Parasite migration and host reaction in mice exposed to irradiated cercariae of Schistosoma mansoni

Exposure to gamma radiation interferred with the ability of schistosomes to reach maturity in mice. Since the death and disintegration of schistosomula stimulated a considerable degree of inflammation, different dosage levels provided contrasting pathological situations. At 50,000 roentgens equivalent physical (rep) cercarial dermatitis with ulceration and marked vasculitis was the main pathological feature; at 5000 rep numerous granulomatous foci were seen in the lung; and at 2500 rep foci of liver cell necrosis and liver granulomata occurred. Irradiation at 2500 rep appeared to be the best dose since the less heavy concentration of parasites in a single organ produced the least amount of objectionable pathological changes. The host tissue reactions to attenuated cercariae were strikingly similar to those observed following a primary exposure of an abnormal host to nonattenuated cercariae and those observed in the susceptible host which had become resistant to a secondary infection following a primary exposure to schistosome cercariae.