Developments in vaccination against bovine neosporosis.

Abstract

Abstract Neospora caninum is a major cause of bovine abortion worldwide, resulting in significant welfare implications and economic loss. Transmission of the parasite occurs via two routes: it can be transmitted transplacentally from dam to foetus, or it can be transmitted by ingestion of oocysts. There are no drugs licensed for use in cattle to control Neospora -associated abortions and although a vaccine is marketed in a limited number of countries, its efficacy has yet to be confirmed. Selected Neospora antigens have been targeted for use in subunit vaccines and have been evaluated in murine models but more work is needed to evaluate these antigens in cattle and to identify delivery methods which can provoke the pro-inflammatory immune response required for protective immunity. Cattle persistently infected with N. caninum are capable of transmitting the parasite to their offspring following recrudescence of infection during pregnancy, but they appear immune to exogenous challenge. The complex host-parasite interactions surrounding this phenomenon are not, at this stage, understood well enough to consider developing a vaccine against endogenous transplacental transmission. However, with our current knowledge, a vaccine that protects a pregnant cow against infection with oocysts and hence prevents exogenous transplacental transmission and abortion, is more feasible and an attractive prospect. This review looks at the issues surrounding development of a vaccine against bovine neosporosis such as live versus subunit vaccines, the difficulties in finding appropriate vaccine candidates and delivery systems and the complex balance of the immune response surrounding infection and pregnancy.