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Borrelia miyamotoisensu lato relapsing fever group spirochetes are emerging as causative agents of human illness (Borrelia miyamotoidisease) in the United States. Host-seeking Ixodes scapularisticks 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. scapularisnymphs 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. miyamotoiDNA 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. scapularisnymphs effectively transmit B. miyamotoirelapsing 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.

The white-footed mouse, Peromyscus leucopus(Rafinesque), is a reservoir for the Lyme disease spirochete Borrelia burgdorferisensu stricto in the eastern half of the United States, where the blacklegged tick, Ixodes scapularisSay (Acari: Ixodidae), is the primary vector. In the Midwest, an additional Lyme disease spirochete, Borrelia mayonii, was recorded from naturally infected I. scapularisand P. leucopus. However, an experimental demonstration of reservoir competence was lacking for a natural tick host. We therefore experimentally infected P. leucopuswith B. mayoniivia I. scapularisnymphal bites and then fed uninfected larvae on the mice to demonstrate spirochete acquisition and passage to resulting nymphs. Of 23 mice fed on by B. mayonii-infected nymphs, 21 (91%) developed active infections. The infection prevalence for nymphs fed as larvae on these infected mice 4 wk post-infection ranged from 56 to 98%, and the overall infection prevalence for 842 nymphs across all 21 P. leucopuswas 75% (95% confidence interval, 72–77%). To assess duration of infectivity, 10 of the P. leucopuswere reinfested with uninfected larval ticks 12 wk after the mice were infected. The overall infection prevalence for 480 nymphs across all 10 P. leucopusat the 12-wk time point was 26% (95% confidence interval, 23–31%), when compared with 76% (95% confidence interval, 71–79%) for 474 nymphs from the same subset of 10 mice at the 4-wk time point. We conclude that P. leucopusis susceptible to infection with B. mayoniivia bite by I. scapularisnymphs and an efficient reservoir for this Lyme disease spirochete.

The hard tick-borne relapsing fever spirochete, Borrelia miyamotoi, has recently gained attention as a cause of human illness, but fundamental aspects of its enzootic maintenance are still poorly understood. Challenges to experimental studies with B. miyamotoi-infected vector ticks include low prevalence of infection in field-collected ticks and seemingly inefficient horizontal transmission from infected immunocompetent rodents to feeding ticks. To reliably produce large numbers of B. miyamotoi-infected ticks in support of experimental studies, we developed an animal model where immunocompromised Mus musculusSCID mice were used as a source of B. miyamotoi-infection for larval and nymphal Ixodes scapularisticks. Following needle inoculation with 1 × 105spirochetes, the SCID mice developed a high spirochetemia (greater than 1 × 107copies of B. miyamotoi purBper mL of blood) that persisted for at least 30 d after inoculation. In comparison, immunocompetent M. musculusCD-1 mice developed transient infections, detectable for only 2–8 d within the first 16 d after needle inoculation, with a brief, lower peak spirochetemia (8.5 × 104– 5.6 × 105purBcopies per mL of blood). All larval or nymphal ticks fed on infected SCID mice acquired B. miyamotoi, but frequent loss of infection during the molt led to the proportion infected ticks of the resulting nymphal or adult stages declining to 22–29%. The ticks that remained infected after the molt had well-disseminated infections which then persisted through successive life stages, including transmission to larval offspring.

Borrelia mayoniiis a newly described member of the Borrelia burgdorferisensu lato complex that is vectored by the black-legged tick (Ixodes scapularisSay) and a cause of Lyme disease in Minnesota and Wisconsin. Vertebrate reservoir hosts involved in the enzootic maintenance of B. mayoniihave not yet been identified. Here, we describe the first isolation of B. mayoniifrom naturally infected white-footed mice (Peromyscus leucopusRafinesque) and an American red squirrel (Tamiasciurus hudsonicusErxleben) from Minnesota, thus implicating these species as potential reservoir hosts for this newly described spirochete.

A novel species within the Borrelia burgdorferisensu lato complex, Borrelia mayonii, was recently described and found to be associated with Lyme borreliosis in the Upper Midwest of the United States. The blacklegged tick, Ixodes scapularis, is naturally infected with B. mayoniiin the Upper Midwest and has been experimentally demonstrated to serve as a vector for this spirochete. Natural vertebrate reservoirs for B. mayoniiremain unknown. In this study, we demonstrate that an experimental spirochete host, the CD-1 strain outbred white mouse, can maintain active infection with B. mayoniifor up to 1year: infected mice consistently yielded ear biopsies containing motile spirochetes from 29 to 375days after they were first infected via tick bite. Infection rates in resultant nymphal ticks varied greatly both over time for larvae fed on the same individual mouse at different time points after infection (2–42%) and for larvae fed on different mice at a given time point up to 8 months after infection (0–48%). Infection rates were lower in nymphs fed as larvae on mice 10–12 months after infection (2–3% for 5 mice and 9.8% for 1 mouse). In addition to ear biopsies, B. mayoniiwas detected from bladder, heart, and spinal cord of infected mice when they were sacrificed 163–375days after initial infection via tick bite. Examination of blood from mice determined to be infected with B. mayoniiby ear biopsy did not produce evidence of B. mayoniiDNA in blood taken 8–375days after the mice were first infected via tick bite.

Bacterial vector-borne diseases, including Borreliaspecies, present a significant diagnostic, clinical, and public health challenge due to their overlapping symptoms and the breadth of causative agents and arthropod vectors. The relapsing fever (RF) borreliae encompass both established and emerging pathogens and are transmitted to humans by soft ticks, hard ticks, or lice.