Neosporosis and bovine abortion in Scotland.

Bovine neosporosis has been reported as a cause of abortion worldwide. A pilot serological survey of its incidence in Scotland suggested that around 8% of investigated abortions may be due to Neospora. To investigate this further sera were collected from cows that had just aborted and, when possible, from their aborted calves. During the first 19 months of the survey 367 maternal sera and 451 fetal sera were collected and have been analysed by means of an IgG IFAT for antibody to N. caninum. Of these, 280 maternal serum samples were paired with fetal samples and to date 116 of them have been examined also by an IFAT for IgM antibody to the parasite. Of the 451 fetal sera examined 54 had titres of 1/64 or greater. Thus 12% of aborted fetuses were considered to have evidence of infection. Of the 280 fetal sera (paired with maternal sera) 13.6% were positive and of the 116 fetal sera examined for IgM and IgG antibody, 12.9% (15) were positive by IgG IFAT and 9.5% (11) were positive by IgM IFAT (6 were positive by both tests). Thus 17.2% (20) were positive by one or both tests. Of the 280 maternal samples, paired with fetal sera, 17 (6.1%) had titres of 1/512 or more and had positive fetuses and 21 (7.5%) had titres of less than 1/512 and had positive fetuses. Thus, approximately half of the seropositive fetuses were born to darns with low antibody titres (< 1/512). It is concluded that examination of a single maternal serum sample for IgG antibody to N. caninum is not the best method of serodiagnosis of bovine Neospora abortion. Analysis of fetal serum for evidence of IgM and/or IgG antibody to the parasite is a better method. Preliminary results suggest a fetal infection rate of between 12 and 17% in aborting cattle in Scotland.