During the past decade, the intracellular protozoan parasite Neo:,pora caninum
has been identified as a major cause of reproductive disease in cattle throughout the
world. Abortion occurring during the middle of gestation is the primary clinical sign
of infection in cattle. These abortions and associated infertility lead to significant
economic loss in the cattle industries of countries where the disease has been
identified.
In this thesis, a major objective was to establish the prevalence of the disease,
particularly in cattle, and in sheep in Ireland, and to identify the factors of
epidemiological importance in cattle, which may be useful in designing any future
eradication or control programmes at a later date. It was also decided to examine the
pathogenesis of the disease in both species to determine the influence of infection at
different stages of gestation on the outcome of the pregnancy following experimental
infection. Finally, the role of vaccination in the prevention of abortion in cattle and
sheep following experimental infection during pregnancy was also investigated.
The results of studies described in this thesis, confirm that neosporosis is very
prevalent in the Irish cattle herd. It has also been shown to exist in the Irish sheep
flock, but its importance has not yet been fully evaluated. The stage of gestation
during which the dam becomes infected has been shown, at least in sheep, to determine
the outcome of pregnancy. Finally, vaccination, in sheep, did not provide protection
against abortion following experimental challenge of the dan1s during pregnancy. In
the absence of abortion in the cattle trials it was not possible to comment on the
efficacy of the vaccine in the bovine.