Induction of hepatosplenic disease by single pairs of the Philippine, Formosan, Japanese, and Chinese strains of Schistosoma japonicum.

Abstract

For a comparison of the ability of the four geographically distinct strains of Schistosoma japonicum to produce hepatosplenic disease, Swiss albino female mice were exposed to two or three cercariae each of the Philippine, Formosan, Japanese, or Chinese strains. Approximately 40% of them acquired one pair of worms, and the remainder were used as controls. For each geographic strain, at eight, 10, 12, 20, and 40 weeks after exposure to cercariae, 10 animals with bisexual infections and 10 controls were investigated for enlargement of liver and spleen, portal hypertension, fall in hematocrit, number of schistosome eggs in the liver, and histopathologic changes. The Philippine and Formosan strains were consistently the most virulent, the Japanese strain was intermediate in virulence, and the Chinese strain was least virulent. In spite of the continued accumulation of large numbers of eggs in the livers (reaching a peak of 103,000 in infections with the Formosan strain), hepatosplenic disease remained in a relatively steady state from 10 to 40 weeks or showed some amelioration (Philippine strain) at 40 weeks. This phenomenon appeared to be related to a marked decrease in the host's granulomatous response to the eggs as the infection progressed.