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. (Am J Vet Res