Spatial and temporal patterns of porcine reproductive and respiratory syndrome virus (PRRSV) genotypes in Ontario, Canada, 2004–2007

Abstract

BackgroundThe spread of PRRSV among pig herds has been investigated experimentally, but few observational studies have investigated this subject. Because PRRSV is endemic and live modified vaccines are used in Ontario, the spatial and temporal distributions of 6 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.ResultsA 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.ConclusionsAlthough the literature indicates that PRRSV can spread via aerosol between pig herds, the present study found no strong evidence of this occurring in Ontario. 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. It 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.

Modeling the spatio-temporal dynamics of porcine reproductive & respiratory syndrome cases at farm level using geographical distance and pig trade network matrices

“…To the best of our knowledge very few models have been published to predict PRRS status in the US swine industry. A study conducted by [17] in Ontario, Canada investigated evidence of spread of PRRSV genotypes and determined if spread could be attributed to supplier or ownership connections between herds. The spatial and temporal distributions of six PRRSV genotypes were investigated from 2004 to 2007.…”

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

“…Similarly, in a molecular study in Canada, Thakur et al [102] found that the predominant relationship between strains within a cluster were the introduction of infected pigs into farms. Also in Canada, Kwong et al [103] and Rosendal et al [104] identified the source of gilts as one of the main causes for explaining the spread of different strains in the country.…”

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

“…140 Others have involved broad classifications based on PRRSV types (European vs North American) on the basis of serologic results, 77 genotypes on the basis of RFLP patterns, 35,141 classification based on phylogenetic trees and different cutoff points to categorize variants into groups, 40,41,142 or matrices of similarities to assess correlations between the similarity of nucleotide sequences and spatial and other proximities among herds. Some studies relied on serologic evidence of PRRSV circulation in various herd types.…”

“…145 As a part of such investigations, one of the largest uncertainties continues to be importance of area spread (also commonly referred to as local spread), which is often discussed in the context of airborne transmission. Furthermore, several authors reported the possibility of area spread for some discrete genotypes, although such spread was not identified as the dominant mechanism of spread 41,141 or could be explained in some cases because of common sources of animals. In other studies, 35,140 existence of area spread could not be identified.…”

“…Investigators of epidemiological studies 40,77 identified area spread and argued that aerosol transmission played a critical role in transmission. 141 Few studies have been conducted to investigate membership in important networks such as ownership, 35,41,141,144,145 sources of animals and semen, 35,77,140,141 or transportation or service providers. Furthermore, several authors reported the possibility of area spread for some discrete genotypes, although such spread was not identified as the dominant mechanism of spread 41,141 or could be explained in some cases because of common sources of animals.…”