TISSUE-RESPONSE OF GOATS TO SINGLE OR REPEATED LOW-LEVEL DOSES AND TOA MASSIVE CHALLENGE DOSE OF SCHISTOSOMA-BOVIS

The inflammatory tissue response to Schistosoma bovis in the small int estine and liver of goats was studied by light microscopy 32 weeks aft er they had been exposed to 10 weekly ('trickle') doses of 200 cercari ae or to a single dose of 400 cercariae, and 32 weeks after the same d osing schedules followed by a challenge exposure to 2000 cercariae in week 16 of the experiment, and 16 weeks after a single exposure to 200 0 cercariae in week 16 (challenge control). The tissue egg counts in t he small intestine were highest in the challenge control group and com parable in the other groups, and corresponded well with the numbers of inflammatory foci per histological section of gut wall. The tissue eg g counts in the liver were also highest in the challenge control group , but diffuse hepatic portal fibrosis was more pronounced in the group s with a primary exposure followed by a challenge. The intestinal path ology was compatible with a smaller component of vigorous and acute in flammatory reactions to the eggs in the older than in the more recent infections. The magnitude and morphological characteristics of the inf lammatory tissue response did not differ markedly between the goats ex posed to the trickle infections and the single doses, and they were no t substantially affected by the challenge infection.