Multiple Reassortments, Limited Geographic Spread, and Comparable Pathogenicity of Crimean-Congo Hemorrhagic Fever Viruses in Sivas Province, Türkiye

Crimean-Congo hemorrhagic fever virus (CCHFV) is a segmented RNA virus that can cause severe hemorrhagic fever and is primarily transmitted to humans and other mammals through tick bites. Since segment reassortment can increase genetic diversity and disease severity, we sampled infected ticks and humans in Sivas Province, Türkiye, a region with high CCHFV prevalence. Analysis of 113 human and 23 Hyalomma tick CCHFV samples revealed three main phylogenetic clades in Sivas. The most common clade (SIVAS-2) was involved in multiple reassortants. Phylogenetic analysis indicated multiple independent reassortment events involving all three CCHFV genome segments. The most common reassortant (1.1.2) was detected only in the Zara district of Sivas in both humans and ticks. We found that most infections were geographically limited to local spread and that infections with more than one variant and reassortment were exceptional. We found no significant clinical differences between human SIVAS-1, SIVAS-2 and the 1.1.2 reassortant infections. Thus, within the limits of the available sample size, we found no evidence that the two parental forms differed in disease severity or that the 1.1.2 reassortant was associated with increased severity. Continued CCHFV surveillance could uncover future forms of the virus with altered characteristics.