Serological and molecular detection and phylogenetic characterization of Taylorella equigenitalis in horses in Iraq

Contagious equine metritis caused by Taylorella equigenitalis is an important venereal disease of equids that can impair reproductive performance and facilitate transmission through clinically inapparent carriers. Information on T. equigenitalis infection in Iraqi horses remains limited. This study aimed to determine the serological and molecular occurrence of T. equigenitalis in horses in Iraq, evaluate associations with clinical and epidemiological factors, and characterize PCR-positive isolates using sequencing and phylogenetic analysis.

A total of 157 adult horses from Baghdad, Babylon, Nineveh, and Wasit provinces were examined from March to September 2025. Clinical information was recorded, and blood and genital swab samples were collected. Serum samples were examined using a qualitative enzyme-linked immunosorbent assay (ELISA), whereas DNA extracted from genital swabs was subjected to conventional polymerase chain reaction (PCR) targeting the 16S rRNA gene. PCR-positive products were sequenced, submitted to GenBank, and analyzed phylogenetically. Associations between infection status and clinical and epidemiological variables were statistically evaluated.

Of the 157 horses, 52 (33.12%) were ELISA-positive and 23 (14.65%) were PCR-positive for T. equigenitalis. Twenty-one (13.38%) horses were positive by both methods, 31 (19.74%) were ELISA-positive/PCR-negative, two (1.27%) were ELISA-negative/PCR-positive, and 103 (65.61%) were negative by both methods. In mares, seropositivity was significantly associated with reproductive disorders, with the highest proportion detected among those with abnormal vaginal discharge (68.42%), whereas PCR positivity was highest among mares with infertility (50%). Seropositivity was higher in horses aged >10 years (62.86%) and females (52.38%), whereas PCR positivity was highest among horses aged >5-6 years (38.1%) and females (25%). Sequencing of 23 PCR-positive isolates generated GenBank accession numbers PZ146151.1-PZ146173.1. The Iraqi isolates showed 97.18%-99.12% sequence identity with an Iranian T. equigenitalis isolate (DQ840456.1).

The findings provide serological and molecular evidence of T. equigenitalis infection among horses in Iraq and demonstrate associations with reproductive and epidemiological characteristics. Combined serological and molecular surveillance, routine screening of breeding horses, and higher-resolution molecular studies are warranted to clarify transmission dynamics and strengthen prevention and control strategies.