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A new coccidian species parasitizing white-necked thrushes Turdus albicollis Vieillot, 1818 is described from the Parque Nacional do Itatiaia, in Southeastern Brazil. Isospora machadoae sp. nov. has oocysts that are sub-spherical, 22.2 × 21.2 µm, with bilayered wall, ~1.3 μm thick. Outer layer is rough with micropyle and micropyle cap. Oocyst residuum is absent, but one or two polar granules are present. Sporocysts are ellipsoidal, 13.3 × 9.7 µm. The Stieda body is flattened to half-moon-shaped and substieda body rounded. Sporocyst residuum is present, composed of scattered spherules of different sizes. Sporozoites are vermiform with a refractile body and a nucleus. These parasitized thrushes had no apparent clinical signs of coccidiosis or high densities of oocysts in feces. This condition may be associated with a specific low pathogenicity of I. machadoae sp. nov. and/or with the conserved habitat of these birds, which ensures the ecological niches and thus the immunocompetence to wildlife.

The aim of the present study was to report and describe Isospora albicollis Lainson and Shaw, 1989 parasitizing a white-necked thrush Turdus albicollis Vieillot, 1818 and a pale-breasted thrush Turdus leucomelas Vieillot, 1818 in two different localities: the Itatiaia National Park and Cacaria, in southeastern Brazil. The oocysts identified were ovoidal, 24.4 × 19.7 μm, with a smooth, bilayered wall, around 1.4 μm thick. Oocyst residuum was absent, but a micropyle and a polar granule were present. The sporocysts were ellipsoidal, 15.4 × 10.1 μm. The Stieda body was knob-like to rounded and the sub-Stieda body was prominent and wide. Sporocyst residuum was present, usually as a cluster of granules that appear to be membrane-bounded. The sporozoites were vermiform with one posterior refractile body and a centrally located nucleus. Besides recording the new host T. leucomelas, the identification of I. albicollis in the Itatiaia National Park and Cacaria, in southeastern Brazil, provide records of new localities for its parasitism, and reveals the wide distribution and dispersion of this coccidium in Brazil. Resumo O objetivo do presente estudo foi relatar e descrever Isospora albicollis Lainson e Shaw, 1989, parasitando um sabiá-coleira Turdus albicollis Vieillot, 1818 e um sabiá-barranco Turdus leucomelas Vieillot 1818, em duas localidades diferentes: Parque Nacional do Itatiaia e Cacaria, no Sudeste do Brasil. Os oocistos identificados foram ovóides, 24,4 × 19,7 μm, com uma parede lisa e dupla, com cerca de 1,4 μm de espessura. Resíduo do oocisto foi ausente, mas uma micrópila e um grânulo polar foram presentes. Esporocistos elipsoidais, 15,4 × 10,1 μm, corpo de Stieda em forma de botão a arredondado e corpo de sub-Stieda proeminente e largo. Resíduo do esporocisto presente, usualmente como um aglomerado de grânulos que parecem estar envolvidos por uma membrana. Esporozoítos vermiformes com um corpo refráctil posterior e um núcleo centralizado. Além de registrar o novo hospedeiro T. leucomelas, a identificação de I. albicollis no Parque Nacional de Itatiaia e Cacaria, no Sudeste do Brasil, fornece registros de novas localidades para seu parasitismo e revela a ampla distribuição e dispersão desse coccídio no Brasil.