Porcine Reproductive And Respiratory Syndrome Virus Transmission Research Articles

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

BackgroundDuring 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.ResultsAll (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.ConclusionsPRRSV 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.

Betulonic Acid Inhibits Type-2 Porcine Reproductive and Respiratory Syndrome Virus Replication by Downregulating Cellular ATP Production.

Porcine reproductive and respiratory syndrome (PRRS), caused by PRRS virus (PRRSV) infection, has been a serious threat to the pork industry worldwide and continues to bring significant economic loss. Current vaccination strategies offer limited protection against PRRSV transmission, highlighting the urgent need for novel antiviral approaches. In the present study, we reported for the first time that betulonic acid (BA), a widely available pentacyclic triterpenoids throughout the plant kingdom, exhibited potent inhibition on PRRSV infections in both Marc-145 cells and primary porcine alveolar macrophages (PAMs), with IC50 values ranging from 3.3 µM to 3.7 µM against three different type-2 PRRSV strains. Mechanistically, we showed that PRRSV replication relies on energy supply from cellular ATP production, and BA inhibits PRRSV infection by reducing cellular ATP production. Our findings indicate that controlling host ATP production could be a potential strategy to combat PRRSV infections, and that BA might be a promising therapeutic agent against PRRSV epidemics.

A dicoumarol-graphene oxide quantum dot polymer inhibits porcine reproductive and respiratory syndrome virus through the JAK-STAT signaling pathway.

Porcine reproductive and respiratory syndrome virus (PRRSV) causes substantial economic losses in the global swine industry. The current vaccine options offer limited protection against PRRSV transmission, and there are no effective commercial antivirals available. Therefore, there is an urgent need to develop new antiviral strategies that slow global PRRSV transmission. In this study, we synthesized a dicoumarol-graphene oxide quantum dot (DIC-GQD) polymer with excellent biocompatibility. This polymer was synthesized via an electrostatic adsorption method using the natural drug DIC and GQDs as raw materials. Our findings demonstrated that DIC exhibits high anti-PRRSV activity by inhibiting the PRRSV replication stage. The transcriptome sequencing analysis revealed that DIC treatment stimulates genes associated with the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signalling pathway. In porcine alveolar macrophages (PAMs), DIC-GQDs induce TYK2, JAK1, STAT1, and STAT2 phosphorylation, leading to the upregulation of JAK1, STAT1, STAT2, interferon-β (IFN-β) and interferon-stimulated genes (ISGs). Animal challenge experiments further confirmed that DIC-GQDs effectively alleviated clinical symptoms and pathological reactions in the lungs, spleen, and lymph nodes of PRRSV-infected pigs. These findings suggest that DIC-GQDs significantly inhibits PRRSV proliferation by activating the JAK/STAT signalling pathway. Therefore, DIC-GQDs hold promise as an alternative treatment for PRRSV infection.

High-throughput screening unveils nitazoxanide as a potent PRRSV inhibitor by targeting NMRAL1

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) poses a major threat to the global swine industry, yet effective prevention and control measures remain elusive. This study unveils Nitazoxanide (NTZ) as a potent inhibitor of PRRSV both in vitro and in vivo. Through High-Throughput Screening techniques, 16 potential anti-PRRSV compounds are identified from a library comprising FDA-approved and pharmacopeial drugs. We show that NTZ displays strong efficacy in reducing PRRSV proliferation and transmission in a swine model, alleviating viremia and lung damage. Additionally, Tizoxanide (TIZ), the primary metabolite of NTZ, has been identified as a facilitator of NMRAL1 dimerization. This finding potentially sheds light on the underlying mechanism contributing to TIZ’s role in augmenting the sensitivity of the IFN-β pathway. These results indicate the promising potential of NTZ as a repurposed therapeutic agent for Porcine Reproductive and Respiratory Syndrome (PRRS). Additionally, they provide valuable insights into the antiviral mechanisms underlying NTZ’s effectiveness.

Detection of PRRSV-1 in tongue fluids under experimental and field conditions and comparison of different sampling material for PRRSV sow herd monitoring.

Infection with porcine reproductive and respiratory syndrome virus (PRRSV) leads to significant economic losses worldwide. One of the initial measures following an outbreak is to stabilise the herd and to prevent vertical transmission of PRRSV. The objective of this study was to detect PRRSV in different sampling material, both in an experimental model and on a commercial piglet producing farm, with a focus on evaluating the suitability of tongue fluid samples. In the experimental model, PRRSV negative pregnant gilts were infected with PRRSV-1 AUT15-33 on gestation day 85 and necropsy of gilts and foetuses was performed three weeks later. 38.3% of individual foetal serum and 39.4% of individual foetal thymus samples were considered PRRSV RT-qPCR positive. Tongue fluids from individual foetuses showed a 33.0% positivity rate. PRRSV RNA was detected in all but one sample of litter-wise pooled processing fluids and tongue fluids. In the field study, the investigated farm remained PRRSV positive and unstable for five consecutive farrowing groups after the start of the sampling process. Tongue fluid samples pooled by litter in the first investigated farrowing group had a 54.5% positivity rate, with the overall highest viral load obtained in the field study. In this farrowing group, 33.3% of investigated litter-wise pooled processing fluid samples and all investigated serum samples (pools of 4-6 individuals, two piglets per litter) were considered positive. Across all investigated farrowing groups, tongue fluid samples consistently showed the highest viral load. Moreover, tongue fluid samples contained the virus in moderate amounts for the longest time compared to the other investigated sampling material. It can be concluded that the viral load in individual foetuses is higher in serum or thymus compared to tongue fluid samples. However, litter-wise pooled tongue fluid samples are well-suited for detecting vertical transmission within the herd, even when the suspected prevalence of vertical transmission events is low.

Transmission of porcine reproductive and respiratory syndrome virus in domestic pigs via oral ingestion of feed material.

The purpose of this case study was to describe the transmission of porcine reproductive and respiratory syndrome virus (PRRSV) under field and experimental conditions via the consumption of PRRSV-positive swine feed. 1 domestic swine breeding herd and 20 laboratory-maintained experimental domestic pigs. A 2,500-sow PRRSV-naïve biosecure breeding herd became infected during the autumn months. It experienced a feed outage involving a specific bin on October 23 (day 0), with the bin refilled on October 24 (day 1). From October 28 to 30 (days 5 to 7), signs of anorexia and hyperemia were observed in 30 gestating sows after consuming feed from this bin. On November 1 (day 9), blood samples from 10 affected sows were PRRSV positive by reverse transcriptase PCR. In contrast, sows in the same room that had consumed feed from other bins were clinically normal and PRRSV negative. To investigate whether the feed delivery introduced PRRSV to the herd, on November 2 (day 10) 4 samples of feed material from the interior walls of the index bin were collected and tested by reverse transcriptase PCR. All 4 samples were positive for PRRSV RNA with cycle threshold values ranging from 26 to 29. Nucleic acid sequencing indicated that the open reading frame 5 region of the PRRSV in feed samples was 100% homologous to PRRSV from index cases. To assess viability of the virus, PRRSV-naïve pigs were allowed to consume the index feed bin samples and became infected with PRRSV based on viral RNA in oral fluid samples, clinical signs, and postmortem lesions. These results suggest that feed was a likely source of PRRSV introduction to the herd. This is the first report of PRRSV transmission through feed.

Modeling the Seasonal Variation of Windborne Transmission of Porcine Reproductive and Respiratory Syndrome Virus between Swine Farms.

Modeling the windborne transmission of aerosolized pathogens is challenging. We adapted an atmospheric dispersion model named the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to simulate the windborne dispersion of porcine reproductive and respiratory syndrome virus (PRRSv) between swine farms and incorporated the findings into an outbreak investigation. The risk was estimated semi-quantitatively based on the cumulative daily deposition of windborne particles and the distance to the closest emitting farm with an ongoing outbreak. Five years of data (2014:2018) were used to study the seasonal differences of the deposition thresholds of the airborne particles containing PRRSv and to evaluate the model in relation to risk prediction and barn air filtration. When the 14-day cumulative deposition was considered, in winter, above-threshold particle depositions would reach up to 30 km from emitting farms with 84% of them being within 10 km. Long-distance pathogen transmission was highest in winter and fall, lower in spring, and least in summer. The model successfully replicated the observed seasonality of PRRSv, where fall and winter posed a higher risk for outbreaks. Reaching the humidity and temperature thresholds tolerated by the virus in spring and summer reduced the survival and infectivity of aerosols beyond 10-20 km. Within the data limitations of voluntary participation, when wind was assumed to be the sole route of PRRSv transmission, the predictive performance of the model was fair with >0.64 AUC. Barn air filtration was associated with fewer outbreaks, particularly when exposed to high levels of viral particles. This study confirms the usefulness of the HYSPLIT model as a tool when determining seasonal effects and distances and informs the near real-time risk of windborne PRRSv transmission that can be useful in future outbreak investigations and for implementing timely control measures.

Toosendanin activates caspase-1 and induces maturation of IL-1β to inhibit type 2 porcine reproductive and respiratory syndrome virus replication via an IFI16-dependent pathway

Porcine reproductive and respiratory syndrome virus (PRRSV) is a prevalent and endemic swine pathogen which causes significant economic losses in the global swine industry. Multiple vaccines have been developed to prevent PRRSV infection. However, they provide limited protection. Moreover, no effective therapeutic drugs are yet available. Therefore, there is an urgent need to develop novel antiviral strategies to prevent PRRSV infection and transmission. Here we report that Toosendanin (TSN), a tetracyclic triterpene found in the bark or fruits of Melia toosendan Sieb. et Zucc., strongly suppressed type 2 PRRSV replication in vitro in Marc-145 cells and ex vivo in primary porcine alveolar macrophages (PAMs) at sub-micromolar concentrations. The results of transcriptomics revealed that TSN up-regulated the expression of IFI16 in Marc-145 cells. Furthermore, we found that IFI16 silencing enhanced the replication of PRRSV in Marc-145 cells and that the anti-PRRSV activity of TSN was dampened by IFI16 silencing, suggesting that the inhibition of TSN against PRRSV replication is IFI16-dependent. In addition, we showed that TSN activated caspase-1 and induced maturation of IL-1β in an IFI16-dependent pathway. To verify the role of IL-1β in PRRSV infection, we analyzed the effect of exogenous rmIL-1β on PRRSV replication, and the results showed that exogenous IL-1β significantly inhibited PRRSV replication in Marc-145 cells and PAMs in a dose-dependent manner. Altogether, our findings indicate that TSN significantly inhibits PRRSV replication at very low concentrations (EC50: 0.16–0.20 μM) and may provide opportunities for developing novel anti-PRRSV agents.

Adapting an Atmospheric Dispersion Model to Assess the Risk of Windborne Transmission of Porcine Reproductive and Respiratory Syndrome Virus between Swine Farms.

Modeling the windborne transmission of aerosolized pathogens is challenging. We adapted an atmospheric dispersion model (ADM) to simulate the windborne dispersion of porcine reproductive and respiratory syndrome virus (PRRSv) between swine farms. This work focuses on determining ADM applicable parameter values for PRRSv through a literature and expert opinion-based approach. The parameters included epidemiological features of PRRSv, characteristics of the aerosolized particles, and survival of aerosolized virus in relation to key meteorological features. A case study was undertaken to perform a sensitivity analysis on key parameters. Farms experiencing ongoing PRRSv outbreaks were assigned as particle emitting sources. The wind data from the North American Mesoscale Forecast System was used to simulate dispersion. The risk was estimated semi-quantitatively based on the median daily deposition of particles and the distance to the closest emitting farm. Among the parameters tested, the ADM was most sensitive to the number of particles emitted, followed by the model runtime, and the release height was the least sensitive. Farms within 25 km from an emitting farm were at the highest risk; with 53.66% being within 10 km. An ADM-based risk estimation of windborne transmission of PRRSv may inform optimum time intervals for air sampling, plan preventive measures, and aid in ruling out the windborne dispersion in outbreak investigations.

Proteomic Investigation Reveals Eukaryotic Translation Initiation Factor 5A Involvement in Porcine Reproductive and Respiratory Syndrome Virus Infection in vitro.

Porcine reproductive and respiratory syndrome virus (PRRSV), one of the most serious animal pathogens in the world, has caused enormous global swine industry losses. An in-depth investigation of the PRRSV-host interaction would be beneficial for preventing and controlling PRRSV infections and transmission. In this study, we performed label-free quantitative proteomic assays to investigate proteome dynamics of porcine alveolar macrophages (PAMs) during infection with highly pathogenic PRRSV (HP-PRRSV) strain HN07-1. Analysis of the results led to identification of 269 significantly differentially expressed host cellular proteins, of which levels of proteins belonging to the eukaryotic translation initiation factor (eIF) family were found to be decreased in abundance in HP-PRRSV-infected PAMs. Furthermore, knockdown of eIF5A expression was demonstrated to markedly suppress HP-PRRSV propagation, as reflected by reduced progeny virus titers in vitro. These results highlight the importance of eIF5A in PRRSV infection, while also demonstrating that PAMs down-regulate eIF5A expression as a host cell antiviral strategy. Results of the current study deepen our understanding of PRRSV pathogenesis and provide novel insights to guide development of effective strategies to combat the virus.

Modelling and assessing additional transmission routes for porcine reproductive and respiratory syndrome virus: Vehicle movements and feed ingredients.

Accounting for multiple modes of livestock disease dissemination in epidemiological models remains a challenge. We developed and calibrated a mathematical model for transmission of porcine reproductive and respiratory syndrome virus (PRRSV), tailored to fit nine modes of between-farm transmission pathways including: farm-to-farm proximity (local transmission), contact network of batches of pigs transferred between farms (pig movements), re-break probabilities for farms with previous PRRSV outbreaks, with the addition of four different contact networks of transportation vehicles (vehicles to transport pigs to farms, pigs to markets, feed and crew) and the amount of animal by-products within feed ingredients (e.g., animal fat or meat and bone meal). The model was calibrated on weekly PRRSV outbreaks data. We assessed the role of each transmission pathway considering the dynamics of specific types of production (i.e., sow, nursery). Although our results estimated that the networks formed by transportation vehicles were more densely connected than the network of pigs transported between farms, pig movements and farm proximity were the main PRRSV transmission routes regardless of farm types. Among the four vehicle networks, vehicles transporting pigs to farms explained a large proportion of infections, sow=20.9%; nursery=15%; and finisher=20.6%. The animal by-products showed a limited association with PRRSV outbreaks through descriptive analysis, and our model results showed that the contribution of animal fat contributed only 2.5% and meat and bone meal only .03% of the infected sow farms. Our work demonstrated the contribution of multiple routes of PRRSV dissemination, which has not been deeply explored before. It also provides strong evidence to support the need for cautious, measured PRRSV control strategies for transportation vehicles and further research for feed by-products modelling. Finally, this study provides valuable information and opportunities for the swine industry to focus effort on the most relevant modes of PRRSV between-farm transmission.

Safety of PRRSV-2 MLV vaccines administrated via the intramuscular or intradermal route and evaluation of PRRSV transmission upon needle-free and needle delivery

Two distinct experiments (Exp) were conducted to evaluate the shedding and efficacy of 2 modified live porcine reproductive and respiratory syndrome virus (PRRSV) type 2 vaccines (MLV) when administered intramuscularly (IM) or intradermally (ID) (Exp A), and the potential of PRRSV transmission using a needle-free device (Exp B). One-hundred fifty-four, 3-week-old castrated-male, pigs were procured from a PRRSV-free herd. In Exp A, 112 pigs were randomly allocated into 4 groups of 21 pigs including IM/Ingelvac MLV (G1), IM/Prime Pac (G2), ID/Prime Pac (G3), and non-vaccination (G4). Twenty-eight remaining pigs were served as non-vaccination, age-matched sentinel pigs. G1 was IM vaccinated once with Ingelvac PRRS MLV (Ing) (Boehringer Ingelheim, Germany). G2 and G3 were IM and ID vaccinated once with a different MLV, Prime Pac PRRS (PP) (MSD Animal Health, The Netherlands), respectively. Following vaccination, an antibody response, IFN-γ-SC, and IL-10 secretion in supernatants of stimulated PBMC were monitored. Sera, tonsils, nasal swabs, bronchoalveolar lavage, urines, and feces were collected from 3 vaccinated pigs each week to 42 days post-vaccination (DPV) and assayed for the presence of PRRSV using virus isolation and qPCR. Age-matched sentinel pigs were used to evaluate the transmission of vaccine viruses and were introduced into vaccinated groups from 0 to 42 DPV. Seroconversion was monitored. In Exp B, 42 pigs were randomly allocated into 5 groups of 3 pigs each including IM/High (T1), ID/High (T2), IM/Low (T3), ID/Low (T4), and NoChal. Twenty-seven remaining pigs were left as non-challenge, age-matched sentinel pigs. The T1 and T2, and T3 and T4 groups were intranasally challenged at approximately 26 days of age with HP-PRRSV-2 at high (106) and low (103 TCID50/ml) doses, respectively. At 7 days post-challenge, at the time of the highest viremia levels of HP-PRRSV-2, T1 and T2, and T3 and T4 groups were IM and ID injected with Diluvac Forte using needles and a need-less device (IDAL 3G, MSD Animal Health, The Netherlands), respectively. Same needles or needle-less devices were used to inject the same volume of Diluvac Forte into sentinel pigs. Seroconversion of sentinels was evaluated. The results demonstrated that PP vaccinated groups (G2 and G3), regardless of the route of vaccination, had ELISA response significantly lower than G1 at 7 and 14 DPV. PP-vaccinated groups (G2 and G3) had significantly higher IFN-γ-SC and lower IL-10 secretion compared to the Ing-vaccinated group (G1). The two different MLV when administered intramuscularly demonstrated the difference in virus distribution and shedding patterns. PP-vaccinated pigs had significantly shortened viremia than the Ing-vaccinated pigs. However, ID-vaccinated pigs had lower virus distribution in organs and body fluids without virus shedding to sentinel pigs. In Exp B, regardless of the challenge dose, sentinel pigs intradermally injected with the same needle-less device used to inject challenged pigs displayed no seroconversion. In contrast, sentinel pigs intramuscularly injected with the same needle used to inject challenged pigs displayed seroconversion. The results demonstrated the transmission of PRRSV by using a needle, but not by using a needle-less device. In conclusion, our results demonstrated that ID vaccination might represent an alternative to improve vaccine efficacy and safety, and may be able to reduce the shedding of vaccine viruses and reduce the iatrogenic transfer of pathogens between animals with shared needles.

PRRSV2 genetic diversity defined by RFLP patterns in the United States from 2007 to 2019.

The genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) increases over time. In 1998, restriction-fragment length polymorphism (RFLP) pattern analysis was introduced to differentiate PRRSV wild-type strains from VR2332, a reference strain from which a commercial vaccine (Ingelvac PRRS MLV) was derived. We have characterized here the PRRSV genetic diversity within selected RFLP families over time and U.S. geographic space, using available ISU-VDL data from 2007 to 2019. The 40,454 ORF5 sequences recovered corresponded to 228 distinct RFLPs. Four RFLPs [2-5-2 (21.2%), 1-7-4 (15.6%), 1-4-4 (11.8%), and 1-8-4 (9.9%)] represented 58.5% of all ORF5 sequences and were used for cluster analysis. Over time, there was increased detection of RFLPs 2-5-2, 1-7-4, 1-3-4, 1-3-2, and 1-12-4; decreased detection of 1-4-2, 1-18-4, 1-18-2, and 1-2-2; and different detection trends for 1-8-4, 1-4-4, 1-26-1, 1-22-2, and 1-2-4. An over-time cluster analysis revealed a single cluster for RFLP 2-5-2, supporting that sequences within RFLP 2-5-2 are still relatively conserved. For 1-7-4, 1-4-4, and 1-8-4, there were multiple clusters. State-wise cluster analysis demonstrated 4 main clusters for RFLP 1-7-4 and 1-8-4, and 6 for RFLP 1-4-4. For the other RFLPs, there was a significant genetic difference within them, particularly between states. RFLP typing is limited in its ability to discriminate among different strains of PRRSV. Understanding the magnitude of genetic divergence within RFLPs helps develop PRRSV regional control programs, placement, herd immunization strategies, and design of appropriate animal movements across borders to minimize the risk of PRRSV transmission.

Dose–response modelling of infectious animal diseases coupled with computational fluid dynamics: A simulation of airborne porcine reproductive and respiratory syndrome virus

Dose–response modelling was performed for several infectious disease viruses using the exponential, exact beta-Poisson, and approximate beta-Poisson models using existing datasets of animal infections. The exact beta-Poisson model was found to provide the best fit of the three models. The aerosol transmission route was found to require the lowest dose to cause infection compared to the intra-nasal and oral transmission routes for porcine reproductive and respiratory syndrome virus (PRRSV) and H9N2 avian influenza virus. Foot and mouth disease virus required lower doses with the aerosol transmission route than the intra-nasal transmission route. Liquid oral transmission required lower doses than feed transmission to cause infection for African swine fever virus and overall oral transmission required low doses to cause infection by porcine epidemic and diarrhoea virus. A computational fluid dynamics simulation was coupled with the dose–response modelling to simulate aerosol transmission of PRRSV in two experimental case studies. The coupled model predicted a probability of infection between 82% and 100% using the exact beta-Poisson model, which was in good agreement with the observed rate of infections in the two experimental case studies (84% and 90%).

Mitigation of Airborne PRRSV Transmission with UV Light Treatment: Proof-of-Concept

Proper treatment of infectious air could potentially mitigate the spread of airborne viruses such as porcine reproductive and respiratory syndrome virus (PRRSV). The objective of this research is to test the effectiveness of ultraviolet (UV) in inactivating aerosolized PRRSV, specifically, four UV lamps, UV-A (365 nm, both fluorescent and LED-based), “excimer” UV-C (222 nm), and germicidal UV-C (254 nm), were tested. The two UV-C lamps effectively irradiated fast-moving PRRSV aerosols with short treatment times (<2 s). One-stage and two-stage UV inactivation models estimated the UV doses needed for target percentage (%) reductions on PRRSV titer. UV-C (254 nm) dose needed for 3-log (99.9%) reduction was 19.43 and 2.44 mJ/cm2, respectively, based on one-stage and two-stage models. UV-C (222 nm) doses needed for a 3-log reduction 2.81 and 1.04 mJ/cm2, based on one-stage and two-stage models, respectively. However, the cost of 222 nm excimer lamps is still economically prohibitive for scaling-up trials. The UV-A (365 nm) lamps could not reduce PRRSV titers for tested doses up to 4.11 mJ/cm2. Pilot-scale or farm-scale testing of UV-C on PRRSV aerosols simulating barn ventilation rates are recommended based on its effectiveness and reasonable costs comparable to HEPA filtration.

Modelling the transmission and vaccination strategy for porcine reproductive and respiratory syndrome virus.

Many aspects of the porcine reproductive and respiratory syndrome virus (PRRSV) between-farm transmission dynamics have been investigated, but uncertainty remains about the significance of farm type and different transmission routes on PRRSV spread. We developed a stochastic epidemiological model calibrated on weekly PRRSV outbreaks accounting for the population dynamics in different pig production phases, breeding herds, gilt development units, nurseries and finisher farms, of three hog producer companies. Our model accounted for indirect contacts by the close distance between farms (local transmission), between-farm animal movements (pig flow) and reinfection of sow farms (re-break). The fitted model was used to examine the effectiveness of vaccination strategies and complementary interventions such as enhanced PRRSV detection and vaccination delays and forecast the spatial distribution of PRRSV outbreak. The results of our analysis indicated that for sow farms, 59% of the simulated infections were related to local transmission (e.g. airborne, feed deliveries, shared equipment) whereas 36% and 5% were related to animal movements and re-break, respectively. For nursery farms, 80% of infections were related to animal movements and 20% to local transmission; while at finisher farms, it was split between local transmission and animal movements. Assuming that the current vaccines are 1% effective in mitigating between-farm PRRSV transmission, weaned pigs vaccination would reduce the incidence of PRRSV outbreaks by 3%, indeed under any scenario vaccination alone was insufficient for completely controlling PRRSV spread. Our results also showed that intensifying PRRSV detection and/or vaccination pigs at placement increased the effectiveness of all simulated vaccination strategies. Our model reproduced the incidence and PRRSV spatial distribution; therefore, this model could also be used to map current and future farms at-risk. Finally, this model could be a useful tool for veterinarians, allowing them to identify the effect of transmission routes and different vaccination interventions to control PRRSV spread.

Proteasomal degradation of nonstructural protein 12 by RNF114 suppresses porcine reproductive and respiratory syndrome virus replication

Porcine reproductive and respiratory syndrome virus (PRRSV) poses a significant threat to the swine industry worldwide, and the development of effective and sustainable measures to control PRRSV transmission remains a pressing problem. The function of PRRSV nonstructural protein 12 (Nsp12), which might play essential roles in viral replication and production, remains unknown. In this study, we identified a new host-restricted factor, porcine RING finger protein 114 (RNF114), as an inhibitor of PRRSV replication through its degradation of viral Nsp12. Western blot, quantitative real-time polymerase chain reaction, and viral titer assays indicated that RNF114 overexpression suppressed PRRSV replication, whereas RNF114 knockdown increased viral titer and nucleocapsid protein levels. Additionally, we observed that PPRSV infection led to increased RNF114 levels during the middle and late phases of infection in both porcine alveolar macrophages and MARC-145 cells. Moreover, screening of PRRSV Nsps showed that RNF114 interacted with viral Nsp12, and that RNF114-specific anti-PRRSV effects were associated with its ubiquitin ligase activity, which involves K27-linked polyubiquitination and degradation of Nsp12 through a proteasome-dependent pathway. These findings identified RNF114 as a critical regulator of PRRSV replication and offer insights into the roles of Nsp12 in PRRSV pathogenesis.

Transmission of influenza A virus and porcine reproductive and respiratory syndrome virus using a novel nurse sow model: a proof of concept

The mechanisms of transmission of influenza A virus (IAV) and porcine reproductive and respiratory syndrome virus (PRRSV) in pigs during the pre-weaning period are not fully elucidated. Since viable IAV and PRRSV can be found on the udder skin of lactating sows and the use of nurse sows is a common management practice, we developed a novel nurse sow model to evaluate the transmission of IAV and PRRSV from lactating sows to their adopted piglets. In two studies, we infected pigs with either IAV or PRRSV who then contaminated the udder skin of lactating dams with their nasal and oral secretions while suckling. Once the skin was confirmed virus positive for IAV and PRRSV, the sows were moved to separate empty clean rooms to adopt IAV and PRRSV negative suckling piglets. After adoption, 1 out of eight (12.5%) piglets tested IAV positive 1-day post-adoption (dpa) and the entire litter (8 out of 8) became positive by 4 dpa. In the case of PRRSV, 3 out of 11 (27.3%) pigs tested rRT-PCR positive 2 dpa and there were 7 out of 11 (63.6%) pigs positive at the termination of the study at 7 dpa. This study documented the transmission of IAV and PRRSV between litters of piglets by nurse sows and highlights the importance of the nurse sow-piglet as a unit that contributes to the maintenance of endemic infections in breeding herds. The use of nurse sows in pig farms, though beneficial for minimizing pre-weaning mortality and maximizing farm productivity, is seemingly detrimental as this practice may facilitate the transmission of IAV and PRRSV to piglets prior to weaning.

Inactivation of airborne porcine reproductive and respiratory syndrome virus (PRRSv) by a packed bed dielectric barrier discharge non-thermal plasma

Porcine reproductive and respiratory syndrome virus (PRRSv) is one of the most significant airborne viruses impacting the pork industry in the US. Non-thermal plasmas (NTPs) are electrical discharges comprised of reactive radicals and excited species that inactivate viruses and bacteria. Our previous experiments using a packed bed NTP reactor demonstrated effective inactivation of bacteriophage MS2 as a function of applied voltage and power. The present study examined the effectiveness of the same reactor in inactivating aerosolized PRRSv. A PRRSv solution containing ∼105 TCID50/ml of PRRSv VR2332 strain was aerosolized at 3 ml/min by an air-jet nebulizer and introduced into 5 or 12 cfm air flow followed by NTP exposure in the reactor. Twin impingers upstream and downstream of the reactor collected samples of the virus-laden air flow for subsequent TCID50 assay and qPCR analyses. An optical particle sizer measured upstream and downstream aerosol size distributions, giving estimates of aerosol filtration by the reactor. The results showed that PRRSv was inactivated to a similar degree as MS2 at the same conditions, with the maximum 1.3-log inactivation of PRRSv achieved at 20 kV and 12 cfm air flow rate. The results demonstrate the potential of properly optimized NTPs in controlling PRRSv transmission.

UV-C irradiation is able to inactivate pathogens found in commercially collected porcine plasma as demonstrated by swine bioassay

Liquid porcine plasma is an animal origin raw material for the manufacturing process of spray-dried porcine plasma that is used in pig nutrition worldwide. In previous studies we found that the application of ultraviolet light C (UV-C) in liquid plasma that was inoculated with a variety of bacteria or viruses of importance in the swine industry can be considered as redundant safety steps because in general achieve around 4 logs reduction for most of these pathogens. However, the final validation of the UV-C light as safety feature should be conducted with commercial liquid plasma and using the pig bioassay model. As a first objective, the potential infectivity of a raw liquid plasma product collected from an abattoir was tested by means of a swine bioassay. We used Porcine circovirus 2 (PCV-2), a ubiquitous virus that has been systematically detected by PCR in porcine plasma at abattoirs as selection criteria for commercial liquid plasma lot. As a second aim of the study, the effects of different doses of UV-C irradiation on the selected raw liquid plasma were assayed in the animal bioassay. Moreover, other swine infecting agents, including Porcine reproductive and respiratory syndrome virus (PRRSV), were also determined in the original plasma and monitored in the inoculated animals. Pigs negative for PCV-2 and PRRSV genome and antibodies were allotted to one of five groups (6 to 8 pigs/ group) and injected intra-peritoneally with 10 mL of their assigned inoculum at 50 d of age. Negative control pigs (group 1) were injected with PBS. Positive control pigs (group 5) were injected with a PCV-2 inoculum. Groups 2, 3 and 4 were injected with liquid porcine plasma that had been subjected to 0 (raw plasma), 3000 or 9000 J/L UV-C irradiation, respectively. Group 2 pigs (0 J/L UV-C) got infection by PRRSV but no PCV-2 infection or seroconversion. However, one pig from group 2 seroconverted to Rotavirus A (RVA) and Hepatitis E virus (HEV) and three group 2 pigs seroconverted to Porcine parvovirus (PPV). Groups 1, 3 and 4 pigs showed no evidence of infection or seroconversion associated with the tested viruses or any other pathogens found in the liquid plasma before UV-C irradiation. Group 5 pigs developed PCV-2 infectivity as expected. UV-C irradiation of liquid plasma at 3000 and 9000 J/L was effective in preventing PRRSV and other pathogens transmission. Moreover, raw liquid plasma was non-infectious for PCV-2 in naïve pigs.