Avian haemosporidians of the genera Plasmodium, Haemoproteus, and Leucocytozoon are common blood parasites in wild birds all over the world. Despite their importance as pathogens potentially compromising host fitness and health, little is known about the exo-erythrocytic development of these parasites, particularly during co-infections which predominate in wildlife. This study aimed to address this issue using Haemoproteus parasites of Fringilla coelebs, a common bird species of the Western Palearctic and host to a variety of haemosporidian parasite lineages. Blood and tissue samples of 20 F. coelebs, positive for haemosporidians by blood film microscopy, were analysed by PCR and sequencing to determine cytochrome b lineages of the parasites. Tissue sections were examined for exo-erythrocytic stages by histology and in situ hybridization applying genus-, species-, and lineage-specific probes which target the 18S rRNA of the parasites. In addition, laser microdissection of tissue stages was performed to identify parasite lineages. Combined molecular results of PCR, laser microdissection, and in situ hybridization showed a high rate of co-infections, with Haemoproteus lineages dominating. Exo-erythrocytic meronts of five Haemoproteus spp. were described for the first known time, including Haemoproteus magnus hCCF6, Haemoproteus fringillae hCCF3, Haemoproteus majoris hCCF5, Haemoproteus sp. hROFI1, and Haemoproteus sp. hCCF2. Merogonic stages were observed in the vascular system, presenting a formerly unknown mode of exo-erythrocytic development in Haemoproteus parasites. Meronts and megalomeronts of these species were distinct regarding their morphology and organ distribution, indicating species-specific patterns of merogony and different host tissue tropism. New pathological aspects of haemoproteosis were reported. Furthermore, phylogenetic analysis of Haemoproteus spp. with regard to their exo-erythrocytic stages points towards separation of non-megalomeront-forming species from megalomeront-forming species, calling for further studies on exo-erythrocytic development of haemosporidian parasites to explore the phylogenetic character of this trait.

疟原虫属、血变形菌属和白细胞虫属的鸟类血孢子虫是世界各地野生鸟类中常见的血液寄生虫。尽管它们作为可能损害宿主健康和健康的病原体很重要，但人们对这些寄生虫的红细胞外发育知之甚少，特别是在野生动物中占主导地位的混合感染期间。本研究旨在利用燕雀属的Haemoproteus寄生虫来解决这个问题，燕鸥是古北界西部的常见鸟类，是多种血孢子虫寄生虫谱系的宿主。通过 PCR 和测序分析了 20 份天花线虫的血液和组织样本，通过血涂片显微镜检查，血孢子虫呈阳性，以确定寄生虫的细胞色素 b 谱系。使用针对寄生虫 18S rRNA 的属、种和谱系特异性探针，通过组织学和原位杂交检查组织切片的外红细胞阶段。此外，还对组织阶段进行激光显微切割，以鉴定寄生虫谱系。 PCR、激光显微切割和原位杂交的综合分子结果显示，共感染率很高，其中以嗜血变形杆菌谱系为主。五个Haemoproteus spp 的红细胞外叶突。首次被描述，包括Haemoproteus magnus hCCF6 、Haemoproteus fringillae hCCF3、 Haemoproteus Majoris hCCF5、 Haemoproteus sp。 hROFI1 和Haemoproteus sp。 hCCF2。 在血管系统中观察到了早熟阶段，呈现出以前未知的血变形杆菌寄生虫的红细胞外发育模式。这些物种的分体和巨分体在形态和器官分布方面是不同的，表明分体的物种特异性模式和不同的宿主组织向性。报道了血液蛋白沉积症的新病理学方面。此外， Haemoproteus spp 的系统发育分析。关于其外红细胞阶段，指出将非巨粒体形成物种与巨粒体形成物种分开，呼吁进一步研究血孢子虫寄生虫的红细胞外发育，以探索该性状的系统发育特征。