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BMC Vet Res. 2017 Dec 1;13(1):370. doi: 10.1186/s12917-017-1295-x.

Asymptomatic infections with highly polymorphic Chlamydia suis are ubiquitous in pigs.

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Yangzhou University College of Veterinary Medicine, Yangzhou, Jiangsu, People's Republic of China.
Centre for Animal Health Innovation, Faculty of Science, Health, Education & Engineering, University of the Sunshine Coast, QLD, Maroochydore, Australia.
Poultry Institute, Chinese Academy of Agricultural Sciences, Yangzhou, Jiangsu, China.
College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA.
Institute of Veterinary Medicine, Jiangsu Academy of Agricultural Sciences; Key Laboratory of Veterinary Biological Engineering and Technology, Ministry of Agriculture, National Center for Engineering Research of Veterinary Bio-Products, Nanjing, China.
Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Institute for Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
Yunnan Agricultural University College of Animal Science & Technology, Kunming, Yunnan, China.
Key Laboratory of Animal Diseases Diagnostic and Immunology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.
Yangzhou University College of Veterinary Medicine, Yangzhou, Jiangsu, People's Republic of China.
College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA.



Chlamydia suis is an important, globally distributed, highly prevalent and diverse obligate intracellular pathogen infecting pigs. To investigate the prevalence and genetic diversity of C. suis in China, 2,137 nasal, conjunctival, and rectal swabs as well as whole blood and lung samples of pigs were collected in 19 regions from ten provinces of China in this study.


We report an overall positivity of 62.4% (1,334/2,137) of C. suis following screening by Chlamydia spp. 23S rRNA-based FRET-PCR and high-resolution melting curve analysis and confirmatory sequencing. For C. suis-positive samples, 33.3 % of whole blood and 62.5% of rectal swabs were found to be positive for the C. suis tetR(C) gene, while 13.3% of whole blood and 87.0% of rectal swabs were positive for the C. suis tet(C) gene. Phylogenetic comparison of partial C. suis ompA gene sequences revealed significant genetic diversity in the C. suis strains. This genetic diversity was confirmed by C. suis-specific multilocus sequence typing (MLST), which identified 26 novel sequence types among 27 examined strains. Tanglegrams based on MLST and ompA sequences provided evidence of C. suis recombination amongst the strains analyzed.


Genetically highly diverse C. suis strains are exceedingly prevalent in pigs. As it stands, the potential pathogenic effect of C. suis on pig health and production of C. suis remains unclear and will be the subject of further investigations. Further study is also required to address the transmission of C. suis between pigs and the risk of 'spill-over' and 'spill-back' of infections to wild animals and humans.


Chlamydia suis; FRET-PCR; MLST; Pig; Tanglegram; ompA

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