Vector competence of the blacklegged tick, Ixodes scapularis, for the recently recognized Lyme borreliosis spirochete Candidatus Borrelia mayonii

A novel species within the Borrelia burgdorferi sensu lato complex, provisionally named Borrelia mayonii, was recently found to be associated with Lyme borreliosis in the Upper Midwest of the United States. Moreover, B. mayonii was detected from host-seeking Ixodes scapularis, the primary vector of B. burgdorferi sensu stricto in the eastern United States. We therefore conducted a study to confirm the experimental vector competence of I. scapularis for B. mayonii (strain MN14-1420), using colony ticks originating from adults collected in Connecticut and CD-1 white mice. Larvae fed on mice 10 weeks after needle-inoculation with B. mayonii acquired spirochetes and maintained infection through the nymphal stage at an average rate of 12.9%. In a transmission experiment, 40% of naïve mice exposed to a single infected nymph developed viable infections, as compared with 87% of mice fed upon by 2-3 infected nymphs. Transmission of B. mayonii by one or more feeding infected nymphs was uncommon up to 48 h after attachment (one of six mice developed viable infection) but occurred frequently when nymphs were allowed to remain attached for 72-96 h or feed to completion (11 of 16 mice developed viable infection). Mice infected via tick bite maintained viable infection with B. mayonii, as determined by ear biopsy culture, for at least 28 weeks. Our results demonstrate that I. scapularis is capable of serving as a vector of B. mayonii. This finding, together with data showing that field-collected I. scapularis are infected with B. mayonii, indicate that I. scapularis likely is a primary vector to humans of this recently recognized Lyme borreliosis spirochete.