Biological characterization and designation of a neotype for Eimeria innocua Moore and Brown 1952: A coccidium (Apicomplexa: Eimeriidae) of turkeys (Meleagris gallopavo Linn.).

Eimeria innocua Moore and Brown 1952 is a mildly pathogenic coccidium described from turkeys. Despite being described over half of a century ago, its endogenous development is currently lacking a detailed description. In this study, the life history of E. innocua was re-examined, including detailed observations on endogenous development. Oocysts measured 21.9 μm $\times$ 19.7 μm (n=140; shape index: 1.1) and sporocysts averaged 13.0 μm $\times$ 7.2 μm (n=75; shape index: 1.8). Experimental infections were used to examine the endogenous development of the parasite every six hr for a period of 120 hours. Samples from the descending and ascending duodenum, upper and mid-jejunum and the jejunum at Meckel's diverticulum were collected for histology; most parasite stages occupied the first four regions. Four generations of merogony were suspected prior to gametogony despite observing only three distinct but similar meront-types. Intracellular sporozoites and stages of the first-generation of merogony sometimes infected CD3⁺ intraepithelial lymphocytes. First-generation meronts contained 16-20 merozoites and were located perinuclear to host enterocytes. The second meront-type was the smallest observed, each possessed 14-16 merozoites and were located apical to enterocyte nuclei. The morphology of third- and fourth-generation meronts (the third meront-type) could not be differentiated unless viewed in a transverse section. It was suspected that third-generation meronts contained 24-30 merozoites and fourth generation meronts possessed 22-24 merozoites. Meront residuum was sometimes observed within meronts of the third-type. Gametogonic stages were first identified at 96 hours post-inoculation (hpi); the first unsporulated oocysts were observed at 108 hpi.