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Neospora caninum is considered a major cause of abortion in cattle. Appropriate techniques for diagnosis of bovine neosporosis, both in vivo and in aborted foetuses, have been developed in the last ten years and some of them are commercially available. For diagnosis in live animals, detection of antibodies in serum or milk has been shown to be the best option both at the herd and the individual level. These techniques are excellent tools to examine N. caninum-associated abortion problems and to adopt some basic herd-control measures. Concerning foetal diagnosis, detection of compatible lesions by histological examination and parasites by PCR in brain (as well as heart and liver) are the best choices. Diagnostic criteria to distinguish foetal infection and Neospora-associated abortion are based not only on the demonstration of the parasite in the foetus but also on the extent and severity of the lesions in the foetus, foetal age and the assessment of neosporosis at the herd level. In the near future, new tools to diagnose infection should help to detect animals with parasite reactivation by testing the immune response to stage-specific antigens and lead to the development of molecular typing methods to characterise different parasite isolates. Finally, uniform diagnostic procedures need to be established between laboratories and countries in order to standardise result interpretation. The role of National or Regional Reference Laboratories is essential in countries or regions where control programmes for the disease are being developed.
Neosporosis is an infectious disease of cattle and other species with a worldwide distribution. In Poland, the seropositivity rate for N. caninum among dairy cattle varies between 6% and 80%, with the highest number of seropositive cows in central and north-eastern voivodeships. In the United States, in 2003 the total annual cost of N. caninum infections was 657 million dollars, and in Great Britain in 2014 it was nearly 14 million pounds. N. caninum results in severe economic losses caused by a decreased milk yield, an increased number of culled cows, a higher newborn calf mortality rate and occasional birth defects. However, the most common result of this disease is abortion, which usually occurs between the 5th and 7th month of gestation. The risk of aborting is 3 times as high for seropositive cows as it is for seronegative cows; up to 21.6% vs. 7.3%, respectively. Cattle can become infected by consuming food and water contaminated with N. caninum oocysts, but the principal route is transplacental transmission usually between the 70th and 210th day of gestation. The ELISA test is most often used to detect the presence of specific antibodies in blood serum. PAG-2 level in the bloodstream can be a good marker for predicting Neospora-induced abortions – in seropositive cows, a level of more than 4.5 ng/ml on the 120th day of gestation means a 7-fold higher risk of pregnancy loss. According to research, live attenuated vaccines are highly efficacious in preventing neosporosis. Unfortunately, the currently available methods of prevention are based on the elimination of seropositive cows from the herd and the limitation of contact with the final hosts of N. caninum.
The course of anti-Neospora antibody kinetics during two consecutive pregnancies has been evaluated in five chronically infected dairy cows. The blood samples of cows were collected monthly. Anti-Neospora antibodies in blood sera were detected by indirect ELISA (ID-VET, France). During whole period of the study cows remained seropositive; with S/P% values (iELISA) ranging from 94 to 214%. The antibody kinetics determined by iELISA showed a significant increase (P<0.0059) of specific IgG antibodies in the third trimester of both pregnancies. The monitored cows gave birth to 10 healthy calves (4 steers and 6 heifers). To confirm the occurrence of vertical transmission of Neospora from mothers to offspring in the herd, dam-daughter serology was performed. Anti-Neospora antibodies was found in 4 from 6 heifers (>6 months old). Study presents original data reporting on the very similar persistent pattern of anti-Neospora antibody levels during the third trimester of pregnancies in all five dairies. Based on the high seropositivity of female offspring, the reactivation of a latent infection of cows rather than a re-infection can be supposed.
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