Risk factors for porcine reproductive and respiratory syndrome virus infection and resulting challenges for effective disease surveillance

Abstract

BackgroundThis study aimed to identify risk factors for active porcine reproductive and respiratory syndrome virus (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 – April 2009. The risk factors for active PRRSV infection were identified using multivariable logistic regression analysis. The surveillance system was evaluated using a stochastic scenario tree model.ResultsEvidence of PRRSV circulation was confirmed on 35.1% (95%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 (more than 15000 pigs within 10 km radius from 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 compared to those weaning at 21-27 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 which used live virus vaccine had lower probabilities for detection compared to those which did not.ConclusionsRisk factors identified highlight the importance of biosecurity measures for the incursion of PRRSV infection. The results further indicate 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.

Development of a stochastic agent-based model to evaluate surveillance strategies for detection of emergent porcine reproductive and respiratory syndrome strains

“…This varied when regional pig density and use of vaccination were considered, with farms in a low pig density area and not using a vaccine having the lowest detection probability. Sensitivity analysis conducted in that study showed that an important parameter, as expected, was the probability that an infected pig would show clinical signs [9]. In a different context, during detection of the PRRS outbreak in Sweden in 2007 [20], active surveillance had a major role, and that particular outbreak was detected from the annual surveillance program and not due to clinical suspicion, even though animals from the whole country were naïve to the virus.…”

Review on the transmission porcine reproductive and respiratory syndrome virus between pigs and farms and impact on vaccination

“…Proximity of infected herds has been considered a hazard, resulting in an increased risk of introduction of the virus by aerosol transmission [101, 112, 113]. Nevertheless, the airborne transmission of PRRSV and its implication on the area spread of the disease seems to be dependent on the strain and on environmental factors.…”

Lessons learned and knowledge gaps about the epidemiology and control of porcine reproductive and respiratory syndrome virus in North America

“…In another cross-sectional study 147 of risk factors for PRRSV circulation in swine herds in the United Kingdom, > 15,000 pigs in a 10-km (6.25-miles) radius, collecting dead pigs (as opposed to incineration of pig carcasses), use of a live PRRSV vaccine, and weaning pigs at 21 to 27 days of age (as opposed to weaning at > 28 days of age) were risk factors for PRRSV circulation. Access of a rendering truck to a pig site as well as absence of a shower at the entrance to the pig site were positively associated with the PRRSV status of sow herds in a Quebec region.…”