Date of Award
5-1-2024
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
College/School/Department
Department of Biomedical Sciences
Dissertation/Thesis Chair
Yi-Pin Lin
Committee Members
Alexander Ciota, April Davis, Nicholas Mantis, Melissa Prusinski
Keywords
Borrelia burgdorferi, dissemination, Lizards, Lyme disease, sylvatic cycle, tolerogenic
Subject Categories
Microbiology
Abstract
Borrelia burgdorferi sensu lato (B. burgdorferi s.l.) spirochetes are the causative agents of Lyme disease (LD, Lyme borreliosis), the leading cause of tick-borne illness in North America (NA), Europe, and throughout temperate zones of the Holarctic region. Ixodes ticks are the only competent genus that permit acquisition, maintenance, and successful transmission of LD bacteria to subsequent hosts. LD spirochetes are unable to effectively pass through transovarial barriers, from adults to eggs, and therefore, next generation larvae are Lyme borreliae-free. Instead, B. burgdorferi s.l. are reliant on maintenance in both vertebrate and arthropod hosts to perpetuate high prevalence in nature. Of the known reservoirs in NA and Europe, the white footed mouse (Peromyscus leucopus) and the European wood mouse (Apodemus sylvaticus) have garnered significant research attention for increasing the prevalence of Borrelia-infected ticks due to their tolerated infections and propensity to infect numerous feeding ticks. Potential strategies for controlling infection of these hosts include fipronil bait to reduce tick infestation, oral OspA vaccination of small mammal reservoirs, and CRISPR modified mice resistant to spirochete colonization. An additional eco-immunological consideration has also been suggested regarding lizards in NA. These findings regard species such as the western fence lizard (Sceloporus occidentalis) as a potential dilution host, imparting a spirochete clearance mechanism upon bloodmeals, leaving the ticks bereft of previous B. burgdorferi s.l. colonization. In this dissertation, I sought to evaluate the reservoir potential of the eastern fence lizard, Sceloporus undulatus, challenged with various B. burgdorferi s.s. ospC type K strains, and uncover underlying immune complement escape mechanisms. Previous work on the lizard’s western counterpart in NA, S. occidentalis revealed that the species contributed heavily to tick development through early bloodmeals as a preferred host, yet it was unable to harbor B. burgdorferi s.l.. Further, clearance of spirochetes in tick bloodmeals was demonstrated by lizard complement, an innate immune defense mechanism clearing pathogens. Thus, a dilution host model was proposed, indicating that S. occidentalis may contribute to the low numbers of LD cases reported from areas west of the Rocky Mountains. I hypothesized that S. undulatus was employing a dilution host effect upon Lyme borreliae laden tick populations, as evidenced by low numbers of reported LD cases in lizard’s southeast native range. And further, as the species continues expanding northward, it may continue to serve as a beneficial dilution host. However, intermittent evidence of B. burgdorferi DNA in lizards from eastern NA has come to light, and limited B. burgdorferi s.l. reservoir competence in lizards, including S. undulatus. Together, these conflicting results bolstered the need for further investigation of lizards in Lyme-endemic regions of the northeastern United States. In Chapter 3, I evaluate field-collected S. undulatus from the New Jersey pine barrens for the presence of Borrelia DNA or seropositivity, yielding low positive results confirming previous work in the area. Using sera from naïve juvenile lizards, I also observed a strain-specific survival of B. burgdorferi sensu stricto (B. burgdorferi s.s.), aligning with previous studies, while revealing a potential lizard specialist type (ospC type K). Selecting for lipoproteins involved in complement evasion, I also found that OspE from sera survival strains explicitly binds to lizard factor H, promoting survival of the innate immune response. These data thus identify complement evasion determinants by a single strain type of B. burgdorferi s.s. in lizard hosts. Previous studies on NA lizards as potential reservoir hosts only explored a limited number of NA B. burgdorferi s.s. strains, all within the ospC type A group, and therefore limited their assessment of genomic divergence. With the support of in vitro results, produced in Chapter 3, which supported both camps toeing the line between lizards as dilution hosts, or as potential reservoirs, I also hypothesized that ospC type K B. burgdorferi s.s. strains could survive and disseminate in lizards in a genotypic manner. I explicitly demonstrated that nonpathogenic strains of B. burgdorferi s.s. transformed with constitutively expressed OspE from B. burgdorferi s.s. B379 (ospC type K) provided a distinct survival phenotype and binding affinity to lizard factor H, allowing the spirochetes to survive the complement alternative pathway. I explored B. burgdorferi s.s. survival in S. undulatus by needle inoculation in Chapter 4, challenging with ospC type K strains, and demonstrated persistence and dissemination. I hypothesized that type K strains would exhibit low levels of survival, while type A would be cleared and unable to migrate from the inoculation site, aligning with previous work. Interestingly, I found that all three strains could disseminate, although B31-5A4 at very low levels. I also showed that only B379 and 297 could be cultured after four weeks of incubation, indicating that B31-5A4 qPCR results were artifacts of escape survival, but eventual clearance. Further, it appeared that B379 yielded robust amplification at distal tissues, and consistent isolation from tissues, while 297 appeared to be weaker. Finally, I sought to examine the immune response of lizards inoculated with these B. burgdorferi s.s. strains, taking a survey of actively expressed immune related genes and comparing cohort profiles by comparing differentially expressed genes between inoculated lizard cohorts. This revealed that 297 and B31-5A4 share a striking resemblance in pathogen inflammatory response. However, B379 colonized lizards elicited a remarkable immune response profile, divergent from the other Borrelia challenged lizard cohorts, aligning closely with the negative control group. These data suggests that B379 inoculation yields a tolerogenic immune response, a host toleration of the pathogen with a diminished induction of triggers that would otherwise lead to clearance. The results of this dissertation highlights my goal of implicating NA lizards in the B. burgdorferi s.s. sylvatic cycle. Interestingly, S. undulatus appears to simultaneously clear strain-specific B. burgdorferi s.s., while tolerating a select type, ospC type K. This supports previous results on standard lab stocks of B. burgdorferi s.s., generally B31 derivatives, were readily cleared by the western US counterpart S. occidentalis, while also providing compelling data reinforcing field surveillance and low lizard competence findings. This also infers that lizards can act as a dilution host for most ospC type strains, but may amplify type K, which is particularly human pathogenic. These findings provide compelling evidence that lizards are quite involved in the Lyme borreliae enzootic cycle and require further attention to explore defined reservoir competence. Collectively, this work serves as a foundation for defining the public health significance of lizard expansion into Lyme-endemic areas and yields insight into mechanisms behind strain-specific survival of B. burgdorferi s.s. in diverse hosts.
Recommended Citation
Nowak, Tristan Anthony, "Implicating North American Lizards In The Borrelia Burgdorferi Sensu Stricto Sylvatic Cycle" (2024). Legacy Theses & Dissertations (2009 - 2024). 3352.
https://scholarsarchive.library.albany.edu/legacy-etd/3352
