A new species of <italic>Cystoisospora</italic> Frenkel, 1977 (Apicomplexa: Sarcocystidae) from <italic>Oecomys mamorae</italic> Thomas (Rodentia: Cricetidae) in the Brazilian Pantanal.

Despite the great diversity of coccidians, to our knowledge, no coccidian infections have been described in <italic>Oecomys</italic> spp. In this context, we examined <italic>Oecomys mamorae</italic> Thomas (Rodentia: Cricetidae) from the Brazilian Pantanal for infections with enteric coccidia. Nine individuals were sampled, and one was found to be infected. The oöcysts were recovered through centrifugal flotation in sugar solution. Using morphological and morphometric features, we described a new species of <italic>Cystoisospora</italic> Frenkel, 1977. Sporulated oöcysts were ovoidal 20.0-29.1 × 16.4-23.2 (26.7 × 21.2) µm and contained two sporocysts, 12.9-19.1 × 9.4-13.9 (16.4 × 12.4) µm, each with four banana-shaped sporozoites. Polar granule and oöcyst residuum were both absent. We documented the developmental forms in the small intestine and described the histopathological lesions in the enteric tract. Our results indicate that the prevalence of <italic>Cystoisospora mamorae</italic> n. sp. in <italic>O</italic>. <italic>mamorae</italic> is low, and tissue damage in the enteric tract is mild, even in the presence of coccidian developmental stages. [ABSTRACT FROM AUTHOR]