Pathogenesis of nonsuppurative encephalitis caused by highly pathogenic Porcine reproductive and respiratory syndrome virus.

Since 2006, an unprecedented epidemic of highly pathogenic Porcine reproductive and respiratory syndrome virus (HP-PRRSV) infection has emerged and prevailed in mainland China, causing so called high fever disease with a nervous symptom that is different from typical porcine reproductive and respiratory syndrome. To investigate this syndrome, the brains of pigs inoculated with HP-PRRSV were analyzed. The nucleic acid of HP-PRRSV was detected in brains by reverse transcription polymerase chain reaction. Histological examination demonstrated nonsuppurative encephalitis with lymphohistiocytic perivascular cuffing and infiltration of these leukocytes into the neuropil. Furthermore, transmission electron microscopy revealed that the HP-PRRSV that infected the endothelial cells crossed the blood-brain barrier into the central nervous system then induced cellular damage to neurons and neuroglial cells. These results provide a general insight into the pathway of HP-PRRSV invasion into brain tissue and the pathogenesis of nonsuppurative encephalitis.