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

Abstract

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.

How relevant are in vitro culture models for study of tick-pathogen interactions?

“…The choice of the species from which cells are derived is crucial in terms of relevance, as certain TBV can infect cell lines derived from multiple different tick genera/ species [74]. For instance, Alkhumra hemorrhagic fever virus, which has been found in Ornithodoros savignyi, replicates in the tick cell lines HAE/CTVM9, RAE/CTVM1, and OME/CTVM24 [202]. Yet detecting viral RNA by RT-PCR, or viral antigens by immunohistochemistry, does not reflect full replication functionality in a particular cell line and/or virus assembly.…”

Article Commentary: Virus Discovery Using Tick Cell Lines

“…5 Since then, ticks have been incriminated as vectors and/or reservoirs of numerous viruses of medical and/or veterinary importance, 6,7 including the emerging pathogens Alkhumra hemorrhagic fever virus, severe fever with thromocytopenia virus, Heartland virus, and Bourbon virus. [8][9][10][11] In addition, many apparently nonpathogenic arboviruses have been isolated from ticks. 6,7 Research on tick-borne viruses has benefited greatly from the availability of tick cell and tissue cultures.…”

Alkhumra hemorrhagic fever virus infection

“…Madani et al . [ 22 ], examined three tick lines for propagation of AHFV. The first was derived from the soft tick Ornithodoros moubata (OME/CTVM 24), and the other two were derived from hard ticks: one from Rhipicephalus appendiculatus (RAE / CTVM 1) and the other from Hyalomma anatolicum (HAE/CTVM 9).…”

“…Whether mosquitoes can be vectors for transmission of this presumably tick-borne virus remains to be proven, however [ 4 , 21 ]. The fact that AHFV was successfully propagated in mosquito cell lines may support the hypothesis that mosquitoes could be vectors for transmitting this virus [ 4 , 21 , 22 ]. On two occasions, different species of mosquitoes were collected and examined for AHFV.…”