A Swiss case-control study to assess Neospora caninum-associated bovine abortions by PCR, histopathology and serology

Neospora caninum is one of the most frequent infectious organisms causing a bortion in cattle worldwide. The present case-control study was designed to assess the importance of bovine neosporosis for causing abortion in Swiss cattle and to identify selected risk factors. Infection was primarily diagn osed by a N. caninum-specific PCR and serology, complemented with histopath ology and immunohistochemistry. A total of 113 case and 113 corresponding c ontrol-farms were studied for 1.5 year. During this time period, 242 aborti ons were reported and referred for bacteriological, virological, parasitolo gical and pathohistological examinations. N. caninum was detected by PCR in the brains of 21% of all aborted fetuses. Microscopic lesions indicative f or cerebral protozoa infection were detected in 84% of PCR-positive fetal b rains. Bovine viral diarrhea virus (BVDV) was demonstrated in 7% of the cas es, and bacterial infections were detected in 4% of the abortions. One or m ore N. caninum-abortions occurred in 20% of the herds (41 case-farms and 3 control-farms). Serological examination of aborting mother cows revealed a significantly higher percentage of N. caninum-seropositive animals (44%) in comparison to the prevalence in a randomly selected population (12%). Howe ver, in eight cases (4% of all investigated abortions) seronegative cows ab orted N. caninum PCR-positive fetuses, and in 50 cases the fetus remained n egative although the respective mother cow was N. caninum-seropositive. Rep etitive serological investigations (at a 3-12 months interval) of 3551 cows from case- and control-farms showed a decrease of the overall N. caninum-s eroprevalence from 17 to 12%. Ninety out of 3008 seronegative animals were converted to N. caninum-seropositivity. Conversely, 212 out of 543 initiall y seropositive animals became seronegative for their second serum sample. T he obtained data underlined the importance of IV. caninum as a causative ag ent for abortion in Swiss cattle. Furthermore, PCR was confirmed to be a va luable diagnostic tool for the primary diagnosis of N. caninum in aborted f etuses. On the other hand, the value of serology appears to be hampered by the temporal instability of N. caninum antibody concentrations in adult cat tle, including especially seronegativity of some individual animals. Thus, seronegativity in a mother cow or heifer does not exclude N. caninum-associ ated abortions. (C) 2001 Elsevier Science B.V. All rights reserved.