Evaluation of two artificial infection methods of live ticks as tools for studying interactions between tick-borne viruses and their tick vectors

Abstract

Up to 170 tick-borne viruses (TBVs) have been identified to date. However, there is a paucity of information regarding TBVs and their interaction with respective vectors, limiting the development of new effective and urgently needed control methods. To overcome this gap of knowledge, it is essential to reproduce transmission cycles under controlled laboratory conditions. In this study we assessed an artificial feeding system (AFS) and an immersion technique (IT) to infect Ixodes ricinus ticks with tick-borne encephalitis (TBE) and Kemerovo (KEM) virus, both known to be transmitted predominantly by ixodid ticks. Both methods permitted TBEV acquisition by ticks and we further confirmed virus trans-stadial transmission and onward transmission to a vertebrate host. However, only artificial feeding system allowed to demonstrate both acquisition by ticks and trans-stadial transmission for KEMV. Yet we did not observe transmission of KEMV to mice (IFNAR−/− or BALB/c). Artificial infection methods of ticks are important tools to study tick-virus interactions. When optimally used under laboratory settings, they provide important insights into tick-borne virus transmission cycles.

Evaluation of Vector Competence of Ixodes Ticks for Kemerovo Virus

“…BSR cells (a clone of BHK-21, [ 9 ]) were used to propagate the KEMV virus and to constitute a virus stock as previously described [ 8 ]. Passage 3 in BSR cells was designated KEMV smb1/Vero2/BSR3, and passage 4 was designated KEMV smb1/Vero2/BSR4 (smb—suckling mouse brain).…”

“…A KEMV titre was determined using a plaque assay as previously described [ 8 , 10 ]. Briefly, virus-infected cells (grown in 75 cm 2 flasks) were harvested on day 5 post-infection, and cell debris was treated with an organic solvent to release virus particles as previously described [ 11 ].…”

“…The system we used to infect ticks was previously described in [ 8 ]. Briefly, cut gerbil skin was used to feed ticks.…”

“…Ticks were placed in a tick chamber and enclosed with a mosquito mesh allowing them to breathe. To attract ticks, the setting was maintained at 37 °C by a circulating warmed water circuit [ 8 ]. In this study, we used 3000 I. ricinus larvae from France, 250 I. ricinus nymphs from Slovakia and 2000 I. persulcatus from Russia.…”

“…We used an artificial feeding system to infect larvae and validated the first two criteria of vector competence (virus acquisition and trans-stadial transmission) for this I. ricinus tick population. The last criterion was not confirmed [ 8 ]. In the current study, we used the same system to infect different tick populations from two distinct Ixodes tick species: I. ricinus larvae from France and nymphs from Slovakia, and I. persulcatus larvae from Russia.…”