- The diagnosis of Ascaris lumbricoides infection is primarily made by identifying its characteristic eggs in the stool.
- These eggs have a distinct thick shell with a rough outer layer, which is pathognomonic.
- Motile larvae and cyst forms are not seen in stool, as Ascaris larvae migrate through tissues, and cyst forms do not exist for this nematode.
- While adult worms may be observed if expelled, stool examination for eggs remains the standard diagnostic method.

Thus, the presence of characteristic Ascaris eggs in stool is diagnostic.

Reference: Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 9th Edition, Vol 2, Chapter 311, p. 2954