Oorsig/Review
The number of vaccinations per season will vary
with the length of the Haemonchus season, the
starting date of vaccination and challenge from
the pasture. When primary immunisation is
in place, only “booster” vaccinations every 6-8
weeks will be required. It is expected that the
number of vaccinations will lessen as the pasture
contamination lowers every year of vaccination.
The results of the registration trial indicated
that a strong protective immunity develops in
vaccinated sheep. After three vaccinations, given
three weeks apart, the experimental vaccine
Wirevax® stimulated a strong circulating
antibody response. Statistically, the mean
antibody titres of the vaccinated sheep were
significantly higher than those measured in the
controls. This immune response was associated
with reductions in faecal egg counts and worm
burdens in vaccinated sheep compared to control
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sheep. In sheep challenged immediately after the
third vaccination, the efficacy based on worm
counts was 86.93% and on faecal egg counts were
reduced by 95.59%. In those sheep that were
challenged 30 days after the third vaccination,
the efficacy was 80.66 % on worm counts and
faecal egg counts were reduced by 80.6%. It
can be concluded that three vaccinations given
at three-week intervals will aid in the control
of haemonchosis in sheep and will significantly
limit new infections for 30 days.
Barnes et al. (1995) developed a mathematical
model
for
simulating
Trichostrongylus
populations in grazing sheep and compared the
use of theoretical vaccines of nominal efficacy with
the use of conventional control methods based
on anthelmintic treatment. It was concluded that
vaccines based on hidden antigens conferred a
protection of 80% of the flock with 80% efficacy
would ensure better control than a conventional
anthelmintic programme. The results of this