Autoimmune hemolytic anemia is a condition where the body is destroying its own red blood cells. The red blood cells are coated with an antigen to which the antibodies attach and cause the cells to lyse or die. There can be many causes for the anemia. Some of the more common causes are bacteria (Streptococcus equi, strangles), viruses (equine infectious anemia), parasites (Babesia equi), neoplasia (lymphosarcoma), and drugs (penicillin). In foals, if the foal's blood is not compatible with the dam's, a condition called neonatal isoerythrolysis can develop.