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Introduction, persistence and fade-out of porcine reproductive and respiratory syndrome virus in a Dutch breeding herd: a mathematical analysis

Published online by Cambridge University Press:  01 February 2000

G. NODELIJK ,
M. C. M. DE JONG ,
A. VAN NES ,
J. C. M. VERNOOY ,
L. A. M. G. VAN LEENGOED ,
J. M. A. POL  and
J. H. M. VERHEIJDEN
G. NODELIJK
Affiliation:
Department of Farm Animal Health, Faculty of Veterinary Medicine, University of Utrecht, P.O. Box 80151, 3508 TD Utrecht, The Netherlands
M. C. M. DE JONG
Affiliation:
Department of Immunology, Pathobiology & Epidemiology, Institute for Animal Science & Health (ID-Lelystad), P.O. Box 65, 8200 AB Lelystad, The Netherlands
A. VAN NES
Affiliation:
Department of Farm Animal Health, Faculty of Veterinary Medicine, University of Utrecht, P.O. Box 80151, 3508 TD Utrecht, The Netherlands
J. C. M. VERNOOY
Affiliation:
Department of Farm Animal Health, Faculty of Veterinary Medicine, University of Utrecht, P.O. Box 80151, 3508 TD Utrecht, The Netherlands
L. A. M. G. VAN LEENGOED
Affiliation:
Department of Farm Animal Health, Faculty of Veterinary Medicine, University of Utrecht, P.O. Box 80151, 3508 TD Utrecht, The Netherlands
J. M. A. POL
Affiliation:
Department of Avian Virology, Institute for Animal Science & Health (ID-Lelystad), P.O. Box 65, 8200 AB Lelystad, The Netherlands
J. H. M. VERHEIJDEN
Affiliation:
Department of Farm Animal Health, Faculty of Veterinary Medicine, University of Utrecht, P.O. Box 80151, 3508 TD Utrecht, The Netherlands
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Abstract

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The objective of this study was to investigate the dynamics of PRRSV infection and to quantify transmission within a breeding herd, and its impact on herd performance. For this purpose a longitudinal study was performed in a closed breeding herd of 115 sows. Statistical methods and Monte Carlo simulations based on stochastic SIR models were used to analyse the observational data. Moreover, a case-control study was performed to determine whether seroconversion of sows during gestation was associated with aberrant litters. The transmission parameter R was estimated to be 3·0 (95% confidence interval 1·5–6·0) for the model version based on the most plausible assumptions that the infectious period lasts 56 days and no lifelong immunity exists after infection. Based on simulations using a breeding herd of equal size the average time-to-extinction was estimated to be 6 years; using a herd of twice the size, it was 80 years. Furthermore, in contrast to the epidemic phase of the disease, the endemic phase was not detrimental to herd performance.

Type
Research Article
Information
Epidemiology & Infection , Volume 124 , Issue 1 , February 2000 , pp. 173 - 182
Copyright
© 2000 Cambridge University Press