Transovarial and transstadial transmission of Borrelia valaisiana, the pathogen of Lyme borreliosis, in the sheep tick, Ixodes ricinus L.

In this study, molecular analysis was used to show the possibility of transovarial and transstadial transmission of Borrelia valaisiana in Ixodes ricinus ticks in the natural biotopes of North-Western Russia. Female ticks collected in nature were fed on rabbits; larvae obtained from these females were fed on white mice. Eggs, female ticks after the egg deposition, larvae and nymphs of ticks after overwintering were studied for Borrelia burgdorferi s.l. within the natural inserts. The identification of Borrelia burgdorferi in ticks was carried out using the PCR method with real-time hybridization-fluorescence detection. The genotyping was performed by sequencing fragments of the intergenic region rrf-rrl. Spirochetes of only one genospecies B. valaisiana, previously not detected in North-Western Russia, were identified in ticks I. ricinus. The isolates of B. burgdorferi were obtained by inoculation of the gut contents of ticks into a prepared nutrient medium BSK-H with 6% rabbit serum (Sigma, USA). The positive reaction for B. valaisiana was observed in six out of 13 I. ricinus females (46.2%), which were successfully fed and laid eggs. Of the six infected female ticks, four (66.7%) (30.8% of the total four out of 13) were able to transmit B. valaisiana to eggs and then to larvae. 50.0% of the infected female ticks (23.1% of the total number) could transmit B. valaisiana to nymphs. In addition, the overwintered larvae and nymphs did not retain B. valaisiana. The subsequent transmission can occur as a result of feeding the overwintered larvae and nymphs on the infected overwintered hosts.