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