Neospora caninum - eine Abortursache beim Rind

Neospora caninum - a causal agent of abortion in cows The present study gives an overview of the current knowledge of N. caninum, particularly concerning the incidence of abortions in cattle populations infected by this parasite. In 1988 the Toxoplasma-like protozoon found in dogs was named N. caninum. In more than 40 countries N. caninum has been diagnosed since that time and about 17 different species were found to host infections by N. caninum. There are reports about 26 isolates. A different species, N. hughesi, was found to infect horses. Three different isolates of this species were described. There are conflicting reports about the exact phylogenetic classification of N. caninum. Especially the taxonomical relationship between Neospora, Toxoplasma and Hammondia is still being discussed controversely. It is generally accepted that N. caninum belongs to the phylum of Apicomplexa, the class of Sporozoa, the subclass of Coccidia, the order of Eucoccidia and the suborder of Eimeriina. During its life cycle N. caninum passes through various phases like sporogony, schizogony and gamogony. Definitive and intermediate hosts are needed for parasite`s development. To date not every detail of the parasite`s life has been investigated. Numerous investigations took place up until 1998 when it became obvious that the dog is a definitive host of N. caninum. Currently there is no evidence that other canids may also function as definitive hosts. It is difficult to distinguish oocysts of N. caninum from those of other eimerian species. N. caninum is transmitted either vertically from a cow to its fetus by tachyzoites or horizontally by ingesting oocysts, tachyzoites or bradyzoites. Reduced fertility and abortions are severe problems caused by neosporosis in cattle populations. Abortions can occur sporadically, endemically or epidemically. Concerning the season in which abortions take place a connection to climatic conditions favouring the survival of oocysts in the environment was suggested. But nevertheless N. caninum induced abortions can happen during the whole of the year. After the infection of a cow by N. caninum its first pregnancy probably results in abortion. During the following pregnancies the fetus of the same cow is likely to become infected, too, but abortion is unprobable. The resulting calf is infected chronically and also gives birth to infected offsprings. Only in exceptional circumstances may abortion occur again during the second or third pregnancy of the same cow. Sometimes stillbirths or malformations occur. The individual immune system of a cow chronically infected by N. caninum plays an important role for the transmission of the fetus and for the probability of abortion. Serological diagnoses of infections by N. caninum have to be confirmed by histopathological examinations to ensure that symptoms observed were really caused by this parasite. But former investigations demonstrate that the confirmation of diagnosis is difficult, especially if tissues dispatched are in bad condition. Immunological studies have been initiated to learn more about the parasitic activities of N. caninum and the host-parasite interaction. There is a chance to develop a vaccine to avoid the transplacental transmission of the parasite. The next step is the prevention of the horizontal infection. In general prevention from infection is of great importance in herds with infertility and abortions. Feeding with contaminated food and water should be avoided. Furthermore placentas potentially infected and stillborn calves should be removed. Affected herds should be examined serologically and histopathologically. Economic losses caused by infections by N. caninum result from reduced fertility, reduced milk production, lower average daily weight gain as well as from abortion. But up to now the severity of economical losses can not be quantified exactly, because aborted fetuses are not examined routinely. There is no zoonotic potential of N. caninum. Allthough it was possible to infect monkeys with a high dose of tachyzoites, there has been no natural infection seen up to now. And no indicate of N. caninum infections in aborted human fetuses were fou

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Ludwig-Maximilians-Universität

Year

2004

Author dc:creator

• Mayr, Astrid Katja

Repository record source_url

https://edoc.ub.uni-muenchen.de/2156/

OAI identifier oai:identifier

oai:edoc.ub.uni-muenchen.de:2156