Twenty isolates of Schistosoma mansoni were obtained from patients, all males 13 to 30 years old, autochtonous from the Village of Capitão Andrade, municipality of Itanhomi, state of Minas gerais, where an evolutive study of Manson's schistosomiasis is being performed since 1973. The isolates came from six patients with schistosome-infections (type I0, six with the hepato-instestinal form (type Ii), and eight with the hepaoesplenic form (type III). Each isolate was inoculated in mice divided in three groups of 16, exposed to 25, 50 and 100 cercariae, respectively. Controls were 12 uninfected mice. After 90 days adult worms were recovered from the portal by perfusion, from four mice of each experimental groups. Mice dying at various intervals and half of the rest f mice in each group sacrificed on the 90th and the 180th days were studied according to the following parameters: 1) weight of liver, spleen, lung and instestine; 2) egg count in the small intestine (proximal and medial) and large intestine (distal). The average numbers of worms obtained by perfusion from groups I, II and III were 21.9%, 22% and 17.8% respectively. The average natural mortality rates of mice submitted to infection with 25,50 and 100 cercariae were, respectively, 12.4%, 23.2% and 40.2% for group I,4.7%, 19.5% and 22.2% for group II and 11.4%, 29.5% and 41.6% for group III, being therefore proportional to the inocula. The weight of the organs of the infected animals and the number of S. mansoni eggs was always proportional to the inoculum and the highest number of eggs were found in the median and proximal portion of the intestines in all three groups. The conclusion was the following: there was no correlation between the clinical forms of schistosomiasis and the behaviour of the isolates of S. mansoni in mice, the parasitological alternations being proportional to the inoculum used and the duration of the infection.
schistosomiasis; experimental behaviour; isolates of Schistosoma mansoni; mice; clinical forms