Porcine reproductive and respiratory syndrome (PRRS) is a viral disease that has a major economic impact for the swine industry, according to Marie-Ève Lambert of the University of Montreal and co-authors there and at the University of Guelph in Canada.

In the introduction to their paper in BMC Veterinary Research, they explain that the control of PRRS is mostly directed towards preventing its spread, which requires a better understanding of the mechanisms of transmission of the virus between herds. Thus, the objectives of their study were to describe the genetic diversity and to assess the correlation among genetic, Euclidean and temporal distances and ownership to better understand pathways of transmission.

A cross-sectional study was conducted on sites located in a high-density area of swine production in Quebec. Geographical coordinates (longitude/latitude), date of submission and ownership was obtained for each site. ORF5 sequencing was attempted on PRRSV-positive sites. Proportion of pairwise combinations of strains having greater than or equal to 98 per cent genetic homology were analysed according to Euclidean distances and ownership.

Correlations between genetic, Euclidean and temporal distances and ownership were assessed using Mantel tests on continuous and binary matrices. Sensitivity of the correlations between genetic and Euclidean as well as temporal distances was evaluated for different Euclidean and temporal distance thresholds.

An ORF5 sequence was identified for 132 of the 176 (75 per cent) PRRSV-positive sites; 122 were wild-type strains. The mean (minimum-maximum) genetic, Euclidean and temporal pairwise distances were 11.6 per cent (0-18.7), 15.0km (0.04-45.7) and 218 days (0-852), respectively.

Significant positive correlations were observed between genetic and ownership, genetic and Euclidean and between genetic and temporal binary distances.

The researchers found that the relationship between genetic and ownership suggests either common sources of animals or semen, employees, technical services or vehicles, whereas that between genetic and Euclidean binary distances is compatible with area spread of the virus. The latter correlation was observed only up to five kilometres.

This study suggests that transmission of PRRSV is likely to occur between sites belonging to the same owner or through area spread within a 5-km distance, concluded Lambert and co-authors. They added that both should be considered in the perspective of prevention.

Reference

Lambert M-È., J. Arsenault, Z. Poljak and S. D’Allaire. 2012. Correlation among genetic, Euclidean, temporal, and herd ownership distances of porcine reproductive and respiratory syndrome virus strains in Quebec, Canada. BMC Veterinary Research, 8:76. doi:10.1186/1746-6148-8-76

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

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

June 2012