Correlation among genetic, Euclidean, temporal, and herd ownership distances of porcine reproductive and respiratory syndrome virus strains in Quebec, Canada

ABSTRACT:
BACKGROUND:

Porcine reproductive and respiratory syndrome (PRRS) is a viral disease that has a major economic impact for the swine industry. Its control is mostly directed towards preventing its spread which requires a better understanding of the mechanisms of transmission of the virus between herds. The objectives of this 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.
RESULTS:

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% 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%) PRRSV positive sites; 122 were wild-type strains. The mean (min-max) genetic, Euclidean and temporal pairwise distances were 11.6% (0-18.7), 15.0 km (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 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 5 km.
CONCLUSIONS:

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. Both should be considered in the perspective of prevention.
PMID: 22676411 [PubMed - as supplied by publisher]

Lambert M, Arsenault J, Poljak Z, D S. Correlation among genetic, Euclidean, temporal, and herd ownership distances of porcine reproductive and respiratory syndrome virus strains in Quebec, Canada. BMC veterinary research 2012;8(1):76-76.

Infectivity of PRRS virus in pig manure at different ambient temperatures

Linhares DCL, Torremorell M, Joo H S, Morrison R B. Infectivity of PRRS virus in pig manure at different ambient temperatures [Veterinary Microbiology, DOI 10.1016/j.vetmic.2012.05.009].

Abstract

PRRSv is an economically important swine pathogen which can be disseminated from infected pig herds via movement of contaminated manure. The process of manure handling and inadequate cleaning of transport vehicles are commonly implicated as sources of PRRSv transmission. Stability of PRRSv in pig manure at different temperatures is unknown. The objective of this study was to determine PRRSv-infectivity half-life in manure and in a cell culture medium at 4, 20, 60 and 80°C. To assure sample consistency across the study, all samples were prepared from common homogenized solutions (MEM and manure) and frozen at -20°C. Samples were thawed, transferred to a water bath set at a specific temperature, inoculated with 100μl of PRRSv at designated time points and then tested for virus infectivity. Regression models were created to estimate PRRSv half-life based on incubation temperature. There was an exponential decrease in PRRSv infectivity with increasing temperature. At every temperature tested, PRRSv had shorter half-life when incubated in manure compared to MEM. PRRSv half-life in MEM and manure was estimated at 112.6 and 120.5h at 4°C, 14.6 and 24.5h at 20°C, 1.6 and 1.7h at 40°C, 2.9 and 8.5min at 60°C, and 0.36-0.59min at 80°C, respectively. Results of this study can be used as basis for developing strategies to inactivate PRRSv present in manure-contaminated environments using heating treatments. For example, these data suggest that submitting transport trailers to temperature of 50°C for 8h would decrease PRRSv from 10(6) TCID(50)/ml to less than 10(1) TCID(50)/ml.

Copyright © 2012 Elsevier B.V. All rights reserved.

PMID:

 

22658630

 

[PubMed - as supplied by publisher]