Coccidiosis in Guinea pigs (Cavia porcellus) has been frequently associated with the presence ofEimeria caviae; however, this coccidium has never been characterized in detail. This study aimed to present the phenotypic and genotypic characterization of E. caviae from guinea pigs reared under rustic breeding conditions in Brazil. Eimeria caviae oocysts are polymorphic, being sub-spherical, ovoidal or ellipsoidal, 20.9 × 17.7 µm, with a smooth or slightly rough and bi-layered wall, ~ 1.0 µm. Micropyle and oocyst residuum are absent, but one polar granule is present. Sporocysts are ellipsoidal, 10.8 × 6.4 µm. Stieda and parastieda bodies are present, sporocyst residuum is present and sporozoites posses a refractile body and a nucleus. Linear regressions and histograms were performed and confirmed the polymorphism of the oocysts. The internal transcribed spacer 1 of the ribosomal RNA gene (ITS-1 rRNA) of the isolates was sequenced and showed no significant similarity to the orthologous region of other Eimeria species.
