Contagious equine metritis (CEM) is caused by the gram-negative bacillus Taylorella equigenitalis. Transmission particularly occurs during mating; stallions latently carry the pathogen on the mucous membrane of the penis, especially in the Fossa urethralis and in the smegma of the prepuce. Transmission from infected mares to stallions is also possible. In mares, an infection leads to endometritis/cervicitis with mucopurulent vaginal discharge and to reduced fertility. Stallions show no clinical signs of the disease.
For exports, a bacteriological examination is required; within the EU, however, detection by PCR is now also recognised as a suitable test method. In Germany, there is an obligation to notify the authorities, if Taylorella equigenitalis is detected.