Volume 23, Issue 1
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Eight baboons () were percutaneously exposed at 3-month intervals to small numbers of cercariae until a total of 700 was reached over a 3-year period. Fecal egg excretion in all had passed peak levels and was fairly steady or even depressed by about 40 months after the initial exposure. At this time 5 were challenged with 1,000 cercariae each. The other 3, serving as controls, were killed and their worms were counted. The 5 experimental baboons were killed 175 days after challenge and their worm burdens were determined. Post-challenge fecal egg excretion was not increased over pre-challenge levels. The difference in mean percent recoveries of penetrating cercariae in the two groups (experimental, 28.7%; control, 46.2%) was highly significant (P > 0.99 < 0.999). These data indicate that baboons can acquire immunity to , as reflected in fecal egg excretion and worm burdens. The immunity is partial in that neither are all worms destroyed nor is reproduction terminated in the survivors.


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