Radiolabeling and autoradiographic tracing of Toxocara canis larvae in male mice.

Artificially hatched infective larvae of Toxocara canis were labeled with 75Se in Medium 199 (Gibco) containing 75Se-methionine. Male CD-1 mice were infected with radiolabeled larvae by intragastric intubation or by intraperitoneal injection. At intervals of 3-56 days mice were killed and the organs prepared for compressed organ autoradiography. Radioactivity of parasitic larvae showed an exponential decrease with time, reflecting catabolism of label with a biological half life of 26 days (effective half life of 21 days) making possible experiments lasting several months. Total body larva counts, estimated by total body autoradiography, displayed an overall downward trend, but the rate of reduction was probably not constant because no significant positive or negative trends were noted from day 14 onward in the numbers of larvae. The carcass accumulated the greatest number of larvae followed by the central nervous system, liver, and lung in that order. When the numbers of larvae were considered in relationship to the mass of tissue, there were 4 groupings: central nervous system, liver, lung, carcass, and kidney, and genito-urinary organ, pelt, and intestine. No significant difference between intragastric and intraperitoneal administration was observed in the larval distribution after the larvae had left the initial site of deposition.