Fig. 1.

Leucocytozoon spp. blood stages (gametocytes) in histological sections of accipitriform birds (a–f Accipiter nisus, g–l Circus aeruginosus, m–r Buteo buteo). Blood stages were labelled by the L. toddi-specific probe during CISH (a, b, d, e, g, h, j, k, m–r) and identified in HE-stained sections (c, f, i, l). a–f Blood stages detected in capillaries and vessels in the heart (a–c), kidneys (d) and lungs (e, f) of an Accipiter nisus infected with L. aff. toddi lMILANS04. Note the presence of larger, elongate signals (a, d, arrowheads) besides numerous smaller roundish signals in the heart (a, b) and kidney (d). In the lung, the shape of the signals appeared wormlike (e). In HE-stained sections, elongate gametocytes were identified (c, f, black arrows), sometimes with a cap-like host cell nucleus visible (c, white arrowhead). g–l Blood stages detected in the heart (g–i) and lung (j–l) of a Circus aeruginosus infected with L. aff. toddi lCIAE03. Also in this individual, elongate (g, arrowheads) or wormlike (j, k) signals were observed alongside smaller roundish signals (g, h). In HE-stained sections, gametocytes were identified in fusiform host cells in heart vessels (i, black arrow) and in the lung (l, black arrow). Infected host cells showed an almond-shaped or cap-like nucleus (i, l, white arrowheads). m–n Blood stages detected in a Buteo buteo infected with L. aff. toddi lBUTBUT07. Blood stages detected in the heart were roundish to oval (m), while blood stages in the lung appeared wormlike (n). o Roundish blood stages detected in the heart of a Buteo buteo infected with L. aff. toddi lBUTBUT08. p Numerous oval to elongate blood stages detected in lung capillaries of a Buteo buteo infected with L. buteonis lBUBT2. q–r Blood stages detected in the heart of a Buteo buteo co-infected with L. buteonis lBUBT2 and L. aff. toddi lBUTBUT03. Blood stage signals were roundish and small or appeared large and elongate (arrowheads). Scale bars = 50 µm; insert scale bars = 20 µm