Comparison of the IFAT and Iscom-ELISA response in bovine foetuses with Neospora caninum infection

The study was carried out to evaluate the efficacy of foetal serology in th e diagnosis of Neospora-associated bovine abortions. Fluids from 14 foetuse s of cows with confirmed neosporosis (Group A), seven foetuses with confirm ed bovine viral diarrhoea virus (BVD infection) (Group B) and 11 aborted fo etuses without demonstrable infection (Group C) were examined. The age of t he foetuses ranged from 4.5 months to 9 months. Albumin concentration (measured by Rocket Immunoelectrophoresis) was not si gnificantly different in Group A compared with that in both Groups B and C, while that in Group B was significantly lower than in Group C. Levels of t otal IgG ranged from 0.01 to 1.78 (mg IgG) ml(-1) measured by single radial immunodiffusion technique. A measurable level of total IgG was found in al l foetuses from Groups A and B, with no significant difference between leve ls in the two groups. Only one foetus in Group C had a detectable level of IgG. All foetuses in Group A had a specific IgG response (titre greater tha n or equal to 20) against Neospora caninum using the IFAT, while no positiv e responses in IFAT were found in Groups B and C. Measurement of specific I gG1 and IgG2 by Iscom-ELISA showed one and three false-negative results, re spectively, in Group A. The IgG1 and IgG2 response in Group A was correlate d according to the Spearman test (r = 0.66). Increasing age of the foetuses correlated significantly with the foetal IgG concentration, the specific I gG and IgG1 + IgG2. On the basis of the results obtained, it was concluded that the IFAT with a cut-off titre of 1:20, was a specific method for diagnosis of neosporosis in foetuses older than 4.5 months. The Iscom-ELISA also showed promising re sults as a method for screening specific antibodies against N. caninum in f oetal fluid. (C) 1999 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.