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Neospora caninum causes abortions in cattle worldwide. The Neospora-cycle of life is heteroxenous. Dogs (Canis familiaris) and coyotes (Canis latrans) are the definitive hosts known at present. Although, transplacental infection is an efficiently mode of transmission in cattle; there are also experimental and field data that prove horizontal transmission. Several techniques are available for diagnosis since neosporosis is recognized as a disease that causes economic losses in cattle. The mechanisms that produce the abortion are not completely understood. The immunomodulation observed during the pregnancy, is associated with a susceptible period where Neospora-abortion can occur. Resistance to the parasite is dependent on T helper cell 1 cytokine responses. This has important repercussions for pregnant female bovine because strong T helper cell 1 cytokine responses are incompatible with successful pregnancy. However, it was demonstrated that chronically infected cows develop immune mechanisms against the abortion caused by a second Neospora-exposure. The comprehension of those mechanisms is needed for the formulation of Neospora-vaccines that prevent bovine neosporosis. General concepts about neosporosis with emphasis in the immune response and perspectives for vaccination are mentioned in the present review.

One hundred and seven pregnant cows, which had been calfhood vaccinated with Brucella abortus strain 19 (S-19) were revaccinated with either S-19 or strain RB51 (S-RB51). All S-19-revaccinated animals seroconverted, while none of the RB51-revaccinated animals seroconverted. Two out of 25 (8%) S-19-revaccinated animals aborted, while none of the 57 RB51-revaccinated group aborted. Four of the S-19-revaccinated animals shed S-19 in the milk for at least 7 days, while only 1 cow shed S-RB51 for at least 3 days (but <7 days) post-parturition. Revaccination of strain 19 calfhood-vaccinated, pregnant cattle with S-RB51 appears to be a safe procedure with no diagnostically negative consequences.