Neurotropism and Encephalitis of a Novel Pegivirus with Experimental Evidence Across Avian Species

Pegiviruses have traditionally been regarded as non-pathogenic viruses with controversial clinical significance. Here, we describe a novel avian pegivirus (partridge pegivirus, ParPgV) associated with field outbreaks of encephalitis in red-legged partridges (Alectoris rufa) in France. Next-generation sequencing identified ParPgV in brain tissues, and full-length genomic characterization revealed two distinct ParPgV strains linked to the outbreaks, confirming their phylogenetic relationship to avian-origin pegiviruses. Histopathology and electron microscopy revealed encephalitic lesions, neuronal degeneration, and virus-like particles within neurons. Field surveillance demonstrated widespread vertical transmission across multiple red-legged partridge flocks. Experimental inoculation of red-legged partridges, grey partridges, and specific-pathogen-free chickens demonstrated viral neurotropism and systemic distribution. Infected red-legged partridges developed cerebellar atrophy detectable by MRI, in the course of transient clinical signs. Detection of negative-strand RNA replication intermediates confirmed active viral replication in neural tissues and lymphoid organs, across the different experimental hosts, and red-legged partridge embryonated eggs. RNAscope in situ hybridization and immunohistochemistry further confirmed the presence of viral RNA and antigen, respectively, in neural and lymphoid tissues. These findings provide the first experimental evidence linking a pegivirus to encephalitis and suggest that pegiviruses may possess underappreciated neuropathogenic potential.