Neospora caninum als Abortursache bei Rindern - Neues zur Pathogenese, Epidemiologie und Diagnose

Acute primary or persistent infection of cattle with Neospora caninum can induce abortion. The abortions are triggered by lesions caused by the protozoon during its obligatory intracellular multiplication in foetal tissues and in the maternal part of the placenta. In addition, the infection may be able to favour abortions indirectly via changes of the immunological equilibrium within the foeto-placental unit, i.e. via an increased production of pro-inflammatory cytokines. In most cases, transplacental transmission of the infection does not cause abortion but leads to the birth of persistently infected, healthy calves. It is assumed that the majority of N. caninum-positive cattle in Germany become prenatally infected via their mother. This vertical route of transmission is very efficient and allows N. caninum to survive for several generations once a breeding line has become infected. Contamination of the forage with N. caninum oocysts shed by definitive hosts is regarded the most important source of infection which is able to introduce N. caninum horizontally into a herd or to spread the infection from one breeding line to another. The dog is the only known definitive host in Europe that can shed N. caninum-oocysts with the faeces. Risk factor studies suggest that dogs kept on cattle farms play a predominant role in spreading the infection horizontally. Other dogs shed N. caninum oocysts, only very rarely; consequently they are regarded as less important for the transmission of the infection. A diagnosis is reached by the direct or indirect demonstration of the infectious agent in foetal tissues. Histological lesions, like multifocal nonsuppurative encephalitis are regarded as characteristic. A seroepidemiological examination of pregnant cattle in the herd may confirm the diagnosis. Since the infection cannot be treated by chemotherapy and as there is no vaccine licensed in Germany, it is of utmost importance to adhere to hygienic measures to reduce the chance for a horizontal transmission of the infection. Vertical transmission can be prevented by excluding seropositive animals from breeding. These measures are only reasonable in herds where abortions are more likely to occur in the infected cattle breeding lines than in the non-infected ones