Trichinella spiralis: modifications of the cuticle of the newborn larva during passage through the lung.

A scintigraphic method was developed to study the distribution of radioactivity after iv injection of 131I-labeled Trichinella spiralis newborn larvae into normal rats. It was found that the radioactivity was immediately retained in the lungs and thereafter slowly released, with a mean transit time in excess of 9 hr, as calculated by image analysis. At various times after iv injection of newborn larvae into normal mice, the lungs were removed and parasites were recovered and counted. Fifty to seventy percent of the larvae injected were recovered after 30 sec, between 10 and 30% after 1 min, and less than 4% at 15 min. These results indicate that during the very rapid passage of newborn larvae through the lungs, labeled components of the cuticle are detached and retained. It is suggested that the modifications produced in the cuticle of the newborn larva during its passage through the lung may increase its resistance to the nonspecific defense mechanisms of the host.