The present impossibility of eradicating of omnipresent worm.

Helminths are the most prevalent infectious agents of humans. In contrast to all other infectious agents, helminths do not multiply within the definitive human host. A consequence of this biological situation is that most infected individuals have levels of infection below a threshold required for the induction of any overt manifestations of disease. Since transmission of of helminthic infections is so effective, largely because of the enormous reproductive potential, it is exceedingly difficult to control transmission and impossible to eradicate infection with the tools available today. A cost-effective strategy for dealing with helminthic infections, therefore, is to control disease by use of chemotherapy targeted to the small proportion of heavily infected individuals, rather than to attempt to eradicate infection by costly methods, including environmental control. For example, this strategy is employed in effectively combatting hookworm disease and schistosomiasis.