It is a highly regulated disease on the state, federal, and international levels. No one knows at this point.
Research is absolutely necessary to find out the answers.
Care must be taken when introducing new animals onto any farm, especially if the new animals are from a farm that has donkeys or mules in residence or the new animals are mares which have been bred to jacks. Nurse mares should be tested, especially if they have been bred to a jack. If blood is sampled to test for evidence of recent exposure to the CEM organism, this should be done between 20 and 30 days after breeding to allow adequate time for development of serum antibodies. Another question posed with CEM is whether our testing protocols are stringent enough to protect our horses. There have been three occasions in recent months when a stallion has been brought into the United States and has been found positive for the CEM organism.