Review on the transmission porcine reproductive and respiratory syndrome virus between pigs and farms and impact on vaccination

Modeling suggests gene editing combined with vaccination could eliminate a persistent disease in livestock

Recent breakthroughs in gene-editing technologies that can render individual animals fully resistant to infections may offer unprecedented opportunities for controlling future epidemics in farm animals. Yet, their potential for reducing disease spread is poorly understood as the necessary theoretical framework for estimating epidemiological effects arising from gene-editing applications is currently lacking. Here, we develop semistochastic modeling approaches to investigate how the adoption of gene editing may affect infectious disease prevalence in farmed animal populations and the prospects and time scale for disease elimination. We apply our models to the porcine reproductive and respiratory syndrome (PRRS), one of the most persistent global livestock diseases to date. Whereas extensive control efforts have shown limited success, recent production of gene-edited pigs that are fully resistant to the PRRS virus have raised expectations for eliminating this deadly disease. Our models predict that disease elimination on a national scale would be difficult to achieve if gene editing was used as the only disease control. However, from a purely epidemiological perspective, disease elimination may be achievable within 3 to 6 y, if gene editing were complemented with widespread and sufficiently effective vaccination. Besides strategic distribution of genetically resistant animals, several other key determinants underpinning the epidemiological impact of gene editing were identified.

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.

Occurrence and Associated Risk Factors of Porcine Reproductive and Respiratory Syndrome Virus and Porcine Circovirus Type 2 Infections in Greece

The objective of the present study was to identify factors associated with the probability of being polymerase chain reaction (PCR) positive and the level of porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2) occurrence in Greek farms. The study included 56 pig farms, with a total population of 22.500 sows, which represent about 40% of the entire capacity of the Greek swine production. A total of 896 blood samples (224 pools*4 samples/pool = 896 samples) from breeding stock, weaners, growers, and finishers were collected from each farm and organized in pools of 4 samples size. Further, data regarding herd health management protocols were collected. The sera were tested for PRRSV and PCV2, using real-time PCR (RT-PCR). The results indicated that both viruses remain a major challenge for the Greek swine industry. Main risk factors involved in the infection process by these viruses were identified. In particular, vaccination programs such as the mass PRRSV vaccination with modified-live virus (MLV) in breeding stock during the last stages of gestation or with killed-virus (KV) during the middle of gestation are more likely to be associated with PRRSV PCR-positivity. Farms with low biosecurity level are associated with higher PRRSV circulation. It has also been revealed that breeding stock is more likely to be associated with PCV2 circulation compared to weaners and growers. In conclusion, our results could be the basis of the development of surveillance protocols for a national monitoring system for PRRSV and PCV2, which could prevent future infection of Greek farms.

Systemic CD4 cytotoxic T cells improve protection against PRRSV-1 transplacental infection

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the major swine pathogens causing reproductive failure in sows. Although modified-live virus (MLV) vaccines are available, only partial protection against heterologous strains is produced, thus vaccinated sows can be infected and cause transplacental infection. The immune effector mechanisms involved are largely unknown.

Methods

The present study investigated the role of cytotoxic lymphocytes, including cytotoxic T cells (CTL), NKT, and NK cells, from blood in preventing PRRSV-1 transplacental infection in vaccinated primiparous sows (two doses vaccinated). Sows from a PRRSV-1 unstable farm were bled just before the last month of gestation (critical period for transplacental infection), then followed to determine whether sows delivered PRRSV-1-infected (n=8) or healthy (n=10) piglets. After that, functions of CTL, NKT, and NK cells in the two groups of sows were compared.

Results

No difference was found through cell surface staining. But upon in vitro re-stimulation with the circulating field virus, sows that delivered healthy piglets displayed a higher frequency of virus-specific CD107a⁺ IFN-γ-producing T cells, which accumulated in the CD4⁺ compartment including CD4 single-positive (CD4 SP) and CD4/CD8α double-positive (CD4/CD8α DP) subsets. The same group of sows also harbored a higher proportion of CD107a⁺ TNF-α-producing T cells that predominantly accumulated in CD4/CD8α double-negative (CD4/CD8α DN) subset. Consistently, CD4 SP and CD4/CD8α DN T cells from sows delivering healthy piglets had a higher virus-specific proliferative response. Additionally, in sows that delivered PRRSV-1-infected piglets, a positive correlation of virus-specific IFN-γ response with average Ct values of umbilical cords of newborn piglets per litter was observed.

Conclusion

Our data strongly suggest that CTL responses correlate with protection against PRRSV-1 transplacental infection, being executed by CD4 T cells (IFN-γ related) and/or CD4/CD8α DN T cells (TNF-α related).

Review: Livestock disease resilience: from individual to herd level

Infectious diseases are a major threat to the sustainable production of high-producing animals. Control efforts, such as vaccination or breeding approaches often target improvements to individual resilience to infections, i.e., they strengthen an animal's ability to cope with infection, rather than preventing infection per se. There is increasing evidence for the contribution of non-clinical carriers (animals that become infected and are infectious but do not develop clinical signs) to the overall health and production of livestock populations for a wide range of infectious diseases. Therefore, we strongly advocate a shift of focus from increasing the disease resilience of individual animals to herd disease resilience as the appropriate target for sustainable disease control in livestock. Herd disease resilience not only captures the direct effects of vaccination or host genetics on the health and production performance of individuals but also the indirect effects on the environmental pathogen load that herd members are exposed to. For diseases primarily caused by infectious pathogens shed by herd members, these indirect effects on herd resilience are mediated both by individual susceptibility to infection and by characteristics (magnitude of infectiousness, duration of infectious period) that influence pathogen shedding from infected individuals. We review what is currently known about how vaccination and selective breeding affect herd disease resilience and its underlying components, and outline the changes required for improvement. To this purpose, we also seek to clarify and harmonise the terminology used in the different animal science disciplines to facilitate future collaborative approaches to infectious disease control in livestock.

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

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

Porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) genetic diversity and occurrence of wild type and vaccine-like strains in the United States swine industry

Porcine reproductive and respiratory syndrome virus genotype 2 (PRRSV-2) genetic diversity in the U.S. was assessed using a database comprising 10 years’ worth of sequence data obtained from swine production systems routine monitoring and outbreak investigations. A total of 26,831 ORF5 PRRSV-2 sequences from 34 production systems were included in this analysis. Within group mean genetic distance (i.e. mean proportion of nucleotide differences within ORF5) per year according to herd type was calculated for all PRRSV-2 sequences. The percent nucleotide difference between each sequence and the ORF5 sequences from four commercially available PRRSV-2 vaccines (Ingelvac PRRS MLV, Ingelvac PRRS ATP, Fostera PRRS, and Prevacent PRRS) within the same lineage over time was used to classify sequences in wild-type or vaccine-like. The mean ORF5 genetic distance fluctuated from 0.09 to 0.13, being generally smaller in years in which there was a relative higher frequency of dominant lineage. Vaccine-like sequences comprised about one fourth of sequences obtained through routine monitoring of PRRS. We found that lineage 5 sequences were mostly Ingelvac PRRS MLV-like. Lineage 8 sequences up to 2011 were 62.9% Ingelvac PRRS ATP-like while the remaining were wild-type viruses. From 2012 onwards, 51.9% of lineage 8 sequences were Ingelvac PRRS ATP-like, 45.0% were Fostera PRRS-like, and only 3.2% were wild-type. For lineage 1 sequences, 0.1% and 1.7% of the sequences were Prevacent PRRS-like in 2009–2018 and 2019, respectively. These results suggest that repeated introductions of vaccine-like viruses through use of modified live vaccines might decrease within-lineage viral diversity as vaccine-like strains become more prevalent. Overall, this compilation of private data from routine monitoring provides valuable information on PRRSV viral diversity.

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.

Description of changes of key performance indicators and PRRSV shedding over time in a naïve breeding herd following a PRRS MLV exposure

Porcine reproductive and respiratory syndrome (PRRS) is an important economic swine disease. The usage of PRRS-modified live vaccines (MLV) is the predominant breeding herd immunologic solution used in the United States to minimize the economic losses associated with wild-type PRRS infection. Most of the current information on the effects of contemporary PRRS MLV vaccination on breeding herd performance under field conditions comes from herds with previous PRRS virus (PRRSV) exposure. Hence, there is little information on key performance indicators (KPI) changes after the exposure to a PRRS MLV in PRRSV-naïve breeding herds. The main objective of this longitudinal observational study was to describe selected KPI changes in a naïve breeding herd after PRRS MLV exposure. The secondary objective was to describe the pattern of detection of PRRSV RNA by the quantitative reverse transcriptase-polymerase chain reaction in processing fluid samples. There were transient increases for mummies during weeks 4-23 (+0.86%); increased pre-weaning mortality on weeks 3-5 (+3.76%); a decrease in live born on weeks 4-5 (-0.46) leading to a decreased pig weaned/litter on weeks 5-10 (-0.69) and increased repeated services on weeks 3-23 (+5.53%). Transient changes observed after PRRS MLV exposures did not move total pigs weaned to outside the control intervals. Starting on week 83 and for 53 consecutive weeks, there was no PRRSV detection in processing fluids, even though two whole-herd MLV exposures occurred within that period.

Integrating animal movements with phylogeography to model the spread of PRRSV in the USA

Viral sequence data coupled with phylodynamic models have become instrumental in investigating the outbreaks of human and animal diseases, and the incorporation of the hypothesized drivers of pathogen spread can enhance the interpretation from phylodynamic inference. Integrating animal movement data with phylodynamics allows us to quantify the extent to which the spatial diffusion of a pathogen is influenced by animal movements and contrast the relative importance of different types of movements in shaping pathogen distribution. We combine animal movement, spatial, and environmental data in a Bayesian phylodynamic framework to explain the spatial diffusion and evolutionary trends of a rapidly spreading sub-lineage (denoted L1A) of porcine reproductive and respiratory syndrome virus (PRRSV) Type 2 from 2014 to 2017. PRRSV is the most important endemic pathogen affecting pigs in the USA, and this particular virulent sub-lineage emerged in 2014 and continues to be the dominant lineage in the US swine industry to date. Data included 984 open reading frame 5 (ORF5) PRRSV L1A sequences obtained from two production systems in a swine-dense production region (∼85,000 mi²) in the USA between 2014 and 2017. The study area was divided into sectors for which model covariates were summarized, and animal movement data between each sector were summarized by age class (wean: 3–4 weeks; feeder: 8–25 weeks; breeding: ≥21 weeks). We implemented a discrete-space phylogeographic generalized linear model using Bayesian evolutionary analysis by sampling trees (BEAST) to infer factors associated with variability in between-sector diffusion rates of PRRSV L1A. We found that between-sector spread was enhanced by the movement of feeder pigs, spatial adjacency of sectors, and farm density in the destination sector. The PRRSV L1A strain was introduced in the study area in early 2013, and genetic diversity and effective population size peaked in 2015 before fluctuating seasonally (peaking during the summer months). Our study underscores the importance of animal movements and shows, for the first time, that the movement of feeder pigs (8–25 weeks old) shaped the spatial patterns of PRRSV spread much more strongly than the movements of other age classes of pigs. The inclusion of movement data into phylodynamic models as done in this analysis may enhance our ability to identify crucial pathways of disease spread that can be targeted to mitigate the spatial spread of infectious human and animal pathogens.

Modeling the Spread of Porcine Reproductive and Respiratory Syndrome Among Pig Farms in Lira District of Northern Uganda

Porcine Reproductive and Respiratory Syndrome (PRRS) is a viral swine disease that causes reproductive failure in breeding sows and respiratory distress in growing pigs. The main objectives were to simulate the transmission patterns of PRRS in Uganda using North American Animal Disease Spread Model (NAADSM) and to evaluate the potential effect of prevention and control options such as vaccination and movement control. The median number of infectious farms at the end of 52 weeks for the baseline scenario was 735 (36.75% of the 2,000 farms). The best effects of vaccination were observed in scenarios 60% farm coverage and 80% farm coverage, which resulted in 82 and 98.2% reduction in the median number of infectious farms at the end of the simulation, respectively. Vaccination of all medium and large farms only (33% of the farms) resulted in a 71.2% decrease in the median number of infectious farms at the end of 52 weeks. Movement control (MC) results showed that the median number of infectious farms at the end of 52 weeks decreased by 21.6, 52.3, 79.4, and 92.4% for scenarios MC 20, MC 40, MC 60, and MC 80%, respectively. This study provides new insights to the government of Uganda on how PRRS can be controlled. The large and medium farms need to be prioritized for vaccination, which would be a feasible and effective way to limit the spread of PRRS in Uganda. Scavenging pigs should be confined at all times, whether in the presence or absence of any disease outbreaks.

Phylogenetically Distinct Near-Complete Genome Sequences of Porcine Reproductive and Respiratory Syndrome Virus Type 2 Variants from Four Distinct Disease Outbreaks at U.S. Swine Farms over the Past 6 Years

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to mutate, causing disruptive PRRS outbreaks in farms that lead to reproductive failure and respiratory disease-associated mortality. We present four new PRRSV type 2 variants in the United States belonging to four distinct orf5 sublineages within lineage 1.

Seroprevalence of porcine reproductive and respiratory syndrome virus on swine farms in a tropical country of the Middle Americas: the case of Costa Rica

Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses to the swine industry worldwide. Little is known regarding the epidemiology of this infection in tropical countries. To address this problem in Costa Rica, a seroepidemiological study was carried out in two phases. In the first phase, a pilot study was conducted in nine farms with the clinical diagnosis of PRRSV. In total, 265 pig serum samples were collected from animals ranging in age from 1 to 15 weeks of age. This study aimed to establish the duration of maternal immunity in piglets, to identify the period of viremia, and to determine when seroconversion occurs. In the second phase, a cross-sectional serology study was performed on a representative sample of the Costa Rican national herds in the second phase. The twenty-five selected farms represent all provinces and were classified according to herd size (100 to 2000 sows). In each farm, pigs aged 8, 10, and 12 weeks were sampled, as well as gilts based on the pilot study. In total 1281 pigs were sampled across all 25 farms. The aim of the cross-sectional study was to quantify the seroprevalence of PRRSV in Costa Rican pig farms and to describe its geographical distribution in this tropical country. The prevalence of positive farms was 44% (11/25), and these farms were located in six of the seven provinces of Costa Rica. Overall, 58% (344/596) of the pigs were seropositive to PRRSV. The age of the pigs and the ecozone where farms were located were significantly related with PRRSV seroprevalence in animals and herds, respectively.

The Combined Effect of Weaning Stress and Immune Activation during Pig Gestation on Serum Cytokine and Analyte Concentrations

Weaning stress can elicit changes in the metabolic, hormone and immune systems of pigs and interact with prolonged disruptions stemming from maternal immune activation (MIA) during gestation. The present study advances the characterization of the combined effects of weaning stress and MIA on blood chemistry, immune and hormone indicators that inform on the health of pigs. Three-week-old female and male offspring of control gilts or gilts infected with the porcine reproductive and respiratory syndrome virus were allocated to weaned or nursed groups. The anion gap and bilirubin profiles suggest that MIA enhances tolerance to the effects of weaning stress. Interleukin 1 beta and interleukin 2 were highest among weaned MIA females, and cortisol was higher among weaned relative to nursed pigs across sexes. Canonical discriminant analysis demonstrated that weaned and nursed pigs have distinct chemistry profiles, whereas MIA and control pigs have distinct cytokine profiles. The results from this study can guide management practices that recognize the effects of the interaction between MIA and weaning stress on the performance and health of pigs.

A New Infectious Unit: Extracellular Vesicles Carrying Virus Populations

Viral egress and transmission have long been described to take place through single free virus particles. However, viruses can also shed into the environment and transmit as populations clustered inside extracellular vesicles (EVs), a process we had first called vesicle-mediated en bloc transmission. These membrane-cloaked virus clusters can originate from a variety of cellular organelles including autophagosomes, plasma membrane, and multivesicular bodies. Their viral cargo can be multiples of nonenveloped or enveloped virus particles or even naked infectious genomes, but egress is always nonlytic, with the cell remaining intact. Here we put forth the thesis that EV-cloaked viral clusters are a distinct form of infectious unit as compared to free single viruses (nonenveloped or enveloped) or even free virus aggregates. We discuss how efficient and prevalent these infectious EVs are in the context of virus-associated diseases and highlight the importance of their proper detection and disinfection for public health. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Whole Genome or Single Genes? A Phylodynamic and Bibliometric Analysis of PRRSV

Diversity, ecology, and evolution of viruses are commonly determined through phylogenetics, an accurate tool for the identification and study of lineages with different pathological characteristics within the same species. In the case of PRRSV, evolutionary research has divided into two main branches based on the use of a specific gene (i.e., ORF5) or whole genome sequences as the input used to produce the phylogeny. In this study, we performed a review on PRRSV phylogenetic literature and characterized the spatiotemporal trends in research of single gene vs. whole genome evolutionary approaches. Finally, using publicly available data, we produced a Bayesian phylodynamic analysis following each research branch and compared the results to determine the pros and cons of each particular approach. This study provides an exploration of the two main phylogenetic research lines applied for PRRSV evolution, as well as an example of the differences found when both methods are applied to the same database. We expect that our results will serve as a guidance for future PRRSV phylogenetic research.

Analysis of ORF5 sequences of Porcine Reproductive and Respiratory Syndrome virus (PRRSV) circulating within swine farms in Costa Rica

Background

Worldwide, Porcine Reproductive and Respiratory Syndrome (PRRS) is among the diseases that cause the highest economic impact in modern pig production. PRRS was first detected in Costa Rica in 1996 and has since then severely affected the local swine industry. Studies of the molecular characterization of circulating strains, correlation with clinical records, and associations with pathogens associated with Porcine Respiratory Disease Complex (PRDC) have not been done in Costa Rica.

Results

Sequencing and phylogenetic analysis of ORF5 proved that PRRSV-2 was the only species detected in all locations analyzed. These sequences were grouped into three clusters. When comparing samples from San Jose, Alejuela, and Puntarenas to historical isolates of the previously described lineages (1 to 9), it has been shown that these were closely related to each other and belonged to Lineage 5, along with the samples from Heredia. Intriguingly, samples from Cartago clustered in a separate clade, phylogenetically related to Lineage 1. Epitope analysis conducted on the GP5 sequence of field isolates from Costa Rica revealed seven peptides with at least 80% amino acid sequence identity with previously described and experimentally validated immunogenic regions. Previously described epitopes A, B, and C, were detected in the Santa Barbara-Heredia isolate.

Conclusions

Our data suggest that the virus has three distinct origins or introductions to the country. Future studies will elucidate how recently introduced vaccines will shape the evolutionary change of circulating field strains.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02925-7.

Porcine reproductive and respiratory syndrome virus seroprevalence in Scottish finishing pigs between 2006 and 2018

BACKGROUND

Porcine reproductive and respiratory syndrome (PRRS) is a major endemic pig disease worldwide and is associated with considerable economic costs.

METHODS

In Scotland, three abattoir surveys were conducted in 2006 (158 farms), 2012-2013 (94 farms) and 2017-2018 (97 farms) to estimate seroprevalence to PRRS virus (PRRSV) in commercial finishing pigs. These surveys covered around 79%, 59% and 66% of the Quality Meat Scotland assured farms slaughtering pigs in Scotland in 2006, 2012-13 and, 2017-18 respectively. In the 2006 survey, six pigs per farm were sampled and tested using the CIVTEST SUIS PRRS E/S test. In the 2012-2013 and 2017-2018 surveys, 10 pigs per farm were sampled and tested using the IDEXX PRRS X3 Ab test. A farm was considered positive if it had one or more seropositive samples.

RESULTS

The prevalence of positive farms was 45.6% (95% CI: 38.0-53.4), 47.8% (95% CI: 38.1-57.9) and 45.4% (95% CI: 35.8-55.3) in the 2006, 2012-2013 and 2017-2018 surveys, respectively, and 70%-75.5% farms did not change their status between sampling periods.

CONCLUSION

The prevalence of PRRSV exposure in Scottish pig herds was high and changed little from 2006 to 2018. These surveys have informed planning for a prospective PRRS control programme in Scotland.

Temporal stability of swine movement networks in the U.S

As a consequence of multi-site pig production practiced in North America, frequent and widespread animal movements create extensive networks of interaction between farms. Social network analysis (SNA) has been used to understand disease transmission risks within these complex and dynamic production ecosystems and is particularly relevant for designing risk-based surveillance and control strategies targeting highly connected farms. However, inferences from SNA and the effectiveness of targeted strategies may be influenced by temporal changes in network structure. Since farm movements represent a temporally dynamic network, it is also unclear how many months of data are required to gain an accurate picture of an individual farm's connectivity pattern and the overall network structure. The extent to which shipments between two specific farms are repeated (i.e., "loyalty" of farm contacts) can influence the rate at which the structure of a network changes over time, which may influence disease dynamics. In this study, we aimed to describe temporal stability and loyalty patterns of pig movement networks in the U.S. swine industry. We analyzed a total of 282,807 animal movements among 2724 farms belonging to two production systems between 2014 and 2017. Loyalty trends were largely driven by contacts between sow farms and nurseries and between nurseries and finisher farms; mean loyalty (percent of contacts that were repeated at least once within a 52-week interval) of farm contacts was 51-60 % for farm contacts involving weaned pigs, and 12-22% for contacts involving feeder pigs. A cyclic pattern was observed for both weaned and feeder pig movements, with episodes of increased loyalty observed at intervals of 8 and 17-20 weeks, respectively. Network stability was achieved when six months of data were aggregated, and only small shifts in node-level and global network metrics were observed when adding more data. This stability is relevant for designing targeted surveillance programs for disease management, given that movements summarized over too short a period may lead to stochastic swings in network metrics. A temporal resolution of six months would be reliable for the identification of potential super-spreaders in a network for targeted intervention and disease control. The temporal stability observed in these networks suggests that identifying highly connected farms in retrospective network data (up to 24 months) is reliable for future planning, albeit with reduced effectiveness.

Porcine Reproductive and Respiratory Syndrome Modified Live Virus Vaccine: A "Leaky" Vaccine with Debatable Efficacy and Safety

Porcine reproductive and respiratory syndrome (PRRS) caused by the PRRS virus (PRRSV) is one of the most economically important diseases, that has significantly impacted the global pork industry for over three decades, since it was first recognized in the United States in the late 1980s. Attributed to the PRRSV extensive genetic and antigenic variation and rapid mutability and evolution, nearly worldwide epidemics have been sustained by a set of emerging and re-emerging virus strains. Since the first modified live virus (MLV) vaccine was commercially available, it has been widely used for more than 20 years, for preventing and controlling PRRS. On the one hand, MLV can induce a protective immune response against homologous viruses by lightening the clinical signs of pigs and reducing the virus transmission in the affected herd, as well as helping to cost-effectively increase the production performance on pig farms affected by heterologous viruses. On the other hand, MLV can still replicate in the host, inducing viremia and virus shedding, and it fails to confer sterilizing immunity against PRRSV infection, that may accelerate viral mutation or recombination to adapt the host and to escape from the immune response, raising the risk of reversion to virulence. The unsatisfied heterologous cross-protection and safety issue of MLV are two debatable characterizations, which raise the concerns that whether it is necessary or valuable to use this leaky vaccine to protect the field viruses with a high probability of being heterologous. To provide better insights into the immune protection and safety related to MLV, recent advances and opinions on PRRSV attenuation, protection efficacy, immunosuppression, recombination, and reversion to virulence are reviewed here, hoping to give a more comprehensive recognition on MLV and to motivate scientific inspiration on novel strategies and approaches of developing the next generation of PRRS vaccine.

Biochemistry and Immune Biomarkers Indicate Interacting Effects of Pre- and Postnatal Stressors in Pigs across Sexes

The effects of maternal immune activation (MIA) elicited by a prenatal stressor and postnatal metabolic or immune stressors on chemical and inflammatory biomarkers were studied in male and female pigs. Pigs exposed to MIA elicited by porcine reproductive and respiratory syndrome virus and matching controls were assigned at two months of age to fasting stress, immune stress, or a saline group. The serum levels of over 30 chemistry and immune analytes were studied. Significantly low levels of blood urea nitrogen were detected in females exposed to MIA, while the highest creatinine levels were identified in fasting females exposed to MIA. The levels of interferon gamma and interleukin 8 were highest in pigs exposed to postnatal immune challenge. The profiles suggest that MIA may sensitize pigs to postnatal stressors for some indicators while making them more tolerant of other stressors. Effectiveness of practices to ameliorate the impact of postnatal stressors on the physiology of the pig could be enhanced by considering the prenatal stress circumstances.

Seroprevalence of the viral pig diseases among backyard pigs in Chiang Mai, Thailand

The Participatory One-Health Disease Detection project (PODD) (www.cmonehealth.org) developed a health-based surveillance system with the local government of Chiang Mai community ownership that has been created a mobile application on smartphone for reporting an abnormal event, especially animal health. Previously, the PODD project has obtained a significant number of pig abnormal events. Therefore, there are likely to be some diseases that are currently circulating among backyard pigs. A cross-sectional serological study was undertaken to determine the risk factors for virus infection and prevalence of antibodies against the classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2) and influenza A virus (IAV) among backyard pigs in Chiang Mai, Thailand. Antibodies against the CSFV, PRRSV and PCV2 in backyard pigs were shown in swine level to be 14 % (95 % CI: 9-20), 14 % (95 % CI: 10-19), and 15 % (95 % CI: 8-23), respectively. For the household level, antibodies against the CSFV, PRRSV and PCV2 were found to be 23 % (95 % CI: 13-37), 22 % (95 % CI: 14-23), and 48 % (95 % CI: 32-63), respectively, while antibodies against IAV were shown to be absent. The use of artificial insemination for breeding purposes has been considered to be a significant risk factor associated with PRRSV (OR = 21.08, 95 % CI: 1.92-232.02) and CSFV (OR = 7.7, 95 % CI: 1.49-39.90) infections. Meanwhile, a risk factor for PCV2 infection was found to significantly involve the feeding of pigs with commercial feed (OR = 9.64, 95 % CI: 1.85-50.26). The findings of this study indicate that infections with CSFV, PRRSV, and PCV2 remain a significant concern and may have an impact on the growth performance of the backyard pigs. The lack of antibodies against the influenza A virus has indicated a low degree of interspecies transmission of influenza A among backyard pigs in Chiang Mai, Thailand. Effective control measures need to be prepared and implemented, and these should include the strict regulation of pig imports as a free source of the viruses along with effective animal quarantine, policies, and appropriate vaccination programs.

Multi-Scale Airborne Infectious Disease Transmission

Airborne disease transmission is central to many scientific disciplines including agriculture, veterinary biosafety, medicine, and public health. Legal and regulatory standards are in place to prevent agricultural, nosocomial, and community airborne disease transmission. However, the overall importance of the airborne pathway is underappreciated, e.g.,, US National Library of Medicine's Medical Subjects Headings (MESH) thesaurus lacks an airborne disease transmission indexing term. This has practical consequences as airborne precautions to control epidemic disease spread may not be taken when airborne transmission is important, but unrecognized. Publishing clearer practical methodological guidelines for surveillance studies and disease outbreak evaluations could help address this situation.To inform future work, this paper highlights selected, well-established airborne transmission events - largely cases replicated in multiple, independently conducted scientific studies. Methodologies include field experiments, modeling, epidemiology studies, disease outbreak investigations and mitigation studies. Collectively, this literature demonstrates that airborne viruses, bacteria, and fungal pathogens have the capability to cause disease in plants, animals, and humans over multiple distances - from near range (< 5 m) to continental (> 500 km) in scale. The plausibility and implications of undetected airborne disease transmission are discussed, including the notable underreporting of disease burden for several airborne transmitted diseases.

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

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

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

BACKGROUND

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) continues to be a major economic issue for the swine industry worldwide, not only due to acute outbreaks but also endemic infections. PRRS disease severity and consequently financial losses can vary greatly between endemically infected farms and estimation of damage is challenging. This study aimed to assess the economic effect of PRRS in a systematic way at individual farm-level for endemically infected herds, using a PRRS cost simulation tool. In total 21 German sow herds with endemic PRRSV infection were investigated. Data on health and production performance, farm management and environment to be fed into the calculator was collected on each farm, and blood samples taken to confirm the PRRSV status.

RESULTS

All study farms experienced a significant loss attributable to PRRS. The median farm budget across all farms was - 31 € per sow and year, compared to a median simulated farm budget of 248 € if these farms had been PRRSV negative. The median total loss attributable to PRRS was 74,181 € per farm per year, corresponding to a median total loss per sow and year of 255 €. The impact of PRRS on farm profits was - 19.1% on average and - 41% in the worst case.

CONCLUSIONS

The calculated losses give a good hint of the economic damage due to PRRS for the pig industry. Even in endemically infected farms, farmers face a non-negligible damage and profit from a concerted PRRS control. The calculator has proven itself in the field to render a valid estimation of losses due to PRRS in endemically infected farms.

Genetic characterization of a novel recombined porcine reproductive and respiratory syndrome virus 2 among Nadc30-like, Jxa1-like and TJ-like strains

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically devastating viral diseases in the global pig industry, including China. Recently, we successfully isolated a porcine reproductive and respiratory syndrome virus (PRRSV) from lung tissue and peripheral blood of piglets at a farm from Dujiangyan in Sichuan, China, and named it the DJY-19 strain. The full-length genome sequence of DJY-19 shared 86.8%-94.1% nucleotide similarity with NADC30-like and NADC30 PRRSV strains. We compared the open reading frame (ORF) 5 gene of DJY-19 with 34 PRRSV strains from Genbank. Phylogenetic analysis showed that DJY-19 clustered with NADC30 strains, characterized by a predicted 131-amino-acid deletion in the nonstructural protein (NSP) 2. The results of homology analysis showed that the homology between DJY-19 and NADC30 (JN654459.1) strains was the highest (95.9%), whereas homology with other domestic strains was lower (80.9%-92.6%). Furthermore, we identified four recombination breakpoints in the DJY-19 genome; they separated the DJY-19 genome into four regions. The 8106-9128 nucleotide (nt) region of DIY-19 was highly similar to the TJ strain, and the 12106-12580 nt region of DIY-19 was highly similar to the JXA1-R strain. Our findings demonstrate that DJY-19 arose from the recombination of North America NADC30 strain and TJ strain and JXA1-R in China. The application of multiple attenuated vaccine strains has led to complex recombination of PRRSV strains in China. This study provides a theoretical basis for making a more reasonable PRRS virus control and prevention strategy.

Long-Lasting Impact of Maternal Immune Activation and Interaction With a Second Immune Challenge on Pig Behavior

The combined effects on pig behavior of maternal immune challenge during gestation followed by a second immune challenge later in life have not been studied. Porcine reproductive and respiratory syndrome virus (PRRSV) infection during gestation can elicit maternal immune activation (MIA) yet the interactions with the offspring response to a second immune challenge after birth remains unexplored. Knowledge on the response to viral challenges in rodents has been gained through the use of the viral mimetic polyinosinic-polycytidylic acid (Poly(I:C)), yet the effects of this immune stimulant on pig behavior have not been assessed. This study advances the understanding of the combined effect of MIA and a second immune challenge later in life on female and male pig behavior. Three complementary experiments enabled the development of an effective Poly(I:C) challenge in pigs, and testing the interaction between PRRSV-elicited MIA, Poly(I:C) challenge at 60 days of age, and sex on behaviors. Individual-level observations on sickness, locomotor, and social behaviors were measured 1-3 h after Poly(I:C) challenge. Vomiting, panting, lethargy, walking, laying, playing, and touching behaviors were analyzed using generalized linear mixed effect models. Results indicated that a Poly(I:C) dose of 1 mg/kg within 1 h after injection increased the incidence of laying and sickness behavior. The Poly(I:C) challenge decreased the incidence of locomotor behaviors and activity levels. Pigs exposed to MIA had lower rates of social behaviors such as playing. The combined effect of PRRSV-elicited MIA and Poly(I:C) immune challenge further sensitized the pigs to behavior disruption across sexes including changes in sternal and lateral laying, walking, lethargy, and touching incidence. Notably, the effects of Poly(I:C) immune challenge alone on behaviors tended to be more extreme in males, whereas the effects of Poly(I:C) following MIA tended to be more extreme in females. Our findings demonstrate that MIA and Poly(I:C) affected behaviors, and the viral mimetic effects shortly after injection can offer insights into the prolonged effect of postnatal viral infections on feeding, social interactions and health status. Management practices that reduce the likelihood of gestational diseases and accommodate for behavioral disruptions in the offspring can minimize the impact of MIA.

Genetic Engineering of Livestock: The Opportunity Cost of Regulatory Delay

Genetically engineered (GE) livestock were first reported in 1985, and yet only a single GE food animal, the fast-growing AquAdvantage salmon, has been commercialized. There are myriad interconnected reasons for the slow progress in this once-promising field, including technical issues, the structure of livestock industries, lack of public research funding and investment, regulatory obstacles, and concern about public opinion. This review focuses on GE livestock that have been produced and documents the difficulties that researchers and developers have encountered en route. Additionally, the costs associated with delayed commercialization of GE livestock were modeled using three case studies: GE mastitis-resistant dairy cattle, genome-edited porcine reproductive and respiratory syndrome virus-resistant pigs, and the AquAdvantage salmon. Delays of 5 or 10 years in the commercialization of GE livestock beyond the normative 10-year GE product evaluation period were associated with billions of dollars in opportunity costs and reduced global food security.

Immunization with a recombinant fusion of porcine reproductive and respiratory syndrome virus modified GP5 and ferritin elicits enhanced protective immunity in pigs

Porcine reproductive and respiratory syndrome (PRRS) has caused huge economic losses in the swine industry worldwide. Live and inactivated vaccines have only been partially successful in generating protective immune responses. The PRRS virus (PRRSV) glycoprotein 5 (GP5) is a major viral antigenic target and is thus suitable for development of genetically engineered PRRSV vaccines. Here, a modified GP5 and ferritin were fused and expressed using a baculovirus system to generate a GP5m-ferritin nanoparticle vaccine. We demonstrated that the GP5m-ferritin vaccine elicited higher serum antibody titers in pigs than inactivated PRRSV. Moreover, immunization with GP5m-Ft promoted a Th1-dominant cellular immune response and enhanced specific T-lymphocyte immune responses. GP5m-ferritin-vaccinated pigs had significantly lower mean rectal temperatures, respiratory scores, viremia, and macroscopic and microscopic lung lesion scores post-challenge compared with unvaccinated pigs. These results indicated that GP5m-ferritin subunit vaccines can elicit specific protective immune responses and represent promising vaccine candidates.

Assessment of the Impact of the Recombinant Porcine Reproductive and Respiratory Syndrome Virus Horsens Strain on the Reproductive Performance in Pregnant Sows

This study assessed the impact of a PRRSV (porcine reproductive and respiratory syndrome virus) recombinant strain (Horsens strain) on the reproductive performance of naïve pregnant sows in the last third of gestation. Fifteen sows were included: four negative reproductive controls (NTX), five infected with a PRRSV-1 field strain (Olot/91, T01), and six infected with the recombinant PRRSV-1 strain (Horsens strain, T02). Piglets were monitored until weaning. Reproductive performance was the primary variable. In sows, viremia and nasal shedding (T01 and T02 groups), and, in piglets, viral load in blood and in lungs, as well as macroscopic lung lesions (T01 and T02 groups), were the secondary variables. The reproductive performance results were numerically different between the two challenged groups. Moreover, viral loads in blood were 1.83 × 10⁶ ± 9.05 × 10⁶ copies/mL at farrowing, 1.05 × 10⁷ ± 2.21 × 10⁷ copies/mL at weaning from piglets born from T01 animals and 1.64 × 10³ ± 7.62 × 10³ copies/mL at farrowing, 1.95 × 10³ ± 1.17 × 10⁴ copies/mL at weaning from piglets born from T02 sows. Overall, 68.8% of T01 piglets and 38.1% of T02 piglets presented mild lung lesions. In conclusion, the results suggest that Horsens strain is less virulent than the field strain Olot/91 under these experimental conditions.

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

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

Porcine reproductive and respiratory syndrome virus dissemination across pig production systems in the United States

Porcine reproductive and respiratory syndrome virus (PRRSV) remains widespread in the North American pig population. Despite improvements in virus characterization, it is unclear whether PRRSV infections are a product of viral circulation within production systems (local) or across production systems (external). Here, we examined the local and external dissemination dynamics of PRRSV and the processes facilitating its spread in three production systems. Overall, PRRSV genetic diversity has declined since 2018, while phylodynamic results support frequent external transmission. We found that PRRSV dissemination predominantly occurred mostly through transmission between farms of different production companies for several months, especially from November until May, a timeframe already established as PRRSV season. Although local PRRSV dissemination occurred mainly through regular pig flow (from sow to nursery and then to finisher farms), an important flux of PRRSV dissemination also occurred in the opposite direction, from finisher to sow and nursery farms, highlighting the importance of downstream farms as sources of the virus. Our results also showed that farms with pig densities of 500 to 1,000 pig/km² and farms located at a range within 0.5 km and 0.7 km from major roads were more likely to be infected by PRRSV, whereas farms at an elevation of 41 to 61 meters and surrounded by denser vegetation were less likely to be infected, indicating their role as dissemination barriers. In conclusion, our results demonstrate that external dissemination was intense, and reinforce the importance of farm proximity on PRRSV spread. Thus, consideration of farm location, geographic characteristics and animal densities across production systems may help to forecast PRRSV collateral dissemination.

Serological evidence for the presence of wobbly possum disease virus in Australia

Wobbly possum disease virus (WPDV) is an arterivirus that was originally identified in common brushtail possums (Trichosurus vulpecula) in New Zealand, where it causes severe neurological disease. In this study, serum samples (n = 188) from Australian common brushtail, mountain brushtail (Trichosurus cunninghami) and common ringtail (Pseudocheirus peregrinus) possums were tested for antibodies to WPDV using ELISA. Antibodies to WPDV were detected in possums from all three species that were sampled in the states of Victoria and South Australia. Overall, 16% (30/188; 95% CI 11.0-22.0) of possums were seropositive for WPDV and 11.7% (22/188; 95% CI 7.5-17.2) were equivocal. The frequency of WPDV antibody detection was the highest in possums from the two brushtail species. This is the first reported serological evidence of infection with WPDV, or an antigenically similar virus, in Australian possums, and the first study to find antibodies in species other than common brushtail possums. Attempts to detect viral RNA in spleens by PCR were unsuccessful. Further research is needed to characterise the virus in Australian possums and to determine its impact on the ecology of Australian marsupials.

Gilt Vaccination with a Mixed Administration of a PRRS MLV and a PPV1 Subunit Vaccine Protects against Heterologous PRRSV1 Infection and Prevents Detrimental Effects on Piglet Performance

The efficacy of the combined administration of a porcine reproductive and respiratory syndrome (PRRS) modified live virus (MLV) vaccine and a porcine parvovirus 1 (PPV1) subunit vaccine in gilts was addressed in two experiments. Experiment A aimed to establish a 4-week onset of immunity (OOI). Gilts were randomly distributed in three treatment groups: non-vaccinated control animals (group 1), animals vaccinated with the combined vaccine (group 2), and a third group that consisted of animals vaccinated with the PRRS MLV vaccine alone (group 3). Four weeks after the first vaccination, gilts were challenged with a heterologous PRRS virus 1 (PRRSV1) and euthanized three weeks after. Besides this, experiment B pursued a 17-week duration of immunity (DOI). In this case, gilts were distributed in the same treatment groups, but for the third group, which consisted of non-vaccinated, non-challenged animals were used instead. For the DOI assessment, gilts were artificially inseminated 4 weeks after the first vaccination, challenged at day 90 of gestation, and followed up, together with their offspring, until day 20 post-farrowing. Serology and viremia post-challenge were determined in gilts from both experiments, while farrowing and piglet performance were only evaluated in experiment B. Overall, the combined vaccine helped to protect gilts from viremia post-challenge and, consequently, to prevent PRRS clinical symptoms and diminish the proportion of piglets infected congenitally or early in life. The combined vaccine also elicited a significant improvement in piglet survival rate and growth performance until weaning. The present results reveal efficacy and lack of interference of the mixed use of the tested vaccines against PRRSV1 infection, with at least 4-week OOI and 17-week DOI.

Resilience Effects of SGK1 and TAP1 DNA Markers during PRRSV Outbreaks in Reproductive Sows

The porcine reproductive and respiratory syndrome virus (PRRSV) is a major infectious stressor that causes serious health problems and productivity drops. Based on previous genome-wide analyses, we selected SGK1 and TAP1 as candidate genes for resilience, and genotyped three mutations, including a 3'UTR variant SGK1_rs338508371 and two synonymous variants TAP1_rs1109026889 and TAP1_rs80928141 in 305 Landrace × Large White sows. All polymorphisms affected the reproductive performance in the outbreak, but not during the endemic phase, thereby indicating a potential use of these markers for resilience. Moreover, some genotypes were associated with a stable performance across PRRSV phases. Thus, in the outbreak, the SGK1_rs338508371 AA sows had less piglets born alive (p < 0.0001) and more stillborns (p < 0.05) while other sows were able to keep their productivity. During the outbreak, TAP1_rs80928141 GG sows had less piglets born alive (p < 0.05) and both TAP1 polymorphisms influenced the number of mummies in an additive manner (p < 0.05). Remarkably, TAP1_rs80928141 AA sows had around one mummy more than GG sows (p < 0.01). Resilience to PRRSV could be improved by including the SGK1 and TAP1 markers in crossbreeding and/or selection schemes, as they contribute to maintaining a stable number of piglets born alive and lost, particularly mummies, despite the outbreak.

Evaluation of local and systemic immune responses in pigs experimentally challenged with porcine reproductive and respiratory syndrome virus

The host-associated defence system responsible for the clearance of porcine reproductive and respiratory syndrome virus (PRRSV) from infected pigs is currently poorly understood. To better understand the dynamics of host–pathogen interactions, seventy-five of 100 pigs infected with PRRSV-JA142 and 25 control pigs were euthanized at 3, 10, 21, 28 and 35 days post-challenge (dpc). Blood, lung, bronchoalveolar lavage (BAL) and bronchial lymph node (BLN) samples were collected to evaluate the cellular immune responses. The humoral responses were evaluated by measuring the levels of anti-PRRSV IgG and serum virus-neutralizing (SVN) antibodies. Consequently, the highest viral loads in the sera and lungs of the infected pigs were detected between 3 and 10 dpc, and these resulted in moderate to mild interstitial pneumonia, which resolved accompanied by the clearance of most of the virus by 28 dpc. At peak viremia, the frequencies of alveolar macrophages in infected pigs were significantly decreased, whereas the monocyte-derived DC/macrophage and conventional DC frequencies were increased, and these effects coincided with the early induction of local T-cell responses and the presence of proinflammatory cytokines/chemokines in the lungs, BAL, and BLN as early as 10 dpc. Conversely, the systemic T-cell responses measured in the peripheral blood mononuclear cells were delayed and significantly induced only after the peak viremic stage between 3 and 10 dpc. Taken together, our results suggest that activation of immune responses in the lung could be the key elements for restraining PRRSV through the early induction of T-cell responses at the sites of virus replication.

Contrasting animal movement and spatial connectivity networks in shaping transmission pathways of a genetically diverse virus

Analyses of livestock movement networks has become key to understanding an industry's vulnerability to infectious disease spread and for identifying farms that play disproportionate roles in pathogen dissemination. In addition to animal movements, many pathogens can spread between farms via mechanisms mediated by spatial proximity. Heterogeneities in contact patterns based on spatial proximity are less commonly considered in network studies, and studies that jointly consider spatial connectivity and animal movement are rare. The objective of this study was to determine the extent to which movement versus spatial proximity networks determine the distribution of an economically important endemic virus, porcine reproductive and respiratory syndrome virus (PRRSV), within a swine-dense region of the U.S. PRRSV can be classified into numerous phylogenetic lineages. Such data can be used to better resolve between-farm infection chains and elucidate types of contact most associated with transmission. Here, we construct movement and spatial proximity networks; farms within the networks were classified as cases if a given PRRSV lineage had been recovered at least once in a year for each of three years analyzed. We evaluated six lineages and sub-lineages across three years, and evaluated the epidemiological relevance of each network by applying network k-tests to statistically evaluate whether the pattern of case occurrence within the network was consistent with transmission via network linkages. Our results indicated that animal movements, not local area spread, play a dominant role in shaping transmission pathways, though there were differences amongst lineages. The median number of case farms inter-linked via animal movements was approximately 4.1x higher than random expectations (range: 1.7-13.7; p < 0.05, network k-test), whereas this measure was only 2.7x higher than random expectations for farms linked via spatial proximity (range: 1.3-5.4; p < 0.05, network k-test). For spatial proximity networks, contact based on proximities of <5 km appeared to have greater epidemiological relevance than longer distances, likely related to diminishing probabilities of local area spread at greater distances. However, the greater overall levels of connectivity of the spatial network compared to the movement network highlights the vulnerability of pig populations to widespread transmission via this route. By combining genetic data with network analysis, this research advances our understanding of dynamics of between-farm spread of PRRSV, helps establish the relative importance of transmission via animal movements versus local area spread, and highlights the potential for targeted control strategies based upon heterogeneities in network connectivity.

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

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

New insights about vaccine effectiveness: Impact of attenuated PRRS-strain vaccination on heterologous strain transmission

Vaccination is the main tool for controlling infectious diseases in livestock. Yet current vaccines only provide partial protection raising concerns about vaccine effectiveness in the field. Two successive transmission trials were performed involving 52 pigs to evaluate the effectiveness of a Porcine Reproductive and Respiratory Syndrome (PRRS) vaccinal strain candidate against horizontal transmission of a virulent heterologous strain. PRRS virus, above the specified limit of detection, was observed in serum and nasal secretions for all but one pig (the exception only tested positive for serum), indicating that vaccination did not protect pigs from becoming infected and shedding the heterologous strain. However, vaccination delayed the onset of viraemia, reduced the duration of shedding and significantly decreased viral load throughout infection. Serum antibody profiles indicated that 4 out of 13 (31%) vaccinates in one trial had no serological response (NSR). A Bayesian epidemiological model was fitted to the data to assess the impact of vaccination and presence of NSRs on PRRS virus transmission dynamics. Despite little evidence for reduction in the transmission rate, vaccinated animals were on average slower to become infectious, experienced a shorter infectious period and recovered faster. The overall PRRSV transmission potential, represented by the reproductive ratio R₀ was lower for the vaccinated animals, although there was substantial overlap in the credibility intervals for both groups. Model selection suggests that transmission parameters of vaccinated pigs with NSR were more similar to those of unvaccinated animals. The presence of NSRs in a population, however, seemed to only marginally affect the transmission dynamics. The results suggest that even when vaccination can't prevent infection, it can still have beneficial impacts on the transmission dynamics and contribute to reducing a herd's R₀. However, biosecurity and other measures need to be considered to decrease contact rates and lower R₀ below 1.

Isolation and characterization of a new population of nasal surface macrophages and their susceptibility to PRRSV-1 subtype 1 (LV) and subtype 3 (Lena)

Sialoadhesin (Sn) and CD163 have been recognized as two important mediators for porcine reproductive and respiratory syndrome virus (PRRSV) in host macrophages. Recently, it has been demonstrated that the highly virulent Lena strain has a wider macrophage tropism than the low virulent LV strain in the nasal mucosa. Not only CD163⁺Sn⁺ macrophages are infected by Lena but also CD163⁺Sn⁻ macrophages. This suggests that an alternative receptor exists for binding and internalization of PRRSV Lena in the CD163⁺Sn⁻ macrophages. Further investigation to find the new entry receptor was hampered by the difficulty of isolating these macrophages from the nasal mucosa. In the present study, a new population of CD163⁺Sn⁻ cells has been identified that is specifically localized in the nasal lamina propria and can be isolated by an intranasal digestion approach. Isolated nasal cells were characterized using specific cell markers and their susceptibility to two different PRRSV-1 strains (LV and Lena) was tested. Upon digestion, 3.2% (flow cytometry)—6.4% (confocal microscopy) of the nasal cells were identified as CD163⁺ and all (99.7%) of these CD163⁺ cells were Sn⁻. These CD163⁺Sn⁻ cells, designated as “nasal surface macrophages”, showed a 4.9 times higher susceptibility to the Lena strain than to the LV strain. Furthermore, the Lena-inoculated cell cultures showed an upregulation of CD163. These results showed that our new cell isolation system is ideal for the further functional and phenotypical analysis of the new population of nasal surface macrophages and further research on the molecular pathogenesis of PRRSV in the nose.

Establishment and characterization of the pig tonsil epithelial (PT) cell line as a new model for persist infection of Japanese Encephalitis Virus

Japanese encephalitis virus (JEV) causes a serious zoonotic disease worldwide, pig is the reservoir and amplifying host of JEV. JEV can persist infect tonsil in pig, but the relation between persist infection in tonsil and reservoir are not clear until now. A stable pig tonsil cell line is necessary for JEV persist infection research. In this study, we established a continuous epithelial cell line, named PT cell, from the pig tonsil. This cell is susceptible to JEV. We determined the growth characteristics, molecular properties, microstructure profiles of PT cell. JEV is easy to enter PT cell which may partly explain the reason of persist infection. We further determined that LMAN2L, a mannose lectin proteins, is the primary viral receptors for JEV entry in PT cell. IFITM3, an cellular surface antiviral factor, is underexpression in PT cell after JEV infection. All these results provide solid evidence that PT cell will promote additional research on JEV persist infection in pig tonsil.

Network analysis of pig movements in Argentina: Identification of key farms in the spread of infectious diseases and their biosecurity levels

This study uses network analysis to evaluate how swine movements in Argentina could contribute to disease spread. Movement data for the 2014-2017 period were obtained from Argentina's online livestock traceability registry and categorized as follows: animals of high genetic value sent to other farms, animals to or from markets, animals sent to finisher operations and slaughterhouse. A network analysis was carried out considering the first three movement types. First, descriptive, centrality and cohesion measures were calculated for each movement type and year. Next, to determine whether networks had a small-world topology, these were compared with the results from random Erdös-Rényi network simulations. Then, the basic reproductive number (R₀ ) of the genetic network, the group of farms with higher potential for disease spread standing at the top of the production chain, was calculated to identify farms acting as super-spreaders. Finally, their external biosecurity scores were evaluated. The genetic network in Argentina presented a scale-free and small-world topology. Thus, we estimate that disease spread would be fast, preferably to highly connected nodes and with little chances of being contained. Throughout the study, 31 farms were identified as super-spreaders in the genetic network for all years, while other 55 were super-spreaders at least once, from an average of 1,613 farms per year. Interestingly, removal of less than 5% of higher degree and betweenness farms resulted in a >90% reduction of R₀ indicating that few farms have a key role in disease spread. When biosecurity scores of the most relevant super-spreaders were examined, it was evident that many were at risk of introducing and disseminating new pathogens across the whole of Argentina's pig production network. These results highlight the usefulness of establishing targeted surveillance and intervention programmes, emphasizing the need for better biosecurity scores in Argentinean swine production units, especially in super-spreader farms.

Development of a biosecurity assessment tool and the assessment of biosecurity levels by this tool on Japanese commercial swine farms

It is well known that infectious diseases such as porcine reproductive and respiratory syndrome (PRRS) and porcine epidemic diarrhea (PED) decrease herd productivity and lead to economic loss. It is believed that biosecurity practices are effective for the prevention and control of such infectious diseases. Therefore, the objective of the present study was to investigate whether or not an association between biosecurity level and herd productivity, as well as disease status exists on Japanese commercial swine farms. The present study was conducted on 141 farms. Biosecurity in each farm was assessed by a biosecurity assessment tool named BioAsseT. BioAsseT has a full score of 100 and consists of three sections (external biosecurity, internal biosecurity and diagnostic monitoring). Production data for number of pigs weaned per sow per year (PWSY) and post-weaning mortality per year (PWM) were collected for data analysis. Regarding PRRS status, the farms were categorized into two groups: unknown or unstable and stable or negative. In addition, these farms were categorized based on their PED status, either positive or negative. The total BioAsseT score was associated with herd productivity: as total score increased by 1, PWSY increased by 0.104 pigs and PWM decreased by 0.051 % (P <  0.05). Herd productivity was associated with the score of external and internal biosecurity (P <  0.05), but did not correlate with the score of diagnostic monitoring. Regarding PRRS status, farms with an unknown or unstable status had lower total score than those with stable or negative status (P < 0.05). Similarly, PED positive farms had a lower total score compared to PED negative farms (P <  0.05). In conclusion, the present study provides evidence for the association between high biosecurity levels and increased herd productivity as well as a decreased risk for novel introductions of infectious diseases such as PED.

Immunological response to porcine reproductive and respiratory syndrome virus in young pigs obtained from a PRRSV-positive exposure status herd in a PRRSV endemic area

Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus (PRRSV), remains a major economic threat to swine production throughout the world. The aim of this study was to investigate the humoral and cell-mediated immune responses to PRRSV in 10 PRRSV vaccinated and 10 non-vaccinated young pigs obtained from a PRRSV-seropositive herd under field conditions. On day 35 days of post-vaccination (dpv), two PRRSV seropositive mixed-litter pigs were added to each group to co-mingle the animals. Serum and whole blood samples were collected from all pigs on the first day of vaccination, as well as on the 21, 35, 49, and 63 dpv. The PRRSV-specific humoral and cell-mediated immune response was determined by ELISA and flow cytometry analysis. The PRRSV ELISA sample to positive (S/P) ratio was found to be positive at the threshold level until the age of 84 days in both non-vaccinated and vaccinated groups, whereas the IFN-γ positive staining cytotoxic (CD8⁺) cells were rapidly expressed in the early periods of vaccination and co-mingling, but were not found to be specific to PRRSV. This result might have been due to an unspecific response to stress antigens. Further studies should be conducted to obtain more immune response data over long-term observation periods and to study the effect of PRRSV endemic strain vaccinations in endemically-infected herds.

Predicting vaccine effectiveness in livestock populations: A theoretical framework applied to PRRS virus infections in pigs

Vaccines remain one of the main tools to control infectious diseases in domestic livestock. Although a plethora of veterinary vaccines are on the market and routinely applied to protect animals against infection with particular pathogens, the disease in question often continues to persist, sometimes at high prevalence. The limited effectiveness of certain vaccines in the field leaves open questions regarding the required properties that an effective vaccine should have, as well as the most efficient vaccination strategy for achieving the intended goal of vaccination programmes. To date a systematic approach for studying the combined effects of different types of vaccines and vaccination strategies is lacking. In this paper, we develop a theoretical framework for modelling the epidemiological consequences of vaccination with imperfect vaccines of various types, administered using different strategies to herds with different replacement rates and heterogeneity in vaccine responsiveness. Applying the model to the Porcine Reproductive and Respiratory Syndrome (PRRS), which despite routine vaccination remains one of the most significant endemic swine diseases worldwide, we then examine the influence of these diverse factors alone and in combination, on within-herd virus transmission. We derive threshold conditions for preventing infection invasion in the case of imperfect vaccines inducing limited sterilizing immunity. The model developed in this study has practical implications for the development of vaccines and vaccination programmes in livestock populations not only for PRRS, but also for other viral infections primarily transmitted by direct contact.

Machine-learning algorithms to identify key biosecurity practices and factors associated with breeding herds reporting PRRS outbreak

Investments in biosecurity practices are made by producers to reduce the likelihood of introducing pathogens such as porcine reproductive and respiratory syndrome virus (PRRSv). The assessment of biosecurity practices in breeding herds is usually done through surveys. The objective of this study was to evaluate the use of machine-learning (ML) algorithms to identify key biosecurity practices and factors associated with breeding herds self-reporting (yes or no) a PRRS outbreak in the past 5 years. In addition, we explored the use of the positive predictive value (PPV) of these models as an indicator of risk for PRRSv introduction by comparing PPV and the frequency of PRRS outbreaks reported by the herds in the last 5 years. Data from a case control study that assessed biosecurity practices and factors using a survey in 84 breeding herds in U.S. from 14 production systems were used. Two methods were developed, method A identified 20 variables and accurately classified farms that had reported a PRRS outbreak in the previous 5 years 76% of the time. Method B identified six variables which 5 of these had already been selected by model A, although model B outperformed the former model with an accuracy of 80%. Selected variables were related to the frequency of risk events in the farm, swine density around the farm, farm characteristics, and operational connections to other farms. The PPVs for methods A and B were highly correlated to the frequency of PRRSv outbreaks reported by the farms in the last 5 years (Pearson r = 0.71 and 0.77, respectively). Our proposed methodology has the potential to facilitate producer's and veterinarian's decisions while enhancing biosecurity, benchmarking key biosecurity practices and factors, identifying sites at relatively higher risk of PRRSv introduction to better manage the risk of pathogen introduction.

Dynamics and Differences in Systemic and Local Immune Responses After Vaccination With Inactivated and Live Commercial Vaccines and Subsequent Subclinical Infection With PRRS Virus

The goals of our study were to compare the immune response to different killed and modified live vaccines against PRRS virus and to monitor the antibody production and the cell mediated immunity both at the systemic and local level. In the experiment, we immunized four groups of piglets with two commercial inactivated (A1-Progressis, A2-Suivac) and two modified live vaccines (B3-Amervac, B4-Porcilis). Twenty-one days after the final vaccination, all piglets, including the control non-immunized group (C5), were i.n., infected with the Lelystad strain of PRRS virus. The serum antibody response (IgM and IgG) was the strongest in group A1 followed by two MLV (B3 and B4) groups. Locally, we demonstrated the highest level of IgG antibodies in bronchoalveolar lavages (BALF), and saliva in group A1, whereas low IgA antibody responses in BALF and feces were detected in all groups. We have found virus neutralization antibody at DPV 21 (days post vaccination) and higher levels in all groups including the control at DPI 21 (days post infection). Positive antigen specific cell-mediated response in lymphocyte transformation test (LTT) was observed in groups B3 and B4 at DPV 7 and in group B4 at DPV 21 and in all intervals after infection. The IFN-γ producing lymphocytes after antigen stimulation were found in CD4-CD8+ and CD4+CD8+ subsets of all immunized groups 7 days after infection. After infection, there were obvious differences in virus excretion. The virus was detected in all groups of piglets in serum, saliva, and occasionally in feces at DPI 3. Significantly lower virus load was found in groups A1 and B3 at DPI 21. Negative samples appeared at DPI 21 in B3 group in saliva. It can be concluded that antibodies after immunization and infection, and the virus after infection can be detected in all the compartments monitored. Immunization with inactivated vaccine A1-Progressis induces high levels of antibodies produced both systemically and locally. Immunization with MLV-vaccines (Amervac and Porcilis) produces sufficient antibody levels and also cell-mediated immunity. After infection virus secretion gradually decreases in group B3, indicating tendency to induce sterile immunity.

Nuclear localization signal in TRIM22 is essential for inhibition of type 2 porcine reproductive and respiratory syndrome virus replication in MARC-145 cells

Porcine reproductive and respiratory syndrome virus (PRRSV) infection causes one of the most economically important swine diseases worldwide. Tripartite motif-containing 22 (TRIM22), a TRIM family protein, has been identified as a crucial restriction factor that inhibits a group of human viruses. Currently, the role of cellular TRIM22 in PRRSV infection remains unclear. In the present study, we analyzed the effect of TRIM22 on PRRSV replication in vitro and explored the underlying mechanism. Ectopic expression of TRIM22 impaired the viral replication, while TRIM22-RNAi favored the replication of PRRSV in MARC-145 cells. Additionally, we observed that TRIM22 deletion SPRY domain or Nuclear localization signal (NLS) losses the ability to inhibit PRRSV replication. Finally, Co-IP analysis identified that TRIM22 interacts with PRRSV nucleocapsid (N) protein through the SPRY domain, while the NLS2 motif of N protein is involved in interaction with TRIM22. Although the concentration of PRRSV N protein was not altered in the presence of TRIM22, the abundance of N proteins from simian hemorrhagic fever virus (SHFV), equine arteritis virus (EAV), and murine lactate dehydrogenase-elevating virus (LDV) diminished considerably with increasing TRIM22 expression. Together, our findings uncover a previously unrecognized role for TRIM22 and extend the antiviral effects of TRIM22 to arteriviruses.

Detection of porcine reproductive and respiratory syndrome virus (PRRSV) 1-7-4-type strains in Peru

Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses to the swine industry worldwide. While PRRSV has been endemic in North America since 1989, it was not until 1999 that the virus was first described in South America. Notably, recently an increased number of PRRSV outbreaks have been reported in South American countries. However, epidemiological information related to these outbreaks is limited and the genetic characteristics of the PRRSV strains circulating in the region are poorly understood. In this study, we describe the genetic analyses of PRRSV strains associated with severe PRRS outbreaks in Peru. Samples originating from 14 farms located in two Departments in Peru (Lima and Arequipa), were subjected to RT-PCR amplification of the PRRSV ORF5 gene and sequencing followed by restriction fragment length polymorphism (RFLP) analysis. Results demonstrated the circulation of PRRSV-2 in Peru. Notably ORF5 RFLP typing revealed that 15 (75%) of the PRRSV strains detected in this study belong to the RFLP 1-7-4 type. Phylogenetic analysis showed that the Peruvian strains are closely related to the highly virulent PRRSV 1-7-4 strains that emerged in the US in 2013-2014. Results here indicate the presence of highly virulent PRRSV 1-7-4 strains in Peru and provide important information on the geographical distribution of PRRSV, confirming the recent geographical expansion of this important swine pathogen towards South America.