Eosinophilic pleural effusion by dirofilariasis

: A 44-year-old man visited our hospital because of right chest pain. Pleural effusion in the right lung was detected on a chest radiograph. A chest CT scan demonstrated no abnormal lesions in either lung field, but passive atelectasis due to the pleural effusion was present. Since many eosinophils were found in the exudative pleural effusion, a parasitic infection was suspected. An enzyme-linked immunosorbent assay test led to a diagnosis of eosinophilic pleural effusion by dirofilariasis. Pleural effusion disappeared spontaneously and the level of anti-Dirofilaria immitis antibody decreased. Continued careful observation is necessary in such cases.