Transmission of Borrelia miyamotoi sensu lato relapsing fever group spirochetes in relation to duration of attachment by Ixodes scapularis nymphs

Abstract

Borrelia miyamotoi sensu lato relapsing fever group spirochetes are emerging as causative agents of human illness (Borrelia miyamotoi disease) in the United States. Host-seeking Ixodes scapularis ticks are naturally infected with these spirochetes in the eastern United States and experimentally capable of transmitting B. miyamotoi. However, the duration of time required from tick attachment to spirochete transmission has yet to be determined. We therefore conducted a study to assess spirochete transmission by single transovarially infected I. scapularis nymphs to outbred white mice at three time points post-attachment (24, 48, and 72h) and for a complete feed (>72-96h). Based on detection of B. miyamotoi DNA from the blood of mice fed on by an infected nymph, the probability of spirochete transmission increased from 10% by 24h of attachment (evidence of infection in 3/30 mice) to 31% by 48h (11/35 mice), 63% by 72h (22/35 mice), and 73% for a complete feed (22/30 mice). We conclude that (i) single I. scapularis nymphs effectively transmit B. miyamotoi relapsing fever group spirochetes while feeding, (ii) transmission can occur within the first 24h of nymphal attachment, and (iii) the probability of transmission increases with the duration of nymphal attachment.

Keywords: Borrelia miyamotoi; Ixodes scapularis; Transmission; Vector.

Fig. 1

Serological reactivity post-tick exposure for 19 mice (strips 1–14 and 16–20) that tested positive for B. miyamotoi DNA in their blood. Strip 15 illustrates lack of reactivity post-tick exposure for a mouse that did not test positive for B. miyamotoi DNA in its blood.

Fig. 2

Examples of serological reactivity for mice (A) after exposure to B. miyamotoi-infected I. scapularis nymphs for mouse E19 testing positive for B. miyamotoi DNA in its blood and (B) before (left strip) and after (right strip) exposure to B. miyamotoi-infected I. scapularis nymphs for mice (C94, D10, D22, D24, D81, D82, D96, E15, E27, E32) testing negative for B. miyamotoi DNA in their blood.