Application of an economic calculator to determine the cost of porcine reproductive and respiratory syndrome at farm-level in 21 pig herds in Germany

The effect of matrine and glycyrrhizic acid on porcine reproductive and respiratory syndrome virus in Vitro and in vivo

Porcine reproductive and respiratory syndrome (PRRS) is endemic worldwide, seriously affecting the development of the pig industry, but vaccines have limited protective effects against PRRSV transmission. The aim of this study was to identify potential anti-PRRSV drugs. We examined the cytotoxicity of seven compounds formulated based on the mass ratio of glycyrrhizic acid to matrine and calculated their inhibition rates against PRRSV in vitro. The results showed that the seven compounds all had direct killing and therapeutic effects on PRRSV, and the compounds inhibited PRRSV replication in a time- and dose-dependent manner. The compound with the strongest anti-PRRSV effect was selected for subsequent in vivo experiments. Pigs were divided into a control group and a medication group for the in vivo evaluation. The results showed that pigs treated with the 4:1 compound had 100% morbidity after PRRSV challenge, and the mortality rate reached 75% on the 8th day of the virus challenge. These results suggest that this compound has no practical anti-PRRSV effect in vivo and can actually accelerate the death of infected pigs. Next, we further analyzed the pigs that exhibited semiprotective effects following vaccination with the compound to determine whether the compound can synergize with the vaccine in vivo. The results indicated that pigs treated with the compound had higher mortality rates and more severe clinical reactions after PRRSV infection (p < 0.05). The levels of proinflammatory cytokines (IL-6, IL-8, IL-1β, IFN-γ, and TNF-α) were significantly greater in the compound-treated pigs than in the positive control-treated pigs (p < 0.05), and there was no synergistic enhancement with the live attenuated PRRSV vaccine (p < 0.05). The compound enhanced the inflammatory response, prompted the body to produce excessive levels of inflammatory cytokines and caused body damage, preventing a therapeutic effect. In conclusion, the present study revealed that the in vitro effectiveness of these agents does not indicate that they are effective in vivo or useful for developing anti-PRRSV drugs. Our findings also showed that, to identify effective anti-PRRSV drugs, comprehensive drug screening is needed, for compounds with solid anti-inflammatory effects both in vitro and in vivo. Our study may aid in the development of new anti-PRRSV drugs.

Investigation of PRRS Virus Infection in Hungarian Wild Boar Populations during Its Eradication from Domestic Pig Herds

Porcine Reproductive and Respiratory Syndrome (PRRS) significantly impacts the pig farming industry globally, leading to economic losses due to reduced productivity. This study focuses on assessing the presence and impact of PRRS within Hungarian wild boar populations amidst efforts to eradicate the virus from domestic pig herds. We used a combination of serological and virological tests on samples collected from wild boars across Hungary to evaluate the prevalence of PRRS virus and its potential transmission risks to domestic pigs. Our findings reveal a low seropositivity rate in wild boars, suggesting a minimal role of wild boars in the transmission of PRRS to domestic pig populations. Moreover, no relationship was found between domestic pig and wild boar densities, emphasizing the limited interaction and consequent risk of disease spread between these populations. We confirm the effectiveness of Hungary's PRRS eradication measures among domestic herds and highlight the negligible risk posed by wild boars in re-introducing the PRRS virus.

Role of N-linked glycosylation in porcine reproductive and respiratory syndrome virus (PRRSV) infection

Porcine reproductive and respiratory syndrome (PRRSV) is an enveloped single-stranded positive-sense RNA virus and one of the main pathogens that causes the most significant economical losses in the swine-producing countries. PRRSV is currently divided into two distinct species, PRRSV-1 and PRRSV-2. The PRRSV virion envelope is composed of four glycosylated membrane proteins and three non-glycosylated envelope proteins. Previous work has suggested that PRRSV-linked glycans are critical structural components for virus assembly. In addition, it has been proposed that PRRSV glycans are implicated in the interaction with host cells and critical for virus infection. In contrast, recent findings showed that removal of N-glycans from PRRSV does not influence virus infection of permissive cells. Thus, there are not sufficient evidences to indicate compellingly that N-glycans present in the PRRSV envelope play a direct function in viral infection. To gain insights into the role of N-glycosylation in PRRSV infection, we analysed the specific contribution of the envelope protein-linked N-glycans to infection of permissive cells. For this purpose, we used a novel strategy to modify envelope protein-linked N-glycans that consists of production of monoglycosylated PRRSV and viral glycoproteins with different glycan states. Our results showed that removal or alteration of N-glycans from PRRSV affected virus infection. Specifically, we found that complex N-glycans are required for an efficient infection in cell cultures. Furthermore, we found that presence of high mannose type glycans on PRRSV surface is the minimal requirement for a productive viral infection. Our findings also show that PRRSV-1 and PRRSV-2 have different requirements of N-glycan structure for an optimal infection. In addition, we demonstrated that removal of N-glycans from PRRSV does not affect viral attachment, suggesting that these carbohydrates played a major role in regulating viral entry. In agreement with these findings, by performing immunoprecipitation assays and colocalization experiments, we found that N-glycans present in the viral envelope glycoproteins are not required to bind to the essential viral receptor CD163. Finally, we found that the presence of N-glycans in CD163 is not required for PRRSV infection.

Research progress on the N protein of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease caused by the porcine reproductive and respiratory syndrome virus (PRRSV). PRRSV exhibits genetic diversity and complexity in terms of immune responses, posing challenges for eradication. The nucleocapsid (N) protein of PRRSV, an alkaline phosphoprotein, is important for various biological functions. This review summarizes the structural characteristics, genetic evolution, impact on PRRSV replication and virulence, interactions between viral and host proteins, modulation of host immunity, detection techniques targeting the N protein, and progress in vaccine development. The discussion provides a theoretical foundation for understanding the pathogenic mechanisms underlying PRRSV virulence, developing diagnostic techniques, and designing effective vaccines.

Role of microRNAs in host defense against porcine reproductive and respiratory syndrome virus infection: a hidden front line

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most globally devastating viruses threatening the swine industry worldwide. Substantial advancements have been achieved in recent years towards comprehending the pathogenesis of PRRSV infection and the host response, involving both innate and adaptive immune responses. Not only a multitude of host proteins actively participate in intricate interactions with viral proteins, but microRNAs (miRNAs) also play a pivotal role in the host response to PRRSV infection. If a PRRSV-host interaction at the protein level is conceptualized as the front line of the battle between pathogens and host cells, then their fight at the RNA level resembles the hidden front line. miRNAs are endogenous small non-coding RNAs of approximately 20-25 nucleotides (nt) that primarily regulate the degradation or translation inhibition of target genes by binding to the 3'-untranslated regions (UTRs). Insights into the roles played by viral proteins and miRNAs in the host response can enhance our comprehensive understanding of the pathogenesis of PRRSV infection. The intricate interplay between viral proteins and cellular targets during PRRSV infection has been extensively explored. This review predominantly centers on the contemporary understanding of the host response to PRRSV infection at the RNA level, in particular, focusing on the twenty-six miRNAs that affect viral replication and the innate immune response.

The scene of lung pathology during PRRSV-1 infection

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important infectious diseases for the pig industry worldwide. The disease was firstly reported in 1987 and became endemic in many countries. Since then, outbreaks caused by strains of high virulence have been reported several times in Asia, America and Europe. Interstitial pneumonia, microscopically characterised by thickened alveolar septa, is the hallmark lesion of PRRS. However, suppurative bronchopneumonia and proliferative and necrotising pneumonia are also observed, particularly when a virulent strain is involved. This raises the question of whether the infection by certain strains results in an overstimulation of the proinflammatory response and whether there is some degree of correlation between the strain involved and a particular pattern of lung injury. Thus, it is of interest to know how the inflammatory response is modulated in these cases due to the interplay between virus and host factors. This review provides an overview of the macroscopic, microscopic, and molecular pathology of PRRSV-1 strains in the lung, emphasising the differences between strains of different virulence.

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.

Spatiotemporal Distribution of PRRSV-1 Clades in Hungary with a Focus on the Era of Disease Eradication

Porcine reproductive and respiratory syndrome (PRRS) is the cause of the most severe economic losses in the pig industry worldwide. PRRSV is extremely diverse in Europe, which poses a significant challenge to disease control within a country or any region. With the combination of phylogenetic reconstruction and network analysis, we aimed to uncover the major routes of the dispersal of PRRSV clades within Hungary. In brief, by analyzing >2600 ORF5 sequences, we identified at least 12 clades (including 6 clades within lineage 1 and 3 clades within lineage 3) common in parts of Western Europe (including Denmark, Germany and the Netherlands) and identified 2 novel clades (designated X1 and X2). Of interest, some genetic clades unique to other central European countries, such as the Czech Republic and Poland, were not identified. The pattern of PRRSV clade distribution is consistent with the route of the pig trade among countries, showing that most of the identified clades were introduced from Western Europe when fatteners were transported to Hungary. As a result of rigorous implementation of the national eradication program, the swine population was declared officially free from PRRSV. This map of viral diversity and clade distribution will serve as valuable baseline information for the maintenance of PRRSV-free status in the post-eradication era.

Eradication of PRRS from Hungarian Pig Herds between 2014 and 2022

Porcine reproductive and respiratory syndrome (PRRS) is a widespread infectious disease that is currently a major cause of economic losses in pig production. In Hungary, a National PRRS Eradication Program has been introduced to attain a more efficient, economic, and competitive international market position. The program has been also approved by the EU, but the resulting legal obligations have imposed a burden on Hungarian producers to comply with EU competition rules. The implementation of the program has been carried out by the veterinary authorities with the consent of, continuous support from and monitoring conducted by organisations within the pig sector as well as a scientific committee. The PRRS eradication program in Hungary was based on a regional territorial principle and was compulsory for all pig holdings within the regions. In Hungary, large fattening farms operate as all-in/all-out or continuous flow systems. Large-scale breeding herds are predominantly farrow-to-finish types. Although its significance has decreased in recent decades, 20% of the Hungarian pig population is still kept on small (backyard) farms (<100 animals). All PRRSV-infected large-scale farms had to develop a unit-adapted eradication plan, including external and internal biosecurity measures, vaccinations, etc. It was crucial to render each fattening unit free of the disease, as fattening units play a significant role in spreading the virus within the country. The eradication efforts mainly implemented were depopulation-repopulation methods, but on some farms a testing and removal method has been used. As the eradication progressed over the years, the introduction of infected fattening pigs was restricted. Thanks to these measures, Hungarian large-scale fattening farms became PRRSV-free by the end of 2018. The PRRSV-free status of small-scale herds was achieved by the end of 2015 and was maintained between 2016 and 2021. By 31 December 2021, all breeding pigs in large-scale farms in Hungary were free of wild-type PRRS virus. By 31 March 2022, the total pig population of the country, including all backyard farms and fattening units, achieved PRRSV-free status. The future goal is to ensure and maintain the PRRSV-free status of Hungary via strict import regulations of live animals combined with the continuous and thorough screening of incoming and resident herds for the presence of the virus.

Activated macrophages of CD 163 gene edited pigs generated by direct cytoplasmic microinjection with CRISPR gRNA/Cas9 mRNA are resistant to PRRS virus assault

Porcine reproductive and respiratory syndrome virus (PRRSV) infects placental and lung macrophages, causing a global epidemic with economic loss. Attempts to develop an effective vaccine to control the disease have not been effective. Currently, developing PRRSV disease-resistant pigs via a gene editing (GE) strategy to mutate the PRRSV receptor or to delete the binding domain on the macrophage appears promising. In this study, we used the strategy of Edinburg University to construct two guide RNAs (gRNAs) located on the proximal front and post sites of exon 7. Directive microinjection of two gRNAs and Cas9 mRNA into the cytoplasm of pronuclear zygotes efficiently generated four piglets confirmed as CD163 knockout (KO) and/or CD163 exon 7 deleted (CD163ΔE7). In four GE piglets, three pigs carried two chromosome CD163 KO or ΔE7. Peripheral blood mononuclear cells (PBMCs) from three GE and wild-type (WT) pigs were activated into macrophages for in vitro transfection. The results showed that the activated macrophages from all GE pigs were significantly more viable than those from WT pig. Current results suggest that we have successfully generated PRRSV-resistant pigs, although in vivo challenge is needed to validate that the pigs are PRRSV resistant.

The natural compound Sanggenon C inhibits PRRSV infection by regulating the TRAF2/NF-κB signalling pathway

Porcine reproductive and respiratory syndrome (PRRS) is a serious infectious disease and one of the major causes of death in the global pig industry. PRRS virus (PRRSV) strains have complex and diverse genetic characteristics and cross-protection between strains is low, which complicates vaccine selection; thus, the current vaccination strategy has been greatly compromised. Therefore, it is necessary to identify effective natural compounds for the clinical treatment of PRRS. A small molecule library composed of 720 natural compounds was screened in vitro, and we found that Sanggenon C (SC) was amongst the most effective natural compound inhibitors of PRRSV infection. Compared with ribavirin, SC more significantly inhibited PRRSV infection at both the gene and protein levels and reduced the viral titres and levels of protein expression and inflammatory cytokine secretion to more effectively protect cells from PRRSV infection and damage. Mechanistically, SC inhibits activation of the NF-κB signalling pathway by promoting TRAF2 expression, thereby reducing PRRSV replication. In conclusion, by screening natural compounds, we found that SC suppresses PRRSV infection by regulating the TRAF2/NF-κB signalling pathway. This study contributes to a deeper understanding of the therapeutic targets and pathogenesis of PRRSV infection. More importantly, our results demonstrate that SC has potential as a candidate for the treatment of PRRS.

Seroprevalence of Viral Enzootic Diseases in Swine Backyard Farms in Serbia

Contrary to pig farming in developed Western countries, in a large part of the world, pigs are still traditionally kept in small backyard farms, usually for family needs. Their main characteristics are low biosecurity, swill feeding, natural breeding and uncontrolled trade. Given the high number of backyard farms in Serbia and the risk they are thought to pose to intensive pig farming, the main aim of this study was to evaluate the prevalence of major viral diseases of swine among traditionally kept pigs in small holdings with low biosecurity. For this investigation, 222 serum samples from 69 backyard holdings were randomly selected and tested for antibodies to Porcine Reproductive and Respiratory Syndrome virus (PRRSV), Aujeszky's disease virus (ADV), Porcine Parvovirus (PPV) and Swine influenza Virus (SIV) by enzyme-linked immunosorbent assay (ELISA). The herd-level seroprevalence of PRRS, Aujeszky's disease and PPV was 2.9%, 27.5% and 37.7%, respectively. Swine influenza seroconversion was not confirmed in any of the tested holdings. Despite widely distributed PPV and AD in backyard farms in Serbia, almost 50% of them are still negative for all the tested diseases. The backyard farms must be monitored, and owners must be educated as their role in eradication programs and obtaining country-free status may be crucial.

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.

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.

Levels of neutralizing antibodies against resident farm strain or vaccine strain are not indicators of protection against PRRSV-1 vertical transmission under farm conditions

BACKGROUND

Vertical transmission is key for the maintenance of porcine reproductive and respiratory syndrome virus (PRRSV) infection. In vaccinated farms, vertical transmission can still occur despite sows having some level of immunity because of repeated vaccination or contact with the wild-type virus. The present study aimed to correlate the age of sows and the amplitude of neutralizing antibodies (Nab) (heterologous neutralization) with PRRSV-1 vertical transmission (VT). For this purpose, umbilical cords of 1,554 newborns (corresponding to 250 litters) were tested for PRRSV by RT-PCR in two PRRSV-unstable vaccinated farms. In parallel, the sows were bled after farrowing and the levels of antibodies were determined by ELISA and by the viral neutralization test against the vaccine virus, the virus circulating in the farm, and other unrelated contemporary PRRSV-1 strains. The relationship between the parity and the probability of delivering infected piglets and the presence of broadly Nabs examined.

RESULTS

The proportion of VT events in the two examined farms ranged from 18.9% to 23.0%. Young sows (parity 1-2) were 1.7 times more likely to have VT than older sows (p < 0.05). Despite higher ELISA S/P antibody ratios in younger sows (p < 0.05), NAb against the resident farm strain were at a similar level between sows delivering infected and healthy piglets regardless of age, mostly with low titers (2-3 log2). The titers of NAb against the vaccine virus were also low, and no correlations with VT were observed. When a panel of another 4 strains (1 isolated in the 1990s, and 3 contemporary strains) were used for the neutralization test, most sow sera were not capable of neutralizing the contemporary strains.

CONCLUSIONS

Titers of NAb could not be correlated with the occurrence of PRRSV VT. The amplitude of NAb present in most vaccinated sows is limited with a considerable proportion unresponsive regarding NAb production.

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.

miR-204 suppresses porcine reproductive and respiratory syndrome virus (PRRSV) replication via inhibiting LC3B-mediated autophagy

Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) has been regarded as a persistent challenge for the swine farms worldwide. microRNAs (miRNAs) play key roles in regulating almost every important biological process, including virus-host interaction. In this study, we found that miR-204 was highly expressed in cells that were not permissive to PRRSV infection compared with cells susceptible to PRRSV infection. Subsequently, we demonstrated that overexpression of miR-204 significantly inhibited PRRSV replication in porcine alveolar macrophages (PAMs). Through bioinformatic analysis, we found that there existed a potential binding site of miR-204 on the 3'UTR of microtubule associated protein 1 light chain 3B (MAP1LC3B, LC3B), a hallmark of autophagy. Applying experiments including luciferase reporter assay and UV cross-linking and immunoprecipitation (CLIP) assay, we demonstrated that miR-204 directly targeted LC3B, thereby downregulating autophagy. Meanwhile, we investigated the interplay between autophagy and PRRSV replication in PAMs, confirming that PRRSV infection induces autophagy, which in turn facilitates viral replication. Overall, we verify that miR-204 suppresses PRRSV replication via inhibiting LC3B-mediated autophagy in PAMs. These findings will provide a novel potential approach for us to develop antiviral therapeutic agents and controlling measures for future PRRSV outbreaks.

Alternative Samples for Porcine Reproductive and Respiratory Syndrome Surveillance in an Endemic PRRSV-1-Infected Breeding Herd: A Descriptive Study

Knowing porcine reproductive and respiratory syndrome (PRRS) status is essential for designing herd management protocols. For this, weaning-age pigs are a key subpopulation. Recently, different alternatives to blood sampling have been introduced because they are easier, welfare-friendly and cost-saving tools. Moreover, most of them allow the testing of more animals and seem to be more sensitive in low-prevalence scenarios. However, these studies were implemented mainly in PRRSV-2-infected herds. The first objective of our study was to compare the rate of detection of PRRSV-1 by RT-qPCR in individual serum samples, family oral fluid samples (FOF) and udder wipes (UW) collected the day before weaning. The second objective was to evaluate the suitability of pooling. The study was performed on a 210-sow farrow-to-finish farm which was PRRSV-1 infected and unstable. A total of 119 litters were sampled. The rate of detection of PRRSV-1 in blood samples, FOF and UW was 10.9%, 7.6% and 0.8%, respectively. The agreement between sera and FOF was almost perfect even if the detection capacity of sera was numerically superior to FOF. The Ct values of positive sera were statistically lower than those of FOF. Two modalities of pooling (1:3 and 1:5) were tested for sera and FOF. For sera, both modalities did not impact the PRRSV-1 status either at the litter level or at the batch one. On the other hand, whatever the modality (pooled by 3 or 5), most of the pools of FOF gave negative results, misclassifying many litters and batches.

Sampling Strategies in PRRS Elimination in Hungary: An Observational Study Involving Four Farrow-to-Finish Swine Herds

PRRS elimination strategies often rely on depopulation-repopulation. However, this approach is accompanied by a long-term loss of production. With adequate control measures, such as well-designed immunization programs and technological changes along with prevalence-based laboratory testing, the virus-free status of the most vulnerable age groups in swine herds can be achieved. The most common reason for acquiring PRRSV at large farrow-to-finish swine farm units is that the previously settled fattening pigs serve as a source of infection for the newly reared PRRS-free animals. Following such unwanted events, PRRSV may persist in an affected establishment for several years. In this observational study, we selected four farrow-to-finish type swine herds. We implemented different laboratory testing protocols to find the most optimal solution for a successful PRRS elimination program. To aid our objectives, we used a DIVA PCR technique. The PRRS DIVA PCR assay is a fast, reliable method to identify sows shedding farm-specific PRRSV strain(s). As a result of elimination efforts at the sentinel pig herds, we found that reliable detection of wild-type PRRSV shedding among sows requires sampling at least three weaned piglets per litter. The strict adherence to this sampling protocol, the systematic use of laboratory methods that quickly detect the presence of wild virulent virus in the herd during the rearing period and the culling of DIVA PCR positive litters and their sows decreased the presence of the resident virus markedly. These procedures at Hungarian farrow-to-finish type farms successfully inhibited the wild-type PRRSV infection of different age groups. The results of this study demonstrate that applying this methodology together with strict biosecurity measures enabled us to reach PRRS-vaccinated-free status in large, farrow-to-finish herds within two years.

Histopathological Pulmonary Lesions in 1st-Day Newborn Piglets Derived from PRRSV-1 MLV Vaccinated Sows at the Last Stage of Gestation

Modified live virus (MLV) vaccines for the control of porcine respiratory and reproductive syndrome virus (PRRSV) have been associated with the vertical and horizontal transmission of vaccine viruses. The present study aimed to describe pathological lung lesions in piglets born by gilts vaccinated with PRRSV-1 MLV. In total, 25 gilts were vaccinated at late gestation (100th day) and were divided into five groups according to the different vaccines (Vac) used: no vaccine-control group, Vac-1-strain DV, Vac-2-strain VP-046 BIS, Vac-3-strain 94881, Vac-4-strain 96V198. Within the first 0-9 h of the farrowing, blood samples were collected from all newborn piglets and lung samples were exanimated grossly, histopathologically and with scanning electron microscopy. PRRSV (RT-PCR-positive) and antibodies were detected in the serum of piglets from gilts vaccinated with Vac-2. In these piglets, moderate to severe interstitial pneumonia with thickened alveolar septa was noticed. Type II pneumocyte hyperplasia was also observed. The rest of the trial piglets showed unremarkable lung lesions. Phylogenetic analysis revealed the 98.7% similarity of the PRRSV field strain (GR 2019-1) to the PRRS MLV vaccine strain VP-046 BIS. In conclusion, the Vac-2 PRRSV vaccine strain can act as an infectious strain when vaccination is administrated at late gestation, causing lung lesions.

PRRSV-1 Stabilization Programs in French Farrow-to-Finish Farms: A Way to Reduce Antibiotic Usage

Infection with the porcine reproductive and respiratory syndrome virus type 1 (PRRSV-1) has serious economic consequences for the pig industry. Swine practitioners and other agricultural advisors often describe an increase in antibiotic use when PRRSV-1 is circulating. Our objective was to assess the impact of PRRSV-1 stabilization programs on reducing antibiotic use in 19 French farrow-to-finish farms that successfully implemented such a protocol between 2007 and 2019. For each farm, we compared the global antibiotic consumption, including all physiological stages (expressed in mg/PCU and ALEA) one year before (P1) and one year after (P2) the implementation of the protocol, and the change between P1 and P2 was calculated in percentages. The data were also analyzed by level of consumption. We showed that antibiotic use decreased significantly between P1 and P2 if expressed in mg/PCU and showed a decreased tendency in terms of exposure (ALEA) after PRRSV-1 stabilization. Concerning the change from P1 to P2, depending on the level of consumption in P1, our results showed that the higher the consumption levels were in P1, the greater the antibiotic reduction in P2. This study highlights the ability of a stabilization protocol against PRRSV-1 to reduce antibiotic use, especially on farms that have high consumption rates. These hopeful results show that further investigations about the relationship between PRRSV-1 and antibiotic usage could be beneficial.

Economic losses associated with respiratory and helminth infections in domestic pigs in Lira district, Northern Uganda

This study sought to quantify direct economic losses due to respiratory and gastrointestinal (GI) helminth infections in domestic pigs in Uganda. In a longitudinal study design with repeated measures, farm visits were made at 2 month intervals from October 2018 to September 2019. Weaner and grower pigs (n = 288) aged 2-6  months from 94 farms were sampled. The pigs were monitored for growth and screened for exposure to four important respiratory pathogens: porcine circovirus type 2 (PCV2), porcine reproductive and respiratory syndrome virus (PRRSv), Mycoplasma hyopneumoniae (M. hyo), Actinobacillus pleuropneumoniae (App) using ELISA tests. Farm management practices were recorded and used to generate management level scores. Treatment expenses incurred were recorded throughout the study. A mixed effects model was fitted to quantify effects of respiratory and helminth infections on average daily weight gains (ADGs), with farm and pig as random effects. Analysis of variance (ANOVA) was used to determine differences in mean treatment costs by farm management standard. Financial losses were estimated from average carcass dressing percentage, ADG reductions during fattening (200  days). Results showed a grower pig in a given farm exposed to PRRSv and Ascaris spp. had significantly lower ADG by 17.10 gr/day and 16.80 grams/day respectively, compared to a similar unexposed pig (p < 0.05). Mean treatment costs per pig declined significantly with increase in management standard scores (MSS), from USD 1.13 per pig in MSS 1 (poor management) farms to USD 0.95 for MSS 3 (better management) farms (p < 0.05). We show that monetary losses due to PRRSv and Ascaris spp. infection amounted to USD 6.6 ± 2.7 and 6.50 ± 3.2 (Mean ± SEM) per pig, respectively during 200 days of fattening. This study strengthens evidence that improving management practices to reduce infections mitigates economic losses. To guide interventions, further studies are required to unravel the full extent of indirect economic losses.

Exploring pig farmers' decision-making concerning biosecurity measures against African Swine Fever

African Swine Fever (ASF) is a growing threat to the German pig production sector. Rigorous biosecurity measures can prevent the introduction of ASF in domestic pig farms. Increased efforts have been made to inform pig farmers and other stakeholders in the industry regarding disease prevention measures for ASF. As part of quality management in animal disease prevention, we investigated the extent to which these efforts were successful and how knowledge transfer needs to be improved. Applying a qualitative study design with open, structured face-to-face interviews, this study aimed at assessing pig farmers' decision-making processes concerning the implementation of biosecurity measures against ASF and deducing the best-fitted pathways to improve the dissemination of information among pig farmers. We developed a modified theoretical model using the Health Belief Model, Protection Motivation Theory, and Theory of Planned Behaviour as the basis for our interview questionnaire and analysis. We showed that despite the steady spread of ASF into and within Germany, most pig farmers did not perceive an increased threat to their farms. However, many pig farmers communicated their uncertainty on how to correctly implement biosecurity measures according to the law. This study identified the importance of veterinary officials and farm veterinarians as referents on the topic of biosecurity and the need for clear standards concerning biosecurity regulations. Further, it suggests the need for closer cooperation between pig farmers and these referents, and a focus on joint decision-making, taking into account the individual circumstances of the farmers.

The Impact of PRRS Eradication Program on the Production Parameters of the Hungarian Swine Sector

BACKGROUND

The Hungarian national eradication program of PRRS was successfully completed between 2014 and 2022. There were doubts about the efficiency of the eradication program in Hungary from the beginning to the tune that it might only be carried out efficiently through depopulation-repopulation of the infected herds, which is a very costly procedure. In our study, we investigated the impact of the depopulation-repopulation procedure, which played a prominent role in the PRRS eradication program on the productivity of the Hungarian swine sector-namely, on the number of slaughter pigs per sow per year and the total live slaughter weight per sow per year.

MATERIAL AND METHODS

Since 2014, we monitored the evolution of the PRRS eradication through the depopulation-repopulation approach on the large-scale breeding herds in Hungary. Most producers replaced their herds with animals that were free of PRRS and other infectious diseases (mycoplasmosis, actinobacillosis, swine dysentery, atrophic rhinitis, etc.). On this basis, we evaluated the change in the number of slaughter pigs per sow per year as a consequence of depopulation-repopulation of the herds being carried out. In the statistical analysis linear regression was used.

CONCLUSIONS

The results of our study demonstrate that the PRRS eradication program with the herd depopulation-repopulation approach led to a considerable improvement of the productivity of Hungarian pig farming. This result also demonstrates that, independent of the PRRS eradication, it is still necessary to consider investments into the individual production units to increase efficiency, and to carry out herd depopulation-repopulation in cases where the current genetics limits improvements in productivity.

Influence of deoxynivalenol-contaminated feed on the immune response of pigs after PRRSV vaccination and infection

The impact of the Fusarium mycotoxin deoxynivalenol (DON) on the immune response against porcine reproductive and respiratory syndrome virus (PRRSV) vaccination and infection was investigated. Forty-two weaned piglets were separated into seven groups and received three different diets: Low DON (1.09 ppm), High DON (2.81 ppm) or No DON. These three treatments were split further into either vaccinated (Ingelvac PRRSFLEX EU) and challenged with PRRSV 28 days post-vaccination, or only infected at day 28. A seventh group received no DON, no vaccination, and no infection. Two weeks after challenge infection, when pigs were euthanized, the number of IFN-γ producing lymphocytes in the blood of vaccinated animals was lower in pigs on High DON compared to animals on Low DON or No DON. Intracellular cytokine staining showed that vaccinated animals fed with the Low DON diet had higher frequencies of TNF-α/IFN-γ co-producing CD4⁺ T cells than the other two vaccinated groups, particularly in lung tissue. Vaccinated animals on High DON had similar viral loads in the lung as the non-vaccinated groups, but several animals of the Low DON or No DON group receiving vaccination had reduced titers. In these two groups, there was a negative correlation between lung virus titers and vaccine-specific TNF-α/IFN-γ co-producing CD4⁺ T cells located either in lung tissue or blood. These results indicate that after PRRSV vaccination and infection, high levels of DON negatively influence immune parameters and clearance of the virus, whereas low DON concentrations have immunomodulatory effects.

A Serological Investigation of Porcine Reproductive and Respiratory Syndrome and Three Coronaviruses in the Campania Region, Southern Italy

Porcine coronaviruses and reproductive and respiratory syndrome (PRRS) are responsible for severe outbreaks that cause huge economic losses worldwide. In Italy, three coronaviruses have been reported historically: porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV) and porcine respiratory coronavirus (PRCV). Although repeated outbreaks have been described, especially in northern Italy, where intensive pig farming is common, there is a worrying lack of information on the spread of these pathogens in Europe. In this work, we determined the seroprevalence of three porcine coronaviruses and PRRSV in the Campania region, southern Italy. A total of 443 samples were tested for the presence of antibodies against porcine coronaviruses and PRRSV using four different commercial ELISAs. Our results indicated that PEDV is the most prevalent among porcine coronaviruses, followed by TGEV, and finally PRCV. PRRSV appeared to be the most prevalent virus (16.7%). For coronaviruses, seroprevalence was higher in pigs raised in intensive farming systems. In terms of distribution, TGEV is more widespread in the province of Avellino, while PEDV and PRRSV are more prevalent in the province of Naples, emphasizing the epidemic nature of both infections. Interestingly, TGEV-positive animals are more common among growers, while seropositivity for PEDV and PRRSV was higher in adults. Our research provides new insights into the spread of swine coronaviruses and PRRSV in southern Italy, as well as a warning about the need for viral surveillance.

The Antiviral Activity of Caprylic Monoglyceride against Porcine Reproductive and Respiratory Syndrome Virus In Vitro and In Vivo

Porcine reproductive and respiratory syndrome (PRRS) is a disease with a major economic impact in the global pig industry, and this study aims to identify potential anti-PRRSV drugs. We examined the cytotoxicity of four medium-chain fatty acids (MCFAs) (caprylic, caprylic monoglyceride, decanoic monoglyceride, and monolaurin) and their inhibition rate against PRRSV. Then the MCFAs with the best anti-PRRSV effect in in vitro assays were selected for subsequent in vivo experiments. Potential anti-PRRSV drugs were evaluated by viral load assay, pathological assay, and cytokine level determination. The results showed that caprylic monoglyceride (CMG) was the least toxic to cells of the four MCFAs, while it had the highest PRRSV inhibition rate. Then the animals were divided into a low-CMG group, a medium-CMG group, and a high-CMG group to conduct the in vivo evaluation. The results indicated that piglets treated with higher concentrations of caprylic monoglyceride were associated with lower mortality and lower viral load after PRRSV infection (p < 0.05). The pulmonary pathology of the piglets also improved after CMG treatment. The levels of pro-inflammatory cytokines (IL-6, IL-8, IL-1β, IFN-γ, TNF-α) were significantly downregulated, and the levels of anti-inflammatory cytokine (IL-10) were significantly upregulated in the CMG-treated piglets compared to the positive control group (p < 0.05). Taken together, the present study revealed for the first time that caprylic monoglyceride has strong antiviral activity against PRRSV in vitro and in vivo, suggesting that caprylic monoglyceride could potentially be used as a drug to treat PRRS infection.

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

The economic impact after the outbreak of porcine reproductive and respiratory syndrome (PRRS) has been proven to be tremendous for pig production worldwide. However, the economic impact of the disease is not well understood in China. In our previous study, we acquired and analyzed the main production data (the number of weaned piglets, health costs, delayed marketing age, etc.) from the management system before and after the PRRS outbreaks occurring in November 2014, March 2015, December 2016, and February 2017. This study aimed to analyze and quantify the economic losses of the four PRRS outbreaks in Chinese herds. A straightforward approach was used to calculate additional costs and decreased revenues based on the PRRS-induced production deficiencies by average cost-of-production indices calculated from annual estimates of costs between 2014 and 2017. The results showed that economic losses varied between ¥668.14 and ¥1004.43 per sow in breeding herds from the outbreaks to regain the basic performance, with an average of ¥822.75 per sow, and the mean costs in the fattening herds (including nursery pigs) were ¥601.62 per sow, ranging from ¥318.64 to ¥937.14. Overall, the economic impact of PRRS on the whole herd was ¥1424.37 per sow. The majority of the losses were due to the reduction in the number of weaned piglets for breeding herds, and the increased feed cost (occupying 44.88%) was the primary source of loss for fattening herds. Our study fills the gap in knowledge of PRRS economics in China, enriches the data for veterinary economics, and re-stresses the necessity for producers and veterinarians to control PRRS effectively.

Development of a farm-specific real-time quantitative RT-PCR assay for the detection and discrimination of wild-type porcine reproductive respiratory syndrome virus and the vaccine strain in a farm under eradication

Porcine reproductive and respiratory syndrome (PRRS) is one of the most important diseases of swine causing severe economic losses worldwide, therefore intensive efforts are taken to eliminate PRRS virus (PRRSV) from infected herds for complete eradication. The most efficient, fastest but at the same time the most expensive eradication method is depopulation-repopulation. In order to reduce costs, a number of farms prefer to perform their eradication process with continuous production using modified live vaccine (MLV) immunisation. However, the commercial PRRSV RT-PCR kits do not have the capacity to discriminate infected from vaccinated animals. In this paper, we describe a simple discriminatory duplex TaqMan RT-PCR assay based on common forward and reverse primers, as well as two differently labelled MLV- and wild-type PRRSV-specific probes. The discriminatory PCR test we designed is a fast and efficacious method for processing large quantities of samples. The assay is cheap, flexible, easy to apply in different herds using different MLVs, but should be checked, and can be modified based on the sequence data obtained during the permanent monitoring examinations. Owing to its simplicity the test can serve as a significant complementary assay for PRRS control and elimination/eradication.

A novel strategy for optimal component formula of anti-PRRSV from natural compounds using tandem mass tag labeled proteomic analyses

BACKGROUND

Porcine Reproductive and Respiratory Syndrome (PRRS) is one of the most important porcine viral diseases which have been threatening the pig industry in China. At present, most commercial vaccines fail to provide complete protection because of highly genetic diversity of PRRSV strains. This study aimed to optimize a component formula from traditional Chinese medicine(TCM)compounds with defined chemical characteristics and clear mechanism of action against PRRSV.

METHODS

A total of 13 natural compounds were screened for the anti-PRRSV activity using porcine alveolar macrophages (PAMs). Three compounds with strong anti-PRRSV activity were selected to identify their potential protein targets by proteomic analysis. The optimal compound formula was determined by orthogonal design based on the results of proteomics. MTT assay was used to determine the maximum non-cytotoxic concentration (MNTC) of each compound using PAMs. QPCR and western blot were used to investigate the PRRSV N gene and protein expression, respectively. The Tandem Mass Tag (TMT) technique of relative quantitative proteomics was used to detect the differential protein expression of PAMs treated with PRRSV, matrine (MT), glycyrrhizic acid (GA) and tea saponin (TS), respectively. The three concentrations of these compounds with anti-PRRSV activity were used for orthogonal design. Four formulas with high safety were screened by MTT assay and their anti-PRRSV effects were evaluated.

RESULTS

MT, GA and TS inhibited PRRSV replication in a dose-dependent manner. CCL8, IFIT3, IFIH1 and ISG15 were the top four proteins in expression level change in cells treated with MT, GA or TS. The relative expression of IFIT3, IFIH1, ISG15 and IFN-β mRNAs were consistent with the results of proteomics. The component formula (0.4 mg/mL MT + 0.25 mg/mL GA + 1.95 μg/mL TS) showed synergistic anti-PRRSV effect.

CONCLUSIONS

The component formula possessed anti-PRRSV activity in vitro, in which the optimal dosage on PAMs was 0.4 mg/mL MT + 0.25 mg/mL GA + 1.95 μg/mL TS. Compatibility of the formula was superposition of the same target with GA and TS, while different targets of MT. IFN-β may be one of the targets of the component formula possessed anti-PRRSV activity.

Pattern of Antibiotic Consumption in Two Italian Production Chains Differing by the Endemic Status for Porcine Reproductive and Respiratory Syndrome

The aim of this case study was to quantify antibiotic (AB) use in Italian weaning (W) and fattening (F) units differentiated for porcine reproductive and respiratory syndrome (PRRS) occurrence. Farms were classified as either PRRS negative (–) or PRRS positive (+) based on the circulation of the virus among the animals. In all the farms, the modified live PRRS virus (PRRSV) vaccine was provided to all the animals. In the PRRS– farms, the level of circulating antibodies was low, and the disease, in its clinical form, did not occur. In the PRRS+ farms, the level of circulating antibodies against the virus was high, and the disease was recurrent. Data regarding AB consumption were collected from 2017 to 2020, and the active compounds (ACs) were expressed as milligrams of AC/total kilogram of body weight (BW) produced. Each AC was classified into one of four categories according to the European Medicines Agency classification of ABs for prudent and responsible use in animals: Avoid, Restrict, Caution, and Prudence. Data regarding the ACs in each category were analyzed using a linear model that included production phase, PRRS status, and their interaction as factors. Performance parameters, average age of the pigs at the end of each phase, daily live weight gain, feed-to-gain ratio, total losses, cost index, and medication costs were significantly influenced by the PRRS chain. The use of class B ABs was not affected by production phase or PRRS status. Conversely, for class C ABs, interaction between the two factors (p = 0.02) was observed; W/PRRS+ and F/PRRS+ showed the greatest AB use for this class (p = 0.003). For class D ABs, the interaction was significant (p = 0.01); class C and D ABs were used more in the weaning (p = 0.07) than in the fattening phase (p = 0.003). For the weaning phase, the use of class C and D ABs was greater in the PRRS+ than in the PRRS– chain (p < 0.01). In conclusion, PRRS status affected the growth of pigs and economic performance. Moreover, PRRS status significantly influenced the use of ABs during all the growing periods with the greatest impact being on the weaning phase.

Transcriptomic Analysis of Liver Indicates Novel Vaccine to Porcine Reproductive and Respiratory Virus Promotes Homeostasis in T-Cell and Inflammatory Immune Responses Compared to a Commercial Vaccine in Pigs

One of the largest impediments for commercial swine production is the presence of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), a devastating RNA viral infection that is responsible for over $1 billion in loss in the U.S. annually. The challenge with combating PRRSV is a combination of the effect of an extraordinary rate of mutation, the ability to infect macrophages, and subversion of host immune response through a series of actions leading to both immunomodulation and immune evasion. Currently there are a handful of commercial vaccines on the market that have been shown to be effective against homologous infections, but struggle against heterologous or mixed strain infections. However, vaccination is the current best strategy for combating PRRSV, making research into new vaccine technology key. To address these issues with PRRSV and host antiviral functions a novel modified-live vaccine (MLV) able to stimulate known antiviral interferons was created and examined for its ability to potentiate effective immunity and better protection. Here, we examine gene expression in the liver of pigs vaccinated with our novel vaccine, given the liver's large role in antiviral responses and vaccine metabolism. Our study indicated that pigs administered the novel vaccine experience homeostatic gene expression consistent with less inflammation and T-cell depletion risk than pigs administered the commercial vaccine.

First Study to Describe the Prevalence of Porcine Reproductive and Respiratory Syndrome Virus and Porcine Circovirus Type 2 among the Farmed Pig Population in the Hong Kong Special Administrative Region

Infection of pig farms with porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) causes substantial economic losses globally. However, little epidemiological data of PRRSV and PCV2 in the Hong Kong Special Administrative Region (HKSAR) were available. This pilot study aimed to provide baseline information of the prevalences of PPRSV and PCV2 in the HKSAR. A complex survey was conducted from 3 February 2020 to 11 March 2021 on 29 of the 40 pig farms in the HKSAR, with five pigs each from seven age groups (representing key production stages) tested using a real-time PCR. Evidence of presence of PRRSV European strain (PRRSV-1), PRRSV North American strain (PRRSV-2) and PCV2 was confirmed on 48%, 86% and 79% of farms, with overall prevalences of 7.6% (95% CI: 4.8–10.3%), 12.2% (95% CI: 9.6–14.7%) and 20.3% (95% CI: 14.3–26.2%) in the HKSAR pig population based on pooling results from all pigs across all farms. PRRSV-1 and PRRSV-2 were more prevalent in younger pigs, with the highest prevalences of 32.1% (95% CI: 20.8–45.0%) and 51.5% (95% CI: 38.9–64.0%) for 8-week-old pigs. In contrast, the distribution of PCV2 prevalence across age groups appeared to be more symmetrical, with higher prevalences reported in pigs from 12 weeks old to 24 weeks old but lower prevalences in younger pigs and sows. The results of this study demonstrate that PRRSV-1, PRRSV-2 and PCV2 are widely spread across pig farms in the HKSAR, which indicates that the current farm management and control protocols should be improved. We recommend the implementation of on-farm intervention strategies combined with ongoing surveillance to reduce these viruses, and their consequences, in the HKSAR pig population.

Heterologous Challenge with PRRSV-1 MLV in Pregnant Vaccinated Gilts: Potential Risk on Health and Immunity of Piglets

Simple Summary

Modified live virus (MLV) vaccines are considered as the key component to control the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV). The majority of pig farms apply the ‘mass’ vaccination strategy in breeding female animals. However, this PRRS MLV vaccination protocol involves the risk of inoculation of sows in the last stage of gestation, resulting in possible infection of the fetus as the virus can efficiently cross the placenta during the last period of pregnancy. Thus, we evaluated the ability of the vaccine virus to act as a pathogenic strain, to be transmitted to fetuses and to affect the health status of neonatal piglets. The results indicated that the study gilts transmitted the vaccine virus to their offspring, as well as that the PRRSV-infected piglets showed a poor clinical performance. Consequently, the pig farms that apply PRRS MLV vaccination in a routine blanket vaccination strategy must avoid inoculating pregnant gilts the last week before their parturition.

Abstract

The objective of the present study was to evaluate the potential risks of the four commercial PRRS-1 MLV vaccines in pregnant vaccinated gilts at the last stage of gestation under field conditions. The study was conducted at four pig farms, including 25 gilts from each farm (25 × 4 = 100 gilts), which were equally allocated to five different study groups. A PRRS-1 MLV vaccination was applied on the 100th day of their pregnancy with the different commercial vaccines that are available in the Greek market. The results indicated virus congenital infection and viremia in piglets (20/200 = 10% PRRSV infected piglets), and detection of PRRSV-specific antibodies (181/200 = 90.5% piglets found with PRRSV antibodies). The subsequent phylogenetic analyses revealed high percentages of similarity between the PRRSV-1 strain detected in infected litters and the PRRSV-1 vaccine strain to which the study gilts had been previously exposed to. Health status analyses of trial piglets resulted in differences between litters from vaccinated sows and litters from non-vaccinated sows at 110th day of gestation as regards the number of weak-born piglets, mummies, and piglets with splay-leg and/or respiratory symptoms. The current study’s results indicate several potential dangers of the PRRS MLV vaccination in late gestation.

Efficacy of the Synergy Between Live-Attenuated and Inactivated PRRSV Vaccines Against a NADC30-Like Strain of Porcine Reproductive and Respiratory Syndrome Virus in 4-Week Piglets

The NADC30-like strain of porcine reproductive and respiratory syndrome virus (PRRSV) is a novel strain responsible for substantial economic losses to swine production in China. This study evaluated the cross-protective efficacy of the synergy between live-attenuated and inactivated PRRSV vaccines compared with a single vaccination with PRRS modified-live virus (MLV) vaccine against challenge with NADC30-like strain, v2016/ZJ/09-03. A total of 45 PRRSV free pigs were randomly divided into five groups: (1) strict control (SC); (2) positive control (PC); (3) single MLV dose (M1); (4) primed intramuscularly with MLV and boosted with killed vaccine 3 weeks later (MK1); and (5) intramuscular prime MLV boosted subcutaneously with killed vaccine B 3 weeks later (MK2). Serological tests in MK groups revealed no differences in both anti-N and anti-GP protein antibodies compared with M1 group, and failed to provide further protection against clinical signs, virus shedding, and gross lesions. However, the viremic titer, gross lung lesions, and average daily weight gain were significantly improved in the MLV vaccinated groups, suggesting that MLV provides substantial cross-protection against the NADC30-like virus. Thus, as a booster, the killed vaccine confers minimal additional protection in NADC30-like infected piglets.

Interpretable machine learning applied to on-farm biosecurity and porcine reproductive and respiratory syndrome virus

Effective biosecurity practices in swine production are key in preventing the introduction and dissemination of infectious pathogens. Ideally, on-farm biosecurity practices should be chosen by their impact on bio-containment and bio-exclusion; however, quantitative supporting evidence is often unavailable. Therefore, the development of methodologies capable of quantifying and ranking biosecurity practices according to their efficacy in reducing disease risk has the potential to facilitate better-informed choices of biosecurity practices. Using survey data on biosecurity practices, farm demographics, and previous outbreaks from 139 herds, a set of machine learning algorithms were trained to classify farms by porcine reproductive and respiratory syndrome virus status, depending on their biosecurity practices and farm demographics, to produce a predicted outbreak risk. A novel interpretable machine learning toolkit, MrIML-biosecurity, was developed to benchmark farms and production systems by predicted risk and quantify the impact of biosecurity practices on disease risk at individual farms. By quantifying the variable impact on predicted risk, 50% of 42 variables were associated with fomite spread while 31% were associated with local transmission. Results from machine learning interpretations identified similar results, finding substantial contribution to predicted outbreak risk from biosecurity practices relating to the turnover and number of employees, the surrounding density of swine premises and pigs, the sharing of haul trailers, distance from the public road and farm production type. In addition, the development of individualized biosecurity assessments provides the opportunity to better guide biosecurity implementation on a case-by-case basis. Finally, the flexibility of the MrIML-biosecurity toolkit gives it the potential to be applied to wider areas of biosecurity benchmarking, to address biosecurity weaknesses in other livestock systems and industry-relevant diseases.

The Function of the PRRSV-Host Interactions and Their Effects on Viral Replication and Propagation in Antiviral Strategies

Porcine reproductive and respiratory syndrome virus (PRRSV) affects the global swine industry and causes disastrous economic losses each year. The genome of PRRSV is an enveloped single-stranded positive-sense RNA of approximately 15 kb. The PRRSV replicates primarily in alveolar macrophages of pig lungs and lymphatic organs and causes reproductive problems in sows and respiratory symptoms in piglets. To date, studies on how PRRSV survives in the host, the host immune response against viral infections, and pathogenesis, have been reported. PRRSV vaccines have been developed, including inactive virus, modified live virus, attenuated live vaccine, DNA vaccine, and immune adjuvant vaccines. However, there are certain problems with the durability and effectiveness of the licensed vaccines. Moreover, the high variability and fast-evolving populations of this RNA virus challenge the design of PRRSV vaccines, and thus effective vaccines against PRRSV have not been developed successfully. As is well known, viruses interact with the host to escape the host’s immune response and then replicate and propagate in the host, which is the key to virus survival. Here, we review the complex network and the mechanism of PRRSV–host interactions in the processes of virus infection. It is critical to develop novel antiviral strategies against PRRSV by studying these host–virus interactions and structures to better understand the molecular mechanisms of PRRSV immune escape.