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Risk Factors for PRRS Virus Infection and Resulting Challenges for Effective Disease Surveillance

01 November 2012

Evidence of porcine reproductive and respiratory syndrome virus (PRRSV) circulation was confirmed on 35 per cent of the farms in this UK study. Active PRRSV infection was more likely on farms that used a live virus vaccine, were located in areas with many other pigs or had mortalities collected from the farm.

In a paper published recently in BMC Veterinary Research, Martina Velasova of the Royal Veterinary College in Hatfield, UK and co-authors there and at the Animal Health and Veterinary Laboratories Agency (AHVLA) in Bury St Edmunds describe their study aimed to identify risk factors for active PRRSV infection at farm level and to assess the probability of an infected farm being detected through passive disease surveillance in England.

Data were obtained from a cross-sectional study on 147 farrow-to-finish farms conducted from April 2008 to April 2009. The risk factors for active PRRSV infection were identified using multi-variable logistic regression analysis. The surveillance system was evaluated using a stochastic scenario tree model.

Evidence of PRRSV circulation was confirmed on 35.1 per cent (95 per cent confidence interval, CI: 26.8-43.4) of farms in the cross-sectional study, with a higher proportion of infected farms in areas with high pig density (i.e. where there were more than 15,000 pigs within a 10-km radius of the farm).

Farms were more likely to have active PRRSV infection if they used the live virus vaccine (Porcilis PRRS; OR=7.5, 95%CI: 2.5-22.8), were located in high pig density areas (OR=2.9, 95%CI: 1.0-8.3) or had dead pigs collected (OR=5.6, 95%CI: 1.7-18.3).

Farms that weaned pigs at 28 days of age or later had lower odds of being PRRSV positive than those weaning at 21 to 27 days (OR=0.2, 95%CI: 0.1-0.7). The probability of detecting an infected farm through passive surveillance for disease was low (mode=0.074, 5th and 95th percentiles: 0.067; 0.083, respectively). In particular farms that used live virus vaccine had lower probabilities for detection than those that did not.

Risk factors identified highlight the importance of biosecurity measures for the incursion of PRRSV infection, concluded Verasova and co-authors. They add that a combined approach of surveillance for infection and disease diagnosis is needed to assist effective control and/or elimination of PRRSV from the pig population.


Velasova M., P. Alarcon, S. Williamson and B. Wieland. 2012. Risk factors for porcine reproductive and respiratory syndrome virus infection and resulting challenges for effective disease surveillance. BMC Veterinary Research, 8:184. doi:10.1186/1746-6148-8-184

Further Reading

You can view the full report (as a provisional PDF) by clicking here.

Find out more information on Porcine Reproductive Respiratory Syndrome (PRRS) by clicking here.

November 2012

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