Medical helminthology is concerned with the study of parasitic worms. These parasites are responsible for an enormous burden of infection throughout the world. Although some of helminthic infections are life-threatening, their impact on human health is incalculable. Two billion people are infected by soil-transmitted helminths such as Ascaris lumbricoides, hookworms, and Trichuris trichiura. Other helminthic infections include filariases and food-borne trematode and tapeworm infections. All of these infections may cause chronic morbidity and debilitation.
Most helminths have no independent existence outside the host and are therefore truly parasitic. As they rely on the host for sustenance, it is not in their interest to cause the host harm. The pathogenic manifestations of helminthic disease are ordinarily due to physical factors related to the location of the worms, their life cycle, or their size.