Dissemination of Borrelia burgdorferi, the agent of Lyme borreliosis, in comparison to Borrelia persica, the agent of tick-borne relapsing fever, in a murine model

Liang, Liucun (2019): Dissemination of Borrelia burgdorferi, the agent of Lyme borreliosis, in comparison to Borrelia persica, the agent of tick-borne relapsing fever, in a murine model. Dissertation, LMU München: Tierärztliche Fakultät

Abstract

Borrelia persica (Bp) is the most prevalent species causing tick-borne relapsing fever (TBRF) in Central Asia and the Middle Eastern countries whilst B. burgdorferi sensu stricto (Bbss) is an endemic genospecies causing Lyme borreliosis (LB) in North America and Europe. TBRF patients commonly suffer from recurrent fever attacks due to spirochete proliferation and antibody-mediated killing of these organisms in the blood, whereas during the early stage of infection LB patients commonly show skin lesions (erythema migrans). If left untreated, LB patients may develop to a chronic phase with Lyme arthritis or other tissue lesion due to inflammatory responses (e.g., acrodermatitis chronica atrophicans). Despite a severe debate over the exact dissemination pathways employed by borrelia organisms, little is known how Bp and Bbss disseminate in the body of mammalian hosts. Hence, a murine model with a novel and precise infection approach was established to explore the dissemination route of host-adapted Bp and Bbss organisms post intradermal (ID) and intravenous (IV) inoculation in immunocompetent C3H/HeOuJ mice. Since borreliae are able to express differentially outer surface proteins (Osps) in vitro and in vivo, it was necessary to generate the host-adapted bacteria from immunodeficient NOD-SCID mice. An ID inoculation of 1.0 x 10^5 culture-derived Bp organisms per animal resulted in the peak of spirochetemia with 8.8 x 10^6 cells per ml blood of NOD-SCID mouse. However, 1.0 x 10^6 and 1.0 x 10^8 cultured Bbss caused spirochetemia with a low load resulting in up to 4.9 x 10^4 and 7.2 x 10^4 organisms per ml blood, respectively. Interestingly, hematogenous Bp spirochetes were detectable by both qPCR and cultivation at least one day earlier when compared to Bbss. It seems that Bp is more efficient in entering the bloodstream and multiplying in the circulation of the immunodeficient mice than Bbss. Compared to the ID injection the strict IV inoculation via the jugular vein in C3H/HeOuJ mice was the most critical step to clarify whether host-adapted Bp and Bbss organisms are capable of leaving the bloodstream for further colonization in mammalian tissues. After either ID or IV inoculation of 7.2 x 10^5 host-adapted Bp organisms, these spirochetes were detectable up to day 24 in C3H/HeOuJ mice. Bp counts reached up to 1.9 x 10^6 and 4.1 x 10^6 per ml blood sampled at day 12 post ID and IV challenge, respectively. Correspondingly, antibody detection with collected plasma and serum samples showed that specific antibodies to Bp were induced. Notably, all brain tissue samples from both ID and IV inoculated C3H/HeOuJ mice were positive for Bp when tested with molecular methods and cultivation. In contrast, neither the Bbss ospA gene nor viable spirochetes were found in the blood of any C3H/HeOuJ mouse inoculated either ID or IV with approx. 3 x 10^3 host-adapted Bbss spirochetes. Interestingly, on day 49/50 after ID injection, Bbss spirochetes were re-isolated from most tissue samples collected from the ears, skins (injection areal), tibiotarsal joints, urinary bladders, and hearts. Strong antibody responses against Bbss were detected in all ID inoculated animals. In contrast, after IV injection of host-derived Bbss organisms, neither borrelial DNA nor viable spirochetes were present in any tissue sample collected from these animals. In addition, they did not produce specific antibodies against Bbss. In summary, 1) Bp is excellently capable of adapting to and surviving in the bloodstream. The spirochete disseminates predominantly via hematogenous route to distant organs (e.g., brain) to establish a persistent infection; 2) Bbss is a tissue-bound spirochete that migrates primarily via non-hematogenous routes. Intradermal deposition will cause a successful persistent infection while the blood vessel system is an impasse for this bacterium. The animal model applied in this study mimics the natural infection conditions of tick bite as closely as possible. Borreliae were used in an inoculum dose expected to be deposited by ticks in the skin of mammal hosts or in a development phase (host-adapted) they most likely express in blood. The detailed characterization of the spirochetes' dissemination pathways provides an advanced understanding of the pathogenicity mechanism of TBRF and LB species, and can help to improve diagnostic approaches or therapeutic strategies. Notably, blood transfusion of Bp may poses a high risk of infection to recipients whereas the risk to become infected with Bbss is nonexistent.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: Lyme borreliosis, Borrelia burgdorferi, tick-borne relapsing fever, Borrelia persica, dissemination pathways
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 590 Tiere (Zoologie)
• Fakultäten: Tierärztliche Fakultät
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 27. Juli 2019
• 1. Bericht­erstatter:in: Straubinger, Reinhard