Relapses in ducks chronically infected with Leucocytozoon simondi and Parahaemoproteus nettionis

Six Pekin ducks, experimentally infected with L. simondi the previous summer, were observed from September to May. From March to May, a general increase in gametocytaemia occurred, with the appearance of both round and elongate gametocytes. The course of gametocytaemia was observed during the "relapse season" of 33 wild ducks. Seven were found to be infected with L. simondi, seven with Parahaemoproteus nettionis, and six with both species. One wild duck exhibited numerous young forms of both parasites in the blood. It was killed and the organs were examined. "Relapse schizonts" of L. simondi were fairly numerous in the lungs of the duck and a single schizont was seen in the heart. The morphology was characteristic, particularly the elongate parasites, enclosed in a well-marked capsule or cyst wall.