Developmental biology and migration of Strongyloides ratti in the rat.

Most recent authors suggest that larvae of the threadworm, Strongyloides ratti, migrate from a cutaneous infection site to the small intestine via the naso-frontal region of the head. However, the proportion of larvae that successfully reach the intestine having followed this pathway had not been determined. Using compartmental analysis we have obtained a comprehensive quantitative description of larval migration during a primary infection of rats with S. ratti. Mean residence times in organs through which larvae migrate were calculated and the proportion of the larvae arriving in the small intestine via the head was estimated as 0.5-0.86, depending on the mathematical model used to generate the estimate. With 50% or more of successful larvae using this pathway it is now reasonable to recognize the "head route" as an important migratory pathway for larvae traveling to their intestinal predilection site. During the first 12 hr in the host, larvae were difficult to recover from the skin and subjacent muscles of the infection site. Apparently, upon invading a host, many larvae enter a quiescent phase during which Baermannization, an active recovery technique, fails to recover them. Infections were short-lived, with the daily finite mortality rate for adult worms attaining 50-80% on day 16 of infection.