Cecal coccidiosis in turkeys: Comparative biology of Eimeria species in the lower intestinal tract of turkeys using genetically typed, single oocyst-derived lines.

Differentiating the Eimeria species causing cecal coccidiosis in turkeys is challenging. To obtain benchmark biological data for Eimeria gallopavonis Hawkins 1952 and Eimeria meleagridis Tyzzer 1929 and to support the stability of the species concept for each, genetically typed, single oocyst-derived lines of E. gallopavonis Weybridge strain and E. meleagridis USAR97-01 were used to redescribe the biological, pathological, and morphological features of these parasites. Oocysts of E. meleagridis and E. gallopavonis overlap in dimensions, but oocysts of the former have a single polar granule compared with multiple in the latter. Mature first-generation meronts of E. gallopavonis were observed histologically as early as 48 h post-inoculation alongside the villi in jejunum (before and after Meckel's diverticulum), ileum, cecal neck and rectum, but not cecal pouches. Three asexual cycles were observed suggesting that early workers apparently overlooked one asexual cycle. Examination of endogenous development of a culture labeled "Eimeria adenoeides Weybridge strain" suggested that this strain (found in a number of publications as a large oocyst strain of "Eimeria adenoeides") matched the species description of E. gallopavonis and so has been renamed herein. Macroscopic lesions induced by E. gallopavonis consisted of caseous material distally from posterior of the yolk stalk through the remaining intestinal tract, excluding the cecal pouches. For E. meleagridis, only the first asexual generation was observed outside of the cecal pouches within the jejunum around the yolk stalk. Second- and 3rd-generation asexual stages developed almost exclusively in the cecal pouches (but not cecal necks). Macroscopic lesions described for E. meleagridis were similar to those of E. adenoeides. Marked corrugation of the cecal serosal surface was observed. Cecal pouches contained creamy colored, caseous material varying from loose material to granular. Distinguishing features of the Eimeria species infecting the lower part of the small intestine are summarized in the present study, and new type specimens were designated for E. gallopavonis and E. meleagridis to provide a stable reference for future work with these parasites.

The complete mitochondrial genome sequence of Eimeria innocua (Eimeriidae, Coccidia, Apicomplexa).

The complete mitochondrial genome of Eimeria innocua KR strain (Eimeriidae, Coccidia, Apicomplexa) was sequenced. This coccidium infects turkeys (Meleagris gallopavo), Bobwhite quails (Colinus virginianus), and Grey partridges (Perdix perdix). Genome organization and gene contents were comparable with other Eimeria spp. infecting galliform birds. The circular-mapping mt genome of E. innocua is 6247 bp in length with three protein-coding genes (cox1, cox3, and cytb), 19 gene fragments encoding large subunit (LSU) rRNA and 14 gene fragments encoding small subunit (SSU) rRNA. Like other Apicomplexa, no tRNA was encoded. The mitochondrial genome of E. innocua confirms its close phylogenetic affinities to Eimeria dispersa.

Sequence-based genotyping clarifies conflicting historical morphometric and biological data for 5 Eimeria species infecting turkeys.

Unlike with Eimeria species infecting chickens, specific identification and nomenclature of Eimeria species infecting turkeys is complicated, and in the absence of molecular data, imprecise. In an attempt to reconcile contradictory data reported on oocyst morphometrics and biological descriptions of various Eimeria species infecting turkey, we established single oocyst derived lines of 5 important Eimeria species infecting turkeys, Eimeria meleagrimitis (USMN08-01 strain), Eimeria adenoeides (Guelph strain), Eimeria gallopavonis (Weybridge strain), Eimeria meleagridis (USAR97-01 strain), and Eimeria dispersa (Briston strain). Short portions (514 bp) of mitochondrial cytochrome c oxidase subunit I gene (mt COI) from each were amplified and sequenced. Comparison of these sequences showed sufficient species-specific sequence variation to recommend these short mt COI sequences as species-specific markers. Uniformity of oocyst features (dimensions and oocyst structure) of each pure line was observed. Additional morphological features of the oocysts of these species are described as useful for the microscopic differentiation of these Eimeria species. Combined molecular and morphometric data on these single species lines compared with the original species descriptions and more recent data have helped to clarify some confusing, and sometimes conflicting, features associated with these Eimeria spp. For example, these new data suggest that the KCH and KR strains of E. adenoeides reported previously represent 2 distinct species, E. adenoeides and E. meleagridis, respectively. Likewise, analysis of the Weybridge strain of E. adenoeides, which has long been used as a reference strain in various studies conducted on the pathogenicity of E. adenoeides, indicates that this coccidium is actually a strain of E. gallopavonis. We highly recommend mt COI sequence-based genotyping be incorporated into all studies using Eimeria spp. of turkeys to confirm species identifications and so that any resulting data can be associated correctly with a single named Eimeria species.