Unravelling the patterns of exo-erythrocytic development of Haemoproteus parasites (Haemoproteidae, Haemosporida), with first case of abortive tissue stages in a naturally infected bird

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This study aims to understand the exo-erythrocytic development of Haemoproteus parasites in naturally infected Thrush nightingales Luscinia luscinia (Muscicapidae). Thrush nightingale Luscinia luscinia were caught at the Ventė Cape (Ventės ragas Ornithological Station, 55º20′E38.93ʺN, 21º11′34.05ʺE, https://www.vros.lt, Lithuania), in May 2021 and 2023 using mist nets and a large ‘Rybachy’ type funnel trap. From each bird, a blood sample was obtained by puncture of the brachial vein with a sterile needle and collected using a heparinized microcapillary. Infections were confirmed in eight bird individuals by microscopic examination and PCR-based methods. Organs of these birds were examined using histology and chromogenic in situ hybridization, which applied genus-specific and lineage-specific oligonucleotideprobes targeting the 18S ribosomal RNA of the parasites. Exo-erythrocytic meronts of Haemoproteus attenuatus (lineage hROBIN1) were found and described for the first time in six of this avian host. Additionally, numerous megalomeronts attributed to Haemoproteus majoris (lineage hWW2) were observed in the gizzard and the heart of one individual. Two cases of empty capsular-like walls of megalomeronts were seen in the gizzard, indicating that the megalomeronts had already ruptured and degenerated. The extensive microscopic examination did not reveal gametocytes of H. majoris, obviously indicating an abortive development. This study recognised patterns in the exo-erythrocytic development of H. attenuatus, and is also the first documentation of abortive Haemoproteus infection in a naturally infected bird during exo-erythrocytic development. The raw data containing additional detailed information about the samples used; parasite species and lineages identified; organs infected; type, number and measurement of tissue stages seen; as well as the sequence alignments used for phylogenetic analyses are deposited in Mendeley data repository.

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