Systemic isosporosis in three species of passerine birds

Systemic isoporosis (atoxoplasmosis) is a disease caused by apicomplexan parasites of the genus Isospora, with systemic distribution due to an extraintestinal part of the cycle. In this report we described the gross and histological lesions of systemic isosporosis in 15 passeriform birds from three different species: Sporophila maximiliani (great-billed seed finch), Serinus canaria (island canary), and Saltator similis (green-winged saltator), all captive birds originating from different properties in Minas Gerais, Brazil. Between 2017 and 2022, 15 passerines were sent to the Veterinary School of the Universidade Federal de Minas Gerais for post mortem examination, as well as fixed tissue samples for histopathological analysis. Histologically, the lamina propria of the small intestine in 13 out of 15 birds showed marked histiocytic and lymphoplasmacytic infiltrates with rare heterophils. Merozoites compatible with Isospora spp. were observed within the cytoplasm of macrophages and extracellularly. Inflamathory infiltrates associated with merozoites were also seen in different organs like liver (9/15), lungs (4/15), heart (3/15), spleen (1/15), and skeletal muscle (1/15). To further characterize the pathogen, DNA was extracted from frozen tissues of one bird (Saltator similis), and 23 S large subunit ribosomal RNA and cytochrome c oxidase subunit 1 (COI) genes were amplified and sequenced. Systemic isosporosis affects various passerine species; however, this is the first report in Sporophila maximiliani. This study enabled the characterization and description of the histological lesions associated with systemic isosporosis in this species.