A single mutation in Crimean-Congo hemorrhagic fever virus discovered in ticks impairs infectivity in human cells.

Crimean-Congo Hemorrhagic Fever (CCHF) is the most widely distributed tick-borne viral infection in the world. Strikingly, reported mortality rates for CCHF are extremely variable, ranging from 5 to 80% (1). CCHF virus (CCHFV, Nairoviridae) exhibits extensive genomic sequence diversity across strains (2, 3). It is currently unknown if genomic diversity is a factor contributing to variation in its pathogenicity. We obtained complete genome sequences of CCHFV directly from the tick reservoir. These new strains belong to a solitary lineage named Europe 2 that is circumstantially reputed to be less pathogenic than the epidemic strains from Europe 1 lineage. We identified a single tick-specific amino acid variant in the viral glycoprotein region that dramatically reduces its fusion activity in human cells, providing evidence that a GPC variant, present in ticks, have severely impaired function in human cells.