Phocanema decipiens: Intestinal penetration in the laboratory rat

Larval Phocanema decipiens from cod muscles were fed singly or repeatedly to Sprague-Dawley rats and the condition of the rats was monitored. Rats given two larvae each week for 10 weeks were considered to be sensitized. “Sensitized” and “naive” rats were each exposed to larvae during laparotomy and the tissue pathology was examined from 5 hr to 14 days after penetration—no differences were found. This is evidence against the “two-hit hypothesis” of pathology resulting largely from prior sensitization of the host. The lesion was also comparable to that made in the intestine with a sterile pin. Tissue changes showed acute inflammation followed by monocyte infiltration and then fibrocytes and granulation tissue finally left a fibrotic scar. Penetration of larvae through exposed intestinal loops of anesthetized and laparotomized rats was described using a closed-circuit TV system. These records are related to potentiometric recordings of isolated larvae in which a mean mechanical force of 1 g was typical with a maximum of 3.5 g generated by the integrated movement of the whole body. A force of 10 to 12 g/mm² was needed to penetrate the mucosa, muscularis, and serosa. The movements of the host's intestine and the rhythmic probing of the larvae clearly facilitate penetration. The data are used to support the hypothesis that mechanical factors of the larval force and the strength of the intestine dominate the pathological potential of P. decipiens. It is concluded that P. decipiens presents a very small pathological potential to the intact human gastrointestinal tract.