Fig. 4

Tissue stages of Leuocytozoon sp. TUMER01 in histological sections of two Eurasian blackbirds (Turdus merula) detected by CISH (inserts a–d) and identified in HE-stained sections of the bursa of Fabricius (a), heart (b) and kidney (c, d). Megalomeronts observed in the bursa of Fabricius (a) and kidney (c) consisted of densely packed homogenous masses of merozoites (a), surrounded by cells of unclear origin (arrowheads) or featured cytomeres enclosed by a thin wall (c). In the heart (b), a mature meront featuring merozoites and a defined wall was identied (white arrow). In the kidney, numerous merozoites of 1–2 µm (short arrows), barely identifiable in HE-stained sections, were located in the interstitial tissue, resulting in a strong, scattered CISH signal between renal tubules (d). Histopathological changes such as fibrosis (a, white arrowheads) and non-suppurative inflammation (c, d, asterisks) were associated with the parasite stages. Scale-bars: 50 µm