Porcine Reproductive And Respiratory Syndrome Virus Status Research Articles

Assessment of changes in antibiotic use in grow-finish pigs after the introduction of PRRSV in a naïve farrow-to-finish system

Responsible antibiotic usage (ABU) is crucial for both animal and human health and requires constant improvement of antimicrobial stewardship (AMS). The presence of porcine reproductive and respiratory syndrome virus (PRRSV), a viral pathogen with immunosuppressive effects on swine, can intensify bacterial co-infections, alter antibiotic pharmacokinetics, and potentially lead to increased ABU. This study aimed to measure ABU changes in the grow-finish population associated with PRRSV infection and describe the antibiotic classes employed to manage clinical signs from a farrow-to-finish genetic multiplier system. Three PRRSV statuses (naïve, positive epidemic, and positive endemic) were established to classify the lots based on PRRSV circulation, with a total of 135,063 animals evaluated. The number of pig treatments per animal days at risk (PTDR) was calculated by administration route to quantify ABU across PRRSV status using negative binomial regression and non-parametric tests (P-value < 0.05). Moreover, to improve ABU comparability in the international scenario, the milligrams per population correction unit (mg/PCU) was calculated according to the European Medicines Agency guidelines. In the nursery phase, there was a statistically significant difference between PRRSV statuses for the overall PTDR (injectable and water routes of administration), with an ABU increase of 3.79 and 2.51 times the naïve PTDR for positive epidemic and endemic status, respectively. For the finishing phase, there was a statistically significant difference between PRRSV statuses in the injectable PTDR, with an ABU increase of 2.74 and 2.28 times the naïve PTDR level for positive epidemic and endemic statuses, respectively. In the nursery phase, the mean mg/PCU was 22.27 mg/PCU for naïve, 86.71 for positive epidemic, and 33.37 for positive endemic statuses; in the finishing phase, 81.31, 76.55, and 67.09 mg/PCU, respectively. The most frequently injected antibiotic in the nursery phase was ampicillin, with 49 % of total injections, followed by lincomycin (31 %) and enrofloxacin (20 %), and in the finishing phase, 72 % of injections were lincomycin, followed by enrofloxacin (28 %). The results highlight that the PRRSV outbreak in the source was associated with a grow-finish ABU increase, revealing the importance of preventing PRRSV infection to potentially decrease ABU and improve AMS within swine production systems.

Exploring Serum Copeptin and Hematological Profile: A Comparative Analysis after Intradermal versus Intramuscular Porcine Reproductive and Respiratory Syndrome Virus Vaccination in Piglets

This study aimed to investigate the impact of intradermal (ID) and intramuscular (IM) vaccination with a porcine reproductive and respiratory syndrome virus (PRRSV)-modified live vaccine (MLV) in piglets on serum copeptin levels and hematological profile. This study included 104 suckling piglets (2 weeks of age) from a commercial farrow-to-finish pig farm suffering from positive unstable PRRSV status. Animals were assigned to four groups, with two replicates (13 piglets/group/replicate); group A: IM vaccination with a PRRSV MLV vaccine, group B: ID vaccination with the same vaccine, group C: ID of Diluvac Forte, and group D: IM of Diluvac Forte. Blood samples were collected from the same three pigs/group/replicate at 4, 7, and 10 weeks of age. Blood samples were used for the performance of the complete blood count, and they were also examined by PCR for PRRSV and by ELISA for copeptin. No significant differences in serum copeptin levels and the number of blood cell counts (packed cell volume—PCV, numbers of white blood cells—WBCs, and platelets number—PLTs) were noticed in the same group over time and among groups. In conclusion, it seems that the vaccination against PRRSV does not affect the levels of the released copeptin. Based on our results, the measurement of serum copeptin could not be proposed as a potential stress biomarker in pigs.

Evaluation of a Porcine Endogenous Reference Gene (Internal Sample Control) in a Porcine Reproductive and Respiratory Syndrome Virus RT-qPCR.

Endogenous reference genes are used in gene-expression studies to "normalize" the results and, increasingly, as internal sample controls (ISC) in diagnostic quantitative polymerase chain reaction (qPCR). Three studies were conducted to evaluate the performance of a porcine-specific ISC in a commercial porcine reproductive and respiratory syndrome virus (PRRSV) reverse transcription-qPCR. Study 1 evaluated the species specificity of the ISC by testing serum from seven non-porcine domestic species (n = 34). In Study 2, the constancy of ISC detection over time (≥42 days) was assessed in oral fluid (n = 130), serum (n = 215), and feces (n = 132) collected from individual pigs of known PRRSV status. In Study 3, serum (n = 150), oral fluid (n = 150), and fecal samples (n = 75 feces, 75 fecal swabs) from commercial herds were used to establish ISC reference limits. Study 1 showed that the ISC was porcine-specific, i.e., all samples from non-porcine species were ISC negative (n = 34). In Study 2, the ISC was detected in all oral fluid, serum, and fecal samples, but differed in concentration between specimens (p < 0.05; mixed-effects regression model). The results of Study 3 were used to establish ISC reference limits for the 5th, 2.5th and 1.25th percentiles. Overall, the ISC response was consistent to the point that failure in detection is sufficient justification for re-testing and/or re-sampling.

Evaluating oral swab samples for PRRSV surveillance in weaning-age pigs under field conditions.

The use of serum and family oral fluids for porcine reproductive and respiratory syndrome virus (PRRSV) surveillance in weaning-age pigs has been previously characterized. Characterizing more sample types similarly offers veterinarians and producers additional validated sample options for PRRSV surveillance in this subpopulation of pigs. Oral swab sampling is relatively easy and convenient; however, there is sparse information on how it compares to the reference sample type for PRRSV surveillance under field conditions. Therefore, this study's objective was to compare the PRRSV reverse-transcription real-time polymerase chain reaction (RT-rtPCR) test outcomes of oral swabs (OS) and sera samples obtained from weaning-age pig litters. At an eligible breeding herd, six hundred twenty-three weaning-age piglets from 51 litters were each sampled for serum and OS and tested for PRRSV RNA by RT-rtPCR. PRRSV RT-rtPCR positivity rate was higher in serum samples (24 of 51 litters, 83 of 623 pigs, with a mean cycle threshold (Ct) value of RT-rtPCR-positive samples per litter ranging from 18.9 to 32.0) compared to OS samples (15 of 51 litters, 33 of 623 pigs, with a mean Ct of RT-rtPCR positive samples per litter ranging from 28.2 to 36.9); this highlights the importance of interpreting negative RT-rtPCR results from OS samples with caution. Every litter with a positive PRRSV RT-rtPCR OS had at least one viremic piglet, highlighting the authenticity of positive PRRSV RT-rtPCR tests using OS; in other words, there was no evidence of environmental PRRSV RNA being detected in OS. Cohen's kappa analysis (Ck = 0.638) indicated a substantial agreement between both sample types for identifying the true PRRSV status of weaning-age pigs.

Considerations in the use of processing fluids for the detection of PRRSV RNA and antibody.

Surveillance is mandatory for tracking the progress of porcine reproductive and respiratory syndrome virus (PRRSV) control and elimination efforts in breeding herds. Processing fluids, the fluid recovered from tissues collected at castration and/or tail docking, are used for breeding herd surveillance by large segments of the industry, but the basic diagnostic characteristics of processing fluids are largely undescribed. We undertook 3 studies to address this information gap. In study 1, we found no differences among the PRRSV RT-rtPCR results obtained with 4 commercial RNA extraction kits. In study 2, we found that PRRSV RNA was highly stable in processing fluid samples at -20°C or 4°C, but detrimental effects were observed at ≥22°C within 24 h. In study 3, using a modified PRRSV ELISA at a sample:positive cutoff of ≥0.5, we found excellent discrimination in the detection of PRRSV antibody (IgM, IgA, IgG) in processing fluids from herds of known PRRSV status. Judicious handling of processing fluid samples from sow herds, and the use of methods available in veterinary diagnostic laboratories, can provide a foundation for reliable PRRSV surveillance.

Investigation of Fas (APO-1)-Related Apoptosis in Piglets Intradermally or Intramuscularly Vaccinated with a Commercial PRRSV MLV.

Porcine reproductive and respiratory syndrome virus (PRRSV) induces apoptosis through the activation of death receptors, including cell-surface Fas receptor. The aim of this study was to investigate the impact of intradermal (ID) and intramuscular (IM) vaccination with a commercial PRRSV-modified live vaccine in piglets on Fas-related apoptosis. The study included 104 suckling piglets from a commercial farrow-to-finish pig farm, suffering from positive unstable PRRSV status. Animals were assigned in four groups: group A-Porcilis PRRS ID-vaccinated pigs, group B-Porcilis PRRS IM-vaccinated pigs, group C-Diluvac ID adjuvant-administered pigs, and group D-Diluvac IM adjuvant-administered pigs. Vaccines were administered at 2 weeks of age. Blood samples were collected from the same pigs at 4, 7, and 10 weeks of age. Sera were examined by quantitative real-time reverse transcription-PCR (qRT-PCR) for PRRSV and by ELISA for soluble Fas (sFas). At 4 weeks of age, all groups were negative qRT-PCR for PRRSV; at 7 weeks only group A was negative; and at 10 weeks all groups were positive. sFas was significantly increased in groups C (4 vs. 7, 4 vs. 10, and 7 vs. 10 weeks) and D (7 vs. 10 weeks). Significant differences among groups were noticed only at 10 weeks (A vs. C, A vs. D, B vs. C, B vs. D). A significant positive and moderate correlation between PRRSV viral load and Fas level was observed. In unvaccinated piglets, increased serum sFas levels reveal apoptotic suppression compared with vaccinated piglets. In the latter, vaccine-derived antibodies limit the infection and may attribute to the reduced Fas expression, suggesting a weak induction of lymphocyte-mediated cytotoxicity.

Next Generation of Voluntary PRRS Virus Regional Control Programs.

Porcine reproductive and respiratory syndrome virus (PRRSV) became pandemic in the 1980's and today remains one of the most significant pathogens of the global swine industry. At the herd level, control of PRRSV is complicated by its extreme genetic diversity and its ability to persist in pigs, despite an active immune response. Ultimately, PRRSV control or elimination requires the coordination and active cooperation of producers and veterinarians at the regional level. Early voluntary PRRSV regional control programs focused on routine diagnostic testing and voluntary data-sharing regarding the PRRSV status of participants' herds, but no pre-defined action plans or decision trees were developed to secure project successes (or recover from failures). Given that control of PRRSV is paramount to producer profitability, we propose a coordinated approach for detecting, controlling, and ultimately eliminating wild-type PRRSV from herds participating in regional projects. Fundamental to project success is real-time, multi-platform communication of all data, information, and events that concern the regional project and project participants. New to this approach is the concept of agreed-upon action plans to be implemented by project participants in response to specific events or situations. The simultaneous and coordinated implementation of these strategies allows for early detection of wild-type PRRSV virus introductions and rapid intervention based on agreed-upon response plans. An example is given of a project in progress in the Midwest USA.

A comparison of three sampling approaches for detecting PRRSV in suckling piglets

Determining whether porcine reproductive and respiratory syndrome virus (PRRSV) is circulating within a breeding herd is a longstanding surveillance challenge. Most commonly, piglets in farrowing rooms are sampled to infer the PRRSV status of the sow herd, with sample size based on the expectation of hypergeometric distribution and piglet selection based on simple random sampling (SRS), i.e., randomly selecting individuals from a population in a manner that all individuals have equal chance of being selected. Conceptually straightforward, the assumptions upon which it is based (homogeneous population and independence of individuals) rarely hold in modern swine facilities. Alternative approaches for sample selection include two-stage stratified sampling (2SS), i.e., randomly selecting litters (first stratum) and randomly selecting piglets (second stratum) within selected litters, and risk-based sampling (RBS), i.e., selecting litters with a higher risk of having viremic piglets, and randomly selecting pigs within those litters. The objectives of this study were to 1) characterize the pattern of distribution of PRRSV-viremic piglets in farrowing rooms and 2) compare the efficiency of SRS, 2SS, and RBS for the detection of PRRSV-viremic piglets. In 12 sow farms, serum samples were collected from all 4510 piglets in 422 litters housed in 23 farrowing rooms and tested for PRRSV RNA. At the population level, the distribution of PRRSV-viremic pigs was analyzed for population homogeneity and spatial clustering. At the litter level, litter size and sow parity were evaluated as risk factors. A non-homogeneous distribution of PRRSV-viremic piglets was observed in nearly all farrowing rooms (15/16), and spatial clustering detected on 11 occasions (11/16). Simulated sampling based on farrowing room data determined that 2SS required 1-to-25 fewer samples than SRS to detect ≥ 1 viremic piglet in 13 of 16 rooms and the same number of samples in 3 rooms. RBS required 1-to-7 fewer samples than 2SS to detect ≥ 1 viremic piglet in 7 of 16 rooms, the same number of samples in 6 rooms, and 1 more sample in 3 rooms. Notably, SRS was less efficient than either 2SS or RBS in detecting PRRSV-viremic piglets in farrowing rooms, regardless of the confidence level. It may be concluded that the core assumptions upon which most current surveillance methods are based do not hold in modern farrowing room facilities. Simulation-based sample size tables for SRS and 2SS are provided.

Effect of PRRSV stability on productive parameters in breeding herds of a swine large integrated group in Spain

BackgroundIn breeding herds, porcine reproductive and respiratory syndrome (PRRS) clinically manifests as increased abortions, number of stillbirths, and pre-weaning mortality, and as a direct consequence, results in a decrease of the number of piglets weaned per sow per year. Breeding farm classification according the PRRS virus (PRRSV) status (unstable or stable) is a key control strategy for this disease. The aim of this study was to evaluate the production improvement related to achieving a PRRSV stable status in breeding herds in Spain. For this purpose, epidemiological and productivity data were collected from a systematic PRRSV monitoring program in 35 breeding herds from a large integrated swine group in Spain. A comparative statistical analysis was conducted using four key production indicators (KPI) between different PRRSV status and a generalized linear mixed model: weekly abortions/1000 sows (ABTHS), born-alive rate (BAR), pre-weaning mortality rate (PWMR), and number of weaned piglets per 1000 sows (WPTHS).ResultsFrom the 35 monitored farms during a total period of 58 weeks, we collected 49 to 58 weeks of production data and PRRSV classification status for each study farm. This represented a total of 1997 (741 unstable and 1256 stable) weekly data collected that was eligible for the KPI comparative study. PRRSV stability was associated with significant improvement in BAR (+ 1.10 %, p < 0.001), PWMR (-0.88 %, p < 0.002) and WPTHS (+ 24.52, p < 0.0001).ConclusionsThese results demonstrate for the first time the improved production due to achieving PRRSV stability in breeding herds under field conditions in a European country. Increased number of born-alive piglets and a reduction of piglet pre-weaning mortality represents an increase of 1.28 weaned piglets per sow per year if PRRSV stability was achieved and maintained for one-year period in a breeding farm.

Adapting a porcine reproductive and respiratory syndrome virus (PRRSV) oral fluid antibody ELISA to routine surveillance

Distinct from tests used in diagnostics, tests used in surveillance must provide for detection while avoiding false alarms, i.e., acceptable diagnostic sensitivity but high diagnostic specificity. In the case of the reproductive and respiratory syndrome virus (PRRSV), RNA detection meets these requirements during the period of viremia, but antibody detection better meets these requirements in the post-viremic stage of the infection. Using the manufacturer's recommended cut-off (S/P ≥ 0.4), the diagnostic specificity of a PRRSV oral fluid antibody ELISA (IDEXX Laboratories, Inc., Westbrook, ME, USA) evaluated in this study was previously reported as ≥ 97 %. The aim of this study was to improve its use in surveillance by identifying a cut-off that would increase diagnostic specificity yet minimally impact its diagnostic sensitivity. Three sample sets were used to achieve this goal: oral fluids (n = 596) from pigs vaccinated with a modified live PRRSV vaccine under experimental conditions, field oral fluids (n = 1574) from 94 production sites of known negative status, and field oral fluids (n = 1380) from 211 sites of unknown PRRSV status. Based on the analysis of samples of known status (experimental samples and field samples from negative sites), a cut-off of S/P ≥ 1.0 resulted in a diagnostic specificity of 99.2 (95 % CI: 98.8, 99.7) and a diagnostic sensitivity of 96.5 (95 % CI: 85.2, 99.2). Among 211 sites of unknown status, 81 sites were classified as antibody positive using the manufacturer's cut-off; 20 of which were reclassified as negative using a cut-off of S/P ≥ 1.0. Further analysis showed that these 20 sites had a small proportion of samples (18.0 %) with S/P values just exceeding the manufacturer's cut-off (x̄ = 0.5). Whereas the remainder of positive sites (n = 61) had a high proportion of samples (76.3 %) with high S/P values (x̄ = 6.6). Thus, the manufacturer’s cut-off (S/P ≥ 0.4) is appropriate for diagnostic applications, but a cut-off of S/P ≥ 1.0 provided the higher specificity required for surveillance. A previously unreported finding in this study was a statistically significant association between unexpected reactors and specific production sites and animal ages or stages. While beyond the scope of this study, these data suggested that certain animal husbandry or production practices may be associated with non-specific reactions.

Assessing the litter level agreement of RT-PCR results for porcine reproductive and respiratory syndrome virus in testicles, tails and udder wipes diagnostic samples relative to serum from piglets

Porcine reproductive and respiratory syndrome (PRRS) is currently the most detrimental disease in the U.S swine industry. Clinical signs of PRRS virus (PRRSv) infection in breeding herds include reproductive failure with abortions, stillbirths, premature farrowings and increased pre-weaning mortality. Serum from due-to-wean piglets is considered the most suitable specimen to monitor PRRSv infection and stability in breeding herds. However, processing fluids (PF - the serosanguinous exudate resultant of the collection of tails and testicles during processing) are a new specimen proposed to monitor piglets at processing (3–5 days of age) and udder wipes (UW) of lactating sows is yet another specimen to monitor infection status of suckling piglets indirectly. Here, we assessed which specimen type (e.g. sera, testicles, tails or UW) should be used to accurately establish the PRRSv status of a litter. Twenty-four litters were conveniently selected on a farm at 10 weeks post PRRSv outbreak. Blood samples, tails and testicles from every piglet in a litter, and an udder skin wipe from the sow were collected at processing (3–5 days). Individual litter testicles and tails as well as the udder wipe were placed each in a reclosable bag to prevent cross-contamination. Sensitivity (Se), specificity (Sp), negative predictive value (NPV), positive predictive value (PPV) and global agreement at the litter level were calculated using the sera results of the litter as the gold standard. The optimum cycle threshold (Ct) value to classify a sample as negative was ≥35 for serum and ≥36 for the aggregated samples (testicles, tails, and UW) based on the ROC curve analysis. Using those thresholds, the fluid collected from the testicles showed the best overall performance (Se = 92 % [62–100]; Sp = 82 % [48–98], NPV = 90 % [55–100], PPV = 85 % [55–98], global agreement = 87 %) compared to tail fluid and UW. Sensitivity of the tail fluid was 62 % (32–86) and the UW was 23 % (5–54), both of which yielded a 100 % specificity and PPV. This study provides information on the contribution of each of the tissues collected at processing on the detection of PRRSv, which becomes relevant in countries were castration and/or tail docking is banned.

Indirect assessment of porcine reproductive and respiratory syndrome virus status in pigs prior to weaning by sampling sows and the environment

There is a need to develop cost effective approaches to sample large populations in particular to determine the disease status of pigs prior to weaning. In this study we assessed the presence of the porcine reproductive and respiratory syndrome virus (PRRSV) in the environment (surfaces and air) of farrowing rooms, and udder skin of lactating sows as an indirect measure of piglet PRRSV status. Samples were collected at processing and weaning every three weeks for 23 weeks after a PRRSV outbreak was diagnosed in a swine breeding herd. PRRSV was detected at processing in udder skin wipes, environmental wipes and airborne deposited particle samples up to 14 weeks post outbreak and at weaning in udder skin wipes up to 17 weeks post outbreak. Similar sensitivities were observed for udder skin wipes (43% [95% CI: 23%–66%]) and surface wipes (57% [95% CI: 34%–77%]) when compared to serum at the litter level from piglets at processing. PRRSV was detected in the environment and the udder skin of lactating sows, which indicates that aggregate samples of the environment or lactating sows may be used to evaluate the PRRSV status of the herd in pigs prior to weaning. However, the use of environmental samples to detect PRRSV by RT-PCR should not be used as the single method to assess the PRRSV status at the litter level. Furthermore, our findings also highlight potential sources of PRRSV infection for piglets in breeding herds.

Assessment of abattoir based monitoring of PRRSV using oral fluids

Various porcine reproductive and respiratory syndrome virus (PRRSV) regional elimination projects have been implemented in the U.S., but none have yet succeeded. In part, this reflects the need for efficient methods to monitor over time the progress of PRRSV status of participating herds. This study assessed the feasibility of monitoring PRRSV using oral fluids collected at the abattoir. A total of 36 pig lots were included in the study. On-farm oral fluid (n = 10) and serum (n = 10) collected within two days of shipment to the abattoir were used to establish the reference PRRSV status of the population. Oral fluids (n = 3 per lot) were successfully collected from 32 lots (89%) at the lairage. Three veterinary diagnostic laboratories (VDLs) tested the sera (VDL1 and VDL3: n = 316, VDL2: n = 315) and oral fluids (VDL1 and VDL3: n = 319, VDL2: n = 320) for PRRSV antibodies (ELISA) and RNA (rRT-PCR). Environmental samples (n = 64, 32 before and 32 after pigs were placed in lairage) were tested for PRRSV RNA at one VDL. All oral fluids (farm and abattoir) tested positive for PRRSV antibody at all VDLs. PRRSV positivity frequency on serum ranged from 92.4% to 94.6% among VDLs, with an overall agreement of 97.6%. RNA was detected on 1.3% to 1.9%, 8.1% to 17.7%, and 8.3% to 17.7% of sera, on-farm and abattoir oral fluids, respectively. Between-VDLs rRT-PCR agreement on sera and oral fluids (farm and abattoir) ranged from 97.8% to 99.0%, and 79.0% to 81.2%, respectively. Between-locations agreement of oral fluids varied from 31.3% to 50% depending on the VDL. This study reported the application of swine oral fluids collected at the abattoir for monitoring PRRSV, and describes the between-VDL agreement for PRRS testing of serum and oral fluid field samples.

Assessment of area spread of porcine reproductive and respiratory syndrome (PRRS) virus in three clusters of swine farms

Despite decades of porcine reproductive and respiratory syndrome (PRRS) research, outbreaks with emerging and re-emerging PRRS virus (PRRSV) strains are not uncommon in North America. The role of area spread, commonly referred but not limited to airborne transmission, in originating such outbreaks is currently unknown. The main objective of this study was to explore the role of area spread on the occurrence of new PRRSV cases by combining information on genetic similarity among recovered PRRSV isolate's open-reading frame (ORF) 5 sequences and publicly available weather data. Three small regions were enrolled in the study for which high farm-level participation rate was achieved, and swine sites within those regions were readily sampled after reporting of an outbreak in a sow farm. Oral fluid PCR testing was used to determine PRRSV status of farms, and wind roses were generated for assessment of prevailing wind directions during 2-14days preceding the outbreak. Under the conditions of this study, the data did not support the area spread theory as the main cause for these outbreaks. We suggest that for future studies, analysis of animal movement and other links between farms such as personnel, equipment and sharing of service providers should be incorporated for better insights on source of the virus. Furthermore, the development of rapid and easy diagnostic methods for ruling out resident PRRSV is urgently needed.

UK Pigs at the Time of Slaughter: Investigation into the Correlation of Infection with PRRSV and HEV.

Hepatitis E virus (HEV) and porcine reproductive and respiratory syndrome virus (PRRSV) and are both globally prevalent in the pig population. While HEV does not cause clinical disease in pigs, its zoonotic potential has raised concerns in the food safety sector. PRRS has become endemic in the United Kingdom (UK) since its introduction in 1991, and continues to cause considerable economic losses to the swine industry. A better understanding of the current prevalence and diversity of PRRSV and HEV in the UK, and their potential association, is needed to assess risks and target control measures appropriately. This study used plasma, tonsil, and cecal content samples previously collected from pigs in 14 abattoirs in England and Northern Ireland to study the prevalence of several pathogens including PRRSV and HEV. The diversity of PRRSV strains detected in these samples was analyzed by sequencing open reading frame 5 (ORF5), revealing no substantial difference in PRRSV strains from these clinically unaffected pigs relative to those from clinical cases of disease in the UK. Despite the potential immuno-modulatory effect of PRRSV infection, previously demonstrated to affect Salmonella and HEV shedding profiles, no significant association was found between positive PRRSV status and positive HEV status.

UK Pigs at the Time of Slaughter: Investigation into the Correlation of Infection with PRRSV and HEV

Hepatitis E virus (HEV) and porcine reproductive and respiratory syndrome virus (PRRSV) and are both globally prevalent in the pig population. While HEV does not cause clinical disease in pigs, its zoonotic potential has raised concerns in the food safety sector. PRRS has become endemic in the United Kingdom (UK) since its introduction in 1991, and continues to cause considerable economic losses to the swine industry. A better understanding of the current prevalence and diversity of PRRSV and HEV in the UK, and their potential association, is needed to assess risks and target control measures appropriately. This study used plasma, tonsil, and cecal content samples previously collected from pigs in 14 abattoirs in England and Northern Ireland to study the prevalence of several pathogens including PRRSV and HEV. The diversity of PRRSV strains detected in these samples was analyzed by sequencing open reading frame 5 (ORF5), revealing no substantial difference in PRRSV strains from these clinically unaffected pigs relative to those from clinical cases of disease in the UK. Despite the potential immuno-modulatory effect of PRRSV infection, previously demonstrated to affect Salmonella and HEV shedding profiles, no significant association was found between positive PRRSV status and positive HEV status.

Investigation of the Occurrence of Porcine Reproductive and Respiratory Virus in Swine Herds Participating in an Area Regional Control and Elimination Project in Ontario, Canada.

The main goal of this study was to investigate the occurrence of porcine reproductive and respiratory syndrome virus (PRRSV)-specific genotypes in swine sites in Ontario (Canada) using molecular, spatial and network data from a porcine reproductive and respiratory syndrome (PRRS) regional control project. For each site, location, animal movement service provider (truck companies), PRRSV status and sequencing data of the open reading frame 5 (ORF5) were obtained. Three-kilometre buffers were created to evaluate neighbourhood characteristics for each site. Social network analysis was conducted on swine sites and trucking companies to assemble the network and define network components. Three different PRRSV genotypes were used as outcomes for statistical analysis based on the region's phylogenetic tree of the ORF5. Multivariable exact logistic regression was conducted to investigate the association between being positive for a specific genotype and two main exposures of interest: (i) having at least one neighbour within threekm also positive for the same genotype outside the production system and (ii) having at least one positive site for the same genotype in the same truck network component outside the production system. Results showed that the importance of area spread and truck network on PRRSV occurrence differed according to genotype. Additionally, the Ontario PRRS database appears suitable for conducting regional disease investigations. Finally, the use of relatively new tools available for network, spatial and molecular analysis could be useful in investigation, control and prevention of endemic infectious diseases in animal populations.

Correlation between antibodies against porcine reproductive and respiratory syndrome virus and pathological-anatomical organ findings in slaughter pigs at farm level

The porcine reproductive and respiratory syndrome (PRRS) worldwide causes important economic losses in pig production. Its causative agent, the PRRS virus (PRRSV), is one of the most frequently detected infectious agents in relation to respiratory diseases in pigs in Austria. We investigated the correlation between the PRRSV status of pig farms, determined by detection of PRRSV antibodies in the serum of slaughter pigs, and the prevalence of pathological-anatomical lung lesions in slaughter pigs of the respective farms. Between December 1, 2011 and April 16, 2012, a total of 1056 serum samples of slaughter pigs from 66 pig farms were collected at an Austrian abattoir. The presence of PRRSV antibodies was tested by enzyme-linked immunosorbent assay in each sample and the PRRSV status of the respective farms was determined. No PRRSV vaccination was performed on any of the farms. In addition, the pathological-anatomical lung lesions of all slaughter pigs of the 66 farms that were slaughtered between September 1, 2011 and December 11, 2012 were recorded by authorized veterinarians at the abattoir. The prevalence of lung lesions and pleuritis in PRRSV-positive and unsuspected farms was compared and statistically interpreted. Slaughter pigs of PRRSV positive farms had a significantly higher prevalence of severe lung lesions and pleuritis visceralis and parietalis than slaughter pigs of PRRSV unsuspected farms. Pigs of combined farms (nursery and fattening unit at the same location) displayed a tendency for more moderate and severe lung lesions than pigs of exclusive fattening farms. In the present study, the PRRSV status of pig farms displayed a significant influence on the prevalence of lung lesions in the slaughter pigs. Findings untypical for PRRS, including pleuritis, were also found significantly more often on those farms. This leads to the conclusion that other primary and/or secondary infections are involved, which can be exacerbated by the immunosuppressive effect of the PRRSV. There was a tendency for combined farms to be more severely affected than fattening farms.

Probability of detecting Porcine reproductive and respiratory syndrome virus infection using pen-based swine oral fluid specimens as a function of within-pen prevalence

Pen-based oral fluid sampling has proven to be an efficient method for surveillance of infectious diseases in swine populations. To better interpret diagnostic results, the performance of oral fluid assays (antibody- and nucleic acid-based) must be established for pen-based oral fluid samples. Therefore, the objective of the current study was to determine the probability of detecting Porcine reproductive and respiratory syndrome virus (PRRSV) infection in pen-based oral fluid samples from pens of known PRRSV prevalence. In 1 commercial swine barn, 25 pens were assigned to 1 of 5 levels of PRRSV prevalence (0%, 4%, 12%, 20%, or 36%) by placing a fixed number (0, 1, 3, 5, or 9) of PRRSV-positive pigs (14 days post PRRSV modified live virus vaccination) in each pen. Prior to placement of the vaccinated pigs, 1 oral fluid sample was collected from each pen. Thereafter, 5 oral fluid samples were collected from each pen, for a total of 150 samples. To confirm individual pig PRRSV status, serum samples from the PRRSV-negative pigs (n = 535) and the PRRSV vaccinated pigs (n = 90) were tested for PRRSV antibodies and PRRSV RNA. The 150 pen-based oral fluid samples were assayed for PRRSV antibody and PRRSV RNA at 6 laboratories. Among the 100 samples from pens containing ≥1 positive pig (≥4% prevalence) and tested at the 6 laboratories, the mean positivity was 62% for PRRSV RNA and 61% for PRRSV antibody. These results support the use of pen-based oral fluid sampling for PRRSV surveillance in commercial pig populations.

Assessment of the economic impact of porcine reproductive and respiratory syndrome virus on United States pork producers

Objective: To estimate the current annual economic impact of porcine reproductive and respiratory syndrome virus (PRRSV) on the US swine industry. Materials and methods: Data for the analysis was compiled from the US Department of Agriculture, a survey of swine veterinarians on the incidence and impact of PRRSV, and production records (2005 to 2010) from commercial farms with known PRRSV status. Animal-level economic impact of productivity losses and other costs attributed to PRRSV were estimated using an enterprise budgeting approach and extrapolated to the national level on the basis of the US breeding-herd inventory, number of pigs marketed, and number of pigs imported for growing. Results: The total cost of productivity losses due to PRRSV in the US national breeding and growing-pig herd was estimated at US $664 million annually, an increase from the US $560 million annual cost estimated in 2005. The 2011 study differed most significantly from the 2005 study in the allocation of losses between the breeding and the growing-pig herd. Losses in the breeding herd accounted for 12% of the total cost of PRRSV in the 2005 study, compared to 45% in the current analysis. Implications: Despite over 25 years of experience and research, porcine reproductive and respiratory syndrome remains a costly disease of pigs in the United States. Since 2005, some progress has been made in dealing with the cost of productivity losses due to the disease in the growing pig, but these were offset by greater losses in the breeding herd.