Evaluation of the cellular pathway of Orthonairovirus infection in tick cell lines

Crimean-Congo hemorrhagic fever (CCHF) is a severe disease of humans caused by CCHF virus (CCHFV), family Nairoviridae, genus Orthonairovirus. Ticks of the genus Hyalomma are the principal vectors of CCHFV and can transmit the virus to mammalian hosts during blood feeding. Although the pathway of CCHFV infection in mammalian cells has been partially elucidated, no data are available for tick cells. The aim of our study is to investigate the entry of CCHFV into tick cells by adopting Hazara virus (HAZV) as a model. HAZV is an apathogenic virus closely related to CCHFV, and can be easily handled at BSL2 instead of in the BSL4 containment required for CCHFV. We selected a panel of compounds targeting cellular processes involved in CCHFV entry in mammalian cells, and we tested their cytotoxicity in Vero cells and the Hyalomma anatolicum tick cell line HAE/CTVM8. The ability of the compounds to inhibit HAZV infection was evaluated by measuring intracellular viral RNA by qRT-PCR. Firstly, we tested the compounds with Vero cells to verify that HAZV follows the same pathway as CCHFV to enter into mammalian cells. Then we analysed the effect of the compounds on HAZV infection in tick cells. Our preliminary results show that HAZV entry into tick cells requires clathrin-mediated endocytosis. In addition, as described for mammalian cells, alterations in the intraluminal pH of endosomes and cholesterol synthesis reduce the efficiency of viral infection. In conclusion, our results support the hypothesis that HAZV and CCHFV infect tick cells by the same pathway that they follow in mammalian cells.