Evaluation of the Pathogenicity and Transmissibility of a Chilean Isolate of Porcine Reproductive and Respiratory Syndrome Virus

The objective of this study was to determine clinical features, shedding and transmission of a Chilean Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) strain upon experimental inoculation of 4‐week‐old pigs. Six groups of five animals each were used. The G1 (donor) group was inoculated with PRRSV, maintained in an isolation unit for 35 days, and sampled daily to determine shedding in mucosal secretions and faeces, viraemia and seroconversion. An uninfected control group (G6) was equally maintained and sampled under strict isolation. Four other groups (G2 to G5) were exposed to PRRSV via direct contact with G1 for 5‐day periods in a staggered manner, throughout the 35‐day period, and were later placed in an independent isolation unit to monitor infection status for 7 days. All the animals in G1 and G6 were killed at 35 days post‐inoculation (dpi) and the contact groups at 12 days post‐contact (dpc). Samples were obtained from diverse organs for histopathological, immunohistochemical (IHC) and virological analysis. No clinical symptoms were evident in any group, except for a transient fever observed in G1. Histopathologically, all the animals of G1 had interstitial pneumonia, although scarce PRRSV‐positive cells were detected in the lung using IHC. PRRSV‐positive cells (IHC) were detected in the lymphoid tissue of all animals in infected groups, but especially in G3 and G4. Viraemia was detected in G1 (3–35 dpi) and in the all contact groups (5–12 dpc). Likewise, ranging from 3 to 19 dpi, PRRSV was detected in at least one animal from the tonsils and lungs in all infected groups, in nasal and ocular secretions, saliva or faeces. These results indicate that the donor group excreted infectious PRRSV and was able to transmit the infection to susceptible pigs. The critical shedding period was 7–19 dpi, during which, most likely, transmission took place.     

Pathogenicity of porcine reproductive and respiratory syndrome virus (ORF5 RFLP 1‐7‐4 viruses) in China

Porcine reproductive and respiratory syndrome virus (PRRSV) is an RNA virus that causes reproductive failure in sows and respiratory problems in piglets. PRRSV infection leads to substantial pig mortality and causing huge economic losses so that disease outbreaks caused by the new PRRSV strain from other regions have caused great concern in China. In this study, we analysed the pathogenicity of the novel ORF5 RFLP 1‐7‐4‐like PRRSV strain, named PRRSV‐ZDXYL‐China‐2018‐1 in pigs. The viral challenge test showed that PRRSV‐ZDXYL‐China‐2018‐1 infection can cause persistent fever, moderate dyspnoea, serum viraemia and interstitial pneumonia in piglets. The levels of viral loads in serum and PRRSV‐specific antigen were also detected in lung tissues were used one‐step Taq‐Man RT‐qPCR and Immunohistochemistry, respectively. At 28dpi, the level of specific antibodies was increased among infected piglets. Importantly, the new virus appeared be a moderately virulent isolate with pathogenicity compared to HP‐PRRSV strain LQ (JXA1‐like strain). Histological examination revealed severe monocyte haemorrhage and interstitial pneumonia associated with monocyte infiltration in the lung tissue of pigs infected with PRRSV‐ZDXYL‐China‐2018‐1 and LQ‐JXA1 strains. Immunohistochemistry (IHC) results showed positive brown‐red epithelial cells and macrophages in pig lungs. Therefore, it is critical to establish an effective strategy to control the spread of PRRSV in China.     

Fresh Pork and Porcine Reproductive and Respiratory Syndrome Virus: Factors Related to the Risk of Disease Transmission

Porcine reproductive and respiratory syndrome virus (PRRS) is a highly infectious virus. Experimentally, the disease can be induced in naïve pigs by the oral, intranasal and intramuscular routes. Depending on the virulence of the strain of the virus and the age of the pig, peak viremia can occur within 7 days of infection, and live virus can be isolated from blood or lymph nodes for several months post‐infection. Young pigs tend to develop higher titres of viremia than older pigs infected by the same route and dose with the same strain of virus. Porcine reproductive and respiratory syndrome virus survives in pork harvested from infected pigs for extended periods at temperatures of −20 or −70°C. In experimentally infected pigs, survival of PRRS virus in muscle held at 4°C has been demonstrated for at least 7 days, and infectivity of the virus in these samples was confirmed by bioassay. The optimal pH range for the survival of PRRS virus is thought to be 6.0 to 7.5. The elevated pH of non‐meat tissues (generally one pH unit higher) is likely to favour extended survival of PRRS virus in pig carcasses from which all superficial and deep lymph nodes have not been removed. It is likely that exsanguinated carcasses held at 4°C retain sufficient blood or lymph tissue to contain infective doses of PRRS virus. Porcine reproductive and respiratory syndrome virus is rapidly inactivated by heat, providing a predictable method to ensure that pork tissues are free of viable virus and feeding of cooked swill or garbage should not constitute a risk to pigs. While the probability of viable PRRS virus being present in a pig carcass may be low, the risk is not zero. The importation of raw pork into countries where PRRS is not endemic represents a hazard with potentially severe economic consequences.     

Type 2 Porcine Reproductive and Respiratory Syndrome Virus Infection Mediated Apoptosis in B‐ and T‐Cell Areas in Lymphoid Organs of Experimentally Infected Pigs

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection is characterized by persisting in lungs and lymphoid tissue, resulting in systemic lymphoid depletion. The aim of this study was to correlate the histological changes, viral antigen expression and apoptosis phenomena in tonsil, medial retropharyngeal and mediastinal lymph nodes of 12 pigs inoculated with a type 2 PRRSV isolate (Chilean strain 2402). Apoptosis phenomena were observed mainly in lymphocytes and secondly in macrophages of lymph nodes and tonsils of inoculated animals, showing a peak of both apoptotic cells and viral antigen expression at the end of the study (21 dpi). However, the number of apoptotic cells was higher than the number of PRRSV‐positive cells at the end of the study. This finding together with the location of apoptotic cells and PRRSV‐positive cells in different structures of lymphoid organs supports the hypothesis that PRRSV‐positive macrophages might modulate the apoptosis phenomena in other cells, mainly lymphocytes, by means of an indirect mechanism. Furthermore, apoptotic cells were detected both in B‐ and T‐cell areas of lymphoid organs, suggesting that apoptosis phenomena may play a role in the impairment of the host immune response during PRRS.     

Differential Expression of Proinflammatory Cytokines in the Lymphoid Organs of Porcine Reproductive and Respiratory Syndrome Virus‐Infected Pigs

Porcine reproductive and respiratory syndrome (PRRS) is considered one of the most important diseases in the swine industry. Although several studies have been carried out to elucidate the host immune response evoked against PRRS virus (PRRSV), there are several aspects that still remain unclear. The aim of this study was to determine the expression of IL‐1α, IL‐6 and TNF‐α in the lymphoid organs (mediastinal and retropharyngeal lymph nodes and tonsil) of PRRSV‐infected pigs and to determine their correlation with the expression of PRRSV antigen. Proinflammatory cytokine expression was different depending on the body compartment examined. Thus, whereas IL‐1α and TNF‐α were the main cytokines expressed in the mediastinal lymph node, IL‐6 was the most highly expressed cytokine in the retropharyngeal lymph node, and no expression of proinflammatory cytokines was observed in the tonsil. These findings may be related to the impairment of the host immune response evoked after PRRSV infection. Therefore, lymphoid organs and proinflammatory cytokines represent an important target of study for clarifying the immunopathogenesis of PRRS.     

Pathogenicity and Distribution of Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus in Pigs

The pathogenesis of highly pathogenic porcine reproductive and respiratory syndrome virus (PRRSV) strain (HuN4) is poorly understood. Therefore, highly pathogenic PRRSV strain (HuN4) and its derivative strain (HuN4‐F112) (obtained by propagation in MARC145 cells for 112 passages) were inoculated into a total of 48 PRRSV‐sero‐negative pigs (age: 4–5 weeks) by the intranasal route. Virological, pathological and in situ hybridization analyses were performed. The results exhibited that pigs infected with HuN4 showed a loss of appetite, decrease in body weight, raised body temperature and respiratory symptoms, along with interstitial pneumonia lesions. In the HuN4 group, multifocal interstitial pneumonia with macrophage infiltration was found in the lung. The lesions in the lymph node were characterized by collapsed follicles, depletion of germinal centres and reduction in lymphocytes. Perivascular cuffing and glial nodules were observed in the brains of some pigs. By comparison, the HuN4‐F112 group had milder lesions. PRRSV was detected in macrophages, alveolar epithelial cells and vascular endothelial cells in the tonsil and lymph nodes. The PRRSV amounts in the pigs infected with HuN4 were 10⁵–10⁹ copies/ml in the blood and 10¹⁰–10¹¹ copies/g in the lung tissues, whereas the virus amounts with HuN4‐F112 were 10^2.15–10^3.13 copies/ml in the blood and 10^3.0–10^3.6 copies/g in the lung. Our results demonstrate that the PRRS HuN4 virus infects alveolar epithelial cells, macrophages and vascular endothelial cells causing diffuse alveolar damage and lymph node necrosis. Its higher pathogenicity compared with HuN4‐F112 virus may be explained in part by higher replication rate in the previously mentioned organs.     

A recombination between two Type 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV‐1) vaccine strains has caused severe outbreaks in Danish pigs

Porcine reproductive and respiratory syndrome virus (PRRSV) is prevalent in Danish swine herds. In July 2019, PRRSV‐1 was detected in a PRRSV‐negative boar station and subsequently spread to more than 38 herds that had received semen from the boar station. Full genome sequencing revealed a sequence of 15.098 nucleotides. Phylogenetic analyses showed that the strain was a recombination between the Amervac strain (Unistrain PRRS vaccine; Hipra) and the 96V198 strain (Suvaxyn PRRS; Zoetis AH). The major parent was the 96V198 strain that spanned ORFs 1–2 and part of ORF 3 and the minor parent was the Amervac strain, which constituted the remaining part of the genome. The virus seems to be highly transmissible and has caused severe disease in infected herds despite a high level of genetic identity to the attenuated parent strains. The source of infection was presumable a neighbouring farm situated 5.8 km from the boar station.     

Porcine Reproductive and Respiratory Syndrome Virus Vaccines: Current Status and Strategies to a Universal Vaccine

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of PRRS, the most significant infectious disease currently affecting swine industry worldwide. In the United States alone, the economic losses caused by PRRS amount to more than 560 million US dollars every year. Due to immune evasion strategies and the antigenic heterogeneity of the virus, current commercial PRRSV vaccines (killed‐virus and modified‐live vaccines) are of unsatisfactory efficacy, especially against heterologous infection. Continuous efforts have been devoted to develop better PRRSV vaccines. Experimental PRRSV vaccines, including live attenuated vaccines, recombinant vectors expressing PRRSV viral proteins, DNA vaccines and plant‐made subunit vaccines, have been developed. However, the genetic and antigenic heterogeneity of the virus limits the value of almost all of the PRRSV vaccines tested. Developing a universal vaccine that can provide broad protection against circulating PRRSV strains has become a major challenge for current vaccine development. This paper reviews current status of PRRSV vaccine development and discusses strategies to develop a universal PRRSV vaccine.     

Porcine reproductive and respiratory syndrome virus NADC30‐like strain accelerates Streptococcus suis serotype 2 infection in vivo and in vitro

Porcine reproductive and respiratory syndrome (PRRS), an economically significant pandemic disease, commonly results in increased impact of bacterial infections, including those by Streptococcus suis (S. suis). In recent years, PRRS virus (PRRSV) NADC30‐like strain has emerged in different regions of China, and coinfected with S. suis and PRRSV has also gradually increased in clinical performance. However, the mechanisms involved in host innate responses towards S. suis and their implications of coinfection with NADC30‐like strain remain unknown. Therefore, the pathogenicity of NADC30‐like strain and S. suis serotype 2 (SS2) coinfection in vivo and in vitro was investigated in this study. The results showed that NADC30‐like increased the invasion and proliferation of SS2 in blood and tissues, resulting in more severe pneumonia, myocarditis, and peritonitisas well as higher mortality rate in pigs. In vitro, NADC30‐like strain increased the invasion and survival of SS2 in porcine alveolar macrophages (PAM) cells, causing more drastic expression of inflammatory cytokines and activation of NF‐ĸB signalling. These results pave the way for understanding the interaction of S. suis with the swine immune system and their modulation in a viral coinfection.     

Comparative Analysis of Immune Responses in Pigs to High and Low Pathogenic Porcine Reproductive and Respiratory Syndrome Viruses Isolated in China

The CH‐1a and HuN4 strains of porcine reproductive and respiratory syndrome virus (PRRSV) show different pathogenicities in pigs. To understand host immune responses against these viruses, we investigated the dynamic changes in cytokine levels produced in peripheral blood of piglets infected with the highly pathogenic PRRSV HuN4 strain or the CH‐1a strain. Clinical signs, virus loads and serum cytokine levels [interferon(IFN)‐α, Interleukin (IL)‐1, TNF‐α, IL‐6, IL‐12, IFN‐γ, IL‐10 and TGF‐β] were tested. The results showed that while piglets developed effective cellular immune responses against CH‐1a infection, those infected with HuN4 displayed ineffective cellular immunity, organ lesions and persistent elevated levels of immunoregulatory cytokines (IL‐10 and TGF‐β), which delayed the development of PRRSV‐specific immune responses. These results demonstrated that HuN4 infection induced higher cytokine levels than that of CH‐1a infection induced. The changes in inflammatory cytokines intensified the inflammatory reaction and damaged the tissues and organs.     

Outbreak Investigation of NADC30‐Like PRRSV in South‐East China

Epidemiological outbreak investigations were conducted on NADC30‐like porcine reproductive and respiratory syndrome virus (PRRSV) to investigate the prevalence of the disease in south‐east China in 2015. Two more provinces were found to have NADC30‐like PRRSV circulating besides previously reported six provinces. Phylogenetic analysis showed that these virus isolates were clustered in an independent branch and shared high nucleotide similarity to NADC30, a type 2 PRRSV that has been isolated in Unite States in 2008. One NADC30‐like PRRSV strain from Henan province was successfully isolated on porcine alveolar macrophages and was tested on 6‐week‐old specific pathogen‐free pigs for pathogenic study. The virus‐inoculated pigs showed typical PRRSV clinical symptoms, but all pigs survived throughout the study with a period of 14 days. At necropsy, the lungs of infected pigs developed PRRSV‐specific interstitial pneumonia, and virus antigen was detected in lung samples. Therefore, our results indicated NADC30‐like PRRSV has widely spread in China and could cause clinical disease on pigs.     

Emergence of a novel highly pathogenic porcine reproductive and respiratory syndrome virus in China

From 2014 to 2015, four novel highly pathogenic PRRS virus (HP‐PRRSV) strains named 14LY01‐FJ, 14LY02‐FJ 15LY01‐FJ, and 15LY02‐FJ were isolated from high morbidity (100%) and mortality (40%–80%) in piglets and sows in Fujian Province. To further our knowledge about these novel virus strains, we characterized their complete genomes and determined their pathogenicity in piglets. Full‐length genome sequencing analysis showed that these four isolates were closely related to type 2 (North American type, NA‐type) isolates, with 88.1%–96.3% nucleotide similarity, but only 60.6%–60.8% homology to the Lelystad virus (LV) (European type, EU‐type). The full length of the four isolates was determined to be 15017 or 15018 nucleotides (nt), excluding the poly(A) tail. Furthermore, the four isolates had three discontinuous deletions (aa 322–432, aa 483, and aa 504–522) within hypervariable region II (HV‐II) of Nsp2, as compared to the reference strain VR‐2332. This deletion pattern in the four isolates is consistent with strain MN184 and strain NADC30 isolated from America. Phylogenetic and molecular evolutionary analyses indicated that these virulent strains originated from a natural recombination event between the JXA1‐like HP‐PRRSV (JXA‐1 is one of the earliest Chinese HP‐PRRSV strains; sublineage 8.7) and the NADC30‐like (lineage 1) PRRSV. Animal experiments demonstrated that these four strains caused significant weight loss and severe histopathological lung lesions as compared to the negative control group. High mortality rate (40% or 80%) was found in piglets infected with any one of the four strains, similar to that found with other Chinese HP‐PRRSV strains. This study showed that the novel variant PRRSV was HP‐PRRSV, and it is therefore critical to monitor PRRSV evolution in China and develop a method for controlling PRRS.     

Naturally Co‐Infected Boars with both Porcine Reproductive and Respiratory Syndrome Virus and Porcine Circovirus Type 2

In this study, the humoral response against porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2), the presence of the virus in semen and serum and the genetic characteristics of the virus detected in 15 boars from a commercial farm were analysed. The results showed that 53% of the boars presented anti‐PRRSV antibodies and 100% presented anti‐PCV2 antibodies. Porcine reproductive and respiratory syndrome virus was detected in 43% of the boars and 73% were positive to PCV2. The complete ORF5 gene of PRRSV of 14 samples and a fragment of the ORF2 gene of PCV2 of 22 samples were sequenced. Porcine reproductive and respiratory syndrome virus analysis revealed <92% identity in viruses from semen and serum of two boars, whereas in the rest of the boars the identity was >97.5%. As for PCV2, two boars presented an identity <95% in serum and semen and the rest had an identity >96%. The results showed that PRRSV‐ and PCV2‐naturally infected boars can be found, and at least two different strains of viruses from semen and serum can be detected.     

Downregulation of Antigen‐Presenting Cells in Tonsil and Lymph Nodes of Porcine Reproductive and Respiratory Syndrome Virus‐Infected Pigs

Porcine reproductive and respiratory syndrome virus (PRRSV) can persist in different organs of infected pigs, which suggests a failure in the immune response. Antigen‐presenting cells (APCs) play a pivotal role in the induction of effective T‐ and B‐cell responses. In this study, we investigated the changes in the different APC subpopulations and T‐ and B‐cell counts in the tonsil, retropharyngeal and mediastinal lymph nodes of pigs experimentally infected with a European PRRSV field isolate. Our results demonstrated that the expression of S100, SWC3, HLA‐DR molecule and CD3 was diminished in the studied organs throughout the study, observing a significant negative correlation between viral antigen and HLA‐DR expression in both retropharyngeal and mediastinal lymph nodes. In contrast, λ‐light chains showed an increase during the study. Taking all into account, after PRRSV infection, no enhancement in the number of APCs and T cells was observed, suggesting an impairment of the immune function which may allow the persistence of PRRSV into the organism.     

A natural recombinant PRRSV between HP‐PRRSV JXA1‐like and NADC30‐like strains

Porcine reproductive and respiratory syndrome virus (PRRSV ) is a major economically significant pathogen that has adversely affected China's swine industry. Currently, a novel type 2 PRRSV , called the NADC 30‐like strain, is epidemic in numerous provinces of China, and commercial vaccines provide limited protection for infected animals. The extensive recombination phenomenon among NADC 30‐like PRRSV s is identified as a unique molecular characteristic of the virus. However, our understanding of how recombination influences NADC 30‐like PRRSV s is largely inadequate. In this study, we analysed the genetic characteristics of a recombinant NADC 30‐like PRRSV (SC ‐d) and examined its pathogenicity compared with a non‐recombinant NADC 30‐like PRRSV (SD ‐A19) and a highly pathogenic PRRSV (HuN4). SC ‐d has three discontinuous deletions in nsp2, consistent with NADC 30 isolated from the United States in 2008. Furthermore, we identified four recombination breakpoints in the SC ‐d genome, which separated the SC ‐d genome into four regions (regions A, B, C and D). Regions A and C are closely related to the JXA 1‐like strain, one of the earliest Chinese HP ‐PRRSV strains, and regions B and D are closely related to the NADC 30 strain. Moreover, SC ‐d inoculated piglets exhibited a persistent fever, moderate weight loss, mild thymus atrophy and obvious microscopic lung lesions. In summary, the recombinant NADC 30‐like PRRSV SC ‐d strain displayed a higher pathogenicity than the non‐recombinant NADC 30‐like PRRSV SD ‐A19 strain; however, the pathogenicity of the NADC 30‐like PRRSV SC ‐d was lower compared with the HP ‐PRRSV HuN4 strain in piglets. Our findings demonstrate that recombination is responsible for the enormous genetic diversity and pathogenicity variance of the NADC 30‐like PRRSV in China. This study provides a theoretical basis for developing a more reasonable PRRSV control and prevention strategy.     

Phylogenetic analysis of ORF5 and ORF7 of porcine reproductive and respiratory syndrome (PRRS) virus and the frequency of wild‐type PRRS virus in México

Porcine reproductive and respiratory syndrome (PRRS ) is caused by a genetically diverse RNA virus and is an economically significant disease in the swine industry. In this study, a total of 8,126 serum samples were obtained from 275 technified and semi‐technified farms belonging to 30 of the 32 states of Mexico and representative of the eight regions of the country. Anti‐PRRS v antibodies against the PRRS vaccine and an isolated wild Mexican virus were tested by ELISA . Antibodies were found in 15%–49% of the tested sera, with 2.4%–9.8% against the vaccine and 7.7%–26% against the wild virus. The PRRS v virus was detected by RT ‐PCR in 77 of the 1,630 pooled samples tested, representing seven of the eight geographic regions into which the Mexican Republic is divided. The complete sequences of open reading frames 5 and 7 from 20 PRRS v‐positive samples were determined. The analysis of the sequences together with the previously published sequences of historic strains revealed that all the strains belonged to the one, five and eight lineages of the PRRSV 2. Striking differences, particularly in ORF 5 and ORF 7, were found between sequences of the strains and the reference virus, due to insertions and substitutions in positions that play key roles in the recognition, structure and function of the virus. Overall, these results established the magnitude of PRRS virus genetic diversity, and the most frequent virus strain that predominates in Mexico. The PRRSV 2 is presented in the porcine population of Mexico; the circulating strains have important changes in ORF 5 and ORF 7, which probably explain the results obtained in the serological analysis of the wild virus and vaccine strains.     

Visual detection of porcine reproductive and respiratory syndrome virus using CRISPR‐Cas13a

Porcine reproductive and respiratory syndrome virus (PRRSV) has varied constantly and circulated in the pig industry worldwide. The prevention and control of porcine reproductive and respiratory syndrome (PRRS) is complicated. A visual, sensitive and specific diagnostic method is advantageous to the control of PRRS. The collateral cleavage activity of LwCas13a is activated to degrade non‐targeted RNA, when crRNA of LwCas13a bond to target RNA. The enhanced Cas13a detection is the combination of collateral cleavage activity of LwCas13a and recombinase polymerase amplification (RPA). In this study, the enhanced Cas13a detection for PRRSV was established. The novel method was an isothermal detection at 37°C, and the detection can be used for real‐time analysis or visual readout. The detection limit of the enhanced Cas13a detection was 172 copies/μl, and there were no cross‐reactions with porcine circovirus 2, porcine parvovirus, classical swine fever virus and pseudorabies virus. The enhanced Cas13a detection can work well in clinical samples. In summary, a visual, sensitive and specific nucleic acid detection method based on CRISPR‐Cas13a was developed for PRRSV.     

Pathogenicity and Molecular Characterization of Emerging Porcine Reproductive and Respiratory Syndrome Virus in Vietnam in 2007

In 2007, Vietnam experienced swine disease outbreaks causing clinical signs similar to the ‘porcine high fever disease’ that occurred in China during 2006. Analysis of diagnostic samples from the disease outbreaks in Vietnam identified porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV‐2). Additionally, Escherichia coli and Streptococcus equi subspecies zooepidemicus were cultured from lung and spleen, and Streptococcus suis from one spleen sample. Genetic characterization of the Vietnamese PRRSV isolates revealed that this virus belongs to the North American genotype (type 2) with a high nucleotide identity to the recently reported Chinese strains. Amino acid sequence in the nsp2 region revealed 95.7–99.4% identity to Chinese strain HUN4, 68–69% identity to strain VR‐2332 and 58–59% identity to strain MN184. A partial deletion in the nsp2 gene was detected; however, this deletion did not appear to enhance the virus pathogenicity in the inoculated pigs. Animal inoculation studies were conducted to determine the pathogenicity of PRRSV and to identify other possible agents present in the original specimens. Pigs inoculated with PRRSV alone and their contacts showed persistent fever, and two of five pigs developed cough, neurological signs and swollen joints. Necropsy examination showed mild to moderate bronchopneumonia, enlarged lymph nodes, fibrinous pericarditis and polyarthritis. PRRSV was re‐isolated from blood and tissues of the inoculated and contact pigs. Pigs inoculated with lung and spleen tissue homogenates from sick pigs from Vietnam developed high fever, septicaemia, and died acutely within 72 h, while their contact pigs showed no clinical signs throughout the experiment. Streptococcus equi subspecies zooepidemicus was cultured, and PRRSV was re‐isolated only from the inoculated pigs. Results suggest that the cause of the swine deaths in Vietnam is a multifactorial syndrome with PRRSV as a major factor.     

Sequence and Phylogenetic Analyses of the Nsp2 and ORF5 Genes of Porcine Reproductive and Respiratory Syndrome Virus in Boars from South China in 2015

Porcine reproductive and respiratory syndrome virus (PRRSV) is highly genetically diverse; however, little is known about the molecular epidemiology of PRRSV in the boar farms of South China. In this study, 367 samples were collected from boar farms in South China in 2015. The Nsp2 hypervariable region and ORF5 gene were PCR amplified from 66 PRRSV‐positive samples, followed by sequencing and analysis. The percentage of PRRSV antigen‐positive samples was 17.98%; 8.72% were positive for highly pathogenic PRRSV (HP‐PRRSV), and 9.26% were positive for low pathogenic PRRSV (LP‐PRRSV). Sequence alignment and phylogenetic tree analyses revealed three novel patterns of deletion in the hypervariable region of Nsp2, which had not been identified previously. Furthermore, numerous amino acid substitutions were identified in the putative signal peptide and extravirion regions of GP5. These results demonstrate for the first time that the existence of multiple different strains on the same boar farm, and extensive genetic mutation and high infection rate of PRRSV in boars from South China. Our research contributes to the understanding of the epidemiology and genetic characteristics of PRRSV on boar farms.     

Emergence of Porcine Reproductive and Respiratory Syndrome in Sweden: Detection,Response and Eradication

Porcine reproductive and respiratory syndrome (PRRS) is characterized by reproductive failure in sows and respiratory problems in growing pigs. The disease is present in most countries throughout the world but was not diagnosed in Sweden until the summer of 2007 when it was first detected through the national PRRS surveillance program. The immediate mobilization of veterinary authorities, field veterinarians and the pig industry was a prerequisite for preventing the spread of the disease. Within 10 days seven herds were verified as infected and the measures taken included stamping out, cleaning, disinfection and a vacancy period of 3 weeks before the herds were repopulated. To evaluate the effectiveness of these measures, a national sero‐surveillance was carried out during the autumn of 2007. Approximately 90% of the pig production was covered by this screening and all samples tested were negative with regard to antibodies to PRRS virus.