Usutu virus and West Nile virus use a transcellular route of neuroinvasion across an in vitro model of the human blood-brain barrier.

West Nile virus (WNV) leads to thousands of cases of severe neurological disease in humans each year. Usutu virus (USUV) is closely related to WNV, but rarely induces disease in humans. We hypothesised that USUV is less able to cross the blood-brain barrier (BBB) and, consequently, is less likely to infect the brain. Therefore, we developed an in vitro BBB model consisting of primary human brain microvascular endothelial cells, pericytes and astrocytes. Both USUV and WNV invaded across the in vitro BBB via a transcellular mechanism in the absence of barrier disruption. USUV replicated to lower titres than WNV but induced a comparable cytokine and chemokine response, with modulation of key factors associated with barrier function and immune-cell migration. In conclusion, USUV appears attenuated in its ability to replicate at this interface compared with WNV, but further work must be done to identify key determinants underlying the differing clinical presentations.