Influence of herd structure and type of virus introduction on the spread of bovine viral diarrhoea virus (BVDV) on the spread of bovine viral diarrhoea virus (BVDV) within a dairy herdPauline Ezanno1, 2, Christine Fourichon1, 2 and Henri Seegers1, 2
1 INRA, UMR1300, Bio-agression, Épidémiologie et Analyse de Risques, BP 40706, 44307 Nantes, France
2 École Nationale Vétérinaire de Nantes, UMR1300, Bio-agression, Épidémiologie et Analyse de Risques, BP 40706, 44307 Nantes, France
Received 2 October 2007; accepted 14 March 2008; published online 18 March 2008
Abstract - A herd is a population structured into groups not all equally in contact, which may influence within-herd spread of pathogens. Herd structure varies among cattle herds. However, published models of the spread of bovine viral diarrhoea virus (BVDV) assume no herd structure or a unique structure chosen as a representative. Our objective was to identify - for different index cases introduced into an initially BVDV - free dairy herd - risky (favourable) herd structures, which increased (decreased) BVDV spread and persistence compared to a reference structure. Classically, dairy herds are divided into calves, young heifers, bred heifers, lactating cows and dry cows. In the reference scenario, groups are all equally in contact. We evaluated the effect of isolating or merging groups. Three index cases were tested: an open persistently-infected (PI) heifer, an open transiently-infected heifer, an immune heifer carrying a PI foetus. Merging all groups and merging calves and lactating cows were risky scenarios. Isolating each group, isolating lactating cows from other groups, and merging calves and young heifers were favourable scenarios. In most structures, the most risky index cases were the following: first, the entry of a PI heifer; second, the birth of a PI calf; last, the entry of a transiently-infected heifer. Recommendations for dairy herds are to raise young animals together before breeding and to isolate lactating cows from others as much as possible. These recommendations will be less efficient if a PI adult enters into the herd.
Key words: contact structure / epidemiological model / pestivirus / cattle
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© INRA, EDP Sciences 2008