Volume 29, Issue 3
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Previous work has shown that cattle can acquire a strong resistance to infection following repeated natural exposure. Partial resistance to a laboratory challenge with has also been demonstrated in calves after immunization with an irradiated schistosomular or cercarial vaccine. The aim of the present study was to see whether this type of vaccine could protect calves under the very different conditions of natural exposure to in the field. Thirty 6- to 9-month-old calves were each immunized with 10,000 irradiated schistosomula by intramuscular injection and 8 weeks later were released into an enzootic area along with 30 unvaccinated animals. The calves were followed up for 10 months, during which period protection was evidenced by a lower mortality rate, a slower rate of acquisition of infection, and lower fecal egg counts in the vaccinated calves. Necropsy of the survivors showed 60–70% reductions in worm and tissue egg counts of the vaccinated calves as compared to those not vaccinated.


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