
Echinococcosis is a zoonosis caused by the larval stage of cestodes of the genus Echinococcus. The tiny worm lives in the intestines of dogs, their ova pass on to sheep, through feco-oral route, and the larvae come to rest in sheep organs, develop into metacestodes (cysts loaded with protoscoleces). When these organs loaded with protoscoleces are ingested by dogs, the life-cycle is completed and repeats. Humans are accidental intermediate hosts. The most commonly involved organs are liver (75%), lung (15.4%) and spleen (5.1%). The cyst grows slowly and may take 5-20 years to grow into a size to cause symptoms. In 90% of cases Echinococcus granulosus involves a single organ and of these 70% have a single cyst. Usually splenic echinococcal infection is the result of spontaneous rupture and spread of cysts from the liver. Rarely the larvae bypass the liver and lung and reach other organs like the spleen. Spontaneous or traumatic rupture of a hydatid cyst may cause life threatening systemic anaphylaxis and is the main cause of morbidity and mortality in this zoonotic disease. This is a report of primary Echinococcal infection of the spleen, causing massive splenic enlargement without involvement of any other organ. The patient was treated by splenectomy ensuring no spillage of cyst contents despite its about to rupture status. The case report and discussion outline the management protocol for isolated echinococcosis of the spleen.