Disseminated echinococcosis with discordant serology: a rare case of molecularly confirmed Echinococcus granulosus sensu stricto G1 in Poland.

Echinococcosis is a parasitic zoonosis caused primarily by Echinococcus granulosus (cystic echinococcosis, CE) and Echinococcus multilocularis (alveolar echinococcosis, AE). While CE typically manifests with well-formed unilocular cysts, AE presents as an infiltrative, tumour-like process. Mixed or atypical presentations pose diagnostic and therapeutic challenges. We describe a 24-year-old man from Morocco residing in Poland, who presented with progressive abdominal distension, pain, and subacute gastrointestinal obstruction. CT and ultrasound revealed multiple large, septated cysts involving the liver, spleen, peritoneum, and right lung. Serological findings were inconsistent across timepoints, alternating between positivity for E. granulosus and E. multilocularis. No molecular confirmation was available at the time of clinical decision-making. Albendazole therapy led to partial regression of intra-abdominal lesions but not pulmonary ones. Radiological findings were compatible with WHO CE2/CE3b stages, yet extensive dissemination and serological fluctuation suggested AE or a mixed pattern. A retrospective research-based molecular analysis later confirmed E. granulosus sensu stricto (G1 genotype), supporting a CE diagnosis. This case emphasizes the diagnostic uncertainty in disseminated echinococcosis with serological discordance and highlights the value of comprehensive diagnostic strategies, especially in-migrant populations from endemic areas and highlights the importance of emerging molecular diagnostics.