Unexpected Failure of Nymphs to Transmit a North American Strain

Globally, the () complex comprises more than 21 species of spirochetes. Although the USA is home to a diverse fauna of Lyme disease group species, only two are considered responsible for human clinical disease: () and . However, evidence has implicated additional () species in human illness elsewhere. While much research has focused on the (.)-tick interface, tick vectors for most of the other North American Lyme disease group species remain experimentally unconfirmed. In this report we document the ability of to acquire but not transmit a single strain of , a potential human pathogen, in a murine infection model. Pathogen-free larvae were allowed to feed on mice with disseminated (.) or infections. Molted infected nymphs were then allowed to feed on naïve mice to assess transmission to a susceptible host through spirochete culture and qPCR throughout in ticks collected at various developmental stages (fed larvae and nymphs, molted nymphs, and adults). In this study, similar proportions of larvae acquired and (.) but transstadial passage to the nymphal stage was less effective for . Furthermore, infected nymphs did not transmit infection to naïve susceptible mice as determined by tissue culture and serology. In the tick, spirochete levels slightly increased from fed larvae to molted and then fed nymphs, yet the bacteria were absent in molted adults. Moreover, in contrast to (.), failed to exponentially increase in upon completion of feeding in our transmission experiment. In this specific model, was unable to support throughout its life-cycle, and while live spirochetes were detected in infected ticks fed on naïve mice, there was no evidence of murine infection. These data question the vector competence of for . More importantly, this specific - model may provide a tool for researchers to delineate details on mechanisms involved in -tick compatibility.