Host-Parasite Relationships of Fasciola hepatica in the White Mouse. V. Age of Fluke Responsible for the Induction of Acquired Immunity

Abstract

Juvenile Fasciola hepatica 12, 14, 18, 20, and 24 days old were successfully transferred to normal recipient mice. Worms entered the common bile ducts when total worm age was 30 or 32 days. Liver migration time was controlled between 16 to 17 and 3 to 4 days. Flukes 12, 14, 16, 18, 20, and 24 days old were transferred to normal recipients in an attempt to relate the duration of liver migration and fluke age to the stimulation of acquired immunity. When transferred worms had a total age of 40 days immunized mice were given a challenge infection of 2 metacercariae per mouse. At 25 days after challenge these mice were killed and worms were recovered. Immunization with 12-, 14-, 16-, and 18-day-old worms produced a significant reduction in challenge worm burdens when compared to natural immunity controls. Immunization with 20and 24-day-old worms did not stimulate a significant acquired immunity. It is suggested that the duration of liver migration, at least 10 to 11 days, by young worms and not the specific age of the young worm is responsible for the stimulation of acquired immunity. Eightand 16-day-old Fasciola hepatica stimulated acquired immunity in recipient mice as measured by a significant reduction in worm burden following a two-worm challenge infection (Lang and Dronen, 1972). Transferred worms migrated in the liver for 21 to 22 days (8-day-old worms) or 13 to 14 days (16-dayold worms). Following an initial metacercarial infection this strain of F. hepatica did not migrate into the common bile duct until 32 days after infection (Lang, 1972). When total worm age was 32 days, regardless of the age of transfer, worms were located in the common bile ducts. Lang and Dronen (1972) did not determine if worms older than 16 days at transfer would complete development in mice and stimulate acquired immunity. The present study attempts to determine if immature worms older than 16 days can be successfully transferred and, if possible, to determine the maximum worm age for inducing acquired immunity. MATERIALS AND METHODS Mice utilized were an isologous strain used in previous studies with this parasite (Lang and Dronen, 1972). The strain of F. hepatica used in the present study behaves similarly to the one used in previous studies (Lang, 1972). Techniques for infection and necropsy of mice and infection of the snail host (Lymnaea bulimoides Received for publication 20 August 1973. * This work was supported by NSF grant GB31745. Lea) have been described (Lang, 1966, 1967, 1970, 1972). Procedures for the transfer of 16day-old and younger worms have been published (Lang and Dronen, 1972). Young worms, 12, 14, 16, 18, 20, and 24 days old, were transferred aseptically to recipient mice. EXPERIMENTAL PROCEDURES AND RESULTS