Susceptibility of tick cell lines to infection with alkhumra haemorrhagic fever virus

Background: Although Alkhumra haemorrhagic fever virus (AHFV) has been isolated from ticks, epidemiological data suggest that it is transmitted from livestock to humans by direct contact with animals or by mosquito bites, but not by ticks. This study was carried out to assess the ability of the virus to replicate in tick cells in vitro. Methods: AHFV was inoculated into cell lines derived from the hard ticks Hyalomma anatolicum (HAE/CTVM9) and Rhipicephalus appendiculatus (RAE/CTVM1) and the soft tick Ornithodoros moubata (OME/CTVM24). Inoculated cells were directly examined every week for 4 weeks by real-time reverse transcription PCR and by IFAT using polyclonal antibodies. Results: AHFV RNA was detected in all three inoculated tick cell lines throughout the 4-week observation period at levels up to almost twice that of the inoculum, but none of them exhibited a cytopathic effect. AHFV antigen could be detected in all three cell lines by IFAT. Titration of tick cell culture suspension in LLC-MK2 cells yielded AHFV titres of 10. ^6.6 50% tissue culture infective dose (TCID. ₅₀)/ml for OME/CTVM24 and 10. ^5.5 TCID. ₅₀/ml for RAE/CTVM1 cells after 4 weeks of culturing; no viable virus was detected in HAE/CTVM9 cells. Conclusion: This is the first description of propagation of AHFV in tick cells.