Although most commonly found infecting pigs, Ascaris suum, a large roundworm nematode, can also infect humans. This species has the same lifecycle as Ascaris lumbricoides, and also like its cousin, has eggs that are extremely durable in the environment. Although they were long popular in biology classes as a large, easy-to-dissect representative of Nematoda, because the eggs are so resistant and easily spread, the represent a health risk and their use has largely been discontinued. You can virtually dissect one here.
Here in Montana in the 80's, we had a good number of infections of A. suum in children. A survey revealed that most were associated with pigs on farms or pig manure in home gardens. The worms did not mature so eggs were never found in the feces. They were usually identified when a panic-stricken mother brought in a 6-inch worm her child had passed! Identity of the worms as A. suum was finally confirmed in 1995 by DNA.
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