Characteristics of Neospora caninum-associated abortion storms in dairy herds in the Netherlands (1995 to1997)

Abortion storms in 50 dairy herds in The Netherlands were reported in which there was a strong association with Neospora caninum-infection. The durati on of the abortion storms ranged from 6 to 65 d (mean 41.5 d). The cumulati ve proportion of aborting cows ranged from 0.11 to 0.57 (mean 0.26) of the animals at risk. An apparent seasonal influence was noted as most abortion storms occurred during the summer and early autumn. The prevalence of antibodies to N. caninum in 50 herds which had had an abo rtion storm was compared with that of 100 control herds which had no histor y of an abortion storm. Seroprevalence was estimated by testing a 20% cross sectional herd sample using a tachyzoite lysate-based ELISA method. Seropr evalence in case herds (range 17 to 87%, mean 51.5%) was significantly high er than that in control herds (range 0 to 53%, mean 13.9%). For most herds the seroprevalence levels were equal across all age groups, which suggests that the infection had been perpetuated by vertical transmis sion. In these herds, the abortion storms appeared to be induced by factors causing recrudescence of a N. caninum-infection in chronically infected an imals rather than being the result of a recent introduction. In 6 case herd s the seroprevalence in the dairy cows was significantly higher than in the young stock, which may have been attributable to superimposed postnatal in fection. (C) 1999 by Elsevier Science Inc.