Introduction, persistence and fade-out of porcine reproductive and respiratory syndrome virus in a Dutch breeding herd: a mathematical analysis.
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.
Nodelijk
G
G
Department of Farm Animal Health, Faculty of Veterinary Medicine, University of Utrecht, The Netherlands.
de Jong
M C
MC
Van Nes
A
A
Vernooy
J C
JC
Van Leengoed
L A
LA
Pol
J M
JM
Verheijden
J H
JH
D000818:Animals; D016022:Case-Control Studies; D004196:Disease Outbreaks; D019353:Endemic Diseases; D005260:Female; D015994:Incidence; D018445:Infectious Disease Transmission, Vertical; D008137:Longitudinal Studies; D008297:Male; D008954:Models, Biological; D009010:Monte Carlo Method; D009426:Netherlands / Q000453:epidemiology; D016017:Odds Ratio; D019318:Porcine Reproductive and Respiratory Syndrome / Q000453:epidemiology* / Q000635:transmission; D011247:Pregnancy; D015995:Prevalence; D013552:Swine