Characterization of an immunocompetent, young adult mouse model for studying chikungunya virus neuroinvasion and central nervous system infection.

The arthropod-borne chikungunya virus poses a re-emerging global health threat, causing millions of cases worldwide. Neurological complications induced by chikungunya virus are being increasingly reported in vulnerable populations, including infants and young children. However, the mechanisms by which chikungunya virus invades the central nervous system and drives prolonged neurological dysfunction remain poorly defined. Studying neurological chikungunya virus infection has been limited by the lack of an immunocompetent, neurodevelopmentally appropriate small-animal model that reliably develops central nervous system infection and neurological disease by infection routes analogous to natural transmission. Following a screen of ten Collaborative Cross mouse strains, we identified four-to-six-week-old CC041 mice as an immunocompetent, neurodevelopmentally appropriate model that consistently exhibits chikungunya virus neuroinvasion and clinical signs consistent with neurological disease following peripheral inoculation. Central nervous system infection in CC041 mice was dependent on the chikungunya viral strain used, despite comparable viral replication at the inoculation site, and occurred at physiologically relevant inoculation doses without enhancement at higher doses. Comparative analyses with neuroinvasion-resistant C57BL/6J mice demonstrated that susceptibility to neuroinvasion in CC041 mice was associated with enhanced dissemination beyond the site of inoculation, prolonged serum viral load, and lower peripheral type I interferon levels early in infection. In vivo imaging using a reporter chikungunya virus confirmed rapid viral spread and early brain localization in CC041 mice, in contrast to the restricted peripheral infection observed in C57BL/6J mice. Examination of viral antigen expression by immunohistochemistry revealed regionally variable viral localization in the brain, with central nervous system infection occurring independently of virus-induced blood-brain barrier disruption or experimental macrophage depletion. Furthermore, CC041 mice developed clinical signs consistent with neurological disease that persisted beyond the period when infectious virus was detected in the brain. Together, these findings establish CC041 mice as a tractable, immunocompetent model for studying chikungunya virus-associated neurological disease following peripheral infection.