Multiple choice Which is the largest and the most common parasitic worm in humans? Entamoeba histolytica Ascaris lumbricoides Plasmodium Giardia lamblia Amoeba Reveal answer Fill a bubble to check yourself B Correct answer Explanation Ascaris lumbricoides is the largest nematode (roundworm) parasitising the human intestine. Ascariasis is a disease of humans caused by the parasitic roundworm Ascaris lumbricoides.