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Institut für Veterinärpathologie

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.) abortus is 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 World Organisation for Animal Health, WOAH, the former 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 ChlamHealth group.

The Chlamydia research team (Borel group)

Group leader

Nicole Borel, DiplECVP, 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 World Organisation for Animal Health, WOAH, the former Office International des Epizooties, OIE. In the past, Prof. Borel fulfilled research assignments in the USA (University of Louisville, KY, supported by the Swiss National Science Foundation), Germany, Ukraine, Turkey and Namibia. Since April 2020, Nicole Borel is an associate professor at the Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich.

Senior researcher

Hanna Marti,,, 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 Chlamydia research by acquiring her doctoral title ( 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). From 2016 - 2020, Hanna was enrolled in the MD-PhD program at the Life Science Zurich Graduate School and the Microbiology and Immunology (MIM) program of the University of Zurich. Her PhD project concerned the transmission mechanism of tetracycline resistance among Chlamydia suis. Since 2020, Hanna is a postdoctoral fellow in the team, primarily investigating horizontal gene transfer events in Chlamydia, using Chlamydia suis as a model.

Enrique Rayo, PhD., completed his BA in Biology at the Autonomous University of Madrid in 2015, received a MSc in Biological Anthropology at the University of Barcelona in 2016, and finished his doctoral title (Dr.phil.nat.) in Evolutionary Biology at the Institute of Evolutionary Medicine, University of Zürich in 2021. After acting as a scientific and technical assistant for the Eidgenössische Technische Hochschule (ETH) Zürich and the University of Zürich, he joined Prof. Borel’s group in Nov 2022 as a Postdoctoral researcher to study the effects of sexually transmitted infections (STIs) - such as Chlamydia trachomatis and Neisseria gonorrhoeae, on commensal bacterial communities.

Former Postdoctoral fellow. 

Cory Ann Leonard, PhD (Biomedical Science, Microbiology)

Helen Aumayer, PhD (Biomedical Science, Microbiology)

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, 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

Samuel Löhrer, Fabian Hagenbuch, Efe Altuntas and Magda de Arriba Sánchez de la Campa joined the ChlamHealth group in 2022/2023.

Former graduate students (2013 – 2022)

Julia Bünter, Karolin Hoffmann, Carolin Rahn, Sabrina Wanninger, Eveline Staub, Carolina Botta, Janine Fritschi, Lea Rohner, Nina Ostfeld, Silvia Ciuria, Michelle Bressan, Jasmin Kuratli, Delia Onorini.

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, Samuel Löhrer, Fabian Hagenbuch, Germaine Nüesch.

Our research

Currently, our research strategy has three main focuses:

  1. Co-infection models for Chlamydia
  2. Tetracycline-resistance mechanisms in Chlamydia suis

1.         Co-infection models for Chlamydia

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 vitro and in vivo in a murine persistence model. Current research in the Borel group focuses on the potential of co-infection with Neisseria gonorrhoeae to impact latent and persistent chlamydial infection. In vitro and in vivo mouse model studies are used to determine if N. gonorrhoeae is capable of alleviating chlamydial persistence, resulting in resumption of infectious EB production. Furthermore, Chlamydia/N. gonorrhoeae co-infection is investigated in human samples 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. suis is 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). We currently investigate factors that promote or inhibit recombination, as well as tetracycline resistance transfer, in C. suis, explore potential uptake mechanisms of chlamydial and non-chlamydial DNA into C. suis and investigate the distribution of C. suis in the environment.

Additional research projects focus on:

  • Alternative therapeutic strategies to treat fungal skin infections (Collaboration project with the group of Prof. LeibundGut-Landmann)
  • Viability and infectivity of Chlamydia abortus under various environmental conditions
  • Epidemiology of Chlamydia pecorum in Swiss cattle

National Collaborations

Prof. Salomé LeibundGut-Landmann, Section of Immunology, Vetsuisse Faculty and Institute of Experimental Immunology, VSF Zürich; Prof.Michael Hässig, Herd Management, Department of Farm Animals, VSF Zurich; Prof. Anton Fürst, Equine Department, VSF Zurich; Dr. Michael Biggel, Institute for Food Safety and Hygiene, VSF Zurich; Dr. Claudia Dumrese, Flow Cytometry Facility, University of Zurich; Dr. Urs Ziegler, Center for Microscopy and Image Analysis, University of Zurich; Dr. Benjamin Hampel, Checkpoint Clinic Zürich; Prof. Nicola Low, Institute of Social and Preventive Medicine, University of Bern; Dr. Frank Imkamp, Institute of Medical Microbiology, University of Zurich; Dr. Sarah Albini, National Reference Centre for Poultry and Rabbit Diseases, Institute for Food Safety and Hygiene, VSF Zürich.

International collaborations

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 animale Agence 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; Prof. Jan Rupp, Universität Lübeck, Lübeck, Germany; Dr. Kensuke Shima, Universität Lübeck, Lübeck, Germany.

Current funding

Swiss National Science Foundation (SNSF), Federal Food Safety and Veterinary Office (FSVO), Braun Foundation, World Organisation for Animal Health, WOAH (the former Office International des Epizooties, OIE), Sefunda AG, Bundesamt für Gesundheit (BAG.




Weiterführende Informationen

Contact Chlamydia research team