Development of a Chlamydia suis-specific antibody enzyme-linked immunosorbent assay based on the use of a B-cell epitope of the polymorphic membrane protein C

Characteristics of Chlamydia suis Ocular Infection in Pigs

Chlamydia (C.) suis can often be isolated from conjunctival swab specimens from pigs with conjunctivitis or keratoconjunctivitis. In the field, it is assumed to be a multifactorial disease triggered by immunosuppressing factors. This is the first experimental study to provoke clinical signs of conjunctivitis in pigs after C. suis primary mono-infection. Five six-week-old male piglets, free of ocular chlamydia shedding and seronegative for Chlamydia, were conjunctivally infected with the C. suis-type strain S45 (1 × 10⁹ inclusion forming units), while four piglets served as negative controls. The infection group developed clinical signs of conjunctivitis with a peak in the first week post-infection. Immunohistochemical evaluation revealed the presence of Chlamydia not only in the conjunctival epithelium, but also in the enlarged lacrimal glands, lungs, and intestine. No circulating antibodies could be detected during the whole study period of three weeks, although three different test systems were applied as follows: the complement fixation test, MOMP-based Chlamydiaceae ELISA, and PmpC-based C. suis ELISA. Meanwhile, high numbers of IFN-γ-producing lymphocytes within PBMC were seen after C. suis re-stimulation 14 days post-infection. Hence, these data suggest that entry via the eye may not elicit immunological responses comparable to other routes of chlamydial infections.

Co-Occurrence of Chlamydia suis DNA and Chlamydia suis-Specific Antibodies in the Human Eye

Chlamydia suis is a swine pathogen that causes economic losses due to reproductive failure. Recently, C. suis has been detected in human eyes. However, knowledge of the zoonotic potential is still limited. C. suis infections in swine could present a risk for public health because (1) tetracycline-resistant C. suis strains are emerging in the pork industry, (2) tetracycline resistance gene transfers in vitro from C. suis to the human pathogen Chlamydia trachomatis and as previously demonstrated, (3) C. suis and C. trachomatis can be both present in the human eye. Pig farmers were sampled during a seminar in West-Flanders. Conjunctival swabs for detection of C. suis and C. trachomatis and for the detection of mucosal antibodies against C. suis and C. trachomatis were collected. The farmers completed a questionnaire designed to assess information on the following: (1) the health status of their pigs, (2) administration of veterinary drugs, (3) their professional and nonprofessional activities, (4) general health status, (5) smoking habits, (6) use of medication, (7) allergies, and (8) clinical signs/history. Thirty-three on 40 (82.5%) farmers participated. None of the conjunctival swabs contained C. trachomatis DNA and mucosal antibodies against C. trachomatis were not detected. Six of 33 (18.2%) farmers had C. suis DNA in their eyes and 22 of 33 (67%) swabs contained C. suis-specific mucosal antibodies. The older the farmer, higher the chance of finding C. suis antibodies in the eye. There was a significant correlation between the presence of conjunctivitis in the pigs and the occurrence of C. suis DNA in the eye of their owner. This study shows that C. suis may transfer from pigs to the human eye as specific mucosal antibodies were detected in conjunctivae of pig farmers. Veterinarians, general practitioners, and occupational physicians should be aware of the zoonotic potential of C. suis.