Which stage of Giardia is oval with four nuclei and median bodies?

• A. Trophozoite
• B. Cyst
• C. Oocyst
• D. Egg

Answer: (B)

The cyst stage is the oval, environmentally resistant form that Giardia forms for transmission. Mature cysts characteristically contain four nuclei and median bodies, which are distinctive features seen in this stage. This four-nucleus arrangement is a hallmark of the cyst form and explains why it’s the form excreted in feces and capable of initiating infection when ingested. Inside the host, these cysts excyst to release the trophozoites, which are actively motile and typically pear-shaped with two nuclei and multiple flagella. Trophozoites are not environmentally resilient and are the intestinal, disease-causing form. Oocysts and eggs belong to other parasites and do not describe Giardia cysts.