which nematodes commonly cause gastrointestinal infections in humans
E. vermicularis, commonly referred to as the pinworm or seatworm, is a nematode, or roundworm, with the largest geographic range of any helminth. 1 It is the most prevalent nematode in the United States. Humans are the only known host, and about 209 million persons worldwide are infected.. lamblia. G. lamblia is a pear-shaped, flagellated protozoan (Figure 2) that causes a wide variety of gastrointestinal complaints. Giardia is arguably the most common parasite infection of humans worldwide, and the second most common in the United States after pin-worm.