First Report of Haemoproteus (Haemosporida, Haemoproteidae) Megalomeronts in the Brain of an Avian Host, with Description of Megalomerogony of Haemoproteus Pastoris, the Blood Parasite of the Common Starling

SIMPLE SUMMARY: Birds are hosts to diverse blood parasites belonging to many taxonomic groups. Among them, numerous haemosporidian parasites of the genus Haemoproteus are transmitted globally. These pathogens develop in the blood and internal organs of birds. The blood stages (gametocytes) are known for about 150 described species, but the tissues stages or exo-erythrocytic stages (meronts and megalomeronts) are known only fragmentarily for about 10% of the described species. Knowledge on merogony is important in avian medicine for better understanding of pathologies during haemoproteosis. This study reported and characterized the megalomeronts of Haemoproteus pastoris, a parasite of the widespread Common starling (Sturnus vulgaris). Parasites were identified using molecular and microscopy examination tools. Five individual naturally infected birds were sampled, and their organs were examined histologically. Megalomeronts were found in eight different organs. The parasites were described and illustrated. The largest megalomeront, of all observed forms and shapes, reached 800 μm in length. Importantly, Haemoproteus megalomeronts were reported in the brain of avian hosts for the first time, indicating non-described pathology during avian haemoproteosis. This study contributes to a better understanding of the life cycle of avian haemoproteids and opens new perspectives in pathology research during avian haemoproteosis, which is important for birds’ health. ABSTRACT: Species of Haemoproteus (Haemoproteidae, Haemosporida) are common bird pathogens. Recent molecular studies combined with histopathology research have reported development of megalomeronts of these parasites in various organs, sometimes resulting in the death of the avian host. Five Common starlings (Sturnus vulgaris) were found naturally infected with Haemoproteus pastoris lineage hLAMPUR01. The parasite was identified using microscopic examination of blood films and DNA sequences. Infected bird organs were investigated histologically for (i) the presence of exo-erythrocytic stages and (ii) the patterns of development (morphology and localization) in different host individuals. For the first time, megalomeronts of Haemoproteus parasites were seen developing in the brain, while numerous others at different stages of maturation were found in the intestine, pancreas, kidneys, lungs, esophagus, spleen, gizzard, and trachea. Megalomeronts were predominantly roundish or oval, up to 800 μm, they were surrounded by a capsular-like wall and developed asynchronously in the same bird individual. After megalomeront maturation and rupture, a massive infiltration of blood cells occurred, indicating the hemorrhagic processes. Review of available data showed that different Haemoproteus species produce markedly different megalomeronts, morphology of which can probably be predicted using phylogenetic analysis based on partial sequences of cytochrome b gene.