Behavior of Parasitic Stages of Helminths in a Thermal Gradient

Parasitic stages of helminths responded positively to a thermal gradient. Movement toward higher temperatures was observed in several nematode, trematode, cestode, and acanthocephalan species. The thermotactic response was faulty in that migration continued into areas of the gradient where thermal damage and death occurred. A free-living oligochaete also migrated in the gradient, but stopped before damage occurred. With Nippostrongylus adults, migration could be reversed by a rapid reversal of the thermal gradient, and worms of a 7-day-old infection migrated more rapidly than those of an 18-day-old infection.