Blood parasites of the genus Haemoproteus (Haemosporida, Haemoproteidae) are cosmopolitan and prevalent in birds. Numerous species and lineages of these pathogens have been identified. Some of the infections are lethal in avian hosts mainly due to damage of organs by tissue stages, which remain insufficiently investigated. Several closely related lineages of Haemoproteus majoris, a common parasite of passeriform birds, have been identified. One recent study described megalomeronts of unique morphology in the lineages hPHYBOR04 and hPARUS1 of H. majoris and suggested that the similar tissues stages might also be features in other phylogenetically closely related lineages of the same parasite species. This study aimed to test if (i) megalomeronts are present during the development of the lineage hPHSIB1 of H. majoris and if (ii) they are similar to the other investigated lineages of this species in regard of their morphology and location in organs. One adult wood warbler Phylloscopus sibilatrix, an Afrotropical migrant, naturally infected with H. majoris lineage hPHSIB1 was wild-caught after seasonal spring migration and screened using microscopic examination of blood films and histological sections of organs as well as using PCR-based testing. Bayesian phylogenetic analysis placed the lineages hPHSIB1, hPHYBOR04 and hPARUS1 in one, well-supported clade. Parasitaemia was high (6.5%) in the examined wood warbler, numerous megalomeronts were found in kidneys, and a few in the intestine. Megalomeronts of the lineage hPHSIB1 were morphologically hardly distinguishable from those of lineages hPHYBOR04 and hPARUS1; only negligible differences in the maturation stage of the cytomeres were seen. The kidneys were the main location site of the megalomeronts in all three lineages of this parasite species. This study shows that closely related lineages of H. majoris produce megalomeronts of similar morphology and predominant location in kidneys, while the normal function of this organ may be affected by the presence of numerous large megalomeronts. Megalomeronts of different avian Haemoproteus species are markedly variable in morphology and location, but phylogenetically closely related lineages possess cryptic megalomeronts. This finding suggests that phylogenies based on partial cytb gene could provide information for prediction of patterns of exo-erythrocytic development of closely related Haemoproteus parasites and are worthy of attention in planning haemosporidian parasite tissue stage research.

血变形杆菌属（Haemosporida，Haemoproteidae）的血液寄生虫是世界性的，在鸟类中普遍存在。已经确定了这些病原体的许多种和谱系。一些感染在禽类宿主中是致死性的，主要是由于组织阶段对器官的损害，对此尚缺乏充分的研究。已鉴定出大变形血球（Passeriform鸟类的常见寄生虫）的几个密切相关的血统。一项最近的研究描述了大果螺旋体hPHYBOR04和hPARUS1谱系中独特形态的黑素单体并建议相似的组织阶段也可能是同一寄生虫物种的其他系统发育密切相关的谱系中的特征。这项研究的目的是测试（i）大果螺旋体hPHSIB1谱系发育过程中是否存在黑素粒，以及（ii）就其形态和在器官中的位置而言，是否与该物种的其他谱系相似。一名成年的木莺Phylloscopus sibilatrix，一名非裔移民，自然感染了马氏杆菌。春季春季迁徙后，hPHSIB1系被野生捕获，并通过显微镜检查血膜和器官的组织学切片以及基于PCR的检测进行了筛选。贝叶斯系统发生分析将谱系hPHSIB1，hPHYBOR04和hPARUS1放在一个支撑良好的进化枝中。在被检查的木莺中，寄生虫血症很高（6.5％），在肾脏中发现了大量的黑黄素，在肠道中发现了一些。hPHSIB1谱系的巨噬细胞在形态上与hPHYBOR04和hPARUS1谱系几乎没有区别。仅观察到在细胞色素成熟阶段的差异可忽略不计。在该寄生虫物种的所有三个谱系中，肾脏是黑龙的主要定位点。这项研究表明，H。majoris密切相关的血统在肾脏中会产生具有相似形态和主要位置的黑甲龙，而大量大型黑甲龙的存在可能会影响该器官的正常功能。不同禽类变形杆菌的巨角类在形态和位置上都有明显的差异，但在系统发育上密切相关的谱系具有隐性半角龙。这一发现表明，基于部分cytb基因的系统发育可以为预测紧密相关的变形血红球菌寄生虫的外红细胞发育模式提供信息，并在计划血吸虫性寄生虫组织阶段研究中值得关注。