Contagious equine metritis ( CEM) is a venereal disease that affects horses, donkeys, mules, zebras and other members of the equid family. It doesn’t affect humans. Latest situation On 9 June 2021 a stallion at an equine premises in Devon tested positive for Contagious Equine Metritis ( CEM). Three mares which had close contact with the infected horse at the same premises are currently under investigation. The source of infection is believed to be contact with a stable mate abroad, before arriving in the UK. The last outbreak of How to spot Stallions do not show clinical signs of the disease, but they can carry it.