BPEX Veterinary Projects Manager, Charlotte Evans, looked at a mathematical model of a farrow-finish pig herd that was developed and used to investigate the within-herd transmission dynamics of PRRSV, and to examine patterns of on-farm persistence and fade-out.

The model was structured to represent the management of a typical European pig herd and was run for various isolation practices of purchased gilts, contact structure, herd size and the frequency of re-introduction of infectious gilts.

With a herd size of 327 sows with identical management, fade-out of virus occurred within four weeks in 21.9 per cent of simulations. Without isolation of gilts from sows, fade-out within 250 days decreased from 81.6 per cent to 14.3 per cent.

Fade-out of virus was most likely to occur within breeding females before virus reached young stock. Persistence was more likely once PRRSV was present in piglets which in turn infected rearing-pigs.

The probability of persistence was higher with increased herd size, increased contact between different age groups and increased re-introduction of infectious gilts. The ability of the model to capture the variability in cross-sectional, age-related serological patterns suggests that the processes of re-introduction, persistence and fade-out of PRRSV play critical roles in PRRSV epidemiology.

Reference

Evans C.M., G.F. Medley, S.J. Creasey and L.E. Green. 2009. A stochastic mathematical model of the within-herd transmission dynamics of porcine reproductive and respiratory syndrome virus (PRRSV): Fade-out and persistence. Preventative Veterinary Medicine (in press). doi:10.1016/j.prevetmed.2009.11.001

Further Reading

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You can view the abstract and full report (fee payable) by clicking here.

Further Reading

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Find out more information on porcine reproductive respiratory syndrome (PRRS) by clicking here.