Relationships between circulating leucocytes and Leucocytozoon simondi in mallard, Anas platyrhynchos, ducklings

Leucocytozoon simondi is an apicomplexan blood parasite of waterfowl that frequently causes significant mortality, and thus is expected to provoke a significant immune response in hosts. Using blood smears collected in consecutive weeks from 30 wild-stock mallard, Anas platyrhynchos, ducklings, we tested with repeated measures analyses for associations between leucocyte profiles and L. simondi infection intensities. With each of the five weeks of leucocyte profiles as response variables, we found evidence of fewer circulating heterophils and more circulating lymphocytes in the third week of infection associated with more intense L. simondi infections from the second week, but no significant relationships between leucocytes and the other four weeks of L. simondi infection. With each of the five weeks of L. simondi infection intensities as response variables, we found no associations with leucocyte profiles. Collectively, our results did not reveal tight links between leucocyte profiles and parasitism by L. simondi. Our data suggest that L. simondi was relatively benign to our wild ducks.