Chlamydia suis, an emerging Chlamydiaceae species in pigs?

Chlamydiaceae are Gram-negative obligate intracellular bacteria that can infect a broad range of animals and humans. Chlamydial infection of livestock, companion animals, and other animals may result in conjunctivitis, enteritis, pneumonia, abortion, rhinitis or arthritis but there is also a high incidence of apparently asymptomatic infections. Pigs can become infected by Chlamydophila pecorum, Chlamydophila abortus, Chlamydophila psittaci and Chlamydia suis (Everett et al., 1999). Chlamydial infections are nearly endemic in the Belgian pig population as 96% of the examined sera reacted positive in a recombinant major outer membrane protein (MOMP) antigen-based ELISA (Vanrompay et al., 2004). The purpose of this study was to examine the current serological status of our pig herd and to identify the chlamydial species involved in infecting Belgian pigs. At present, 193 (97%) of 200 examined farms tested positive for Chlamydiaceae-specific antibodies. We tried to identify the Chlamydiaceae species using a diagnostic platform comprising of culture, a Chlamydiaceae-species specific microarray and a PCR for the detection of the Chlamydia suis tetracyclin resistant gene tet(C). Our results were in accordance with the serological results, as Chlamydiaceae, and especially C. suis was highly prevalent in slaughtered pigs, in pigs ending up in the autopsy room of the Provincial Laboratory for the Prevention of Animals Diseases and in four different farms dealing with reproductive disorders. Furthermore, we could demonstrate C. suis in the eyes, the respiratory, the intestinal and the reproductive tract of sows and in semen samples of boars. We found no other species, with the exception of one Cp. pecorum and one Cp. abortus strain. In the present study, we demonstrated emerging tet(C) positive C. suis strains among Chlamydiaceae infections in pigs. Moreover, C. suis, for which Koch’s postulates have already been fulfilled in the past, are widespread in pigs throughout the world. Research towards the development of preventive measurements like probiotics (Pollmann et al., 2005) or vaccines should be promoted. In the future, the spread of tetracyclin resistant C. suis strains, for instance through international trading of boar sperm, should be carefully monitored as this may present a treat to human health.