Pathogenesis of Crimean-Congo Hemorrhagic Fever

Although Crimean-Congo hemorrhagic fever (CCHF) is a widespread tick-borne disease, little is known about its pathogenesis. The interaction of the virus with host cells is most likely responsible for the pathogenesis of CCHF. The main contributors are endothelial cells (ECs) and immune cells. There are 2 theories underlying the CCHF pathogenesis: One is that the virus interacts with the ECs directly and the other that it interacts indirectly via immune cells with subsequent release of soluble mediators. ECs are activated upon infection by the upregulation of soluble molecules and proinflammatory cytokines. Probably, in severe cases, deregulation and excessive release of the cytokines accompanied by endothelial activation have toxic effects, leading to increased vascular permeability, vasodilatation, and subsequently hypotension, multiple organ failure, shock, and death. Studies indicate that CCHF virus (CCHFV) also can impair the innate immune system and cause a delay in adaptive immune response, which is critical for the clearance of CCHFV. The virus has many different ways to block the immune response, leading to uncontrolled viral replication followed by systemic spread of the virus throughout the body. Partial activation of dendritic cells and macrophages, delayed induction of interferons, weak antibody response, apoptosis of lymphocytes, and hemophagocytosis are some of these tactics. However, there are many points waiting for clarification about the pathogenesis of CCHF. Although the high risk of contagiousness limits research, we need more studies to understand the CCHF pathogenesis better. Here we review the main characteristics of the pathogenesis of CCHF.