Pendl Lab, Untere Roostmatt 7, 6300, Zug, Switzerland.
Nature Research Centre, Akademijos 2, 08412, Vilnius, Lithuania.
Malar J. 2022 May 15;21(1):148. doi: 10.1186/s12936-022-04166-x.
Species of Plasmodium (Haemosporida, Plasmodiidae) are remarkably diverse haemoparasites. Information on genetic diversity of avian malaria pathogens has been accumulating rapidly, however exo-erythrocytic development of these organisms remains insufficiently addressed. This is unfortunate because, contrary to Plasmodium species parasitizing mammals, the avian malaria parasites undergo several cycles of exo-erythrocytic development, often resulting in damage of various organs. Insufficient knowledge on the exo-erythrocytic development in most described Plasmodium species precludes the understanding of mechanisms of virulence during avian malaria. This study extends information on the exo-erythrocytic development of bird malaria parasites.
A roadkill fieldfare (Turdus pilaris) was sampled in Switzerland and examined using pathologic, cytologic, histologic, molecular and microbiologic methods. Avian malaria was diagnosed, and erythrocytic and exo-erythrocytic stages of the parasite were identified using morphologic characteristics and barcode DNA sequences of the cytochrome b gene. The species-specific characteristics were described, illustrated, and pathologic changes were reported.
An infection with Plasmodium matutinum lineage pLINN1 was detected. Parasitaemia was relatively low (0.3%), with all erythrocytic stages (trophozoites, meronts and gametocytes) present in blood films. Most growing erythrocytic meronts were markedly vacuolated, which is a species-specific feature of this parasite's development. Phanerozoites at different stages of maturation were seen in leukocytes, macrophages, and capillary endothelial cells in most organs examined; they were particularly numerous in the brain. Like the erythrocytic meronts, growing phanerozoites were markedly vacuolated. Conspicuous exo-erythrocytic development and maturation in leucocytes suggests that this fieldfare was not adapted to the infection and the parasite was capable to escape from cellular immunity.
This is the first report of exo-erythrocytic development of the malaria parasite lineage pLINN1 during single infection and the first report of this lineage in the fieldfare. The findings of multiple phanerozoites in brain, skeletal muscle, and eye tissue in combination with signs of vascular blockage and thrombus formation strongly suggest an impaired vision and neuromuscular responsiveness as cause of the unexpected collision with a slowly moving car. Further studies on exo-erythrocytic stages of haemosporidian parasites are pivotal to understand the true level of populational damage of avian malaria in wild birds.
疟原虫（Haemosporida，疟原虫科）是一种非常多样化的血寄生虫。关于禽疟原虫病原体遗传多样性的信息正在迅速积累，然而这些生物体的外红细胞发育仍未得到充分解决。这很不幸，因为与寄生哺乳动物的疟原虫不同，禽疟原虫经历了几个外红细胞发育周期，常常导致各种器官受损。由于对大多数描述的疟原虫物种的外红细胞发育了解不足，因此无法理解禽疟期间的毒力机制。本研究扩展了鸟类疟原虫寄生虫外红细胞发育的信息。
在瑞士采集了一只路边死亡的旅鸫（Turdus pilaris），并使用病理、细胞学、组织学、分子和微生物学方法进行了检查。诊断出禽疟，并使用形态特征和细胞色素 b 基因的条形码 DNA 序列鉴定寄生虫的红细胞内和外红细胞期。描述了种特异性特征，并报告了病理变化。
检测到感染了 Plasmodium matutinum 谱系 pLINN1。寄生虫血症相对较低（0.3%），血液涂片上存在所有红细胞期（滋养体、裂殖体和配子体）。大多数生长中的红细胞裂殖体明显有空泡化，这是该寄生虫发育的一种种特异性特征。在检查的大多数器官中，白细胞、巨噬细胞和毛细血管内皮细胞中可见处于不同成熟阶段的 Phanerozoites；它们在大脑中特别多。与红细胞裂殖体一样，生长中的 Phanerozoites 明显有空泡化。白细胞中明显的外红细胞发育和成熟表明，这只旅鸫没有适应感染，寄生虫能够逃避细胞免疫。
这是首次报道在单次感染期间疟原虫谱系 pLINN1 的外红细胞发育，也是首次在旅鸫中报道该谱系。在脑、骨骼肌和眼组织中发现多个 Phanerozoites，加上血管阻塞和血栓形成的迹象，强烈表明视力受损和神经肌肉反应能力下降是导致旅鸫与缓慢行驶的汽车意外碰撞的原因。进一步研究血孢子虫的外红细胞阶段对于了解野生鸟类中禽疟的真实种群损伤水平至关重要。
