Senecavirus A seroprevalence and risk factors in United States pig farms.

Senecavirus A (SVA) is a non-enveloped, single-stranded, positive-sense RNA virus belonging to the Picornaviridae family. Senecavirus A is constantly associated with outbreaks of vesicular disease in pigs and has been reported in several countries since its first large-scale outbreak in 2014. Senecavirus A's clinical disease and lesions are indistinguishable from other vesicular foreign animal diseases (FAD). Therefore, an FAD investigation needs to be conducted for every SVA case. For this reason, SVA has been attributed as the cause of an alarming increase in the number of yearly FAD investigations performed by the United States Department of Agriculture (USDA). The objectives of this study were to estimate the seroprevalence of SVA antibodies in breeding and growing pig farms in the United States and to determine the farm-level risk factors associated with seropositivity. A total of 5,794 blood samples were collected from 98 and 95 breeding and growing pig farms in 17 states. A farm characteristics questionnaire was sent to all farms, to which 80% responded. The responses were used to conduct logistic regression analyses to assess the risk factors associated with SVA seropositivity. The estimated farm-level seroprevalences were 17.3% and 7.4% in breeding and growing pig farms, respectively. Breeding farms had 2.64 times higher odds of SVA seropositivity than growing pig farms. One key risk factor identified in breeding farms was the practice of rendering dead animal carcasses. However, the adoption of a higher number of farm biosecurity measures was associated with a protective effect against SVA seropositivity in breeding farms.

Evaluation of dam parity and internal biosecurity practices in influenza infections in piglets prior to weaning.

Influenza is an important respiratory disease of pigs and humans. Controlling influenza in pigs is challenging due to the substantial genetic diversity of influenza A virus (IAV). In this study, we assessed the impact of internal biosecurity practices directed at limiting exposure of piglets to IAV before weaning; evaluated the association of sow parity with IAV prevalence in piglets and the levels of maternally derived antibodies (MDA), and documented the frequency of detection of IAV on farmworkers' hands and the instruments used when handling pigs. The control group included litters in rooms where no specific changes were made to standard farm procedures. The treatment group included litters in rooms where no cross-fostering or nurse sows use was allowed, and where farmworkers were required to change gloves between litters when handling pigs. Both, younger (≤ Parity 3) and older parity sows (>Parity 3) were represented in all rooms included in the study. Overall, litters in the treatment group had lower IAV prevalence (29.9 %) than litters in the control group (44.2 %) (p < 0.001), and at day 8 of age the litters from the control group had 7.5 times higher IAV prevalence than the litters from the treatment group. However, at weaning differences were not found (77.2 % vs. 81 % for treatment vs. control, respectively, p = 0.41). There were no differences in IAV detection between parity groups at any of the sampling points (p = 0.86) and incidence of detection in sows from farrowing to weaning was 29 %. Piglets that tested ELISA negative were 1.3 times more likely to test IAV positive than piglets that were ELISA positive for IAV antibody test, suggesting that effective colostrum intake may reduce the likelihood of infection. IAV was detected on 46 % of the instruments used when handling piglets and on 58 % of farmworkers' hands, indicating the potential risk for mechanical transmission of IAV in pigs. Overall, we showed that the implementation of internal biosecurity practices that limit IAV exposure to newborn piglets helped delay IAV infections but were not sufficient to reduce the prevalence of IAV infection in litters at weaning.

Growing pig incidence rate, control and prevention of porcine epidemic diarrhea virus in a large pig production system in the United States.

BACKGROUND: In 2013, PEDV was introduced in the United States (U.S.) and rapidly spread across the country. Here we describe the occurrence of PEDV in the growing pig herd of one large U.S. production system through an active surveillance set in place between October 2019 and November 2020 designed to assess disease status upon placement into the growing pig site, before shipping to the slaughter plant and when diarrhea events were present at the site. We also assessed the impact of preventive procedures implemented in PEDV incidence that comprised site-specific equipment segregation and biosecurity changes regarding personnel movement between sites. RESULTS: 36.50% (100/274) of the sites had at least one PEDV introduction event before preventive procedures were implemented, yielding an incidence rate of 2.41 per 100 farm-weeks. Most (63/100) of them occurred in sites where animals were placed negative and PEDV was detected in clinical samples in a median of 8 weeks post placement. After preventive procedures were implemented, the overall PEDV incidence rate dropped to 0.37 per 100 farm-weeks (84.65% reduction, p < 0.001). CONCLUSION: These results highlight the importance of systematic surveillance to identify the burden of diseases, areas of improvement in prevention and control, and to allow the measurement of the impact of policy/protocol changes.

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.

Spatial relative risk and factors associated with porcine reproductive and respiratory syndrome outbreaks in United States breeding herds.

Details of incident cases of porcine reproductive and respiratory syndrome (PRRS) in United States breeding herds were obtained from the Morrison's Swine Health Monitoring Project. Herds were classified as cases if they reported an outbreak in a given season of the year and non-cases if they reported it in a season other than the case season or if they did not report a PRRS outbreak in any season. The geographic distribution of cases and non-cases was compared in each season of the year. The density of farms that had a PRRS outbreak during summer was higher in Southern Minnesota and Northwest-central Iowa compared to the density of the underlying population of non-case farms. This does not mean that PRRS outbreaks are more frequent during summer in absolute terms, but that there was a geographical clustering of herds breaking during summer in this area. Similar findings were observed in autumn. In addition, the density of farms reporting spring outbreaks was higher in the Southeast of the United States compared to that of the underlying population of non-case farms. A similar geographical clustering of PRRS outbreaks was observed during winter in the Southeast of the United States. Multivariable analyses, adjusting for the effect of known confounders, showed that the incidence rate of PRRS was significantly lower during winter and autumn during the porcine epidemic diarrhea (PED) epidemic years (2013-2014), compared to PRRS incidence rates observed during the winter and autumn of PED pre-epidemic years (2009-2012). After 2014, an increase in the incidence rate of PRRS was observed during winter and spring but not during autumn or summer. Pig dense areas were associated with a higher incidence rate throughout the year. However, this association tended to be stronger during the summer. Additionally, herds with ≥2500 sows had an increased incidence rate during all seasons except spring compared to those with <2500 sows. PRRS incidence was lower in year-round air-filtered herds compared to non-filtered herds throughout the year. We showed that not only the spatial risk of PRRS varies regionally according to the season of the year, but also that the effect of swine density, herd size and air filtering on PRRS incidence may also vary according to the season of the year. Further studies should investigate regional and seasonal drivers of disease. Breeding herds should maintain high biosecurity standards throughout the year.

Estimation of the burden of leptospirosis in New Zealand.

BACKGROUND: Human leptospirosis mainly affects people in close occupational contact with domestic livestock and their products in New Zealand. The disease has an unquantified impact on both human health and animal production in the country. This study aimed to estimate the burden of leptospirosis in terms of disability-adjusted life years (DALYs) and cost associated with loss due to absence from work, treatment of disease, animal production loss and cost of vaccination. METHODS: Previously published studies of abattoir workers farmers, and veterinarians, reporting annual risks of influenza-like illness attributable to Leptospira infection, were used to estimate the expected number of cases in a year. The cost of lost animal production was based on results of observational studies in beef cattle, sheep and deer conducted in New Zealand. RESULTS: Expected median annual number of severe and mild cases of human leptospirosis was 2,025 (95% probability interval [95% PI] 1,138-3,422). Median annual DALYs were 0.42 (95% PI: 0.06-2.40) per 100,000 people for the entire population, and 15.82 (95% PI: 2.09-90.80) per 100,000 people working in at-risk occupations (i.e. abattoir workers, farmers and veterinarians). Human infection resulted in a median cost of 4.42 (95% PI: 2.04-8.62) million US dollars (USD) due to absence from work and disease treatment. Median production loss cost in beef cattle, sheep and deer was USD 7.92 (95% PI: 3.75-15.48) million, while median vaccination cost in cattle, (including dairy), sheep and deer was USD 6.15 (95% PI: 5.30-7.03) million. Total annual cost of leptospirosis plus vaccination was USD 18.80 (95% PI: 13.47-27.15) million, equivalent to USD 440,000 (95% PI: 320,000-640,000) per 100,000 people. CONCLUSION: This study provides an estimate of the disease burden and cost of leptospirosis in New Zealand that could support occupational health authorities and livestock industries in assessing interventions for this disease.

Individual or Common Good? Voluntary Data Sharing to Inform Disease Surveillance Systems in Food Animals.

Livestock producers have traditionally been reluctant to share information related to their business, including data on health status of their animals, which, sometimes, has impaired the ability to implement surveillance programs. However, during the last decade, swine producers in the United States (US) and other countries have voluntarily begun to share data for the control and elimination of specific infectious diseases, such as the porcine reproductive and respiratory syndrome virus (PRRSv). Those surveillance programs have played a pivotal role in bringing producers and veterinarians together for the benefit of the industry. Examples of situations in which producers have decided to voluntarily share data for extended periods of time to support applied research and, ultimately, disease control in the absence of a regulatory framework have rarely been documented in the peer-reviewed literature. Here, we provide evidence of a national program for voluntary sharing of disease status data that has helped the implementation of surveillance activities that, ultimately, allowed the generation of critically important scientific information to better support disease control activities. Altogether, this effort has supported, and is supporting, the design and implementation of prevention and control approaches for the most economically devastating swine disease affecting the US. The program, which has been voluntarily sustained and supported over an extended period of time by the swine industry in the absence of any regulatory framework and that includes data on approximately 50% of the sow population in the US, represents a unique example of a livestock industry self-organized surveillance program to generate scientific-driven solutions for emerging swine health issues in North America.

Factors affecting Porcine Reproductive and Respiratory Syndrome virus time-to-stability in breeding herds in the Midwestern United States.

The time needed to wean porcine reproductive and respiratory syndrome (PRRS) virus negative pigs consistently from a breeding herd after an outbreak is referred to as time-to-stability (TTS). TTS is an important measure to plan herd closure as well as to manage economic expectations. Weekly PRRS incidence data from 82 sow farms in six production systems located in the Midwestern United States were used for the analysis. The objective of this study was to evaluate the effect of recorded predictors on TTS in participant sow farms. The median TTS was 41.0 weeks (1st quartile 31.0 weeks-3rd quartile 55.0 weeks). In the final multivariable mixed-effects Cox model, farms that experienced winter (hazard ratio (HR) 2.18, 95% confidence interval (CI) 1.28-3.70) and autumn (HR 1.91, 95% CI 1.16-3.13) PRRS outbreaks achieved stability sooner than farms that experienced PRRS outbreaks during summer. No statistically significant difference (p = 0.76) was observed between the TTS of farms that had a PRRS outbreak during spring and summer (HR 1.09, 95% CI 0.62-1.91). Additionally, farms that had a PRRS outbreak associated with a 1-7-4 restriction fragment length polymorphism (RFLP) cut pattern took significantly longer to achieve stability (HR 0.44, 95% CI 0.27-0.72) compared to farms which had a non-1-7-4 PRRS outbreak. Finally, farms that had a previous PRRS outbreak within a year achieved stability sooner (HR 2.18, 95% CI 1.23-3.86) than farms that did not have a previous PRRS outbreak within a year. This study provides information that may result useful for planning herd closure and managing expectations about the time needed to wean PRRS virus negative pigs in breading herds according to the season of the year when the outbreak occurred and the RFLP cut pattern associated with the outbreak virus.