The economic impact of porcine reproductive and respiratory syndrome outbreak in four Chinese farms: Based on cost and revenue analysis

Conserved Antagonization of Type I Interferon Signaling by Arterivirus GP5 Proteins

Arteriviruses can establish persistent infections in animals such as equids, pigs, nonhuman primates, rodents, and possums. Some Arteriviruses can even cause overt and severe diseases such as Equine Arteritis in horses and Porcine Reproductive and Respiratory Syndrome in pigs, leading to huge economic losses. Arteriviruses have evolved viral proteins to antagonize the host cell's innate immune responses by inhibiting type I interferon (IFN) signaling, assisting viral evasion and persistent infection. So far, the role of the Arterivirus glycoprotein 5 (GP5) protein in IFN signaling inhibition remains unclear. Here, we investigated the inhibitory activity of 47 Arterivirus GP5 proteins derived from various hosts. We demonstrated that all GP5 proteins showed conserved activity for antagonizing TIR-domain-containing adapter proteins inducing interferon-β (TRIF)-mediated IFN-β signaling through TRIF degradation. In addition, Arterivirus GP5 proteins showed a conserved inhibitory activity against IFN-β signaling, induced by either pig or human TRIF. Furthermore, certain Arterivirus GP5 proteins could inhibit the induction of IFN-stimulated genes. These findings highlight the role of Arterivirus GP5 proteins in supporting persistent 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.

Caffeic acid phenethyl ester: an effective antiviral agent against porcine reproductive and Respiratory Syndrome Virus

Porcine Reproductive and Respiratory Syndrome (PRRS) presents a formidable viral challenge in swine husbandry. Confronting the constraints of existing veterinary pharmaceuticals and vaccines, this investigation centers on Caffeic Acid Phenethyl Ester (CAPE) as a prospective clinical suppressant for the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV). The study adopts an integrated methodology to evaluate CAPE's antiviral attributes. This encompasses a dual-phase analysis of CAPE's interaction with PRRSV, both in vitro and in vivo, and an examination of its influence on viral replication. Varied dosages of CAPE were subjected to empirical testing in animal models to quantify its efficacy in combating PRRSV infections. The findings reveal a pronounced antiviral potency, notably in prophylactic scenarios. As a predominant component of propolis, CAPE stands out as a promising candidate for clinical suppression, showing exceptional effectiveness in pre-exposure prophylaxis regimes. This highlights the potential of CAPE in spearheading cutting-edge strategies for the management of future PRRSV outbreaks.

Prevalence and genetic evolution of porcine reproductive and respiratory syndrome virus in commercial fattening pig farms in China

BACKGROUND

To investigate the prevalence and evolution of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) at commercial fattening pig farms, a total of 1397 clinical samples were collected from a single fattening cycle at seven pig farms in five provinces of China from 2020 to 2021.

RESULTS

The RT‒PCR results revealed that PRRSV was present on all seven farms, and the percentage of PRRSV-positive individuals was 17.54-53.33%. A total of 344 partial NSP2 gene sequences and 334 complete ORF5 gene sequences were obtained from the positive samples. The statistical results showed that PRRSV-2 was present on all seven commercial fattening farms, and PRRSV-1 was present on only one commercial fattening farm. A total of six PRRSV-2 subtypes were detected, and five of the seven farms had two or more PRRSV-2 subtypes. L1.8 (L1C) PRRSV was the dominant epidemic strain on five of the seven pig farms. Sequence analysis of L1.8 (L1C) PRRSV from different commercial fattening pig farms revealed that its consistency across farms varied substantially. The amino acid alignment results demonstrated that there were 131 aa discontinuous deletions in NSP2 between different L1.8 (L1C) PRRSV strains and that the GP5 mutation in L1.8 (L1C) PRRSV was mainly concentrated in the peptide signal region and T-cell epitopes. Selection pressure analysis of GP5 revealed that the use of the PRRSV MLV vaccine had no significant episodic diversifying effect on L1.8 (L1C) PRRSV.

CONCLUSION

PRRSV infection is common at commercial fattening pig farms in China, and the percentage of positive individuals is high. There are multiple PRRSV subtypes of infection at commercial fattening pig farms in China. L1.8 (L1C) is the main circulating PRRSV strain on commercial fattening pig farms. L1.8 (L1C) PRRSV detected at different commercial fattening pig farms exhibited substantial differences in consistency but similar molecular characteristics. The pressure on the GP5 of L1.8 (L1C) PRRSV may not be directly related to the use of the vaccines.

Evaluation of Truck Cab Decontamination Procedures following Inoculation with Porcine Epidemic Diarrhea Virus and Porcine Reproductive and Respiratory Syndrome Virus

This experiment aimed to evaluate commercially available disinfectants and their application methods against porcine epidemic diarrhea virus (PEDV) and porcine reproductive and respiratory syndrome virus (PRRSV) on truck cab surfaces. Plastic, fabric, and rubber surfaces inoculated with PEDV or PRRSV were placed in a full-scale truck cab and then treated with one of eight randomly assigned disinfectant treatments. After application, surfaces were environmentally sampled with cotton gauze and tested for PEDV and PRRSV using qPCR duplex analysis. There was a disinfectant × surface interaction (p < 0.0001), indicating a detectable amount of PEDV or PRRSV RNA was impacted by disinfectant treatment and surface material. For rubber surfaces, 10% bleach application had lower detectable amounts of RNA compared to all other treatments (p < 0.05) except Intervention via misting fumigation, which was intermediate. In both fabric and plastic surfaces, there was no evidence (p > 0.05) of a difference in detectable RNA between disinfectant treatments. For disinfectant treatments, fabric surfaces with no chemical treatment had less detectable viral RNA compared to the corresponding plastic and rubber (p < 0.05). Intervention applied via pump sprayer to fabric surfaces had less detectable viral RNA than plastic (p < 0.05). Furthermore, 10% bleach applied via pump sprayer to fabric and rubber surfaces had less detectable viral RNA than plastic (p < 0.05). Also, a 10 h downtime, with no chemical application or gaseous fumigation for 10 h, applied to fabric surfaces had less detectable viral RNA than other surfaces (p < 0.05). Sixteen treatments were evaluated via swine bioassay, but all samples failed to produce infectivity. In summary, commercially available disinfectants successfully reduced detectable viral RNA on surfaces but did not eliminate viral genetic material, highlighting the importance of bioexclusion of pathogens of interest.

Glycoprotein 5-Derived Peptides Induce a Protective T-Cell Response in Swine against the Porcine Reproductive and Respiratory Syndrome Virus

We analyzed the T-cell responses induced by lineal epitopes of glycoprotein 5 (GP5) from PRRSV to explore the role of this protein in the immunological protection mediated by T-cells. The GP5 peptides were conjugated with a carrier protein for primary immunization and booster doses. Twenty-one-day-old pigs were allocated into four groups (seven pigs per group): control (PBS), vehicle (carrier), PTC1, and PTC2. Cytokine levels were measured at 2 days post-immunization (DPI) from serum samples. Cytotoxic T-lymphocytes (CTLs, CD8+) from peripheral blood were quantified via flow cytometry at 42 DPI. The cytotoxicity was evaluated by co-culturing primed lymphocytes with PRRSV derived from an infectious clone. The PTC2 peptide increased the serum concentrations of pro-inflammatory cytokines (i.e., TNF-α, IL-1β, IL-8) and cytokines that activate the adaptive cellular immunity associated with T-lymphocytes (i.e., IL-4, IL-6, IL-10, and IL-12). The concentration of CTLs (CD8+) was significantly higher in groups immunized with the peptides, which suggests a proliferative response in this cell population. Primed CTLs from immunized pigs showed cytolytic activity in PRRSV-infected cells in vitro. PTC1 and PTC2 peptides induced a protective T-cell-mediated response in pigs immunized against PRRSV, due to the presence of T epitopes in their sequences.

Stochastic model to assess bioeconomic impact of PRRS on pig farms in Costa Rica

Despite the economic importance of PRRS and its high prevalence in Costa Rica, there are no studies on the bioeconomic impact of the disease in the country or, even, in Central America. Such studies are essential in finding cost-effective preventive measures tailored for different production circumstances. Therefore, the objective of this study was to evaluate economic and production parameters of a PRRSV-infection for a medium-sized farrow-to-finish pig farm system in Costa Rica with a farm-level stochastic Monte Carlo simulation model. The effect of PRRS was assessed by scenario analysis, in which a baseline PRRS-free situation was compared against three alternative scenarios that assumed low, medium and high PRRS effects. The PRRS effects were based on data from local farms, scientific literature and expert opinion. Sensitivity analyses were performed to assess the impact of key input parameters on output variables. Results show that at the animal level, changes between the baseline and the PRRS-high scenario were estimated as: + 25 d in age to slaughter, - 9.9 pigs to slaughter (per breeding sow/yr), + 6% annual replacement rate, - 255 d in sow productive lifetime, - 6.9 mo in age at culling of sows, and + 24 non- productive days. For a medium size local farm (n = 588 sows), a reduction of 5826 fat pigs to slaughter per farm/yr from baseline compared to PRRS-high scenario was observed. PRRS-induced loss per farm per year was estimated at -US $142,542, US $180,109 and -US $524,719 for PRRS-low, medium and high scenarios, respectively. Revenues/costs ratio changed from 1.12 in the baseline to 0.89 in the PRRS-high scenario. The production cost per kg carcass weight increased from US $2.63 for the baseline to US $3.35 in the PRRS-high scenario. PRRS-induced loss was estimated at US $77.1 per slaughtered pig/yr and US $892 per breeding sow/yr for the PRRS-high scenario. Results from the model indicate that pig farms with medium to high prevalence of PRRS will require optimal market conditions in order to have positive economic outcomes. These results can be helpful in the design of better control strategies for PRRS.

Long non-coding RNA LOC103222771 promotes infection of porcine reproductive and respiratory syndrome virus in Marc-145 cells by downregulating Claudin-4

Porcine reproductive and respiratory syndrome (PRRS) is an important swine disease caused by infection of porcine reproductive and respiratory syndrome virus (PRRSV), which leads to huge loss in swine industry. How to effectively control PRRS is challenging. Long non-coding RNA (lncRNA) are key regulator of viral infections and anti-virus immunological responses, therefore, further understanding of lncRNAs will aid to identification of novel regulators of viral infections and better design of prevention and control strategies to viral infection related diseases and immune disorders. We demonstrated that PRRSV infection upregulated the expression of lncRNA LOC103222771 in Marc-145 cells and porcine alveolar macrophage cells (PAMs) and that LOC103222771 is mainly located in cytoplasm. Knockdown of LOC103222771 could inhibit the PRRSV infection in Marc-145 cells. RNA-seq analysis and subsequent validation revealed increased expression of Claudin-4 (CLDN4) in Marc-145 when LOC103222771 was specifically downregulated，suggesting that LOC103222771 might be an upstream regulator of CLDN4, an important component of tight junctions for establishment of the paracellular barrier that controls the flow of molecules in the intercellular space between epithelial cells. We and others showed that Downregulation of CLDN4 could boost the infection of PRRSV. Collectively, LOC103222771/CLDN4 signal axis might be a novel mechanism of PRRSV pathogenesis, implying a potential therapeutic target against PRRSV infection.

Genetic background influences pig responses to porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly infectious and economically significant virus that causes respiratory and reproductive diseases in pigs. It results in reduced productivity and increased mortality in pigs, causing substantial economic losses in the industry. Understanding the factors affecting pig responses to PRRSV is crucial to develop effective control strategies. Genetic background has emerged as a significant determinant of susceptibility and resistance to PRRSV in pigs. This review provides an overview of the basic infection process of PRRSV in pigs, associated symptoms, underlying immune mechanisms, and roles of noncoding RNA and alternative splicing in PRRSV infection. Moreover, it emphasized breed-specific variations in these aspects that may have implications for individual treatment options.

The economic impact of endemic respiratory disease in pigs and related interventions - a systematic review

BACKGROUND

Understanding the financial consequences of endemically prevalent pathogens within the porcine respiratory disease complex (PRDC) and the effects of interventions assists decision-making regarding disease prevention and control. The aim of this systematic review was to identify what economic studies have been carried out on infectious endemic respiratory disease in pigs, what methods are being used, and, when feasible, to identify the economic impacts of PRDC pathogens and the costs and benefits of interventions.

RESULTS

By following the PRISMA method, a total of 58 studies were deemed eligible for the purpose of this systematic review. Twenty-six studies used data derived from European countries, 18 from the US, 6 from Asia, 4 from Oceania, and 4 from other countries, i.e., Canada, Mexico, and Brazil. Main findings from selected publications were: (1) The studies mainly considered endemic scenarios on commercial fattening farms; (2) The porcine reproductive and respiratory syndrome virus was by far the most studied pathogen, followed by Mycoplasma hyopneumoniae, but the absence or presence of other endemic respiratory pathogens was often not verified or accounted for; (3) Most studies calculated the economic impact using primary production data, whereas twelve studies modelled the impact using secondary data only; (4) Seven different economic methods were applied across studies; (5) A large variation exists in the cost and revenue components considered in calculations, with feed costs and reduced carcass value included the most often; (6) The reported median economic impact of one or several co-existing respiratory pathogen(s) ranged from €1.70 to €8.90 per nursery pig, €2.30 to €15.35 per fattening pig, and €100 to €323 per sow per year; and (7) Vaccination was the most studied intervention, and the outcomes of all but three intervention-focused studies were neutral or positive.

CONCLUSION

The outcomes and discussion from this systematic review provide insight into the studies, their methods, the advantages and limitations of the existing research, and the reported impacts from the endemic respiratory disease complex for pig production systems worldwide. Future research should improve the consistency and comparability of economic assessments by ensuring the inclusion of high impact cost and revenue components and expressing results similarly.

Development of a one-step reverse transcription-quantitative polymerase chain reaction assay for the detection of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) is an important disease that severely affects the swine industry and, therefore, warrants rapid and accurate diagnosis for its control. Despite the progress in developing diagnostic tools, including polymerase chain reaction (PCR)-based methods such as reverse transcription quantitative PCR (RT-qPCR) to diagnose PRRSV infection, its diagnosis at the genetic level is challenging because of its high genetic variability. Nevertheless, RT-qPCR is the easiest and fastest method for diagnosing PRRSV. Therefore, this study aimed to develop an RT-qPCR assay for rapid and accurate diagnosis of PRRSV by encompassing all publicly available PRRSV sequences. The developed assay using highly specific primers and probes could detect up to 10 copies of PRRSV-1 and -2 subtypes. Furthermore, a comparison of the performance of the developed assay with those of two commercial kits widely used in South Korea demonstrated the higher efficiency of the developed assay in detecting PRRSV infections in field samples. For PRRSV-1 detection, the developed assay showed a diagnostic agreement of 97.7% with the results of ORF5 sequencing, while for commercial kits, it showed 95.3% and 72.1% agreement. For PRRSV-2, the developed assay showed a diagnostic agreement of 97.7%, whereas the commercial kits showed 93% and 90.7% agreement. In conclusion, we developed an assay with higher accuracy than those of the tested commercial kits, which will contribute markedly to global PRRSV control.

Protective Efficacy of a Candidate Live-Attenuated Vaccine Derived from the SD-R Strain against NADC34-like Porcine Reproductive and Respiratory Syndrome Virus

NADC34-like porcine reproductive and respiratory syndrome virus (PRRSV) strains were first detected in China in 2017 and became major circulating strains in 2021. Our previous study showed that the live-attenuated vaccine candidate SD-R strain could provide broad cross-protection against different NADC30-like PRRSVs (sublineage 1.8). However, the protective effect of SD-R against NADC34-like PRRSV is unclear. Here, a novel NADC34-like PRRSV, LNTZJ1341-2012, was isolated from a pig farm experiencing disease in 2020. Sequence analysis revealed that LNTZJ1341-2012 belonged to PRRSV-2 sublineage 1.5, exhibited the same Nsp2 amino-acid deletion characteristics as IA/2014/NADC34, and had not recombined with other strains. Additionally, a good challenge model was established to evaluate the protection afforded by the candidate SD-R vaccine against infection with a representative NADC34-like strain (LNTZJ1341-2012). The control piglets in the challenge experiment displayed clinical signs typical of PRRSV infection, including transient fever, high viremia, mild clinical symptoms, and histopathological changes in the lungs and submaxillary lymph nodes. In contrast, SD-R vaccination significantly reduced serum and lung tissue viral loads, and vaccinated piglets did not show any clinical symptoms or histopathological changes. Our results demonstrated that LNTZJ1341-2012 is a mildly virulent NADC34-like PRRSV and that the live-attenuated vaccine SD-R can prevent the onset of clinical signs upon challenge with the NADC34-like PRRSV LNTZJ1341-2012 strain, indicating that SD-R is a promising vaccine candidate for the swine industry.

A novel strategy to attenuate porcine reproductive and respiratory syndrome virus by inhibiting viral replication in the target pulmonary alveolar macrophages via hematopoietic-specific miR-142

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen for the global pork industry. Although modified live virus (MLV) vaccines are commonly used for PRRSV prevention and control,  they still carry a risk of infecting the host and replicating in target cells, thereby increasing the likehood of virus recombination and reversion to virulence. In this study, we inserted the target sequence of miR-142 into the nsp2 hypervariable region of PRRSV to inhibit viral replication in its host cells of pigs, with the aim of achieving virus attenuation. The chimeric virus RvJX-miR-142t was successfully rescued and retained its growth characteristics in MARC-145 cells. Furthermore, it did not replicate in MARC-145 cells transfected with miRNA-142 mimic. We also observed limited replication ability of RvJX-miR-142t in pulmonary alveolar macrophages, which are the main cell types that PRRSV infects. Our animal inoculation study showed that pigs infected with RvJX-miR-142t displayed less severe clinical symptoms, lower viremia titers, lighter lung lesions, and significantly lower mortality rates during the first 7 days post-inoculation, in comparison to pigs infected with the backbone virus RvJXwn. We detected a partially deletion of the miR-142 target sequence in the RvJX-miR-142t genome at 14 dpi. It is highly possible that the reversion of viral virulence observed in the later timepoints of our animal experiment was caused by that. Our study provided a new strategy for attenuating PRRSV and confirmed its effectiveness. However, further studies are necessary to increase the stability of this virus under host selection pressure.

Tylvalosin Tartrate Improves the Health Status of Swine Herds during Immunization with Porcine Reproductive and Respiratory Syndrome Virus-Inactivated Vaccine

Porcine reproductive and respiratory syndrome (PRRS) is a devastating disease that affects pigs and is responsible for severe economic losses. The commercial PRRSV-inactivated vaccine (CH-1a strain) in China was recently selected to control PRRS in large populations of PRRS-positive sows and was found to effectively reduce the rate of stillbirth abortion based on clinical observations. However, stress from vaccine inoculation (e.g., fever, anorexia, abortions, and slow body weight gain) usually appears after immunization on many swine farms. In this study, we fed piglets a diet medicated with tylvalosin tartrate during PRRSV-inactivated vaccine immunization. We found that tylvalosin tartrate attenuated the increase in total white blood cells induced by immunization at day one post-immunization (DPI) and induced an increase in monocyte counts after seven DPI. There was also attenuation in the intensity of the inflammatory response induced by vaccination and elevation of serum IFN-γ concentrations at three and seven DPI after immunization. The administration of tylvalosin tartrate could also attenuate the reduction in the percentage of CD8⁺ T cells induced by PRRSV-inactivated vaccine immunization at seven DPI. These results demonstrated that in addition to tylvalosin tartrate being able to control respiratory and enteric bacterial infections in swine farms, it can also improve the stress status of swine herds during PRRSV-inactivated vaccine immunization.

Epidemiological investigation and genetic evolutionary analysis of PRRSV-1 on a pig farm in China

Porcine reproductive and respiratory syndrome virus (PRRSV) has brought serious economic losses to pig industry. PRRSV-1 have existed in China for more than 25 years. The prevalence and features of PRRSV-1 on Chinese farms are unclear. We continuously monitored PRRSV in a pig farm with strict biosafety measures in Henan Province, China, in 2020. The results showed that multiple types of PRRSV coexisted on this single pig farm. PRRSV-1 was one of the main circulating strains on the farm and was responsible for infections throughout nearly the entire epidemic cycle. Phylogenetic analysis showed that PRRSV-1 isolates from this pig farm formed an independent branch, with all isolates belonging to BJEU06-1-like PRRSV. The analysis of selection pressure on ORF5 on this branch identified 5 amino acids as positive selection sites, indicating that PRRSV-1 had undergone adaptive evolution on this farm. According to the analysis of ORF5 of PRRSV-1 on this farm, the evolutionary rate of the BJEU06-1-like branch was estimated to be 1.01 × 10^-2 substitutions/site/year. To further understand the genome-wide characteristics of PRRSV-1 on this pig farm, two full-length PRRSV-1 genomes representative of pig farms were obtained. The results of amino acid alignment revealed that although one NSP2 deletion was consistent with BJEU06-1, different new features were found in ORF3 and ORF4. According to the above results, PRRSV-1 has undergone considerable evolution in China. This study is the first to report the prevalence and characteristics of PRRSV-1 on a large farm in mainland China, which will provide a reference for the identification and further prevention and control of PRRSV-1.