However, there can be problems. Hazards associated with leech therapy include infection, excessive blood loss that may require blood transfusion, and allergic reactions. Sometimes the leeches slip off patients and re- attach themselves to other parts of the body that are not in need of treatment. Once they are full, leeches will look for a warm, dark place to digest their meal, and may burrow into wounds or enter the patient's mouth or other orifices. To prevent escapes, nurses must keep careful count of the leeches.