Exo‐Erythrocytic Development of <i>Haemoproteus belopolskyi</i> (Haemosporida, Haemoproteidae) in the Type‐Vertebrate Host <i>Hippolais icterina</i> , With Remarks on Phenotypic Variation in Avian Haemoproteids

The patterns of exo-erythrocytic development remain poorly understood for most described Haemoproteus parasites. Three modes of exo-erythrocytic development have been recognized so far: Haemoproteus species that develop only meronts, only megalomeronts, and both morphotypes. The factors underlying the occurrence of these different tissue stages in certain Haemoproteus lineages remain unclear, emphasizing the need for further research on these parasites, which can cause severe disease in non-adapted avian hosts. We investigated, for the first time, the tissue merogony of Haemoproteus belopolskyi in the type-vertebrate host, the Icterine Warbler, Hippolais icterina (Acrocephalidae). Twenty-two naturally infected birds were examined using an integrative approach that included microscopy, nested PCR, traditional histology, chromogenic in situ hybridization, and laser capture microdissection. Phylogenetic analysis of the parasite's partial cytochrome b gene showed a close relationship among the detected Haemoproteus lineages. Megalomeronts of H. belopolskyi were found in the kidneys and heart of eight individuals. In addition to big megalomeronts, small immature meront-like structures were seen in the renal tubules. Molecular analyses and systematic comparison of these structures showed that they represent young (initial) stages of megalomeront development. Laser capture microdissection demonstrated that both the immature and advanced megalomeronts belonged to the H. belopolskyi lineage hHIICT1, indicating that H. belopolskyi produces only megalomeronts and highlighting the importance of integrative analyses to identify tissue stages of different sizes and morphologies.