Similarities in Antiviral Humoral Immune Response to Nucleocapsid Proteins of Hazara and Crimean–Congo Hemorrhagic Fever Virus ^†

Hazara virus (HAZV), a tick-borne agent of the nairoviruses, is closely related to Crimean–Congo hemorrhagic fever virus (CCHFV). Hazara virus has not been reported as a pathogen for humans and can be studied under BSL-2 conditions, whereas CCHFV causes severe hemorrhagic diseases, with up to 30% mortality rate in humans, and requires BSL-4 facilities to be handled. Serologic and phylogenetic similarities between the two viruses would therefore be an interesting area of research. In this study, we evaluated the immunological similarities between these two viruses using nucleocapsid protein as a model. Here, we evaluated cross-reactivity between CCHFV and HAZV rNP, which forms virus-like particles when expressed in Pichia pastoris. In Western blot assays using CCHFV-infected human and immunized mice and rabbit sera, cross-reactions were detected between the nucleoproteins of both viruses. Virus-like particles were visualized by transmission electron microscopy (TEM) and monitored by dynamic light scattering (DLS). These results suggest that nucleocapsid proteins of HAZV and CCHFV share similarities regarding the antiviral humoral response in both species.