# Persistent Infections in Tick Cell Lines: The Role of Viral-Derived DNA Forms in Hazara Virus Replication and Cellular Survival

## TL;DR

This study explores how Hazara virus establishes persistent infections in tick cells by producing virus-derived DNA, which helps balance viral replication and cell survival.

## Contribution

The study identifies virus-derived DNA as a key factor in persistent infections and demonstrates its role in regulating viral replication and cell viability.

## Key findings

- HAZV replication in tick cells leads to virus-derived DNA (vDNAs) production, which is crucial for persistent infections.
- AZT treatment reduces vDNAs and increases viral particle production, leading to higher cell death.
- vDNAs are localized in both cytoplasm and nucleus, and their formation depends on HAZV infection.

## Abstract

Crimean–Congo hemorrhagic fever virus (CCHFV) causes severe or fatal infections in humans and is geographically widespread. The virus has coevolved with its tick vectors, establishing persistent infections critical to its transmission. This study explored the mechanisms underpinning these persistent infections, using tick cell lines and the Hazara virus (HAZV) as a biosafety level 2 (BSL-2) model for CCHFV. Initially, an RT-qPCR protocol was developed to detect HAZV in tick cells. The study then focused on the production of virus-derived DNA (vDNAs) by tick cells as a defensive response to infection. These vDNAs regulate viral particle production, enabling tick cells to maintain viability and establish persistent infections. The experiments characterized vDNAs production, viral titers, and subcellular localization, and they examined the effect of the reverse transcriptase inhibitor azidothymidine triphosphate (AZT). The results showed that all tested tick cell lines supported HAZV replication, achieving persistent infections without cytopathic effects. vDNAs was detected in both the cytoplasm and nucleus, and its formation was dependent on HAZV infection. Importantly, vDNAs presence was linked to infection persistence; cells treated with AZT exhibited a marked reduction in vDNAs production and an associated increase in viral particle production, which correlated with higher cell death. These findings underscore the critical role of vDNAs in balancing viral replication and promoting long-term cell survival in tick cells, highlighting their importance in the coevolution of tick-borne viruses and their vectors.