Role of transportation in spread of porcine epidemic diarrhea virus infection, United States.

After porcine epidemic diarrhea virus (PEDV) was detected in the United States in 2013, we tested environmental samples from trailers in which pigs had been transported. PEDV was found in 5.2% of trailers not contaminated at arrival, , suggesting that the transport process is a source of transmission if adequate hygiene measures are not implemented.

Assessment of porcine reproductive and respiratory syndrome virus (PRRSV) farm surface contamination through environmental sampling.

BACKGROUND: During the fall of 2020, the porcine reproductive and respiratory syndrome virus (PRRSV) L1C.5 variant emerged and rapidly spread throughout southern Minnesota generating questions regarding possible transmission routes. This study aimed to investigate whether PRRSV could be detected on surfaces inside and outside pig barns housing L1C.5 variant PRRSV-positive pigs to illustrate the potential for indirect transmission of PRRSV. Seven Midwestern U.S. PPRS-positive breeding or growing pig farms and one PRRS-negative farm were conveniently selected. Internal and external barn surfaces were wiped using a PBS moistened cloth and the resulting liquid was submitted to the University of Minnesota Veterinary Diagnostic Laboratory for PRRSV RT-PCR testing and virus isolation. RESULTS: All (n = 26) samples from PRRSV-negative farm tested negative. Nineteen (13%) out of 143 samples from positive farms yielded positive RT-PCR results. Positive samples originated primarily from exhaust fan cones and doorknobs, followed by anteroom floor and mortality carts/sleds. Virus isolation attempted on two samples did not yield positive results. CONCLUSIONS: PRRSV contamination can occur on surfaces inside and outside pig barns that are in frequent contact with farm personnel. Although virus isolation attempts were negative, our results illustrate the potential for PRRSV to be transmitted indirectly through contaminated materials or farm personnel. The study supports the implementation of biosecurity practices by farm personnel to prevent the introduction of PRRSV into farms and the prevention of PRRSV transmission between farms.

Comparison of a novel rapid sampling method to serum and tonsil scraping to detect PRRSV in acutely infected sows.

Few practical methods are available to monitor the PRRSV status of the sows. Common sampling methods for sows like serum sampling, and tonsil scraping involve restraining individual sows and are labor-intensive, time-consuming, relatively invasive, and therefore, have limited use in large-scale production settings. Thus, a practical and rapid method of sampling large numbers of sows is needed. This study aimed to develop a new sampling method, named tonsil-oral scraping (TOSc) and compare TOSc to serum and tonsil scraping in terms of PRRSV qPCR detection rate and Ct values in thirty matched sows, thirty days after PRRSV outbreak. TOSc recovered a mixture of oral fluids and tonsil exudates from the sow oral cavity within seconds without restraining the animals. Results showed that, numerically, the TOSc samples had higher PRRSV qPCR detection rate (100 %) compared to serum (16.8 %) and tonsil scraping (73.1 %). Moreover, TOSc samples had lower average Ct values (29.7) than tonsil scraping (30.7) and serum (35.2). There was no significant difference in the detection rate between TOSc and tonsil scraping (Tukey test, p = 0.992), while there was a significant difference between serum and tonsil scraping (Tukey test, p < 0.001), as well as between serum and TOSc (Tukey test, p < 0.001). In terms of Ct values, there was no statistically significant difference between TOSc and tonsil scrapings (Dunn Test, p > 0.05), while there was a significant difference between tonsil scraping with serum (Dunn Test, p < 0.01), and TOSc with serum (Dunn Test, p < 0.01). Our results suggest great potential of the TOSc as a novel, practical, and rapid tool for PRRSV RNA detection in sows to assess sow herd status.

Characterizing best practices for tonsil-oral-scrubbing (TOSc) collection for PRRSV RNA detection in sows.

BACKGROUND: A Tonsil-Oral-Scrubbing (TOSc) method was developed to sample the sow's oropharyngeal and tonsillar area without snaring and has shown comparable porcine reproductive and respiratory syndrome virus (PRRSV) RNA detection rates with tonsil scraping in infected sows. This study investigated the effect of specific TOSc collection factors on the PRRSV RT-rtPCR results (detection rates and Ct values). Those factors include whether the sow was snared or not snared at TOSc collection ("snared" vs. "not snared"); whether the sow was laying down or standing at collection ("laying down" vs. "standing"); and type of collectors used for TOSc collection ("TOSc prototype" vs. "Spiral-headed AI catheter (SHAC)"). Volume of fluid was compared between "snared" and "not snared" groups, and collection time was compared between "laying down" and "standing" groups as well. RESULTS: The effect for each factor was assessed in three independent studies following the same design: TOSc was collected twice from each studied sow, once with the baseline level for a factor ("not snared", or "standing", or "TOSc prototype"), and another time followed by the other level of the paired factor ("snared", "laying down", or "SHAC", correspondingly). Results showed that "not snared" TOSc had numerically higher PRRSV RNA detection rate (60.7% vs. 52.5%, p = 0.11), significantly lower median Ct values (31.9 vs. 32.3, p < 0.01), and significantly higher volume of fluid than "snared" samples (1.8 mL vs. 1.2 mL, p < 0.01); "laying down" TOSc samples did not differ statistically (60.7% vs. 60.7%) in the PRRSV RNA detection rate, obtained numerically lower median Ct values (30.9 vs. 31.3, p = 0.19), but took 40% less collection time compared to "standing" TOSc samples; samples collected using the "TOSc prototype" had numerically higher PRRSV RNA detection rate (91.7% vs. 88.3%, p = 0.27) and significantly lower median Ct values (32.8 vs. 34.5, p < 0.01) than that from "SHAC". CONCLUSIONS: Under the conditions of this study best practices for TOSc collection aiming higher detection rate of PRRSV RNA while minimizing time for collection were suggested to be sampling TOSc without snaring, when sows are laying down, and using a prototype TOSc collector.

Assessing the role of sow parity on PRRSv detection by RT-qPCR through weekly processing fluids monitoring in breeding herds.

The use of processing fluids to monitor the breeding herd's porcine reproductive and respiratory syndrome (PRRS) status has gained industry acceptance. However, little is known about PRRS virus RT-qPCR detection dynamics in processing fluids and factors that may contribute to maintain PRRS virus in the herd after an outbreak. This study aimed to describe weekly RT-qPCR processing fluid results in breeding herds after an outbreak and to evaluate the proportion of RT-qPCR positive results among parity groups. Processing tissues of 15 first parity (P1), 15 second parity (P2), and 15 third parity or higher (P3+) litters (parity groups) were collected weekly for between 19 and 46 weeks in nine breeding herds. Processing fluids were aggregated, and RT-qPCR tested by parity group weekly. Additionally, a subset of 743 processing fluid samples of litters that formed 50 parity groups, as previously described, were RT-qPCR tested individually at the litter level. The agreement between RT-qPCR results of processing fluid samples of parity groups (15 litters) and results based on individual litter testing was assessed using overall percent of agreement, Kappa statistic, and McNemar test. The association between RT-qPCR results and the parity group was evaluated using a generalized estimating equations model, after accounting for the effects of sampling week, breeding herd PRRS control strategy (i.e., open to replacements v/s closed) and herd. An autoregressive correlation structure was used to account for the repeated samplings within a herd in time. The overall agreement was 98 %, and Kappa statistic 0.955 (McNemar p = 1.0). Sensitivity of parity group processing fluid samples was estimated at 100 % (95 % CI 89-100 %), while specificity was estimated at 94 % (95 % CI 71-100 %). Although P1 aggregated litters had on average a higher proportion of RT-qPCR positive results from outbreak week 25 onwards, the proportion was not significantly different to the one observed for P2 and P3+ aggregated litters (p > 0.13). Additionally, herds that interrupted gilt entry had lower odds of PRRS RT-qPCR positivity than herds that continued entering gilts (OR = 0.35, 95 % CI 0.16-0.78). PRRS virus persistence in processing fluids was not affected by the sow parity effect in most of the breeding herds studied. No evidence of disagreement between RT-qPCR results of an aggregated sample of 15 litters and those of individual litters was observed. This level of litter aggregation testing strategy may be of particular use at the last stages of an elimination program under low PRRS virus prevalence.

Comparison of Mycoplasma hyopneumoniae response to infection by route of exposure.

Mycoplasma hyopneumoniae (MHP) is a concern both for pig well-being and producer economic viability. In the absence of fully protective health interventions, producers rely on controlled exposure to induce an immune response in pigs and minimize the clinical outcomes of MHP infection in pig populations. This study compared the effect of route of exposure on MHP infection, antibody response, clinical signs, and pathology. Six-week-old MHP-negative pigs (n = 78) were allocated to negative control (n = 6) or one of three MHP exposure routes: intratracheal (n = 24, feeding catheter), intranasal (n = 24, atomization device), and aerosol (n = 24, fogger). Body weight, cough indices, and samples (serum, oral fluid, tracheal) were collected weekly through 49 days post-exposure (DPE). Intratrachal exposure produced the highest proportion (24/24) of MHP DNA-positive pigs on DPE 7, as well as earlier and higher serum antibody response. Intranasal and aerosol exposures resulted in infection with MHP DNA detected in tracheal samples from 18/24 and 21/24 pigs on DPE 7, respectively. Aerosol exposure had the least impact on weight gain (0.64 kg/day). No difference was observed among treatment groups in coughing and lung lesions at necropsy. While intratracheal inoculation and seeder animals are frequently used in swine production settings, intranasal or aerosol exposure are viable alternatives to achieve MHP infection. Regardless of the route, steps should be taken to verify the purity of the inoculum and, in the case of aerosol exposure, avert the unintended exposure of personnel and animals to other pathogens.

Emergence of a New Lineage 1C Variant of Porcine Reproductive and Respiratory Syndrome Virus 2 in the United States.

We report an ongoing regional outbreak of an emerging porcine reproductive and respiratory syndrome virus (PRRSV2) variant within Lineage 1C affecting 154 breeding and grow-finishing sites in the Midwestern U.S. Transmission seemed to have occurred in two waves, with the first peak of weekly cases occurring between October and December 2020 and the second starting in April 2021. Most of cases occurred within a 120 km radius. Both orf5 and whole genome sequencing results suggest that this represents the emergence of a new variant within Lineage 1C distinct from what has been previously circulating. A case-control study was conducted with 50 cases (sites affected with the newly emerged variant) and 58 controls (sites affected with other PRRSV variants) between October and December 2020. Sites that had a market vehicle that was not exclusive to the production system had 0.04 times the odds of being a case than a control. A spatial cluster (81.42 km radius) with 1.68 times higher the number of cases than controls was found. The average finishing mortality within the first 4 weeks after detection was higher amongst cases (4.50%) than controls (0.01%). The transmission of a highly similar virus between different farms carrying on trough spring rises concerns for the next high transmission season of PRRS.

Survival analysis of two Mycoplasma hyopneumoniae eradication methods.

Mycoplasma hyopneumoniae is an important respiratory pathogen causing significant losses in the swine industry. Eradication of this bacterium from herds results in increased pig performance, productivity, and animal welfare. The objective of this study was to compare the time-to-detection of M. hyopneumoniae in breed-to-wean farms after the application of one of two methods for M. hyopneumoniae eradication. The two methods compared in this study were: 1) Herd closure and medication, and 2) Whole herd medication without extended closure. Fifty-six breed-to-wean farms located in the US Midwest constituted the cohort for this investigation. Herd closure and medication was applied in 45 farms, while whole herd medication was applied in 11 farms. Two mutually exclusive events were recorded for each farm, either detection of M. hyopneumoniae, which was considered the event of interest, or end of follow-up, which was the right-censored event. Farms were monitored until recording the event of interest, or until the end of follow-up, whichever occurred first. Detection of M. hyopneumoniae was assessed by identification of antibodies against the bacterium in sentinel pigs using a commercially available ELISA assay within 6 months post-eradication completion. Moreover, clinical presentation of disease was recorded if observed post-eradication completion. The censored event occurred at the end of the study in November 2016 (administrative censoring). Time-to-detection of M. hyopneumoniae was analyzed with a Cox proportional hazards model. The proportional hazards assumption was assessed using graphical methods. A sensitivity analysis to evaluate the assumption of outcome-independent censoring was also performed. The cumulative incidence of M. hyopneumoniae detection at the end of follow-up was 18.6 % (95% CI: 6.5%, 46.8%) for herd closure and medication, and 36.4% (95% CI: 15.5%, 70.3%) for whole herd medication. An interaction term between the type of eradication method and follow-up time was included in the model to account for the non-proportional hazards. An overall effect of eradication method was present (P = 0.0442). The hazard ratio associated to the time-invariant effect of eradication method was 29.2 (95% CI: 0.95, 894; P = 0.053). The hazard ratio associated with the interaction term was 0.88 (95% CI: 0.65, 1.2; P = 0.405). Under these conditions, eradication using herd closure and medication reduced the likelihood of detecting cases of M. hyopneumoniae in breed-to-wean farms compared to whole herd medication. Detection of M. hyopneumoniae was concentrated during the first 64 months of follow-up in herd closure and medication, and in the first 8 months in whole herd medication.

Benefit-cost analysis to estimate the payback time and the economic value of two Mycoplasma hyopneumoniae elimination methods in breeding herds.

Mycoplasma hyopneumoniae (Mhyo) is generally accepted to be the most common porcine respiratory pathogen worldwide causing big economical losses in swine production by affecting pig's downstream performance. The objective of this study was to develop a partial budget model to determine the payback period and economic value of two Mhyo elimination protocols. Retrospective data recorded from 2004 to 2017 from 70 breeding herds that implemented herd closure or whole-herd medication protocol targeting Mhyo elimination. Close out data was used to estimate differences in downstream performance between Mhyo-negative and positive flows. Assuming a 5000 sows breed-to-finish operation producing 135,870 weaned pigs and 125,000 finishing pigs/year, the total cost for implementing Mhyo elimination was $112,100 using the herd closure protocol, and $185,700 for the medication protocol. Statistically differences (p < 0.05) in downstream performance were observed for ADG and mortality, but not for feed conversion rate. The parameters that accounts for the greatest benefits were related to the improvement in ADG, savings in antibiotic medication in growing pigs and improvement in feed conversion rate. The benefit of Mhyo elimination was $877,375 per farm per year, or $7.00 per pig marketed. The estimated project value after 1 year was $616,121 for the herd closure considering a probability of success of 83%, and $323,177 for the medication protocol for 58% chance of success. The project value reached the break-even point when the cost per sow was $145.64 for the herd closure and $101.78 for the medication protocol. The payback period was 2 months after the start of marketing Mhyo-negative pigs for the herd closure, and 7 months for the medication protocol adjusted for the probability of success for each protocol. The protocols described here can be easily applied with a good success rate and showing that the benefits obtained are greater than the costs of project failure. Even if the farm stayed negative only a year, the economic benefits downstream are worth the investment. This information may help producers and veterinarians on decision-making process to conduct a Mhyo elimination protocol in their herds.

Temporal and spatial dynamics of porcine reproductive and respiratory syndrome virus infection in the United States.

OBJECTIVE: To measure incidence and estimate temporal and spatial dynamics of porcine reproductive and respiratory syndrome virus (PRRSV) infection in US sow herds. ANIMALS: 371 sow herds in the United States from 14 production companies. PROCEDURES: The exponentially weighted moving average was used to monitor incident PRRSV infections for onset of an epidemic. The spatial scan statistic was used to identify areas at significantly high risk of PRRS epidemics. A χ(2) test was used to estimate whether there were significant differences in the quarterly and annual PRRS incidence among time periods, and a bivariable logistic regression model was used to estimate whether PRRSV infection during a given year increased the odds of that herd being infected in the following year. RESULTS: During the 4-year period of this study, 29% (91/319; 2009 to 2010), 33% (106/325; 2010 to 2011), 38% (135/355; 2011 to 2012), and 32% (117/371; 2012 to 2013) of the herds reported new infections. Weekly incidence was low during spring and summer and high during fall and winter. The exponentially weighted moving average signaled the onset of a PRRSV epidemic during the middle 2 weeks of October each year. Disease incidence was spatially clustered. Infection in the previous year increased the odds of infection in 2010 to 2011 and 2011 to 2012. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated a striking repeatability in annual PRRSV temporal and spatial patterns across 4 years of data among herds from 14 production companies, which suggested that efforts to control PRRSV at a regional level should continue to be supported.

Previous infection of sows with a "mild" strain of porcine epidemic diarrhea virus confers protection against infection with a "severe" strain.

Porcine epidemic diarrhea virus (PEDv) infected approximately 50% of the US swine breeding herds from July 2013 to July 2014 as estimated by the Swine Health Monitoring Project. In the absence of effective vaccines or standard control protocols, there is an urgent need for evidence of cross-protective immune countermeasures. Here, we evaluated the response of 3-day-old piglets born to sows exposed seven months earlier to a mild strain of PEDv to challenge with a virulent PEDv isolate. Piglet survival to one week of age was 100% compared to 67% in piglets born to sows not previously exposed, and morbidity was 43% compared to 100%, respectively. At necropsy at 7 days of age, the PEDv Ct value was 23.6 (range 16.6-30.6) in intestinal contents, compared to 17.2 (range 15.9-18.5) (p<0.06) in litters from sows with no previous exposure to PEDv. The findings indicated that durable lactogenic immunity was present in sows previously exposed to a mild strain of PEDv and this immunity induced cross-protection to representative virulent PEDv. Thus, a naturally attenuated form of PEDv provided significant passive immune protection for seven months against piglet challenge with virulent PEDv.

A prospective study evaluating duration of swine breeding herd PRRS virus-free status and its relationship with measured risk.

A variety of methods for eliminating the PRRS virus from pig production sites have been successfully applied. However, success in maintaining a PRRS virus-free status for extended periods of time following elimination has been inconsistent and unpredictable. The objective of this study was to evaluate whether risks measured using version 1 of the American Association of Swine Veterinarians (AASV) PRRS Risk Assessment for the Breeding Herd, season of year and method by which swine breeding herd sites were established PRRS virus-free were associated with how long they retained their virus-free status. Thirty-three swine farrow-to-wean breeding herd sites that were established as PRRS virus-free by either populating a new site with virus-free breeding animals or by completely depopulating the site and repopulating with PRRS virus-free breeding animals were enrolled in this study. Survival analysis, using the Cox proportional hazards model and Kaplan-Meier survival curves, was performed where the outcome was the duration of time PRRS virus-free breeding herd sites remained virus-free ("survived"). Covariates evaluated included the internal and external risk scores measured by the PRRS Risk Assessment for the Breeding Herd as well as the season and the method by which the site was established free of the PRRS virus. All but 5 (15%) of the 33 sites became positive to the PRRS virus during the course of the study and approximately 40% became positive within 1 year from when they were established free of the PRRS virus. A higher external risk score was associated with a greater risk of becoming positive to the PRRS virus and shorter survival times. The internal risk score was not significantly associated with survival. Establishing breeding herd sites free of the PRRS virus in winter months (November through February) was associated with a greater risk of becoming positive to the PRRS virus and shorter survival times compared to those established in non-winter months. The association between the risk of becoming positive to the PRRS virus and the external risk score was confounded by the method the site was established PRRS virus-free.