Pathogenesis of Equid Alphaherpesvirus 1 Infection in the Central Nervous System of Mice.

Equid alphaherpesvirus 1 (EHV-1) causes myeloencephalopathy in horses and occasionally in non-equid species. Although mouse models have been developed to understand EHV-1 pathogenesis, few EHV-1 strains have been identified as highly neurovirulent to mice. The aim of this study was to evaluate the pathogenesis of 2 neurovirulent EHV-1 strains in mice, and to characterize the inflammatory cells and expression of chemokines and the apoptosis marker caspase-3 in the brain of infected mice. C57BL/6J mice were inoculated intranasally with EHV-1 strains A4/72 or A9/92 and evaluated on 1, 2, and 3 days post inoculation (DPI). EHV-1-infected mice showed severe neurological signs at 3 DPI. Ultrastructural analysis revealed numerous viral nucleocapsids and fewer enveloped virions within degenerated and necrotic neurons and in the surrounding neuropil. Histologically, at 3 DPI, there was severe diffuse neuronal degeneration and liquefactive necrosis, prominent microgliosis, and perivascular cuffing composed of CD3+ cells (T cells) and Iba-1+ cells (macrophages), mainly in the olfactory bulb and ventral portions of the brain. In these areas, moderate numbers of neuroglial cells expressed CCL5 and CCL2 chemokines. Numerous neurons, including those in less affected areas, were immunolabeled for cleaved caspase-3. In conclusion, neurovirulent EHV-1 strains induced a fulminant necrotizing lymphohistiocytic meningoencephalitis in mice, with microgliosis and expression of chemokines and caspase-3. This model will be useful for understanding the mechanisms underlying the extensive neuropathology induced by these viral infections.

Equine herpesvirus 1 elicits a strong pro-inflammatory response in the brain of mice.

Equine herpesvirus type 1 (EHV-1) is an emerging pathogen that causes encephalomyelitis in horses and non-equid species. Several aspects of the immune response in the central nervous system (CNS), mainly regarding the role of inflammatory mediators during EHV-1 encephalitis, remain unknown. Moreover, understanding the mechanisms underlying extensive neuropathology induced by viruses would be helpful to establish therapeutic strategies. Therefore, we aimed to evaluate some aspects of the innate immune response during highly neurovirulent EHV-1 infection. C57BL/6 mice infected intranasally with A4/72 and A9/92 EHV-1 strains developed a fulminant neurological disease at 3 days post-inoculation with high viral titres in the brain. These mice developed severe encephalitis with infiltration of monocytes and CD8+ T cells to the brain. The inflammatory infiltrate followed the detection of the chemokines CCL2, CCL3, CCL4, CCL5, CXCL2, CXCL9 and CXCL-10 in the brain. Notably, the levels of CCL3, CCL4, CCL5 and CXCL9 were higher in A4/72-infected mice, which presented higher numbers of inflammatory cells within the CNS. Pro-inflammatory cytokines, such as interleukins (ILs) IL-1α, IL-1ß, IL-6, IL-12ß, and tumour necrosis factor (TNF), were also detected in the CNS, and Toll-like receptor (TLR) TLR2, TLR3 and TLR9 genes were also upregulated within the brain of EHV-1-infected mice. However, no expression of interferon-γ (IFN-γ) and IL-12α, which are important for controlling the replication of other herpesviruses, was detected in EHV-1-infected mice. The results show that the activated innate immune mechanisms could not prevent EHV-1 replication within the CNS, but most likely contributed to the extensive neuropathology. The mouse model of viral encephalitis proposed here will also be useful to study the mechanisms underlying extensive neuropathology.

Heterogenous deposition of ß-amyloid in the brain of aged dogs.

Dogs have been used as animal models for human diseases in which there is beta-amyloid (Aß) deposition in the central nervous system (CNS), such as Alzheimer's and cerebral amyloid angiopathy (CAA). However, many aspects of Aß deposition in the CNS of dogs still remain unknown. This study aimed to evaluate the deposition of Aß in different areas of the CNS of aged dogs from different breeds. Aß was detected in the brains of aged dogs, forming either senile plaques in the neuropil of cortical gray matter or within the walls of parenchymal or leptomeningeal blood vessels. There was a positive correlation between aging and senile plaques or CAA. In dogs older than 8 years, there was no correlation between the area of Aß plaques and age, with frontal, temporal, and occipital cortices being affected with approximately equal frequency. There was a positive correlation between Aß deposition in vessel walls and age. Importantly, CAA was associated with the occurrence of microperivascular hemorrhages in the brains of aged dogs. In conclusion, this study demonstrated that Aß deposition as plaques or within vessel walls are extremely heterogenous in dogs from different breeds and sizes. Although many features of this disease in dogs are similar to those observed in humans, the choice of dog breed and size as a model for human disease will substantially affect the pattern of Aß deposition.