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Morbidity due to helminths in humans is alarming. N.R. Stoll estimated in 1947 that there were 2,200 million helminth infections (distributed very unevenly) among the existing world population of 2,166 million persons--more than one infection per human being! Current estimates suggest that as many as one of every three humans harbors one or more species of parasitic helminths. Helminth infections also stand as an overwhelming obstacle to animal production in many regions of the world. These helminth infections are focused largely in developing countries and, in addition to inflicting immense personal suffering, stand as an important barrier to development in many parts of the world.
The parasitic helminths are a grouping of two very diverse phyla of worms; flatworms, of the phylum Platyhelminthes, and roundworms, of the phylum Nematoda. These two phyla have little in common past a gross worm morphology and the parasitic lifestyle of some members.