Crimean-Congo Hemorrhagic Fever Mouse Model Recapitulating Human Convalescence.

Crimean-Congo hemorrhagic fever virus (CCHFV) is a cause of severe hemorrhagic fever. Its tick reservoir and vector are widely distributed throughout Africa, Southern and Eastern Europe, the Middle East, and Asia. Serological evidence suggests that CCHFV can productively infect a wide variety of species, but only humans develop severe, sometimes fatal disease. The role of the host adaptive immunity in control or contribution to the severe pathology seen in CCHF cases is largely unknown. Studies of adaptive immune responses to CCHFV have been limited due to lack of suitable small animal models. Wild-type mice are resistant to CCHFV infection, and type I interferon-deficient mice typically develop a rapid-onset fatal disease prior to development of adaptive immune responses. We report here a mouse model in which type I interferon-deficient mice infected with a clinical isolate of CCHFV develop a severe inflammatory disease but ultimately recover. Recovery was coincident with development of CCHFV-specific B- and T-cell responses that were sustained for weeks postinfection. We also found that recovery from a primary CCHFV infection could protect against disease following homologous or heterologous reinfection. Together this model enables study of multiple aspects of CCHFV pathogenesis, including convalescence, an important aspect of CCHF disease that existing mouse models have been unsuitable for studying.IMPORTANCE The role of antibody or virus-specific T-cell responses in control of acute Crimean-Congo hemorrhagic fever virus infection is largely unclear. This is a critical gap in our understanding of CCHF, and investigation of convalescence following severe acute CCHF has been limited by the lack of suitable small animal models. We report here a mouse model of CCHF in which infected mice develop severe disease but ultimately recover. Although mice developed an inflammatory immune response along with severe liver and spleen pathology, these mice also developed CCHFV-specific B- and T-cell responses and were protected from reinfection. This model provides a valuable tool to investigate how host immune responses control acute CCHFV infection and how these responses may contribute to the severe disease seen in CCHFV-infected humans in order to develop therapeutic interventions that promote protective immune responses.