Tembusu Virus Entering the Central Nervous System Caused Nonsuppurative Encephalitis without Disrupting the Blood-Brain Barrier

Tembusu virus (TMUV) is an emerging and reemerging zoonotic pathogen that has adversely affected the poultry industry in recent years. TMUV disease is characterized by nonsuppurative encephalitis in ducklings. The duckling infection model was established to study the mechanism of TMUV crossing the blood-brain barrier (BBB) into the central nervous system (CNS). Here, we showed that no obvious clinical symptoms and enhancement of BBB permeability occurred at the early stage of infection (similar to 3 to 5 days postinfection [dpi]), while virus particles were simultaneously observed by transmission electron microscopy in the brain, inducing the accumulation of inflammatory cytokines. Neurological symptoms and disruption of the BBB appeared at the intermediate stage of infection (similar to 7 to 9 dpi). It was confirmed that TMUV could survive and propagate in brain microvascular endothelial cells (BMECs) but did not affect the permeability of the BBB in vivo and in vitro at an early date. In conclusion, TMUV enters the CNS, then causes encephalitis, and finally destroys the BBB, which may be due to the direct effect of TMUV on BMECs and the subsequent response of the inflammatory storm. IMPORTANCE TMUV disease has caused huge losses to the poultry industry in Asia and is potentially harmful to public health. Neurological symptoms and their sequelae are the main characteristics of this disease. However, the mechanism of how this virus enters the brain and causes encephalitis is unclear. In this study, we confirmed that the virus entered the CNS and then massively destroyed the BBB, and the BBB damage was closely associated with the subsequent outbreak of inflammation. TMUV may enter the CNS through the transcellular and Trojan horse pathways. These findings can fill the knowledge gap in the pathogenesis of TMUV-infected poultry and be of benefit for the treatment of TMUV disease. In addition, TMUV is a representative for the study of the infection of avian flavivirus. Therefore, our studies have significance both for the understanding of the full scope of the mechanisms of TMUV and other flavivirus infections and, conceivably, for therapeutics.

Automated summary

TMUV initially enters the central nervous system without causing obvious symptoms or affecting the blood-brain barrier permeability, but leads to the accumulation of inflammatory cytokines. Subsequently, neurological symptoms and disruption of the blood-brain barrier occur, potentially due to the direct effect of TMUV on brain microvascular endothelial cells and the ensuing inflammatory response.