-infected group than in the SP21-infected group. There was a significant difference in the time of anterograde transmission of EHV-9 and SP21 inside the brain. Viraemia was detected in the EHV-9-infected group at 4-5 dpi, while no viraemia was detected in the SP21-infected group. The serum concentration of tumour necrosis factor-α was significantly higher in EHV-9-infected animals than in those infected by SP21 group at 4-5 dpi, but there was no difference in the serum concentration of interferon-γ. The spatiotemporal profiles of viral replication and virus-associated histopathology were remarkably similar, were high in the olfactory bulb and cerebral hemispheres, and decreased progressively towards the medulla oblongata. The mean group scores of the histopathological changes for the entire brain were significantly higher in the EHV-9 group than in the SP21 group at all time points, starting from 3 dpi. These results suggest that the gene products of the open reading frame (ORF)19 and ORF14 play essential roles in the neuropathogenesis of EHV-9, as the two point-mutations detected in SP21 significantly altered the neuropathogenesis of the virus.