Case report of Angiostrongylus costaricensis infection confirmed by histopathological examination.

Abdominal angiostrongyliasis (AA) is an emerging infection caused by the nematode Angiostrongylus costaricensis. Human infection occurs through ingestion of food contaminated with infective third-stage larvae (L3). Although endemic in Central and South America, AA remains underdiagnosed and underrecognized in clinical practice. We report the case of a female patient with a history of bariatric surgery, residing in southern Brazil, who presented with right lower quadrant abdominal pain and mild eosinophilia. Initial diagnostic hypotheses included infectious colitis, neoplasia and ischemic processes. Following surgical intervention and histopathological examination, AA was confirmed by identification of the parasite within a mesenteric artery. This case highlights an atypical presentation and definitive diagnosis established by histopathology despite negative polymerase chain reaction (PCR) results. This report underscores the importance of including AA in the differential diagnosis of abdominal conditions particularly in endemic regions. It also emphasizes the need for enhanced specificity of serological and molecular diagnostic methods.