Evaluation of two artificial infection methods of live ticks as tools for studying interactions between tick‑borne viruses and their tick vectors
Résumé
Ticks represent significant risks for human and animal health. Because they are obligate hematophagous ectoparasites and feed on diverse vertebrate hosts, they are considered as one of the most important vectors of zoonotic pathogens. Ticks can transmit a wide variety of bacteria, parasites
and viruses. In human and veterinary medicine, most tick-borne pathogens are transmitted by various hard ticks belonging to genera Ixodes, Haemaphysalis, Dermacentor, Hyalomma and Rhipicephalus and by certain soft ticks belonging to genera Argas and Ornithodoros. Among tick-
borne pathogens, 170 tick-borne viruses (TBVs) were identified and belong to nine virus families and twelve virus genera. Viruses transmitted via tick bites can cause various symptoms in humans and animals, ranging from mild febrile illness to neurological disorders or even haemorrhagic fevers. The
oversite and existing gaps in our knowledge of ticks and TBV are partly due to the difficulty of setting effective experimental models to assess vector competence or study virus-tick interactions in general. To overcome this gap of knowledge, it is essential to reproduce transmission cycles under
controlled laboratory conditions. In our study, we used viruses belonging to genera Flavivirus or Orbivirus to infect I. ricinus. TBEV is known to be transmitted by I. ricinus and responsible for severe neurological illness in humans in Europe and Asia. It was used as a positive control to assess the
efficacy of both artificial feeding system (AFS) and immersion technique (IT) as infection methods.
Kemerovo virus (KEMV, genus Orbivirus) is suspected to be the causative agent of encephalitis cases in humans in central Europe and Russia. AFS and IT were used to assess for the first time vector competence of I. ricinus for KEMV. The virus has been isolated/detected in I. persulcatus and I. ricinus.
Assessing the efficacy of both infection techniques was based on the three criteria of vector competence: (i) virus acquisition by ticks, (ii) trans-stadial transmission, and (iii) transmission of the viruses to a vertebrate host. 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.