Coinfection and population dynamics of Borrelia bissettii and Borrelia burgdoerferi in a tick-murine borreliosis model

Lyme borreliosis is the most common vector-borne disease in the United States. Borrelia bissettii is a Lyme Borrelia (LB) spirochete that is endemic to multiple regions in the US and Europe. Studies show certain strains of B.bissettii cause pathology in murine hosts and have been implicated in human disease. Because B. bissettii circulates between ticks and small rodents, analogous to B. burgdorferi, we assessed the ability of I. scapularis to transmit B. bissettii in a murine model under both single and dual infection scenarios. Utilizing culture and quantitative PCR, we monitored the population of borreliae in the tick from larval acquisition to adult and measured infection loads in various murine tissues. We show that I. scapularis can acquire B. bissettii and will maintain the infection transstadially, yet it is an incompetent vector in this model. Under dual infection, we characterize the heterogeneous Borrelia population in multiple murine tissues and describe differential acquisition of LB in ticks. Description of this atypical Borrelia infection in ticks may help elucidate the biological processes undergone by the closely related LB spirochete, B. burgdorferi in its tick vector, and expounds our understanding on the ecology of B. bissettii a potential emerging human pathogen.