Suitability and limitations of portion-specific abattoir data as part of an early warning system for emerging diseases of swine in Ontario

<p>Abstract</p> <p>Background</p> <p>Abattoir data have the potential to provide information for geospatial disease surveillance applications, but the quality of the data and utility for detecting disease outbreaks is not well understood. The objectives of this study were to 1) identify non-disease factors that may bias these data for disease surveillance and 2) determine if major disease events that took place during the study period would be captured using multi-level modelling and scan statistics. We analyzed data collected at all provincially-inspected abattoirs in Ontario, Canada during 2001-2007. During these years there were outbreaks of porcine circovirus-associated disease (PCVAD), porcine reproductive and respiratory syndrome (PRRS) and swine influenza that produced widespread disease within the province. Negative binomial models with random intercepts for abattoir, to account for repeated measurements within abattoirs, were created. The relationships between partial carcass condemnation rates for pneumonia and nephritis with year, season, agricultural region, stock price, and abattoir processing capacity were explored. The utility of the spatial scan statistic for detecting clusters of high partial carcass condemnation rates in space, time, and space-time was investigated.</p> <p>Results</p> <p>Non-disease factors that were found to be associated with lung and kidney condemnation rates included abattoir processing capacity, agricultural region and season. Yearly trends in predicted condemnation rates varied by agricultural region, and temporal patterns were different for both types of condemnations. Some clusters of high condemnation rates of kidneys with nephritis in time and space-time preceded the timeframe during which case clusters were detected using traditional laboratory data. Yearly kidney condemnation rates related to nephritis lesions in eastern Ontario were most consistent with the trends that were expected in relation to the documented disease outbreaks. Yearly lung condemnation rates did not correspond with the timeframes during which major respiratory disease outbreaks took place.</p> <p>Conclusions</p> <p>This study demonstrated that a number of abattoir-related factors require consideration when using abattoir data for quantitative disease surveillance. Data pertaining to lungs condemned for pneumonia did not provide useful information for predicting disease events, while partial carcass condemnations of nephritis were most consistent with expected trends. Techniques that adjust for non-disease factors should be considered when applying cluster detection methods to abattoir data.</p

Spread of porcine circovirus associated disease (PCVAD) in Ontario (Canada) swine herds: Part II. Matched case-control study

<p>Abstract</p> <p>Background</p> <p>The emergence of porcine circovirus associated disease (PCVAD) was associated with high mortality in swine populations worldwide. Studies performed in different regions identified spatial, temporal, and spatio-temporal trends as factors contributing to patterns of the disease spread. Patterns consistent with spatial trend and spatio-temporal clustering were already identified in this dataset. On the basis of these results, we have further investigated the nature of local spread in this report. The primary objective of this study was to evaluate risk factors for incidence cases of reported PCVAD.</p> <p>Results</p> <p>A time-matched case-control study was used as a study design approach, and conditional logistic regression as the analytical method. The main exposure of interest was local spread, which was defined as an unidentified mechanism of PCVAD spread between premises located within 3 kilometers of the Euclidean distance. Various modifications of variables indicative of local spread were also evaluated. The dataset contained 278 swine herds from Ontario originally sampled either from diagnostic laboratory submissions or directly from the target population. A PCVAD case was defined on the basis of the producer's recall. Existence of apparent local spread over the entire study period was confirmed (OR = 2.26, 95% CI: 1.06, 4.83), and was further identified to be time-varying in nature - herds experiencing outbreaks in the later part of the epidemic were more likely than control herds to be exposed to neighboring herds experiencing recent PCVAD outbreaks. More importantly, the pattern of local spread was driven by concurrent occurrence of PCVAD on premises under the same ownership (OR_{EXACTwithin ownership}= 25.6, 95% CI: 3.4, +inf; OR_{EXACToutside ownership}= 1.3, 95% CI: 0.45, 3.3). Other significant factors included PRRSv status of a herd (OR_EXACT= 1.9, 95% CI: 1.0, 3.9), after adjusting for geographical location by including the binary effect of the easting coordinate (Easting > 600 km = 1; OR_EXACT= 1.8, 95% CI: 0.5, 5.6).</p> <p>Conclusions</p> <p>These results preclude any conclusion regarding the existence of a mechanism of local spread through airborne transmission or indirectly through contaminated fomites or vectors, as simultaneous emergence of PCVAD could also be a result of concurrent change in contributing factors due to other mechanisms within ownerships.</p

Spread of porcine circovirus associated disease (PCVAD) in Ontario (Canada) swine herds: Part I. Exploratory spatial analysis

<p>Abstract</p> <p>Background</p> <p>The systemic form of porcine circovirus associated disease (PCVAD), also known as postweaning multisystemic wasting syndrome (PMWS) was initially detected in the early 1990s. Starting in 2004, the Canadian swine industry experienced considerable losses due to PCVAD, concurrent with a shift in genotype of porcine circovirus type 2 (PCV2). Objectives of the current study were to explore spatial characteristics of self-reported PCVAD distribution in Ontario between 2004 and 2008, and to investigate the existence and nature of local spread.</p> <p>Results</p> <p>The study included 278 swine herds from a large disease-monitoring project that included porcine reproductive and respiratory syndrome (PRRS) virus-positive herds identified by the diagnostic laboratory, and PRRS virus-negative herds directly from the target population. Herds were included if they had growing pigs present on-site and available geographical coordinates for the sampling site. Furthermore, herds were defined as PCVAD-positive if a producer reported an outbreak of circovirus associated disease, or as PCVAD-negative if no outbreak was noted. Spatial trend was investigated using generalized additive models and time to PCVAD outbreak in a herd using Cox's proportional hazard model; spatial and spatio-temporal clustering was explored using K-functions; and location of most likely spatial and spatio-temporal clusters was investigated using scan statistics. Over the study period, the risk of reporting a PCVAD-positive herd tended to be higher in the eastern part of the province after adjustment for herd PRRS status (<it>P </it>= 0.05). This was partly confirmed for spread (Partial <it>P </it>< 0.01). Local spread also appeared to exist, as suggested by the tentative (<it>P </it>= 0.06) existence of spatio-temporal clustering of PCVAD and detection of a spatio-temporal cluster (<it>P </it>= 0.04).</p> <p>Conclusions</p> <p>In Ontario, PCVAD has shown a general trend, spreading from east-to-west. We interpret the existence of spatio-temporal clustering as evidence of spatio-temporal aggregation of PCVAD-positive cases above expectations and, together with the existence of spatio-temporal and spatial clusters, as suggestive of apparent local spread of PCVAD. Clustering was detected at small spatial and temporal scales. Other patterns of spread could not be detected; however, survival rates in discrete Ontario zones, as well as a lack of a clear spatial pattern in the most likely spatio-temporal clusters, suggest other between-herd transmission mechanisms.</p

Rapid Communication: A comparison of cardiac lesions and heart weights from market pigs that did and did not die during transport to one Ontario abattoir

In-transit losses of market hogs represent a small proportion of all market-weight pigs shipped in a year. This suggests that individual pig factors may be a significant cause of in-transit losses along with more traditionally considered environmental and transport factors. An investigation was performed to determine whether cardiac pathology and heart weights were associated with pigs that did or did not die during transport to an abattoir. The hearts from 70 pigs that died in-transit to one Ontario abattoir and 388 pigs that arrived alive were collected and examined. Hearts from pigs that died during transport demonstrated greater frequencies of cardiac lesions (P \u3c 0.05). These included hypertrophy of ventricle walls (Left: 97% vs. 64%; Right: 86% vs. 57%), dilation of ventricle chambers (Left: 79% vs. 0.5%; Right: 100% vs. 5%), and dilation of the pulmonary artery and aorta (59% vs. 1.5%). Total heart weight to body weight ratios were increased (3.6 vs. 3.3 g/kg) and left ventricle plus septum weight over right ventricle weight ratio was decreased in pigs that died during transport over non–in-transit loss pigs (2.5 vs. 2.8; P \u3c 0.05). This may indicate reduced cardiac function in hogs that died during transport. Pigs with reduced cardiac function would have exercise intolerance and be more susceptible to death during transport due to the increased cardiac workload required during sorting, loading, and transport of the pigs to the abattoir. Further research to quantify cardiac function in pigs with cardiac lesions or abnormal heart weight ratios is warranted

Human Noroviruses in Swine and Cattle

Detection of GII.4 norovirus sequences in animal fecal samples and retail meats demonstrates that noroviruses may be transmitted zoonotically