Many kinds of organisms called...
Many kinds of organisms called flukes can infect humans. The pattern of liver fluke infections needs two hosts: a human and a water snail. Humans eat poorly washed herbage upon which are fluke cysts. Within the human, the larvae hatch, mature, and fluke eggs pass in the human feces. The eggs hatch free-swimming larvae, which invade host snails in water and then shed more larvae into water to infest herbage. The cycle is repeated if this herbage is poorly washed and eaten by humans. It's estimated that 40 to 100 million people in the world suffer from liver or lung fluke infections.