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Patterns of Porcine Reproductive and Respiratory Syndrome Virus Genotypes in Ontario, Canada, 2004-2007

17 June 2014

The main method of transmission of the porcine reproductive and respiratory syndrome virus (PRRSV) in Ontario was found to be common sources of live pigs or similar herd ownership, rather than via aerosols, according to a new study from the University of Guelph.

The spread of PRRSV among pig herds has been investigated experimentally, but few observational studies have investigated this subject, according to Thomas Rosendal and colleagues at the University of Guelph.

In their paper in BMC Veterinary Research, they explain that, because PRRSV is endemic and live modified vaccines are used in Ontario, the spatial and temporal distributions of six PRRSV genotypes were investigated in the province during the period from 2004–2007.

The purpose was to find evidence of spread of PRRSV genotypes and determine if spread could be attributed to supplier or ownership connections between herds. Sequence information from PRRSV ORF5 and related source-herd demographic information were obtained from diagnostic submissions to the Animal Health Laboratory, University of Guelph.

A spatial cluster that could not be attributed to supplier or ownership connections among herds in the cluster was detected for RFLP type 1-3-4. Because of genetic dissimilarity among members of the cluster, it was considered to be a result of past spread of the RFLP type.

A spatio-temporal cluster detected for RFLP type 1-18-4 was attributed to a shared gilt supplier among the herds in the cluster.

Significant spatio-temporal patterns detected for RFLP type 2-5-2, which is considered to be a vaccine-type virus were most likely due to grouping of herds in an ownership that used the corresponding vaccine.

Clustering within herd-ownership was a risk factor for presence of five of the six genotypes investigated in the present study.

Although the literature indicates that PRRSV can spread via aerosol between pig herds, the present study found no strong evidence of this occurring in Ontario, concluded Rosendal and co-authors. Rather, they said, the evidence pointed toward transmission of PRRSV occurring in this population by common sources of animals or similarity of herd ownership, which is a proxy measure for other connections between herds.

The Guelph-based researchers added that is also apparent that the recognition and testing of these connections between herds is a necessary part of interpreting spatio-temporal patterns of PRRSV genotypes.


Rosendal T., C. Dewey, R.t Friendship, S. Wootton, B. Young and Z. Poljak. 2014. Spatial and temporal patterns of porcine reproductive and respiratory syndrome virus (PRRSV) genotypes in Ontario, Canada, 2004–2007. BMC Veterinary Research 2014, 10:83 doi:10.1186/1746-6148-10-83.

Further Reading

You can view the full report by clicking here.
Find out more about PRRS by clicking here.

June 2014

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