The role of viruses in encephalitides of unknown origin in dogs

Idiopathic inflammatory diseases or inflammatory disturbances of unknown etiology are involved in the incidence of brain diseases in dogs. Breed-specific necrotizing encephalitis (NE), such as necrotizing meningoencephalitis and necrotizing leukoencephalitis, has been recognized as an important neuropathological identity in different small-sized dog breeds. Granulomatous meningoencephalomyelitis (GME) is also a type of encephalitis that has been commonly identified in dogs. Other non-suppurative meningoencephalitides of unknown etiology have also been recorded in dogs. Viral etiology has been suspected in such cases of meningoencephalitides of unknown etiology. Different viral pathogens have been identified in encephalitides of unknown etiology in dogs with the use of broadly reactive PCR assays and sequence analysis, as well as the wide use of immunohistochemical assays. Evidence of viral infections is conspicuous even in instances where a virus has not yet been identified. In this mini-review the main encephalitides of unknown etiology will be addressed and the features that might suggest viral infection will be discussed.