Protozoa of the genus Sarcocystis are obligatory heterogenous parasites with both definitive and intermediate hosts. Opossums (Didelphis aurita) can shed multiple species of Sarcocystis with birds as the intermediate host. The pathologies of Sarcocystis species in birds have not been thoroughly elucidated. Therefore, the aim of the present study to determine the main lesions that can occur in acute and chronic infections in intermediate hosts, when they ingest infective sporocysts that are shed in the opossum’s feces, using budgerigars as a model. To this end, 12 budgerigars, Melopsittacus undulatus, were divided into two groups that received an inoculum with 60 and 120 sporocysts. Birds that died or were euthanized were necropsied, and the lung, tongue, liver, brain, heart, and skeletal striated muscles were collected and fixed in 10% formalin for histopathological analysis. The infectivity varied according to the sample and infective dose. Acute histopathological lesions were characterized by evidence of slightly degenerated hepatocyte cords that permeated the region of the blood vessel and hepatic sinusoids. Pulmonary tissue lesions were also observed in the parabronchial region with the presence of inflammatory infiltrates associated with areas of edema and atelectasis. In chronic infections, few mature cysts were observed in the chest, and many mature cysts in the thigh and tongue muscles. Thus, it was possible to conclude that lesions are highly characteristic in acute infection and, in chronic infections, cysts were present but without major lesions. In this case, the preferred organs of parasitism were the thigh and the tongue.

囊藻属的原生动物是定性和中间寄主的强制性异源寄生虫。负鼠（Didelphis aurita）可以脱落多种以鸟为中间宿主的肉囊藻。鸟类中的肉囊藻种类的病理尚未完全阐明。因此，本研究的目的是使用虎皮鹦鹉作为模型，确定中间宿主在急性和慢性感染中摄入在负鼠粪便中脱落的感染性孢子囊时可能发生的主要病变。为此，12虎皮鹦鹉，Melopsittacus undulatus分为两组，分别接种了60和120个孢子囊。对死亡或安乐死的鸟进行尸检，并收集肺，舌，肝，脑，心脏和骨骼横纹肌，并固定在10％福尔马林中进行组织病理学分析。感染性根据样品和感染剂量而变化。急性组织病理学损伤的特征是肝细胞索轻微变性，并渗入血管和肝窦。在支气管旁区域还观察到肺组织损伤，并伴有与水肿和肺不张区域相关的炎性浸润。在慢性感染中，在胸部很少观察到成熟的囊肿，在大腿和舌头肌肉中观察到许多成熟的囊肿。从而，可以得出结论，病变在急性感染中具有很高的特征，而在慢性感染中，存在囊肿，但没有重大病变。在这种情况下，寄生的首选器官是大腿和舌头。