Risk Factors for PRRSV Infection and Resulting Challenges for Effective Disease Surveillance

Of 147 pig herds surveyed in the UK, 35.1 per cent tested positive for the porcine reproductive and respiratory syndrome virus (PRRSV) and a number of risk factors were revealed, along with the prevalence of other viruses.
calendar icon 21 August 2015
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Key Messages

  • 147 farrow to finish (single site in 57,1 per cent) herds in the UK (mainly from North Yorkshire and East Anglia) were sampled for respiratory agents
  • In total, 35.1 per cent of farms tested positive for PRRSV.

Farms were more likely to have active PRRSV infection:

  • were located in high pig density areas (OR=2.9)
  • had dead pigs collected (OR=5.6)
  • entered animals more than 6 times a year vs. 1-6 (OR=2.8)
  • had more than 4 workers vs 1-2 (OR=3.1 up to 6.5)

Farms were less likely to have active PRRSV infection:

  • if they weaned pigs at 28 days of age or later (OR=0.3), but and association with smaller farm size was found.

PRRSV positive farms were also positive:

  • 53.3 per cent for H1N2
  • 31.1 per cent for avian-like H1N1
  • 84.8 per cent for APP
  • 89.1 per cent for PCV2
  • 21.7 per cent for both avian-like H1N1 and H1N2 and
  • 73.9 per cent for both APP and PCV2.

Article Brief

Between April 2008 and April 2009, 147 farrow to finish herds were studied. The median herd size was 300 sows, (16 to 2,000 sows).

Single site production was observed on 84 farms (57.1 per cent) and multiple sites on 63 farms (42.9 per cent). From each farm, 12 blood samples were collected (six 11- to 14-week-old growers and six finishers 15 weeks old).

Classification of a farm as PRRSV+ was based on growing and finishing pigs. Seronegative farms were considered as negative and were not tested by RT-PCR.

The herd prevalence of active PRRSV infection (35.1 per cent) indicates continuous virus circulation or recent virus introduction on a number of farms despite efforts to control the infection.

Lack of clinical signs and poor recognition of clinical signs could contribute to PRRSV infection remaining undetected on farms with active infection. The lower probability of detection of infection in farms using live vaccination compared to those without live vaccination is likely to reflect the reduction of clinical signs due to vaccination.

The goal is to highlight the fact that simple regular biosecurity measures and decisions can increase or reduce the chances of having a PRRS-positive farm:

  • The main ones were the number of new livestock introduction per year
  • The total number of workers
  • The disposal of dead animals, and
  • The pig density in the area of production (more than 15,000 pigs within 10-km radius from the farm)

The risk factors identified highlight the importance of good biosecurity practices in control of PRRS.


Velasova et al. 2012. Risk factors for porcine reproductive and respiratory syndrome virus infection and resulting challenges for effective disease surveillance. BMC Veterinary Research 2012, 8:184

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August 2015

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