SBV case control rund (English)

In the fall of 2011, a new orthobunyavirus was identified in dairy cows with fever, drop in milk production and diarrhoea especially in the eastern regions of the Netherlands and in cows with milk drop in Northwestern Germany.

Problem definition: The impact of the The SBV epidemic on cattle is uncertain, knowledge on impact is necessary for animal health policy makers to decide whether a control program is necessary. A risk factor study may provide tools for intervention and control.

Objectives of the project: The objectives of this study were i) to explore and quantify the risk factors for prevalence of SBV in Dutch dairy herds, ii) to identify herd-level risk factors for SBV-induced malformations in new-born calves in Dutch dairy herds, iii) to describe clinical signs at herd level given the seroprevalence in the herd, and iv) to describe the effects of SBV infection on mortality rates, milk production and reproductive performance.

Results and opportunities: Animal-level seroprevalence will be compared between case and control. Risk factor distribution will be compared between case and control herds. Incidence of malformations in newborn calves at herd level will be compared between case ad control herds. The within-herd impact of SBV infection on milk production and mortality rates will be investigated.

Methodology and time table: A case-control design was used, using data from 75 case herds and 74 control herds. Case herds were selected based on reporting of SBV-related clinical signs in August/September 2011 and/or notification of malformations in newborn calves during the period in which such malformations were notifiable in the Netherlands (Dec. 20, 2011 – July 6, 2012). Control herds were selected based on absence of malformations in newborn calves and anomalies in reproductive performance, and were matched to case herds by region. A maximum of 70 serum samples were collected in each herd to estimate seroprevalences. Seroprevalences were estimated by logistic regression analysis. Risk factors for high within-herd SBV seroprevalence and the probability of malformed newborn calves in a herd were quantified using logistic regression analyses. In addition, within-herd impact of SBV with regard to reproductive performance, milk production and mortality was analyzed descriptively. Final report will be produced autumn 2013.