Chlamydia-related diseases in animals and their zoonotic potential

Chlamydiae are obligate intracellular, Gram-negative bacteria with a worldwide distribution causing diseases in humans and animal hosts. 


Chlamydia (C.) abortusis the most important infectious agent causing abortion in sheep and goats. The Institute of Veterinary Pathology (IVPZ) is the national (designated by the Federal Food Safety and Veterinary Office, FSVO) and international (designated by the Office International des Epizooties, OIE) reference laboratory for ovine chlamydiosis offering accredited direct and indirect diagnostic methods.


The main focus of the research group headed by Prof. Nicole Borel is on Chlamydia-related diseases in animals and their zoonotic potential.


The Chlamydia research team (Borel group)


Group leader. Nicole Borel, Dr. med. vet. Dipl. ECVP, FVH (Pathology), has her research focus in the field of infection pathology, specifically on the pathogenesis of infectious diseases and host-pathogen interactions. Nicole Borel graduated from the Vetsuisse Faculty, University of Zurich, Switzerland. Since 1999, she is working in research, teaching and diagnostic services in the field of Veterinary Pathology. In 2008, she received the Venia Legendi (Habilitation) at the University of Zurich entitled “Chlamydial abortions in ruminants: serological, epidemiological and diagnostic investigations“. Since 2007, Prof. Borel is the official international expert for chlamydial abortion in sheep and goats designated by the OIE. In the past, Prof. Borel fulfilled research assignments in the USA (University of Louisville, KY, supported by the Swiss National Science Foundation), Germany and Namibia. Since April 2020, Nicole Borel is an associate professor at the Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich.


Senior researcher. Cory Ann Leonard, PhD (Biomedical Science, Microbiology), completed her BA in Biology at the University of North Carolina at Asheville in 1999, then worked in clinical microbiology diagnostics prior to pursuing a graduate degree. She received her PhD in Biomedical Sciences/Microbiology from East Tennessee State University in 2013. She continued her education the same year with postdoctoral training at the University of Zurich, in the laboratory of Prof. Nicole Borel, where she studied in vitro Chlamydia infection, focusing on host-pathogen interaction and chlamydial persistence. She undertook a second postdoctoral research position, at the University of Florida in 2017-18, to study the effect of gut bacteria in mouse models, and followed this with a brief research/training position at East Tennessee State University, to gain expertise in mouse models of chlamydial infection/persistence. She is currently a senior scientist in the Borel laboratory, studying in vitro and in vivo Chlamydia-Neisseria gonorrhoeaeco-infection.


Former Postdoctoral fellow.Helen Aumayer, PhD (Biomedical Science, Microbiology), was part of the Borel group from October 2016 to April 2017 investigating Chlamydia-induced NF-kappaB activation in intestines of experimentally infected gnotobiotic piglets.


Scientific consultants. Helena Seth-Smith, PhD (Institute of Biotechnology, University of Cambridge), provides her expertise in microbiology, particularly in the field of genomics since April 2016. Christian Blenn,Toxicologist, Dipl. agr. biol, Dr. sc. ETH Zurich, provides his expertise in cell toxicity and cell death related to wIRA projects since 2013.


Laboratory expertise. Theresa Pesch and Barbara Prähauser are supporting various projects with the establishment and execution of various techniques in molecular biology and cell culture since 2013.


Graduate and undergraduate students. 


Hanna Marti, PhD student, Dr. med. vet., finished her studies in veterinary medicine in January 2013. She has been a part of Prof. Borel’s group since her master thesis in 2011 and further pursued her career in Chlamydiaresearch by acquiring her doctoral title (Dr. med. vet.) in October 2014 investigating the effect of water-filtered infrared A (wIRA) on chlamydial infection. To expand her skillset, she spent the year of 2015 at the UCSF Benioff Children’s Hospital of Oakland Research Institute (CA, USA) in the laboratory of Prof. Deborah Dean, MD/MPH, funded by the Early Postdoc.Mobility Fellowship of the Swiss National Science Foundation (SNSF). Since 2016, Hanna Marti is a PhD student and part of the MD-PhD program at the Life Science Zurich Graduate School and the Microbiology and Immunology (MIM) program of the University of Zurich investigating the transmission mechanism of tetracycline resistance in Chlamydia suis.


Jasmin Kuratli, PhD student, Dr. med. vet., finished her studies in veterinary medicine in January 2016, followed by work in postmortem diagnostic service and research work for her doctoral thesis at the IVPZ. In August 2019, she acquired the doctoral title (Dr. med. vet.) for the research project “Water Filtered Infrared A and Visible Light (wIRA/VIS) Irradiation Reduces Chlamydia trachomatisInfectivity Independent of Targeted Cytokine Inhibition” under the supervision of Prof. Dr. Nicole Borel. Since 2019, she is a PhD student at the Graduate School for Cellular and Biomedical Sciences (GCB) in Bern and works on her PhD project with special focus on anti-chlamydial treatment strategies (wIRA) and drug interactions with Chlamydia trachomatis


Delia Onorini, PhD student, Master of Medical Biotechnology, finished her studies in December 2017 at the University of Bologna. From April to October, 2018, she performed an internship in Prof. Borel’s group investigating the influence of centrifugation and incubation temperature on the infectivity and ultrastructural morphology of eight human and animal chlamydial strains. Since mid-May 2019, Delia Onorini is a PhD student at the Life Science Zurich Graduate School and the Microbiology and Immunology (MIM) program of the University of Zurich investigating the pathogenic interplay, in vitroand in vivo,between Chlamydia trachomatisand Neisseria gonorrhoeae.


Former graduate students (2013 – 2020): Dr. med. vet. Julia Bünter; Dr. med. vet. Karolin Hoffmann; Dr. med. vet. Carolin Rahn; Dr. med. vet. Sabrina Wanninger, Dr. med. vet. Eveline Staub, Dr. med. vet. Carolina Botta, med. vet. Janine Fritschi, med. vet. Nina Ostfeld.


Current doctoral students: med. vet. Lea Rohner, med. vet. Michelle Bressan.


Former and current master and internship students (since 2013): Julia Bünter, Frédéric Dewez, Carolina Botta, Eveline Staub, Aurora Levi, Roberta Biondi, Delia Onorini, Janine Fritschi, Michal Trinkler, Prisca Mattmann, Lea Rohner, Michelle Bressan, Sibylle Baumann, Silvia Ciuria.


Our research

Currently, our research strategy has three main focuses:

  1. Persistence models for Chlamydiain animals and humans
  2. Tetracycline-resistance mechanisms in Chlamydia suis
  3. Alternative therapeutic strategies to treat chlamydial infections



1.         Persistence models for Chlamydia in animals and humans


The chlamydiae are obligate intracellular bacteria with a complex developmental cycle including the infectious elementary body (EB) and the replicating reticulate body (RB). Under adverse environmental conditions, developing chlamydiae may enter a state referred to as persistence, more recently re-named chlamydial stress response or the aberrant RB (AB) phenotype.In vivo, the AB phenotype may contribute to prolonged, chronic inflammation, fibrosis, and scarring through continuing stimulation of the host immune system as seen in Chlamydia-induced infertility in women. Finally, the AB form is more resistant, or even refractory, to antibiotic treatment in vitroand in vivoin a murine persistence model. 

Previous research in the Borel group focused on mixed infections involving Chlamydiaand viral pathogens, which could lead to the chlamydial stress response resulting in ongoing pro-inflammatory processes in the absence of bacterial replication (Borel et al. 2010). As viral infection is known to cause the release of damage/danger associated molecular patterns (DAMPs), we investigated the effect of DAMPs on C. trachomatisand C. pecorum, describing this alternative induction of the chlamydial stress response (Leonard et al. 2015). We further evaluated the Nuclear factor kappa B (NFκB) pro-inflammatory pathway and found that C. pecorum, a chlamydial species primarily found in ruminants and marsupials, induced a stronger NFκB activation than C. suis and C. trachomatis infectionsin vitro. In particular, NFκB is activated as part of the early inflammatory response and during the penicillin-induced chlamydial stress response (Leonard et al. 2016, 2017). Further pursuit in this area of research will lead to a better understanding of chlamydial pathogenesis and might help resolve questions regarding treatment failure. 

Current research in the Borel group focuses on the potential of co-infection with Neisseria gonorrhoeaeto impact persistent chlamydial infection. In vitroand in vivomouse model studies will be used to determine if N. gonorrhoeaeis capable of alleviating chlamydial persistence, resulting in resumption of infectious EB production. Additionally, we will investigate Chlamydia/ N. gonorrhoeae co-infection in human samples and mouse infection models in order to help clarify the pathogenic interplay between these two important bacteria, and specifically how this impacts the severity, infectious bacterial load and duration of chlamydial infection.


2.         Tetracycline-resistance mechanisms in Chlamydia suis

In its main host, the pig,C. suis is associated with respiratory disease, diarrhea and conjunctivitis though it is primarily known to cause inapparent intestinal infections. Moreover, C. suisis the only obligate intracellular bacterium exhibiting antibiotic resistance, via a tetracycline resistance gene inserted within its chromosome, which is problematic due to the wide-spread use of tetracyclines in the pig industry. In a recent publication, we demonstrated that more than 90% of the Swiss fattening pigs are infected with C. suis (Hoffmann et al. 2015). In a follow-up study, around 150 Chlamydia-positive swab samples were selected for isolation, of which more than 50 were tested regarding their tetracycline susceptibility revealing that there is indication for selective pressure for resistance following tetracycline treatment (Wanninger et al. 2016). Comparative genome analysis of 29 isolates further revealed a high level of diversity that is strongly affected by recombination (Seth-Smith et al. 2017) expanding from a previous study conducted by the group of Deborah Dean (CHORI/UCSF, Oakland, CA, USA). In collaboration with Prof. Deborah Dean, we currently investigate factors that promote or inhibit recombination, as well as tetracycline resistance transfer, in C. suis.


3.         Alternative therapeutic strategies to treat chlamydial infections

The obligate intracellular lifecycle of chlamydiae poses challenges for both diagnosis and treatment. Antimicrobial therapy is the treatment of choice for bacterial infections. Considering the possible side effects of antibiotic therapy and the increasing threat of antibiotic resistance, alternative therapeutic strategies are needed. Water-filtered infrared A irradiation (wIRA) has proven efficacy in acute and chronic wound healing processes in clinical settings. Recent in vitroinvestigations by the Borel group revealed that the exposure of chlamydiae prior to host cell infection, and the exposure of Chlamydia-infected cells to wIRA in combination with visible light (wIRA/VIS) irradiation, reduces both the number of chlamydial inclusions that develop within host cells and the subsequent production of infectious chlamydiae, without negative impact on host cell viability. The efficacy of wIRA/VIS irradiation in reducing infectious EBs was demonstrated in animal-infecting as well as human-infecting chlamydial species (Marti et al. 2014, 2015). 

Further work in our lab demonstrated proof of concept for ocular wIRA treatment in both, an in vitro conjunctival cell culture model and an ex vivo animal model of ocular infection (Rahn et al. 2016). It has been previously demonstrated, that thermal und non-thermal effects are involved in the working mechanism of wIRA/VIS anti-chlamydial activity (Marti et al., 2015) and that similar pro-inflammatory cytokine patterns are released upon irradiation as after chlamydial infection (Marti et al., 2014). Additional results confirm that wIRA/VIS anti-chlamydial affects are not eliminated upon gene silencing or pharmaceutical inhibition of host cell cytokines, which indicates that the working mechanism of wIRA/VIS is not dependent on host cell cytokine secretion and that wIRA/VIS might also be a treatment option for patients with an impaired immune system (Kuratli et al., 2018). To further investigate wIRA/VIS in an in vivo model, we developed a guinea pig conjunctivitis model with female Hartley guinea pigs and Chlamydia caviae. Comparison of gross pathology lesions and chlamydial load in the wIRA/VIS treated and control groups revealed significantly reduced pathology scores and chlamydial loads in wIRA/VIS treated animals (unpublished data). Based on these promising results, future studies will investigate the working mechanism of wIRA/VIS, its effect on chronic chlamydial infections and possible future clinical applications. 


National Collaborations.

Prof. H. Bollwein, Clinic of Reproductive Medicine, Department of Farm Animals, VSF Zurich; Prof. Gilbert Greub, Microbiology Institute, Faculty of Biology and Medicine, University of Lausanne, Lausanne; Prof. M. Hässig, Herd Management, Department of Farm Animals, VSF Zurich; Prof. X. Sidler, Division of Swine Medicine, Department of Farm Animals, VSF Zurich; Prof. em. Joachim Frey, Institute of Veterinary Bacteriology, Vetsuisse-Faculty Berne, Berne


International collaborations.

Prof. Deborah Dean, Center for Immunobiology and Vaccine Development, UCSF Benioff Children's Hospital Oakland Research Institute, CA, USA; Dr. Antonietta di Francesco, DIMES, Unit of Microbiology, Department of Veterinary Medical Sciences, University of Bologna, Italy; Dr. Martina Jelocnik, Faculty of Health, Science, Engineering and Education, University of the Sunshine Coast, Queensland, Australia; Dr. Christiane Schnee, Friedrich-Loeffler-Institute, Federal Research Institute for Animal Health, Institute of Molecular Pathogenesis, Jena, Germany; Prof. Rob Schoborg, Department of Microbiology, James H. Quillen College of Medicine, East Tennessee State University, USA, Jonson City, TN, USA; Dr. Karine Laroucau, Unité Zoonoses Bactériennes,Laboratoire de Santé animaleAgence Nationale de Sécurité Sanitaire de l’alimentation, de l’environnement et du travail (ANSES), Maisons-Alfort Cedex – France ; Dr. Aleksandra Inic-Kanada, Institute of Specific Prophylaxis and Tropical Medicine, Medical University of Vienna, Vienna, Austria; Dr. Christine Unterweger, University Clinic for Swine, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine, Vienna, Austria; Prof. Steve Charette, Département de biochimie, de microbiologie et de bio-informatique, Université Laval, Québec, Canada.


Current funding

Swiss National Science Foundation (SNSF), Federal Food Safety and Veterinary Office (FSVO), Braun Foundation, Swiss Academy of Medical Sciences (SAMW), Stiftung für wissenschaftliche Forschung an der Universität Zürich, Office International des Epizooties (OIE)


Selected Publications

  • Botta et al. 2018. Vet Pathol. 2018 Oct 24:300985818806453. doi: 10.1177/0300985818806453.
  • Borel et al. 2018. Vet Pathol. 2018 55(3):374-390. doi: 10.1177/0300985817751218
  • Borel et al. 2018. Pathog Dis. 2018 Nov 1;76(8). doi: 10.1093/femspd/fty081 
  • Hoffmann et al. 2015. PLoS One 10(11):e0143576. doi: 10.1371/journal.pone.0143576 
  • Kuratli & Borel 2019. Front Microbiol. 2019 May 10;10:1053. doi: 10.3389/fmicb.2019.01053.
  • Kuratli et al. 2018. Front Microbiol. 2018 Nov 15;9:2757. doi: 10.3389/fmicb.2018.02757.
  • Leonard et al. 2015. PLoS One 10(8): e0134943. doi: 10.1371/journal.pone.0134943
  • Leonard et al. 2016. Int J Microbiol 2016:3832917. doi: 10.1155/2016/3832917
  • Leonard et al. 2017. Front Cell Microbiol 7:180. doi: 10.3389/fcimb.2017.00180
  • Marti et al. 2015. J Photochem Photobiol 153: 324-33. doi: 10.1016/j.jphotobiol.2015.10.012
  • Marti et al. 2014. PLoS One 14:9(7):e102239. doi: 10.1371/journal.pone.0102239
  • Marti et al. 2018. Front Microbiol9:1414. doi: 10.3389/fmicb.2018.01414 
  • Onorini et al. 2019. Vet Microbiol. 2019 Jun;233:11-20. doi: 10.1016/j.vetmic.2019.04.012.
  • Rahn et al. 2016. J Photochem Photobiol B 165: 340-350. doi: 10.1016/j.jphotobiol.2016.11.001
  • Seth-Smith et al. 2017. Genome Biol and Evol 9(3): 750-760. doi: 10.1093/gbe/evx043 
  • Staub et al. 2018. Sci Rep. 4;8(1):5660. doi: 10.1038/s41598-018-23897-z
  • Wanninger et al. 2016. PLoS One 28;11(11):e0166917. doi: 10.1371/journal.pone.0166917


For more publications from the Borel group, please explore the Zurich Open Repository Archive (ZORA) for “Borel, N”: