Evaluation of vaccination with Neospora caninum protein for prevention of fetal loss associated with experimentally induced neosporosis in sheep.

OBJECTIVE To evaluate the immunologic response of a killed tachyzoite vaccine against Neospora caninum and its effectiveness in preventing fetal loss associated with experimentally induced neosporosis in sheep. ANIMALS 30 Dorset ewes. PROCEDURE Ewes were randomly allocated to receive vaccination on days 1 and 60 of the study with a killed N caninum tachyzoite preparation in a commercially available adjuvant or a saline-adjuvant mixture. A ram was placed on pasture with the ewes from days 15 to 60. Blood was collected from ewes before primary and booster vaccinations and prior to experimental challenge with N caninum tachyzoite performed on day 90; sera were assessed via Neospora agglutination (NA) and immunofluorescence antibody (IFA) assays. Blood was collected from lambs before they suckled, and sera were tested for antibodies against N caninum. RESULTS Of the 14 vaccinated ewes that became pregnant, 12 gave birth to live-born lambs; in contrast, 5 of 11 pregnant control ewes gave birth to live-born lambs. Whereas vaccination improved fetal survival in pregnant ewes challenged with N caninum tachyzoites, it did not appear to have any appreciable effect on transmission of N caninum to offspring, as indicated by results of NA and IFA assays. CONCLUSIONS AND CLINICAL RELEVANCE The N caninum tachyzoite vaccine used in this study appeared to provide protection against fetal loss associated with experimentally induced neosporosis in a high proportion of pregnant ewes.