A descriptive study on spatial and temporal distributions of genetic clusters of porcine reproductive and respiratory syndrome virus infecting pig sites in Quebec, Canada, between 2010 and 2019

BACKGROUND

The wide diversity of porcine reproductive and respiratory syndrome virus (PRRSV) strains combined with incomplete heterologous cross-protection complicates the management of the disease at both the herd and the regional levels. The objectives of this study were to describe the spatial and temporal distribution of various PRRSV genetic clusters infecting pig sites in Quebec, Canada, and to compare PRRSV regional diversity of wild-type sequences over the years.

MATERIALS AND METHODS

A retrospective surveillance-based study was conducted on all pig sites which had PRRSV ORF5 sequences from field submissions transferred into the Laboratoire d'épidémiologie et de médecine porcine database from January 1, 2010 to December 31, 2019. A maximum likelihood phylogenetic tree inferred from multiple sequence alignment was used to identify genetic clusters. For each wild-type cluster gathering ≥ 15 sequences, the number of pig sites in which the cluster was detected per administrative region and per year were displayed on bubble charts and the spatiotemporal distribution of pig sites was illustrated using pie chart maps. A molecular analysis of variance was performed to compare PRRSV wild-type sequence diversity according to the administrative region for each year.

RESULTS

A total of 32 wild-type clusters gathering 1653 PRRSV2 sequences from 693 pig sites were described. Each cluster was detected on up to 132 pig sites and 7 administrative regions over the 10-year period. Annually, the mean (min-max) number of wild-type clusters detected in at least one pig site reached 24 (17-29). Some clusters remained localized on a few sites over time whereas others were widespread over the territory during a few or many years. For each year, regional differences were also observed in PRRSV diversity of wild-type sequences.

CONCLUSIONS

The differences observed in both the spatiotemporal distributions of PRRSV clusters and in the regional diversity of wild-type sequences highlight the importance of ongoing provincial surveillance to improve collective PRRS management strategies.

Contacts posing risks of disease introduction in swine breeding herds in Quebec, Canada: Is the frequency of contacts associated with biosecurity measures?

The introduction of pathogens into swine breeding herds can occur through a variety of contacts involving people, animals, vehicle or various supplies. Appropriate biosecurity is critical to mitigate these risks. A retrospective study was conducted to describe contacts with swine breeding sites over a one-month period and to evaluate their association with biosecurity measures and site characteristics. As part of a larger project, sites which had a recent porcine reproductive and respiratory syndrome virus introduction were selected. A questionnaire, logbooks and pig traceability system were used for collecting data relative to persons or supplies entering the breeding unit, live pig transportation, service vehicles, other animal species, neighboring pig sites and manure spreading around the site. The 84 sites investigated had a median sow inventory of 675. A median of 4 farm staff and 2 visitors entered the breeding unit at least once over the one-month period. A total of 73 sites (87%) received visitor(s), mostly from maintenance and technical services. All sites received at least 3 supply deliveries (median of 8) including semen (99% of sites), small material and/or drugs (98% of sites), bags (87% of sites), and/or equipment (61% of sites). Live pig movements were observed in all sites, with a median number of 5 truck entries on the site or exits from the site. For feed mill, rendering and propane trucks, at least one entry was noted in ≥ 61% of sites. For all service vehicle categories except feed mill and manure vacuum trucks, a single service provider was involved in each site. Dogs and cats were banned from all sites, but wild birds were observed in 8% of sites. Manure spreading within a 100 m radius of pig units was noted in 10% of the sites. With a few exceptions, biosecurity measures were not associated with the frequency of contacts. A 100-sow increase in sow inventory was associated with an increase of 0.34 in the cumulated number of staff entering the breeding unit, of 0.30 in the number of visitors and of 0.19 in the number of live pig movements. Live pig movements were also positively associated with vertically integrated farrow-to-wean (vs. independent farrow-to-wean) production and time interval of 4 weeks or more between farrowing (vs. less than 4). Considering the variety and frequency of contacts observed, biosecurity should be meticulously applied in all breeding herds to prevent endemic and exotic disease introduction.

Positioning Quebec ORF5 sequences of porcine reproductive and respiratory syndrome virus (PRRSV) within Canada and worldwide diversity

Sequencing of ORF5 gene is widely used and considered essential for diagnostics and control of porcine reproductive and respiratory syndrome (PRRS) in Canada. The objective of this study was to position Quebec ORF5 sequences of PRRS virus within Canada and worldwide diversity. Overall, 76.8% of the 5204 sequences gathered from Quebec (n = 5031), Ontario (n = 151) and Manitoba (n = 18) were classified into one of 34 genetic clusters defined as groupings including ≥15 sequences and having ≥70% rapid bootstrap support value from a maximum likelihood (ML)-phylogeny. Following the addition of PRRSV 2 international reference dataset from Shi et al. (2010), the most predominant lineages in our dataset were wild-type 1 and vaccine-like 5.1 (MLV) and 8.9 (ATP). No strains or only a very few (1 or 2) were assigned to lineages 1.3-1.5, 3, 4, 5.2, 6, 7 or 9. Most wild-type clusters (97%) detected in a dataset from Canada did not include any sequence from the international reference dataset. It might reflect recent subpopulations that were absent at the time of Shi's publication. As an example, cluster #25 first appeared in 2007, but since then had expanded considerably and is now the most prevalent wild-type cluster found in Quebec. A total of 117 RFLP patterns were identified and those were poorly correlated with genetic clusters based on phylogeny. Factors modulating PRRSV diversity such as pig movement that occurred within and between provinces should be further investigated in a perspective of disease control.

Impact of alignment algorithm on the estimation of pairwise genetic similarity of porcine reproductive and respiratory syndrome virus (PRRSV)

Background

Porcine reproductive and respiratory syndrome (PRRS) is a major threat to the swine industry. It is caused by the PRRS virus (PRRSV). Determination and comparison of the nucleotide sequences of PRRSV strains provides useful information in support of control initiatives or epidemiological studies on transmission patterns. The alignment of sequences is the first step in analyzing sequence data, with multiple algorithms being available, but little is known on the impact of this methodological choice. Here, a study was conducted to evaluate the impact of different alignment algorithms on the resulting aligned sequence dataset and on practical issues when applied to a large field database of PRRSV open reading frame (ORF) 5 sequences collected in Quebec, Canada, from 2010 to 2014. Five multiple sequence alignment programs were compared: Clustal W, Clustal Omega, Muscle, T-Coffee and MAFFT.

Results

The resulting alignments showed very similar results in terms of average pairwise genetic similarity, proportion of pairwise comparisons having ≥97.5% genetic similarity and sum of pairs (SP) score, except for T-Coffee where increased length of aligned datasets as well as limitation to handle large datasets were observed.

Conclusions

Based on efficiency at minimizing the number of gaps in different dataset sizes with default open gap values as well as the capability to handle a large number of sequences in a timely manner, the use of Clustal Omega might be recommended for the management of PRRSV extensive database for both research and surveillance purposes.

Porcine reproductive and respiratory syndrome virus: web-based interactive tools to support surveillance and control initiatives

Background

Control of porcine reproductive and respiratory syndrome (PRRS) represents a tremendous challenge. The trend is now toward managing the disease collectively. In Quebec, area and regional control and elimination (ARC&E) initiatives started in 2011; diagnostic testing, including ORF5 sequencing, and sharing of information among stakeholders are largely promoted. At the provincial level, a data-sharing agreement was signed by Quebec swine practitioners allowing PRRS virus (PRRSV) sequences to be transferred to a database maintained by the Laboratoire d'épidémiologie et de médecine porcine (LEMP-DB). Several interactive tools were developed and are available to veterinarians to allow comparison of PRRSV ORF5 sequences within ARC&E projects or provincially while managing confidentiality issues.

Results

Between January 1st 2010 and December 31st 2018, 4346 PRRSV ORF5 sequences were gathered into the LEMP-DB, involving 1254 sites and 43 practicing veterinarians. Approximately 34% of the submissions were from ARC&E projects. Using a novel web-based sequence comparison tool, each veterinarian has access to information on his/her client sequences and can compare each sequence with 1) commercial vaccine strains, 2) historical samples from the same site, and 3) all sequences submitted to the database over the last 4 years. Newly introduced PRRSV into breeding herds can be monitored using a new sequence comparison tool based on comparison of sequences at the provincial level. Each month, graphs providing the number of introductions per month and the yearly cumulative are updated. Between August 1st 2014 and December 31st 2018, 233 introductions were detected on 180 different breeding sites. Following a data-sharing agreement, veterinarians involved in ARC&E projects have access to an interactive mapping tool to locate pig sites, compare sequence similarity between participating sites and visualize the results on the map.

Conclusions

The structure developed in Quebec to collect, analyse and share sequencing data was efficient to provide useful information to the swine industry at both provincial and regional levels while dealing with confidentiality issues.

Aplasia Cutis Congenita (Epitheliogenesis Imperfecta) in Swine: Observations from a Large Breeding Herd

Epitheliogenesis imperfecta has been reported in several animal species, and its inheritance is suspected to be autosomal recessive. This term has been used to describe two different diseases, namely epidermolysis bullosa and aplasia cutis congenita, which are both grossly characterized by an absence of epidermis or mucosal epithelium and are most frequently reported on the distal limbs and oral cavity. Epitheliogenesis imperfecta has been described in swine, but the literature on the subject is scarce. To better characterize this condition, 70 piglets with congenital skin defects macroscopically compatible with epitheliogenesis imperfecta were examined. In all but 1 case, only 1 piglet per litter was affected. Of the affected piglets, 65 (93%) were male, suggesting a sex-related problem. More than half of the piglets had multiple skin lesions. All defects were located on the caudal half of the body, and none was found in the oral cavity. Most lesions were characterized by an absence of epidermis and part of the dermis and adnexae. Adnexal dysplasia was also observed at several sites, both with and without epitheliogenesis imperfecta, suggesting a developmental problem. Fluid-filled, congenital subcutaneous bullae were noted grossly on 7 piglets; their relationship, if any, with epitheliogenesis imperfecta remains unknown. As the term epitheliogenesis imperfecta has been used in cases of epidermolysis bullosa, the term aplasia cutis congenita seems to be more appropriate to describe these lesions in swine.

Pathology of ear hematomas in swine

The objectives of our study were to describe the pathology of ear hematomas in swine and to add to the comprehension of the pathogenesis of this condition. The pathogenesis of aural hematomas has been studied mainly in dogs; however, disagreements exist about the precise anatomic location of the hemorrhage. Sixteen pigs with ear hematoma at various stages of development were included in this study. The pigs were submitted for routine autopsy for various and unrelated reasons over a period of several years. Based on gross examination, the 16 cases of aural hematomas were subjectively classified as acute (n = 6), subacute (n = 3), and chronic (n = 7). The age of the animals at the time of autopsy ranged from 2 weeks to adulthood, with all acute cases being <7 weeks of age. Morphologic examination of all acute cases revealed that the hematoma developed predominantly in a subperichondral location on both sides of the cartilaginous plate simultaneously. Within these same cases, there were also some areas in which blood-filled clefts had formed within the cartilage itself. Besides fibroplasia, neoformation of cartilage was found to represent a significant part of the repair process. All chronic cases were characterized on cross-section of the ear by the presence of at least 2 distinct, wavy, focally folded, and roughly parallel plates of cartilage separated from each other by fibrous tissue.

The spread of type 2 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) in North America: a phylogeographic approach

The emergence and spread of Type 2 Porcine Reproductive and Respiratory Syndrome virus (Type 2 PRRSV) in North America is heavily influenced by the multiple site production system used in the hog industry. However, it is unclear how anthropogenic factors such has this have shaped the current spatial distribution of PRRSV genotypes. We employed Bayesian phylogeographic analyses of 7040 ORF5 sequences to reveal the recent geographical spread of Type 2 PRRSV in North America. The directions and intensities in our inferred virus traffic network closely mirror the hog transportation. Most notably, we reveal multiple viral introductions from Canada into the United States causing a major shift in virus genetic composition in the Midwest USA that went unnoticed by the regular surveillance and field epidemiological studies. Overall, these findings provide important insights into the dynamics of Type 2 PRRSV evolution and spread that will facilitate programs for control and prevention.

Alopecia areata and humpy-back syndrome in suckling piglets

This report describes an uncommon variant of humpy-back syndrome associated with multiple rib fractures and multisystemic vasculitis in several nursing piglets and, for the first time, a skin disease in swine consistent with alopecia areata. Both conditions were observed concurrently on the farm and occasionally in the same piglets.

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

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 were obtained for each site. ORF5 sequencing was attempted on PRRSV positive sites. Proportion of pairwise combinations of strains having ≥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.

Porcine reproductive and respiratory syndrome virus diversity of Eastern Canada swine herds in a large sequence dataset reveals two hypervariable regions under positive selection

Porcine reproductive and respiratory syndrome virus (PRRSV) is known to be genetically highly variable, but knowledge of sequence diversity from Eastern Canada and its degree of genetic plasticity in or near the principal neutralizing epitope (PNE) in association with evolutionary selective pressure is limited. The purposes of our study were to investigate the extent of strain diversity, the existing glycotypes and the amino acid sites under selective evolutionary pressure in its encoded protein, GP5, for a dataset of 1301 sequences (1998-2009). This was addressed by partitioning and clustering into subgenotypes a large number of open reading frame 5 sequences from the province of Quebec and analyzing the content of these subgenotypes. The overall pairwise diversity was 12% and was comparable to what has been reported around the world. The mean diversity for sequences within subgenotypes was around 7%. No marked variations in subgenotype emergence could be observed through time. Thirty-eight GP5 glycotype patterns were observed which included a newly identified site at position N57 which was already present in 1998. These patterns possessed one to six N-glycosylation sites in total and could be located in eight different positions. No obvious grouping of glycotypes could be established in relation to subgenotypes. Positions N44 and N51 were confirmed to be fixed N-glycosylation positions, whereas other positions where found to be shifting and located in or near hypervariable regions (HVRs) 1 and 2. Both HVRs were under selective evolutionary pressure in half of all subgenotypes including vaccine-like groups. Conversely, the PNE flanked by both HVRs was well conserved among most subgenotypes demonstrating potential molecular constraint in a probable viral binding region. The analysis of this dataset increased knowledge of evolutionary change inferred from genetic data, more specifically regarding the implications of both HVRs in PRRSV diversity.

Risk factors at slaughter associated with presence of Salmonella on hog carcasses in Canada

Despite the application of hazard analysis and critical control point systems at slaughter and during processing, Salmonella contamination is still a significant biological hazard associated with pork products. A better understanding of risk factors in slaughterhouses and of contamination sources is therefore critical to improve control of this bacterium in the abattoirs. The objectives of this study were to identify the risk factors at slaughter that are associated with the presence of Salmonella on hog carcasses and to assess possible sources of contamination. A questionnaire on potential risk factors was developed. Over 7,400 hogs originating from 312 randomly selected production lots were tested. The lots were from 10 different abattoirs located in five different Canadian provinces. At slaughter, blood was collected for serological analysis, and mesenteric lymph nodes (MLN) and carcass swabs were collected for Salmonella analysis. Furthermore, pulsed-field gel electrophoresis was conducted to establish the genetic profiles of selected isolates from carcasses and MLN and to compare these profiles with those recovered from the slaughter environment. Multivariate regression analysis results indicated that the cleanliness of the hogs and the status of the scald water were factors significantly associated with the Salmonella status of the carcasses at the end of the slaughter process. Pulsed-field gel electrophoresis analysis showed that most isolates from carcasses were similar to those from animals (MLN) or the preevisceration environment.

Epidemiology of Streptococcus suis serotype 5 infection in a pig herd with and without clinical disease

The aim of this study was to describe the transmission and the kinetics of the infection caused by Streptococcus suis serotype 5 in a multisite farrow-to-finish pig herd. Most sows carried S. suis serotype 5 in their vaginal tract, but not in their nasal cavities, as demonstrated by immunomagnetic separation (IMS) technique. Their offspring became infected during farrowing, confirming vertical transmission. During the first 4 weeks of life, a low number of piglets were carriers of S. suis serotype 5 in their nasal cavities. However, when clinical signs appeared, the carrier rate significantly increased, suggesting that isolation from nasal cavities is a better indication of active transmission than of a carrier state. Clinical cases were present in animals between 4 and 8 weeks of age, when maternal antibodies were at their lowest level. Up to six different genotypes of the same serotype could be identified by random amplified polymorphic DNA; however, a single clone was responsible for all clinical cases studied. This clone could only be isolated from a single sow, indicating that its prevalence in breeding animals was low. Interestingly, 1 year later, clinical disease associated with S. suis serotype 5 spontaneously disappeared. At that time, the genotype responsible for the clinical signs was not detected in the herd and the levels of antibodies in sows and maternal antibodies in piglets were not higher than those of the previous year.

Molecular epidemiology of porcine reproductive and respiratory syndrome virus (PRRSV) in Québec

Porcine reproductive and respiratory syndrome virus (PRRSV) strains identified in samples from 226 field cases originating from Québec herds and submitted over a 4-year period (March 1998-July 2002) were studied. Sequencing of PRRSV strains was performed on the ORF5 gene amplified product and restriction fragment length polymorphism (RFLP) patterns for enzymes MluI, HincII and SacII were determined on these sequences. Twenty-four other PRRSV isolates including three vaccine strains were also included for comparison purposes and the total of 250 PRRSV strains were used in a phylogenetic analysis. Clinical and epidemiological data were collected through a questionnaire for each of the submitted field cases. About 75% of the cases were submitted during autumn and winter. Over 60% of the cases were submitted for reproductive problems, 33% for respiratory problems and 6% for increased PRRSV serological titers in the herd in absence of clinical signs. In 69% of the cases there was a PRRS vaccination program for the herd. However, only 26% of the animals from which samples were obtained had been vaccinated themselves. The genomic analysis of this large number of strains revealed a great variability of PRRSV ORF5 with 59% of amino acid positions being polymorphic. A total of 29 RFLP patterns were obtained. The main RFLP patterns obtained were 1-8-4 (28%), 1-4-4 (16%), 1-2-4 (9%) and 1-11-4 (9%). The global findings derived from the molecular analysis of 226 PRRSV strains suggest that PRRSV circulating in Québec represent a different sub-population of strains. Vaccine-like strains were identified in 10% of the cases. A phylogenetic tree enabled the identification of 44 groupings comprising two to 23 strains each. Of the 250 sequences analyzed, 183 (73%) could be included in one of these groupings. The data collected from the questionnaires were used to establish epidemiological links between strains within groupings. The main relationships between strains within a grouping were the introduction of infected animals (19%) and area spread (33%). In 40% of the cases from which an area spread was suspected, herds were located within 3 km from another. Aerosol transmission was suspected in several cases, more than half of which belonged to different owners. In 41 herds, more than one strain (2-8) were identified over a period varying from 3 months to 4 years. Data indicated that a PRRSV strain can persist in a herd up to 3.5 years displaying as little as 2% variation in ORF5 during this time. In 78% of the herds with multiple submissions genetically different strains were identified; often within 1 year of the original identification. These genetically distinct strains were often associated with a recrudescence of moderate to severe clinical signs. Coexistence on the same farm of different PRRSV strains was also observed.

Comparative serologic and virologic study of commercial swine herds with and without postweaning multisystemic wasting syndrome

A comparative serologic and virologic study was performed in pigs from 5 herds with postweaning multisystemic wasting syndrome (PMWS) and 2 herds without PMWS in Quebec. In each herd, 60 blood samples were collected at 4-wk intervals from pigs from 3 to 23 wk of age. The serum was evaluated for the presence of antibodies to porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV), as well as for the presence of nucleic acid of PCV2, PRRSV, an porcine parvovirus (PPV), by means of the polymerase chain reaction (PCR). Serologic profiles for PCV2 were very similar in 6 of the 7 herds, including the 2 without PMWS, and were characterized by a gradual decrease in antibody titres from 3 until 11 wk of age, followed by seroconversion at 15 wk, and high PCV2 antibody titres thereafter in all pigs. Only starting at 11 to 15 wk of age could PCV2 viremia be detected, except in 1 herd, in which clinical signs were observed at 6 to 7 wk of age. A PCV2 viremia could be detected within the same pigs for a minimum of 8 wk, and the virus could still be detected in 41% of the serum samples obtained at 23 wk of age. The antibody level did not appear to influence the occurrence of disease, since titres were similar in pigs in the herds with or without PMWS. Infection with PRRSV, as demonstrated by PCR and seroconversion, preceded that of PCV2 by at least 1 mo in both types of herd. Both PRRSV and PCV2 were detected in some pigs in 5 of the 7 herds, including 1 herd without PMWS. Porcine parvovirus could be detected in serum by PCR in 2 herds with PMWS after the onset of clinical signs and also in 1 herd without PMWS. Genomic analysis of PCV2 strains identified in the herds without PMWS indicated complete or very high homology (99.4% to 100%) with the PCV2 strains identified in 4 herds with PMWS. In our field study, the triggering of PMWS in the herds could not be linked to coinfection with either PRRSV or PPV or to the use of a specific immunostimulant, such as vaccines, or to particular genomic differences between the PCV2 strains identified.

Genetic characterization and phylogenetic analysis of porcine circovirus type 2 (PCV2) strains from cases presenting various clinical conditions

Porcine circovirus type 2 (PCV2) has been associated with a newly identified and described disease in swine called the postweaning multisystemic wasting syndrome (PMWS). An association of PCV2 with various other clinical conditions in pigs are also increasingly being reported. To date molecular studies to determine the extent of genetic variations of this virus have been limited. To more fully understand the extent of genetic diversity we report the sequencing of 34 PCV2 strains from Eastern Canada originating from a variety of clinical conditions spanning years 1990-2001 along with the phylogenetic analysis of these strains and that of 36 PCV2 sequences published in GenBank. Sequence analysis of the complete genome indicated that the Canadian PCV2 strains analyzed in the present study are closely related to each other but also to other PCV2 strains originating from Western Canada, US, Europe and Asia. Sequence analysis of ORF1 and ORF2 genes of the 34 strains revealed that the extent of nucleotide variation was greater for the ORF2 than for the ORF1. The amino acid sequences alignment of the PCV2 capsid protein identified three major regions of amino acid heterogeneity, two of which correspond with dominant immunoreactive areas. No repeatable amino acid motifs for these two regions could be associated with PCV2 strains identified from cases of PMWS or other clinical conditions. Phylogenetic analysis of all 70 strains revealed one large cluster composed of strains from Europe, Taiwan, China and Canada. This large cluster could be divided in several sub clusters, in two of which Canadian strains were found closely related to strains from Germany. The remaining strains from Canada and the US were spread in small groupings along the phylogenetic tree and an association with geographic origin could not be established. The genomic characterizations performed in this study indicate that PCV2 strains associated with PMWS are scattered throughout the phylogenetic tree often in groupings including PCV2 strains identified from cases other that PMWS such as, porcine reproductive and respiratory syndrome (PRRS), generalized tremors, porcine dermatitis and nephropathy syndrome (PDNS), arthritis, nervous signs, erysipelas and even healthy pigs.

Infectious agents identified in pigs with multifocal interstitial nephritis at slaughter

One kidney was taken from each of 100 pigs at slaughter; 50 had gross lesions of multifocal interstitial nephritis and 50 had no gross lesions. Forty-nine of the affected kidneys had lesions that were characterised by the presence of either a few randomly distributed or numerous widely disseminated pale foci, 1 to 3 mm in diameter, on the cortical surface (white-dotted kidneys). Microscopically, these focal inflammatory lesions often had a distinct lymphofollicular pattern (follicular nephritis). Lesions of chronic vasculitis were observed in 21 of the affected kidneys. Histologically, the control kidneys had only small and sparse inflammatory foci. Standard bacterial cultures of kidneys of both groups were not significant, and cultures for the isolation of leptospires were all negative. Virological examination of the kidney homogenates by PCR did not reveal any porcine reproductive and respiratory syndrome virus and only a few cases were positive for the porcine circovirus type 1. However, porcine parvovirus (PPV) and porcine circovirus type 2 (PCV-2) were detected in many kidneys of both groups but in a significantly higher proportion of the kidneys with interstitial nephritis. There was a significant association between the lesions and the presence of PPV and PCV-2 with odds ratios of 7.5 (P<0.0001) and 3.4 (P=0.0074), respectively, and the odds ratio increased to 22.7 (P<0.0001) when both viruses were identified in the same kidney. However, a subsample of kidneys taken from both groups were negative by immunohistochemistry for the presence of PPV and PCV-2 antigens.

Antibody response to an autogenous vaccine and serologic profile for Streptococcus suis capsular type 1/2

An autogenous vaccine was developed, using sonicated bacteria, with a strain of Streptococcus suis capsular type 1/2. The objectives of this study were to evaluate the antibody response following vaccination and to assess the changes in antibody levels in pigs from a herd showing clinical signs of S. suis capsular type 1/2 infection in 6- to 8-week-old pigs. An enzyme-linked immunosorbent assay using the vaccine antigen was standardized. Results from a preliminary study involving 2 control and 4 vaccinated 4-week-old pigs indicated that all vaccinated pigs produced antibodies against 2 proteins of 34 and 43 kDa, respectively, and, in 3 out of 4 vaccinated pigs, against the 117-kDa muramidase-released protein. For the serologic profile, groups of 30 pigs from the infected herd were blood sampled at 2, 4, 6, 8, and 10 weeks of age. The lowest antibody level was observed between weeks 6 and 8, presumably corresponding to a decrease in maternal immunity. A marked increase was seen at 10 weeks of age, shortly after the onset of clinical signs in the herd. For the vaccination field trial, newly weaned, one-week-old piglets were divided into 2 groups of 200 piglets each (control and vaccinated); blood samples were collected from 36 piglets in each group at 2-week intervals for 12 weeks. A significant increase (P < 0.05) in antibody response was observed 4 weeks following vaccination and the level of antibodies stayed high until the end of the experiment. In the control group, the increase was only observed at 13 weeks of age, probably in response to a natural infection. The response to the vaccine varied considerably among pigs and was attributed, in part, to the levels of maternal antibodies at the time of vaccination. No outbreak of S. suis was observed in the control or vaccinated groups, so the protection conferred by the vaccine could not be evaluated.

Serologic profile of a cohort of pigs and antibody response to an autogenous vaccine for Actinobacillus suis

Actinobacillus suis is a commensal opportunistic pathogen in swine. However, in recent years, an increasing prevalence of clinical signs associated with A. suis has been observed in high health status herds in North America. The objectives of the study were to assess the kinetics of antibodies to A. suis in pigs from a herd showing clinical signs of A. suis infection and, to evaluate the antibody response in gilts following vaccination with an autogenous vaccine. An enzyme-linked immunosorbent assay (ELISA) using a saline extract of boiled-formalinized whole cells of a field strain as the coating antigen was standardized. This ELISA was used as a tool for monitoring, in a comparative way, the variations in A. suis antibody levels. The herd selected for the serologic profile was negative for Actinobacillus pleuropneumoniae infection and showed clinical signs of A. suis infection in 16 to 19-week-old pigs. A cohort of 20 pigs was blood sampled at 5, 8, 12, and 16 weeks of age. The lowest level of serum antibodies was observed between weeks 8 and 12, this probably corresponding to a decrease in maternal immunity. A marked increase in the antibody response was seen at 16-week of age, at the approximate time of onset of A. suis clinical signs in the herd. The evaluation of serum antibody responses to an autogenous vaccine revealed that the humoral immunity of gilts further increased following vaccination although the level of antibodies was already high prior to vaccination. The magnitude of the response to vaccination was higher when the level of antibodies was low prior to the first injection. The ELISA test seems to detect antibodies against the O-chain LPS.

Cutaneous and systemic necrotizing vasculitis in swine

A systemic vasculitis involving particularly the skin and kidneys has been recently described in swine under the name dermatitis/nephropathy syndrome. Twelve pigs with gross cutaneous lesions typical of this condition were necropsied, and morphologic, immunohistochemical, microbiologic, and epidemiologic characteristics were studied. The pigs were divided into three groups comprising eight pigs with acute lesions, two with chronic lesions, and two with acute lesions kept for sequential skin biopsies. Acute skin lesions consisted of round to irregular, red to purple macules and papules that often coalesced to form large, irregular patches and plaques. With time, the lesions became covered by crusts and faded gradually, sometimes leaving scars. Characteristic distribution included the perineal area of the hindquarters, limbs, dependent parts of the abdomen and thorax, and margins of the ears. In the acute phase of the disease, necrotizing and leucocytoclastic vasculitis of small-caliber blood vessels were observed within the dermis and panniculus and in various extracutaneous locations such as the renal pelvis and synovial membranes. All pigs had macroscopic evidence of pneumonia and generalized lymphadenopathy. Microscopically, they had interstitial pneumonia and perivascular cuffing of mononuclear cells in various tissues including skin. The presence of immunoglobulins and complement was demonstrated by immunofluorescence in and around necrotic vessels of the skin in the early stages. Porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) antigens were detected by immunohistochemistry in macrophages located around vessels of the tissues examined (skin and kidneys) in acute and chronic cases. PRRSV RNA was demonstrated by reverse transcription-polymerase chain reaction in lung and spleen homogenates from all pigs. The PRRSV was isolated in cell culture from 11 of the pigs. These findings suggest that PRRSV infection may play a role in the pathogenesis of this systemic vascular disease of swine.

Development of an immunomagnetic method for selective isolation of Actinobacillus pleuropneumoniae serotype 1 from tonsils

An immunomagnetic separation technique (IMS) for the selective isolation of Actinobacillus pleuropneumoniae serotype 1 was developed. Superparamagnetic polystyrene beads (immunomagnetic beads [IMBs]) were coated with purified rabbit immunoglobulin G specific for A. pleuropneumoniae serotype 1. The antibody concentration, the number of IMBs, the incubation time, and the temperature of incubation influenced the recovery of the target bacteria. The sensitivity of the IMS technique was 1,000-fold higher than that of direct culture. When tonsils from animals from infected herds were tested, significantly more positive tonsils were detected by the IMS technique (68%) than by the standard procedures (22%). The method represents an innovative and highly sensitive approach for the isolation of A. pleuropneumoniae from carrier animals.

Psychodemographic profile of stockpeople working on independent and integrated swine breeding farms in Quebec

As a part of a larger study, the psychodemographic profile of Quebec pig stockpeople was described based on a sample of 48 persons working on independent farms randomly selected in the Richelieu-Saint-Hyacinthe region, and on a convenience sample of 38 others employed by 5 organizations of integrated swine production chosen among the largest ones in Québec. The 2 groups of stockpeople were described separately because of the differences between the 2 types of production. Demographic data (age, sex, level of education, training and experience in swine production, seniority on the farm) were obtained through a face-to-face interview. The personality profile was assessed using a standard personality test (French translation of the Sixteen Personality Factor Questionnaire). Both the stockpersons on independent farms and those employed by the organizations were more reserved, emotionally stable, serious, conscientious, unsentimental, controlled, introverted, and less anxious than the average person in the general population. However, multivariate analyses revealed some differences between these two groups of stock-persons (P = 0.021) as well as between the employees of the different organizations (P = 0.0038). These differences in personality profiles may reflect differences in working conditions, particularly regarding the human relationships, and in corporate cultures of the organizations.

Detection of antibodies against Streptococcus suis capsular type 2 using a purified capsular polysaccharide antigen-based indirect ELISA

In the present study a purified capsular polysaccharide antigen-based indirect ELISA (CPS-ELISA) to detect antibodies against Streptococcus suis capsular type 2 was developed and compared with a whole cell antigen-based ELISA (WCA-ELISA). The WCA-ELISA presented a very low specificity when rabbit antisera to other capsular types were tested. Most of these cross-reactions were due to common proteins. The standardized CPS-ELISA gave satisfactory results using a concentration of 0.1 micrograms/well; most cross-reactions decreased significantly, with some exceptions, such as those shared by capsular types 1/2, 12 and 17. These cross-reactions were mainly due to common epitopes present in the capsule, as shown by immunoblotting. In a second experiment, the CPS-ELISA was used to detect antibodies in experimentally infected piglets. Despite the fact that capsular type 2 S. suis could be reisolated from all infected animals during and/or after the trial, antibody titers against a second infection. Sera from piglets experimentally infected were completely protected against a second infection. Sera from piglets experimentally infected with S. suis capsular types 1/2 or 12 presented cross-reactions at low dilutions, confirming data previously obtained with rabbit sera. Finally, sera of animals from herds with clinical signs associated with S. suis capsular type 2 did not present titers significantly different from those of disease free herds. From our results we concluded that the CPS-ELISA developed in this study can not be used as a diagnostic tool to identify infected animals.

Survey of management and housing in farrowing quarters among independent and integrated swine farms in Québec

Forty-eight randomly selected owner-operated swine breeding farms (independent farms) and 38 belonging to 5 integrated organizations specializing in swine production chosen from the largest in the province of Québec (integrated farms) were separately described regarding their general characteristics, sow feeding, management practises, and housing features in farrowing quarters. The parallel description of these 2 groups of farms aids in understanding what is done in the field. It also provides insight into potential differences between independent and integrated farms. Generally speaking, production tended to be more specialized and concentrated in integrated organizations. Specifically, more new practises seemed to have been adopted on the integrated farms, and their stockpersons seemed to have a more proactive style of management in farrowing quarters. Increased size of operations, proximity of information sources, profits yielded by new practises, and ease of implementation are discussed as explanations for this higher rate of adoption of new techniques among the organizations. These differences between the independent farms and the integrated organizations appeared to be all related to basic differences in their respective sizes. Although some differences were observed within, as well as between, each organization, many similarities were found across the majority of farms within each organization, thus supporting the existence of policies specific to each organization. Although these findings have to be confirmed before being generalized, they tend to suggest that independent swine farms and integrated organizations should be considered differently.

Feeding strategies during the lactation period for first-parity sows

The effects of different feeding regimes during the lactation period on feed intake, body reserves and sow performance were evaluated. A 2 × 2 factorial design was used and 183 first-parity sows were randomly allocated to one of four treatments: sows were fed either two or three meals per day with (wet feed) or without (dry feed) supplemental water at meal time. Primrparous sows were fed ad libitum 12–16 h after parturition. The addition of water at meal time increased (P < 0.01) feed consumption by 5% over the 18-d lactation period. Increased feeding frequency did not influence feed intake. During the first week of lactation, most sows gained weight, but thereafter lost weight, with the rate of weight loss reaching a peak during the last week of lactation. Although feed intake was influenced only by wet feeding, both an increased frequency of daily meals and the use of wet feeding reduced mobilization of body reserves. Wet-fed sows lost less weight than dry-fed sows and the increased feeding frequency reduced backfat loss. Average daily gain of piglets, percentage of sows with a weaning-to-estrus interval of less than 7 d, farrowing rate, and parity-2 litter size were similar among the four groups. A lack of significant improvement in sow performance with different regimes may be partly related to a generally high feed intake and minimal weight and backfat losses. Although our results failed to show a benefit on sow performance, we believe that some of the feeding strategies evaluated could be useful during periods in which sows eat less, such as in the summer, or in some herds that have feed consumption problems. Key words: Sow, feed intake, weight, backfat, reproductive performance

Optimizing longevity in sows and boars

Longevity of sows and boars affects the productivity and economics of the herd. Implement a culling program that is tailored to the specific needs of the producer and the characteristics of the farm. Evaluate the removal policies regularly, estimate the longevity of breeding animals, calculate the nonproductive sow days associated with culling, and determine the major causes of culling and death. Once a longevity problem and its extent have been identified, the underlying problems and predisposing factors can be more easily corrected.

Some observations on cardiac failure in sows

Data pertaining to factors associated with cardiac failure were collected as part of a study on sow mortality in which cardiac failure was the major cause of death. A total of 116 sows from 24 herds was used and divided into two groups: group 1 comprised sows dead of cardiac failure (n = 43), and group 2, sows dead of other causes (n = 73). Individual sow records, clinical history, backfat thickness, body weight, heart weight, selenium content in liver, and urea concentration in aqueous humor were obtained for each sow. Results from the groups were compared using Student's t-test. Maximum and minimum outside daily temperatures were obtained for the study period. A stressful or demanding event for the cardiovascular system of sows was identified in 84% of the cases of cardiac failure: nearly two-thirds of the cases occurred during the peripartum period, and other stressful events included heat, fighting, mating, and transport. More than 40% of the cardiac failures occurred during the months of July and August. Sows dead of cardiac failure were heavier and fatter than sows dead of other causes. The former group also had a significantly smaller heart weight to body weight ratio; this difference was attributed to a greater body weight since the heart weights were similar in the two groups. The hepatic selenium contents and urea concentrations in aqueous humor were not significantly different between the two groups.

A prospective study of sow mortality in breeding herds

This investigation was conducted to study the incidence and the causes of sow mortality in breeding herds. Data were obtained from 24 swine breeding herds with an average inventory of 3755 sows and served gilts for the total sample. Producers were involved for 12 consecutive months and agreed to submit to the diagnostic laboratory every dead or moribund sow and served gilt. The average herd death rate was 3.3% +/- 0.5 (SEM), but varied considerably among herds, ranging from 0% to 9.2%. A total of 137 sows and mated gilts died during the year, and these females had produced an average of 4.2 litters +/- 0.2 (SEM). The number of deaths was significantly higher during the months of July, August and October. The peripartum period appeared to be when sows were most at risk, with 42% of all deaths occurring during this short period of the reproductive cycle. The three major causes of death were heart failure (31.4%), torsions and accidents of abdominal organs (15.3%) and cystitis-pyelonephritis (8.0%). Other causes included endometritis (6.6%), uterine prolapses (6.6%), pneumonia (3.6%), gastric ulcers (3.6%), downer sow syndrome (2.2%), miscellaneous (8.0%) and unknown (14.6%).

Boar culling in swine breeding herds in Minnesota

This investigation was conducted to study boar culling patterns in swine breeding herds. Data were obtained from 84 swine breeding herds and included 440 boars that were culled. Each producer was involved for 12 consecutive months, and recorded every boar that was removed from the herd, the date, and the reason for culling. The annual culling rate for the 84 farms averaged 59.4% +/- 6.4 (SEM). The correlation coefficient between boar and sow culling was 0.52 (p <0.0001). Removal was the result of being overweight (47%), reproductive problems (18%), leg problems (12%), death (7%), and other diseases (4%). From the annual culling rate, the average breeding life of boars was estimated at 20 months. From this study, we concluded that the annual culling rate for boars in commercial herds was high and related to several different factors.

The evaluation of postmortem ocular fluid analysis as a diagnostic aid in sows

This study was undertaken to evaluate the diagnostic usefulness of postmortem ocular fluid analysis in estimating the antemortem status of various serochemical constituents. Chemical values of serum and aqueous and vitreous humors were compared following different procedures. A blood sample and the 2 eyes were collected from each of 100 sows at a nearby abattoir. The results obtained from immediate centrifugation of ocular fluids after sampling were compared with those samples in which centrifugation was delayed by 2 hours. Two different postmortem intervals were used for sampling ocular fluids, 2 and 24 hours. Concentrations of urea, calcium, phosphorus, potassium, sodium, and chloride were determined from serum and humors. Delayed centrifugation did not affect chemical values of ocular fluids nor the relationships between serum and humors. Phosphorus and potassium values increased significantly with the postmortem interval in both aqueous and vitreous humors. The relationships between chemical values of ocular fluids and serum were determined using simple linear regression. There was a poor correlation between ocular fluid and serum values for all electrolytes; a significant correlation was found only for urea concentrations in both humors.

Culling patterns in selected Minnesota swine breeding herds

This investigation was conducted to study culling patterns in swine breeding herds. Data were obtained from 89 Minnesota swine breeding herds and included 5918 sows and 1324 gilts for a total of 7242 culled femaled. Each producer was involved for 12 consecutive months. They were asked to record every female that was removed from the herd, the reason for its culling and its parity. The annual culling rate for the sample averaged 50%, but varied considerably between herds ranging from 15% to 85%. Culled females had produced an average of 3.77 litters. Half of the females culled did not produce more than three litters. Reproductive failure accounted for 32% of all removals. The average parity of the females culled in that category was only 2.37: almost 33% were gilts. Failure to conceive represented 75% of all females culled for reproductive failure. Proportionally, culling as a result of anestrus was higher in gilts. It accounted for 33% of all gilts culled for reproductive failure which was twice as much as for sows. Inadequate performance accounted for 17% of all removals. These sows had produced an average of 5.11 litters. These results indicated that few animals were culled on the basis of first litter performance. Old age comprised 14% of all removals and the average parity at culling for this category was 7.11. Death accounted for 12% and the average parity for these females was 3.40. Locomotor problems and peripartum problems were the cause of 28% and 23% of all deaths, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological responses to treadmill exercise and ambient temperature in normal and malignant hyperthermia susceptible pigs

Ten susceptible and ten resistant pigs to malignant hyperthermia were used to observe the effects of exercise and ambient temperature on selected physiological parameters. Pigs were submitted to a ten minute exercise on a treadmill operating at a speed of 1.8 km/h and inclined to 11 degrees. Exercise in the first group was at an ambient temperature of 14 degrees C, and in the second at 29 degrees C. The right carotid artery was previously cannulated for blood pressure measurements and for repeated blood sampling during exercise. Arterial pressure, heart rate, rectal and cutaneous temperatures were recorded. Levels of cortisol, creatine kinase and its isoenzymes were measured. At 14 degrees C, exercise caused some physiological adjustments in susceptible animals; heart rate, skin temperature and cortisol levels increased (P less than 0.05). In resistant pigs, only the heart rate was elevated significantly following exertional stress at 14 degrees C. Exercise at 29 degrees C produced severe stress and marked physiological changes: heart rate, rectal and skin temperatures and cortisol levels increased significantly in both susceptible and resistant swine. At 29 degrees C, susceptible pigs also had higher levels of serum cortisol, total creatine kinase and MM isoenzyme (P less than 0.05) compared to resistant pigs. The results indicate that, following exertional or thermal stress, susceptible pigs undergo more extensive physiological changes than do resistant pigs. Similar levels of stress prior to slaughter may trigger physiological changes which in the susceptible pigs would likely result in pale, soft exudative myopathy.