Involvement of multiple Chlamydia suis genotypes in porcine conjunctivitis

Chlamydia suis has been detected in numerous disease conditions of pigs, particularly in eye infections. This study examined recurring conjunctivitis cases in five commercial pig farms in Japan. 40.5% of the cases were identified as Chlamydia positive using impression cytology of ocular smears and a genus-specific direct fluorescent antibody. C. suis was detected in 59.5% of the samples using PCR tests targeting 16S-23S rRNA intergenic spacer region (ISR) and ompA gene. Genetic analysis of PCR amplicons revealed nine sequence variants of 16S-23S rRNA ISR and 20 sequence variants within ompA gene. Among C. suis-positive conjunctivitis cases, 36.4% showed concurrent infection with 2-4 varied ompA sequence types and 9.1% showed multiple 16S-23S rRNA ISR sequence types of C. suis. Multiple genotypes were found circulating in four of five farms. All 20 detected strains and 25 previously reported C. suis strains were grouped into four clusters. Japanese C. suis strains were closely related to American and European strains indicating wide distribution of these genetically variant strains. This study is the first to show multiple and genetically diverse C. suis strain associations in pig conjunctivitis.