Direct detection of the porcine reproductive and respiratory syndrome (PRRS) virus by reverse polymerase chain reaction (RT-PCR)

Identification of potential SLA-I-restricted CTL epitopes within the M protein of porcine reproductive and respiratory syndrome virus

CD8+ cytotoxic T lymphocytes (CTLs), are essential for clearance of porcine reproductive and respiratory syndrome virus (PRRSV) infection and regulation of host immune responses. Identification of SLA I-restricted CD8+ CTL epitopes would facilitate PRRSV vaccine development. Here, cells isolated from peripheral blood mononuclear cells (PBMCs) of PRRSV-immunized Large White pigs (JXA1-R strain) were screened for immunodominant PRRSV-2 M protein T cell epitopes via ELISPOT assay. Of nine immunodominant epitopes detected, eight elicited significant IFN-γ secretion responses that varied among individual pigs and according to epitope. To predict which epitopes harbored potential CTL epitopes, swine leukocyte antigen (SLA) class I genes of Large White pigs were cloned and sequenced, yielding fourteen distinct SLA class I gene sequences. Based on ELISPOT and SLA genotyping results, SLA-restricted binding of the fourteen predicted class I proteins to peptides derived from the eight immunodominant epitopes were predicted in-silico. After evaluation of 42 pET-peptide-SLA-I-β2m complexes containing predicted restricted peptides, extracellular SLA class I domains and β2m, ELISA testing of 33 peptide-SLA-I-β2m complexes detected four complexed peptides. These four peptides were evaluated using in vitro complex refolding assays that confirmed that M_2-5 and M_6-1 peptides each formed complexes with SLA-2*0502 and sβ2m, while M_9-1 formed a complex with SLA-2*1201 and sβ2m. ELISPOT results confirmed these three 9-mer potential CTL epitopes efficiently stimulated IFN-γ secretion when presented by SLA class I molecules specified here. This study describes effective CTL epitope identification methods for use in future investigations of swine cellular immunity toward T cell-based vaccine development.

Splenic CD163+ macrophages as targets of porcine reproductive and respiratory virus: Role of Siglecs

CD169 and CD163 have been involved in the process of PRRS virus attachment and infection in macrophages, although recent studies have challenged the requirement for CD169. In addition to CD169, macrophages express other siglecs, whose role in PRRS virus infection is so far unknown. Splenic CD163⁺ macrophages express Siglec-3 and Siglec-5 but almost undetectable levels of CD169. Hence, we considered this cell population appropriate for analysing the role of these siglecs in the attachment and internalization of PRRS virus into macrophages. PRRS virus replicated efficiently in these macrophages, yielding even higher titres than in alveolar macrophages. Besides, a recombinant protein consisting in the ectodomain of porcine Siglec-3 fused to the Fc fragment of human IgG1 (Siglec3-Fc) was able to bind PRRS virus, while binding to Siglec-5-Fc was inconsistent. Antibodies to CD169 but not to Siglec-3 or Siglec-5 blocked the binding and infection of PRRS virus on alveolar macrophages. Unexpectedly, our antibody to CD169 also blocked the binding of PRRS virus to splenic CD163⁺ macrophages, whereas antibodies to Siglec-3 or Siglec-5 had no effect. These results show that very low levels of CD169 expression are enough to support the attachment and internalization of PRRS virus into macrophages, whereas Siglec-3 and Siglec-5 do not seem to contribute to the virus entry in these cells.

Rapid and sensitive detection of type II porcine reproductive and respiratory syndrome virus by reverse transcription loop-mediated isothermal amplification combined with a vertical flow visualization strip

Reverse transcription-loop-mediated isothermal amplification (RT-LAMP) was combined with a vertical flow (VF) nucleic acid detection strip to develop a universal assay for the detection of type II porcine reproductive and respiratory syndrome virus (PRRSV). The loop primers were labeled separately with biotin and fluorescein isothiocyanate (FITC) in this assay. Using optimized parameters, the whole reaction could be completed in <50 min in a completely enclosed environment. The detection limit of this assay was found to be 1 pg RNA, 30 tissue culture infective dose 50 (TCID50) virus, or 230 copies of recombinant plasmid DNA, which is relatively higher than that of RT-LAMP analyzed by agarose gel, RT-LAMP visualized by calcein, and the conventional RT-polymerase chain reaction (PCR). No false-positive results were obtained in the specificity assay. The efficiency of the RT-LAMP method was tested by analyzing 43 clinical samples, and the results were compared with those obtained by RT-PCR analysis, with the respective positive rates of 32.56% and 27.91%. This result confirmed that the method described is a rapid, accurate, and sensitive method for universal type II PRRSV detection. Also, this method can be used for the rapid detection of type II PRRSV during the early phase of an outbreak, especially for rapid veterinary diagnosis on the spot and in rural areas.

Genetic characterization and evolution of H1N1pdm09 after circulation in a swine farm

Following the emergence of the A(H1N1)pdm09 in humans, this novel influenza virus was reverse transmitted from infected people to swine population worldwide. In this study we investigated the molecular evolution of A(H1N1)pdm09 virus identified in pigs reared in a single herd. Nasal swabs taken from pigs showing respiratory distress were tested for influenza type A and A(H1N1)pdm09 by real-time RT-PCR assays. Virus isolation from positive samples was attempted by inoculation of nasal swabs samples into specific pathogen free embryonated chicken eggs (ECE) and complete genome sequencing was performed on virus strains after replication on ECE or from original swab sample. The molecular analysis of hemagglutinin (HA) showed, in four of the swine influenza viruses under study, a unique significant amino acid change, represented by a two-amino acid insertion at the HA receptor binding site. Phylogenetic analysis of HA, neuraminidase, and concatenated internal genes revealed a very similar topology, with viruses under study forming a separate cluster, branching outside the A(H1N1)pdm09 isolates recognized until 2014. The emergence of this new cluster of A(H1N1)pdm09 in swine raises further concerns about whether A(H1N1)pdm09 with new molecular characteristics will become established in pigs and potentially transmitted to humans.

Safety of Porcine Reproductive and Respiratory Syndrome Modified Live Virus (MLV) vaccine strains in a young pig infection model

The objective of this study was to compare the safety of all modified live virus vaccines commercially available in Europe against Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) under the same experimental conditions. For this purpose, one hundred and twenty three-week-old piglets, divided into five groups, were used. On day 0 of the experiment, nine pigs per group were removed and the remaining fifteen were vaccinated with the commercial vaccines Ingelvac PRRS MLV, Amervac PRRS, Pyrsvac-183 and Porcilis PRRS by the IM route or were mock vaccinated and used as controls. On day 3, the nine unvaccinated pigs were re-introduced into their respective groups and served as sentinel pigs. Clinical signs were recorded daily and lung lesions were determined on days 7, 14 and 21, when 5 vaccinated pigs per group were euthanized. Blood samples and swabs were taken every three days and different organs were collected at necropsy to determine the presence of PRRSV. None of the vaccines studied caused detectable clinical signs in vaccinated pigs although lung lesions were found. Altogether, these results indicate that all vaccines can be considered clinically safe. However, some differences were found in virological parameters. Thus, neither Pyrsvac-183 nor Porcilis PRRS could be detected in porcine alveolar macrophage (PAM) cultures or in lung sections used to determine PRRSV by immunohistochemistry, indicating that these viruses might have lost their ability to replicate in PAM. This inability to replicate in PAM might be related to the lower transmission rate and the delay in the onset of viremia observed in these groups

Porcine reproductive and respiratory syndrome virus detection in Thailand during 2005-2010 in relation to clinical problems, pig types, regions, and seasons

The objectives of the present study were to determine the prevalence of porcine reproductive and respiratory syndrome virus (PRRSV) in Thailand between 2005 and 2010. The study was conducted by retrospectively investigating the detection of PRRSV from different pig types including boars, sows, piglets, nursery pigs, and fattening pigs from six regions of Thailand, i.e., the northern, eastern, northeastern, central, western, and southern parts. The data were obtained from cases submitted to the Chulalongkorn University Veterinary Diagnostic Laboratory for PRRSV detection between 2005 and 2010. Frequency analyses and generalized linear models were used to evaluate the prevalence of PRRSV in relation to various factors. In total, 2,273 tissues (n = 636), semen (n = 210) and serum (n = 1,427) samples were included. PRRSV was detected in 32.6 % (740/2,273) of the pigs. The virus was found in 43.1 %, 15.7 %, and 30.3 % in the tissues, semen, and serum samples, respectively (P < 0.001). The prevalence of PRRSV was highest in 2005 (43.6 %) and lowest in 2009 (23.6 %) (P < 0.001). The prevalence of PRRSV was highest in nursery pigs (43.7 %) and lowest in boars (15.4 %) (P < 0.001). The prevalence of PRRSV in the hot season (34.9 %) was higher than that found in the cool season (28.1 %, P = 0.018) but did not differ significantly compared to rainy season (34.0 %, P = 0.486). The strain of PRRSV isolated in the present study was genotype 2 (54.5 %), genotype 1 (31.0 %), and mixed genotypes (14.5 %). It can be concluded that PRRSV was detected in the tissue samples more frequently than the semen and serum samples. The prevalence of PRRSV was high in the nursery pigs. A high prevalence of PRRSV was found in the hot season, indicating that climatic factors may also contribute to the prevalence of PRRSV in Thailand. Of all the PRRSV detected, 31.0 %, 54.5 %, and 14.5 % belonged to genotype 1, genotype 2, and mixed genotypes, respectively.

Identification of serum proteomic biomarkers for early porcine reproductive and respiratory syndrome (PRRS) infection

BACKGROUND

Porcine reproductive and respiratory syndrome (PRRS) is one of the most significant swine diseases worldwide. Despite its relevance, serum biomarkers associated with early-onset viral infection, when clinical signs are not detectable and the disease is characterized by a weak anti-viral response and persistent infection, have not yet been identified. Surface-enhanced laser desorption ionization time of flight mass spectrometry (SELDI-TOF MS) is a reproducible, accurate, and simple method for the identification of biomarker proteins related to disease in serum. This work describes the SELDI-TOF MS analyses of sera of 60 PRRSV-positive and 60 PRRSV-negative, as measured by PCR, asymptomatic Large White piglets at weaning. Sera with comparable and low content of hemoglobin (< 4.52 μg/mL) were fractionated in 6 different fractions by anion-exchange chromatography and protein profiles in the mass range 1-200 kDa were obtained with the CM10, IMAC30, and H50 surfaces.

RESULTS

A total of 200 significant peaks (p < 0.05) were identified in the initial discovery phase of the study and 47 of them were confirmed in the validation phase. The majority of peaks (42) were up-regulated in PRRSV-positive piglets, while 5 were down-regulated. A panel of 14 discriminatory peaks identified in fraction 1 (pH = 9), on the surface CM10, and acquired at low focus mass provided a serum protein profile diagnostic pattern that enabled to discriminate between PRRSV-positive and -negative piglets with a sensitivity and specificity of 77% and 73%, respectively.

CONCLUSIONS

SELDI-TOF MS profiling of sera from PRRSV-positive and PRRSV-negative asymptomatic piglets provided a proteomic signature with large scale diagnostic potential for early identification of PRRSV infection in weaning piglets. Furthermore, SELDI-TOF protein markers represent a refined phenotype of PRRSV infection that might be useful for whole genome association studies.

Porcine reproductive and respiratory syndrome virus: interlaboratory ring trial to evaluate real-time reverse transcription polymerase chain reaction detection methods

To compare the real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) assays used for the diagnosis of Porcine reproductive and respiratory syndrome virus (PRRSV), a Europe-wide interlaboratory ring trial was conducted. A variety of PRRSV strains including North American (NA) and European (EU) genotype isolates were analyzed by the participants. Great differences regarding qualitative diagnostics as well as analytical sensitivity were observed between the individual RT-qPCR systems, especially when investigating strains from the EU genotype. None of the assays or commercial kits used in the ring trial could identify all different PRRSV strains with an optimal analytical and diagnostic sensitivity. The genetic variability of the PRRSV strains, which is supposed to hinder the diagnostic of the RT-PCR because of mutations at the primer binding sites, was also confirmed by sequencing and subsequent phylogenetic analysis. In summary, a major problem in PRRSV diagnostics by RT-qPCR is false-negative results. To achieve maximum safety in the molecular diagnosis of PRRSV, the combined usage of different assays or kits is highly recommended.

Immunisation of pigs with a major envelope protein sub-unit vaccine against porcine reproductive and respiratory syndrome virus (PRRSV) results in enhanced clinical disease following experimental challenge

Disease exacerbation was observed in pigs challenged with virulent porcine reproductive and respiratory syndrome virus (PRRSV) following immunisation with a recombinant GP5 sub-unit PRRSV vaccine (rGP5) produced in E. coli. Eighteen animals were divided into three experimental groups: group A were immunised twice IM with rGP5, 21 days apart; group B acted as positive controls (challenged but not immunised); and group C were negative controls. Pigs in groups A and B were challenged 21 days after the second immunisation of the group A animals. Following challenge, three pigs given rGP5 exhibited more severe clinical signs than the positive controls, including respiratory distress and progressive weight-loss. Although not statistically significant, the more severe disease exhibited by group A animals may suggest previous immunisation as a contributory factor. The mechanisms of these findings remain unclear and no association could be established between the severity of disease, non-neutralising antibody concentrations and tissue viral loads.

Porcine Reproductive and Respiratory Syndrome Virus isolates differ in their susceptibility to neutralization

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is highly heterogenic. This heterogeneity has an effect on antigenic composition of PRRSV and might create differences in sensitivity to neutralization between isolates. The sensitivity to neutralization could be an important feature of PRRSV isolates because it is likely that isolates resistant to neutralization pose a significant challenge for the development of vaccines that elicit broad protective immunity. Nonetheless, little information is available for understanding or categorizing the viral neutralization phenotype of PRRSV isolates. Consequently, the main purpose of this study was to determine whether PRRSV isolates differ in their susceptibility to neutralization and if they can be classified in different categories based on their neutralization phenotype. For this purpose, a panel of 39 PRRSV isolates and a set of 30 hyperimmune monospecific sera were used in cross-neutralization assays. The results of this study indicate that PRRSV isolates differ in their sensitivity to neutralization and k-means clustering system allowed classifying the isolates in four different categories according to their neutralization phenotype: highly sensitive, sensitive, moderately sensitive and resistant to neutralization. Further analyses using two additional clustering systems that considered individual data for the classification of the isolates confirmed that classification obtained by k-means is accurate in most cases and that only in a few instances classification is less stringent. Sequences of GP3, GP4 and GP5 were analyzed but no correlation could be found between the sequence of previously identified neutralizing epitopes or the number of N-linked glycosylation sites in different proteins and the neutralization phenotype of the isolates. These data provide the first systematic assessment of overall neutralization sensitivities of a panel of diverse PRRSV isolates. The classification of the isolates provides a useful tool to facilitate the systematic characterization of neutralizing antibody production elicited by new vaccine candidates.

Comparative pathogenicity of type 1 and type 2 isolates of porcine reproductive and respiratory syndrome virus (PRRSV) in a young pig infection model

Porcine reproductive and respiratory syndrome virus (PRRSV) isolates are classified in two different genotypes, based on genomic heterogeneity: type 1, which comprises European type isolates, and type 2, which includes North American type isolates. It is believed that members of both genotypes differ in some biological properties including pathogenicity, however extensive studies comparing isolates of both genotypes have never been carried out. The objective of the present study was to compare the pathogenic properties of six different PRRSV isolates, three of type 1 and three of type 2, in a young pig infection model. For this purpose, a total of 105 3-week-old piglets were divided in 7 groups of 15 animals that were exposed on day 0 of the experiment to one of the six isolates tested or were mock infected (negative control group). Clinical signs and rectal temperatures were recorded daily and blood samples were taken on days 3, 6, 9, 12, 15, 18 and 21 of the experiment. On days 7, 14 and 21 post-inoculation five animals per group were sacrificed, macroscopic lung lesions were evaluated and different tissue samples were collected to determine viral organic distribution. The results obtained indicate that type 2 isolates are more pneumovirulent than type 1 isolates, as demonstrated by the recording of respiratory clinical signs only in pigs exposed to type 2 viruses and by the severity of macroscopic and microscopic lung lesions in those pigs. However, no clear differences could be established between genotypes in systemic clinical signs or viral load and viral distribution after challenge. These results support the general idea that type 2 isolates induce more severe respiratory disease than type 1 isolates.

Novel H1N2 swine influenza reassortant strain in pigs derived from the pandemic H1N1/2009 virus

Swine influenza monitoring programs have been in place in Italy since the 1990 s and from 2009 testing for the pandemic H1N1/2009 virus (H1N1pdm) was also performed on all the swine samples positive for type A influenza. This paper reports the isolation and genomic characterization of a novel H1N2 swine influenza reassortant strain from pigs in Italy that was derived from the H1N1pdm virus. In May 2010, mild respiratory symptoms were observed in around 10% of the pigs raised on a fattening farm in Italy. Lung homogenate taken from one pig showing respiratory distress was tested for influenza type A and H1N1pdm by two real time RT-PCR assays. Virus isolation was achieved by inoculation of lung homogenate into specific pathogen free chicken embryonated eggs (SPF CEE) and applied onto Caco-2 cells and then the complete genome sequencing and phylogenetic analysis was performed from the CEE isolate. The lung homogenate proved to be positive for both influenza type A (gene M) and H1N1pdm real time RT-PCRs. Virus isolation (A/Sw/It/116114/2010) was obtained from both SPF CEE and Caco-2 cells. Phylogenetic analysis showed that all of the genes of A/Sw/It/116114/2010, with the exception of neuraminidase (NA), belonged to the H1N1pdm cluster. The NA was closely related to two H1N2 double reassortant swine influenza viruses (SIVs), previously isolated in Sweden and Italy. NA sequences for these three strains were clustering with H3N2 SIVs. The emergence of a novel reassortant H1N2 strain derived from H1N1pdm in swine in Italy raises further concerns about whether these viruses will become established in pigs. The new reassortant not only represents a pandemic (zoonotic) threat but also has unknown livestock implications for the European swine industry.

Use of a Multiplex RT-PCR Assay for Simultaneous Detection of the North American Genotype Porcine Reproductive and Respiratory Syndrome Virus, Swine Influenza Virus and Japanese Encephalitis Virus

A multiplex reverse transcriptase-polymerase chain reaction (multiplex RT-PCR) assay was developed and subsequently evaluated for its efficacy in the detection of multiple viral infections simultaneously, in swine. Specific primers for each of the 3 RNA viruses, North American genotype porcine reproductive and respiratory syndrome virus, Japanese encephalitis virus, and swine influenza virus, were used in the testing procedure. The assay was shown to be highly sensitive because it could detect as little as 10⁻⁵ ng of each of the respective amplicons in a single sample containing a composite of all 3 viruses. The assay was also effective in detecting one or more of the same viruses in various combinations in specimens, including lymph nodes, lungs, spleens, and tonsils, collected from clinically ill pigs and in spleen specimens collected from aborted pig fetuses. The results from the multiplex RT-PCR were confirmed by virus isolation. The relative efficiency (compared to the efficiency of separate assays for each virus) and apparent sensitivity of the multiplex RT-PCR method show that this method has potential for application in routine molecular diagnostic procedures.

First Pandemic H1N1 Outbreak from a Pig Farm in Italy

The first outbreak of the pandemic H1N1 virus in a swine breeder farm in Italy in November 2009 was reported. Clinical signs observed in sows included fever, depression, anorexia and agalactia, while in piglets diarrhoea and weight loss. The morbidity in sows was approximately 30% and the accumulated mortality rate was similar with those usually reported in piggeries (<10%). Virus was isolated from piglets (A/Sw/It/290271/09) and the sequencing of the whole genome was then performed. Comparison with all (H1N1)v sequences available in GenBank shows A/Sw/It/290271/09 three unique amino-acid (aa) changes in PB2 (S405T), PB1 (K386R) and PA (K256Q), not yet associated to any well characterized phenotype markers of Influenza viruses. All eight aa at positions representing the so-called species specific swine-human signatures, found in both swine and in the pandemic H1N1v, are also present. The M2 protein displays the C55F and the PA protein the S409N substitutions, both corresponding to enhanced transmission phenotype markers. Phylogenetic analysis showed that the virus was genetically related to the pandemic H1N1 virus. In addition, serological samples were collected from 40 sows, of which 20 resulted positive to the pandemic H1N1 virus by HI test proving a virus circulation in the farm.

Influence of time on the genetic heterogeneity of Spanish porcine reproductive and respiratory syndrome virus isolates

The aim of the present study was to establish the degree of diversity of porcine reproductive and respiratory virus (PRRSV) isolates that circulate in the same geographical area in different years. Nucleotide sequences of open reading frame (ORF) 5 were determined for 28 Spanish field PRRSV isolates from different years and three European-type modified live virus vaccines. Sequences were aligned using Clustal W software and a phylogenetic tree constructed using the neighbour joining method. The results of pairwise homology comparisons of nucleotide and deduced amino acid sequences of these PRRSV isolates indicate a tendency for heterogeneity to increase with time. The study of the phylogenetic tree revealed that Spanish PRRSV isolates constitute two well-defined clades and a group of unrelated sequences. The observed heterogeneity does not appear to be due to temporal evolution exclusively. Early and recent isolates group themselves into different clusters independently of the time of isolation, indicating the co-circulation of different variants and the maintenance of variants of the original isolates in the field.

Development of a novel hot-start multiplex PCR for simultaneous detection of classical swine fever virus, African swine fever virus, porcine circovirus type 2, porcine reproductive and respiratory syndrome virus and porcine parvovirus

A novel hot-start multiplex PCR (mPCR) assay was developed and subsequently evaluated for its effectiveness in simultaneously detecting multiple viral infections of swine. Specific primers for each of five virus genomes, namely classical swine fever virus (CSFV), African swine fever virus (ASFV), porcine circovirus type 2 (PCV2), porcine reproductive and respiratory syndrome virus (PRRSV) and porcine parvovirus (PPV) were used. Combined nucleic acid purification was carried out using a commercial RNA/DNA extraction kit. The mPCR consisted of a two-step procedure which included reverse transcription and PCR amplification. This mPCR and the corresponding separate assays were evaluated comparatively on serial ten-fold dilutions of each virus. Analysis of the sensitivity in comparison to the corresponding single PCR (sPCR) for the detection of each of the five targets was identical for CSFV, PCV2 and PPV, 1 log lower for PRRSV and 2 logs lower for ASFV. No spurious PCR amplification reactions among all five pathogens were noticed with various amounts of DNA and RNA mixtures. All the uninfected controls were scored negative. The relative efficiency of the mPCR developed in this study compared to performing sPCR for each virus, suggests its potential application for routine molecular diagnostic purposes.

Similarity of European porcine reproductive and respiratory syndrome virus strains to vaccine strain is not necessarily predictive of the degree of protective immunity conferred

The objective of this study was to determine the degree of protection conferred by a Lelystad-like modified live virus (MLV) vaccine against a heterologous wild-type porcine reproductive and respiratory syndrome virus (PRRSV) isolate of the same cluster. For this purpose, fourteen 3-week-old piglets were divided into three groups: Group A pigs were vaccinated with a modified live virus vaccine, Group B pigs were used as positive controls, and Group C pigs as negative controls. Twenty-eight days after the last dose of vaccine, all pigs in Groups A and B were inoculated with the Spanish PRRSV strain 5710. To evaluate efficacy, clinical signs were recorded and the presence of challenge virus was determined by virus isolation in blood samples and nasal swabs collected at various time points post-challenge (p.c.) and in tissue samples collected at necropsy 24 days p.c. After challenge, moderate clinical signs were observed in pigs from Groups A and B. In addition, all vaccinated pigs were viremic at least once, although viremia tended to be more sporadic in this group than in Group B pigs. PRRSV was detected in at least one tissue sample from four out of five pigs from Group A and in all pigs from Group B. The results indicate that the protection conferred by the MLV vaccine used in this study against a closely related virulent strain was only partial. The findings suggest that the degree of genetic homology of ORF5 between MLV vaccine and challenge isolate is not a good predictor of vaccine efficacy.

Simple and rapid detection of the porcine reproductive and respiratory syndrome virus from pig whole blood using filter paper

The combination of Flinders Technology Associates filter papers (FTA cards) and real-time PCR was examined to establish a simple and rapid technique for the detection of porcine reproductive and respiratory syndrome virus (PRRSV) from whole pig blood. A modified live PRRS vaccine was diluted with either sterilised saline or pig whole blood, and the suspensions were applied onto the FTA cards. The real-time RT-PCR detection of PRRSV was performed directly with the samples applied to the FTA card without the RNA extraction step. Six whole blood samples from at random selected piglets in the PRRSV infected farm were also assayed in this study. The expected PCR product was successfully amplified from either saline diluted or pig whole blood diluted vaccine. The same PCR ampliocon was detected from all blood samples assayed in this study. This study suggested that the combination of an FTA card and real-time PCR is a rapid and easy technique for the detection of PRRSV. This technique can remarkably shorten the time required for PRRSV detection from whole blood and makes the procedure much easier.

First Results of Detection of PRRSV and CSFV RNA by SYBR Green I-based Quantitative PCR

Porcine reproductive and respiratory syndrome (PRRS) and classical swine fever (CSF) cause significant economic losses to the swine industry worldwide. As both diseases cause similar symptoms, rapid and reliable detection of these diseases is essential for disease surveillance. A quantitative SYBR Green I-based reverse transcription-polymerase chain reaction (RT-PCR) is described for simultaneous and differential diagnosis. The established RT-PCR for the quantitation of PRRSV and CSFV cDNA was found to provide a broad dynamic range, detecting from 10(3) to 10(11) and 10(2) to 10(11) copies of cDNA per reaction, respectively. Sensitivity and specificity of this method were compared with those of conventional RT-PCR and both were equal or superior to the reference method. Reproducibility was tested and the assay was proved very reliable. The assay is timesaving, easy to handle, and highly sensitive and specific. Therefore, it is a powerful tool for detecting PRRSV and CSFV simultaneously for routine outbreak investigation.

Reproductive performance of gilts following vaccination and subsequent heterologous challenge with European strains of porcine reproductive and respiratory syndrome virus

The objective of this study was to evaluate the efficacy of two commercially available modified live virus vaccines for preventing the reproductive and early postnatal consequences of infecting (challenging) pregnant gilts with virulent porcine reproductive and respiratory syndrome virus (PRRSV). For this purpose 21 crossbred gilts were allocated to one or another of four groups (Groups A-D). Group A comprised four gilts neither vaccinated nor challenged; Group B comprised five gilts that were challenged but not vaccinated; Group C comprised seven gilts that were vaccinated (AmervacPRRS) and challenged; Group D comprised five gilts that were vaccinated (Pyrsvac-183) and challenged. Vaccination was 24 days before conception, and challenge was at 90 days of gestation. Both vaccine viruses and the challenge virus were European strains but differed in part from one another on the basis of their genetic (nucleotide) sequence. After challenge PRRSV was isolated from five (100%), four (57%), and two (40%) of the gilts of Groups B, C and D, respectively. Although vaccination failed to prevent a detectable viremia in all of the gilts of Groups C and D after they were challenged (or congenital infection of some of their pigs), it did provide a statistically significant level of protection in regard to the incidence of congenital infection, reproductive performance, and pig health and viability. Namely, for Groups C and D the numbers of liveborn pigs/litter and healthy pigs/litter throughout the early postnatal period were similar to those of Group A (nonvaccinated and nonchallenged) and far exceeded those of Group B (nonvaccinated and challenged).

Simultaneous detection of North American and European porcine reproductive and respiratory syndrome virus using real-time quantitative reverse transcriptase-PCR

Porcine reproductive and respiratory syndrome (PRRS) is 1 of the most economically important diseases of swine. Detection of the etiologic agent, PRRS virus (PRRSV), represents a diagnostic challenge due to the heterogeneity of field isolates as well as the propensity for swine to develop persistent infection in which virus is difficult to detect. Recently European (EU) lineage PRRSV isolates, which are genetically divergent from North American (NA) isolates, have been introduced into NA swine further complicating efforts to diagnose this disease. In this study, real-time (TaqMan) reverse transcriptase (RT)-PCR assays were developed for multiplex detection, differentiation, and quantification of NA and EU PRRSV field isolates. Oligonucleotide primers and dual-labeled probes were selected from conserved regions of open-reading frame 7 and the 3'-untranslated region. The real-time RT-PCR assays described for the NA or EU genotype of PRRSV detected viral RNA from 83/83 strains (74 NA; 9 EU) previously isolated by cell culture between 1992 and 2003. The analytical sensitivity of both assays was consistently found to be less than a single TCID50, which corresponded to 5-10 RNA molecules, and was not significantly reduced when the reactions were performed in a multiplex format. When performing multiplex reactions, sensitive detection was possible even when 1 viral RNA concentration was up to 5,000-fold higher than the second. The diagnostic sensitivity and specificity of the multiplex reaction was found to be at a minimum equivalent to that of both nested RT-PCR and virus isolation.

Effects of two commercial European modified-live vaccines against porcine reproductive and respiratory syndrome viruses in pregnant gilts

The purpose of this study was to assess the effects of two currently available commercial European-type modified-live virus (MLV) vaccines against porcine reproductive and respiratory syndrome in a reproductive pig model. Sixteen 90-day pregnant gilts were divided into four groups and allocated to one of the following intranasal treatments: group A gilts served as negative controls; group B gilts were exposed to a virulent European field strain; group C gilts were exposed to vaccine strain VP046 Bis and group D gilts to vaccine strain All-183. The results indicated that MLV strains can replicate in breeding animals and have the ability to cross the placenta. In particular, viraemia was detected in all gilts in group C and 2/4 gilts in group D, at least at one time point. In addition, transplacental infection was demonstrated in 3/4 gilts in group C and 2/4 gilts in group D. However, congenital and early postnatal infection did not have a marked detrimental effect on piglet performance when compared to negative controls, and no statistically significant differences were observed in most cases. Conversely, the reproductive performance of gilts in group B was significantly worse than that of the other groups. Specifically, the number of born-alive piglets, the survival rate of piglets during lactation and the mean weight of weaned pigs were significantly lower. It was concluded that the two commercial European-type MLV vaccines tested had no marked detrimental effects in pregnant gilts, although the MLV strains can cross the placenta leading to the birth of congenitally infected piglets.

Multiplex PCR method for use in real-time PCR for identification of fish fillets from grouper (Epinephelus and Mycteroperca species) and common substitute species

Mitochondrial 16S rRNA sequences from morphological validated grouper (Epinephelus aeneus, E. caninus, E. costae, and E. marginatus; Mycteroperca fusca and M. rubra), Nile perch (Lates niloticus), and wreck fish (Polyprion americanus) were used to develop an analytical system for group diagnosis based on two alternative Polymerase Chain Reaction (PCR) approaches. The first includes conventional multiplex PCR in which electrophoretic migration of different sizes of bands allowed identification of the fish species. The second approach, involving real-time PCR, produced a single amplicon from each species that showed different Tm values allowing the fish groups to be directly identified. Real-time PCR allows the quick differential diagnosis of the three groups of species and high-throughput screening of multiple samples. Neither PCR system cross-reacted with DNA samples from 41 common marketed fish species, thus conforming to standards for species validation. The use of these two PCR-based methods makes it now possible to discriminate grouper from substitute fish species.

Temporal localization of porcine reproductive and respiratory syndrome virus in reproductive tissues of experimentally infected boars

Porcine reproductive and respiratory syndrome virus (PRRSV) has been reported to be shed in the semen of infected boars. To determine whether the reproductive tissues could be a persistent source of virus and the possible origin of PRRSV found in semen of infected boars, 20 PRRSV-seronegative boars were intranasally inoculated with 5 x 10(6) median tissue culture infective doses (TCID50) of PRRSV and necropsied at different times post-inoculation (p.i.) from Day 2 to Day 37 p.i. Blood samples were collected before experimental inoculation, at necropsy and at different times p.i. At necropsy, epididymal semen and reproductive tissues were collected and the presence of the virus determined by virus isolation. The infection of the boars was demonstrated by the isolation of the virus from the sera of all inoculated boars and by seroconversion. PRRSV was detected in serum samples from Day 2 to Day 23 p.i., although the viremic period was largely dependent on the individual response to infection. Viral replication was proven within different reproductive tissues from Day 2 to Day 23 p.i., being most consistently found in the epididymus. In addition, PRRSV was isolated in semen from Day 4 to Day 10 p.i. The correlation of a diminished viremia and the inability to isolate PRRSV from semen or reproductive tissues may be due to one of two possibilities. First, viremia is responsible for most of the virus isolated from reproductive tissues due to the movement of PRRSV-infected cells out of the blood and into the tissues. Second, viremia may initially seed the reproductive tissues with PRRSV, and then the virus is produced into the reproductive tract and shed into semen at low levels.

The genetic diversity of European type PRRSV is similar to that of the North American type but is geographically skewed within Europe

Porcine reproductive and respiratory syndrome virus (PRRSV) is a recently emerged pathogen. Two PRRSV genotypes exist, North American and European, which are only 55-70% identical at the nucleotide level. Previous studies have shown high nucleotide diversity in the North American genotype and low nucleotide diversity in the European genotype. Here, we analyzed the ORF5 and ORF7 genes for a large number of new European type PRRSV isolates in conjunction with existing database sequences. This new analysis showed that contrary to previous assumptions, genetic diversity is at least as high in the European genotype as in the North American genotype. Furthermore, we showed that genetic diversity of European type PRRSV has a marked geographical pattern, with exceptionally high genetic diversity among Italian sequences. The geographical pattern of diversity in relation to the epidemiology of PRRSV in Europe is discussed. Discrepancies between ORF5- and ORF7-based genealogies were observed, and further analysis of the data set confirmed the presence of recombination. We were therefore able to report the first observation of recombination in wild-type isolates of European genotype PRRSV.

Porcine reproductive and respiratory syndrome (PRRS) with special reference to clinical aspects and diagnosis. A review

After a short introduction on Porcine Reproductive and Respiratory Syndrome (PRRS) regarding the history, the first occurrence in several countries, and the causal virus, designated Lelystad virus, a description is given of the clinical aspects and several diagnostic methods. After some general remarks on the clinical aspects, the epidemic and the endemic phase of the disease are described. Regarding the diagnosis, special attention is paid to the detection of antibodies and of the PRRS Virus (PRRSV). Regarding the detection of antibodies, a description is given of three tests: the immunoperoxidase monolayer assay, the enzyme-linked immunosorbent assay, and the serum neutralization test. Concerning the detection of PRRSV, attention is paid to the isolation of the virus, the demonstration of PRRSV antigens in frozen or fixed tissue using immunohistochemistry or immunofluorescence, the in situ hybridisation technique and the Polymerase Chain Reaction (PCR).

A comparison of virus isolation, immunohistochemistry, fetal serology, and reverse-transcription polymerase chain reaction assay for the identification of porcine reproductive and respiratory syndrome virus transplacental infection in the fetus

Virus isolation (VI), immunohistochemistry (IHC), fetal serology, and reverse-transcription polymerase chain reaction assay (RT-PCR) were performed on samples from 107 fetuses comprising 10 litters taken from sows experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV). In addition to comparing the relative sensitivity and specificity of each test, RT-PCR was evaluated with respect to the relative suitability of thoracic fluids and tissues as samples, the effects of autolysis, and the effects of pooling of fetal specimens. VI, IHC, and fetal serology identified PRRSV infection in 48.6%, 23.4%, and 14.9% of 107 fetuses, respectively, and identified at least 1 infected fetus in 10, 10, and 5 of 10 litters, respectively. In utero death with autolysis reduced the test efficacy of all 3 methods. Fetal thoracic fluid and tissues were equally suitable for RT-PCR detection of PRRSV. Pooling fetal tissues or fluids from VI-positive animals with comparable material from negative controls had no detrimental effect on RT-PCR results when evaluated at dilutions of 1:1, 1:2, 1:4, and 1:8. The results of RT-PCR testing were positive in 100%, 94.4%, and 83.3% of VI-positive specimens allowed to autolyze at 4, 21, or 37 C, respectively, for 24, 48, and 96 hours. Compared with the other testing modalities, RT-PCR appeared to be impacted the least by the adverse effects of autolysis.

Quantitative TaqMan RT-PCR for the detection and differentiation of European and North American strains of porcine reproductive and respiratory syndrome virus

Since two different types of porcine reproductive and respiratory syndrome virus (PRRSV), the European (EU) and the North American (US) strain, occur or coexist in European swine herds, their rapid and reliable detection and differentiation is essential for disease surveillance. A quantitative TaqMan reverse transcription-polymerase chain reaction (RT-PCR) is described for PRRSV detection and strain differentiation. Sensitivity and specificity were compared with a conventional PRRSV RT-PCR and to the detection of both PRRSV types in cell cultures and both were found to be equal or superior to the reference methods. Reproducibility was tested and proved that the assay was very reliable. Standard dilutions included in each test allowed absolute quantitation of the amount of viral RNA. The TaqMan assay described below is time-saving, easy to handle, exhibits a decreased risk of cross-contamination and is highly sensitive and specific. It is, therefore, considered to be a powerful tool for the rapid detection and differentiation of PRRSV.

Rapid detection of porcine reproductive and respiratory syndrome viral nucleic acid in blood using a fluorimeter based PCR method

Porcine reproductive and respiratory syndrome virus (PRRSV) is an Arterivirus recognised world wide as an important cause of reproductive failure and pneumonia in pigs. American and European strains of PRRSV, differentiated antigenically and genomically, have been reported. PRRSV infections are currently diagnosed using serology, virus isolation and/or immunocytochemistry. In order to overcome various drawbacks associated with these techniques, conventional, block-based RT-PCR methods for the detection of PRRSV nucleic acid in clinical samples have been described. These methods require gel electrophoresis for analysis of PCR products and present high risk of DNA carry-over contamination between the samples tested. We describe the detection of PRRSV RNA in serum samples and in blood impregnated filter disks (FDs), obtained from experimentally inoculated pigs, using a closed-tube, fluorimeter-based PCR assay. The assay eliminates the use of gel electrophoresis, and is as sensitive and specific as the conventional block-based PCR assay, detecting positive samples as early as 1 day post-inoculation. We also report a rapid fluorimeter based PCR method for differentiating American and European strains of PRRSV.

Analysis of cellular immune response in pigs recovered from porcine respiratory and reproductive syndrome infection

The cellular immune response to a European isolate of porcine reproductive and respiratory syndrome (PRRS) virus in animals recovered from the experimental infection has been studied in vitro. Peripheral blood mononuclear cells (PBMC) from these pigs proliferated specifically when they were stimulated with PRRS virus. This response was not detectable until 4 weeks after inoculation and remained for more than 3 months. Addition of blocking monoclonal antibodies to the cultures showed that this proliferation was mainly dependent on CD4(+) cells with the participation of SLA-class II molecules. T-cell cultures established by stimulating responding cells with PRRS virus and maintained in culture for up to 3 weeks showed an increase of CD8(+) CD4(+) and CD4(-) CD8(+) subsets within activated cells, gated according to their light scatter parameters, whereas CD4(+) CD8(-) cells declined along the time in culture. Within the activated cells, those expressing the TcR gammadelta receptor also increased, being most of them also positive for the CD8 marker. By RT-PCR, T-cells responding to the virus showed a Th1 type cytokine production pattern. During the culture period the cytotoxic activity against K-562 cells increased from 15 to 35% of specific lysis. This cellular immune response may play a relevant role in the clearance of PRRS virus and the recovery of the infection.

Detection of porcine reproductive and respiratory syndrome virus by reverse transcription-polymerase chain reaction using different regions of the viral genome

Serologic studies have revealed strain variability between American and European isolates and among American isolates of porcine reproductive and respiratory syndrome virus (PRRSV). The objective of this study was to develop an assay for the routine diagnosis of PRRSV in field specimens using reverse transcription-polymerase chain reaction (RT-PCR) amplification of conserved genomic regions. Twenty-four field isolates of PRRSV from different regions of the USA were analyzed in the study. Six primer pairs from open reading frames (ORFs) 4, 6, and 7 of the American strain (ATCC VR-2332) and from ORF 1b of the Lelystad strain were used for the amplification of the viral genome by PCR. Amplification products of the expected sizes were obtained from all isolates by PCR amplification of ORF 7, the gene encoding the nucleocapsid protein. Oligonucleotide primers designed to amplify ORFs 4 and 6 detected 92% and 96% of the isolates, respectively, whereas primers for the amplification of ORF 1b detected 88% of all isolates. The specificity of the amplified products of ORF 7 from 7 field isolates and 2 reference strains was confirmed by chemiluminescent hybridization using an internal digoxigenin-labeled DNA probe. Sequence analysis of this region indicated variation in the nucleotide sequence of 2 isolates that did not hybridize with the internal probe. These results indicate that ORF 7 may serve as a potential target for the detection of PRRSV strains by RT-PCR and that genomic variability should be considered when nucleic acid hybridization is used to confirm the specificity of PCR amplification for diagnostic purposes.

Sensitive detection and typing of porcine reproductive and respiratory syndrome virus by RT-PCR amplification of whole viral genes

Following the recent use of a live vaccine against porcine reproductive and respiratory syndrome virus (PRRSV) in Denmark, both American (vaccine) and European-type PRRSV now coexist in Danish herds. This situation highlighted a requirement for supplementary tests for precise virus-typing. As a result, we developed a RT-PCR assay able to detect as well as type PRRSV. To provide maximal sequence information, complete viral open reading frames (ORFs 5 and 7) were targeted for amplification. The RT-PCR test was able to amplify complete PRRSV ORFs from complex materials such as boar semen containing as little as 1 TCID50 ml(-1) of PRRSV. Typing of viruses was accomplished by any one of three strategies: (i) use of type-specific PCR primers, (ii) size determination of ORF 7 amplicons, (iii) DNA sequencing. All three typing strategies showed complete concordance with the currently used method of typing with monoclonal antibodies (MAbs) when used on a panel of PRRSV field isolates covering the period 1992-1997. The ORF 7-based test had particularly desirable characteristics, namely, highly sensitive detection of PRRSV without apparent type bias, typing of the detected virus, discrimination between pure and mixed virus populations, and semi-quantitative assessment of type ratios in mixed populations, all in a single PCR reaction. In addition, the obtained sequence data were used to predict two simple and rapid strategies (single-enzyme restriction length polymorphy analysis and oligonucleotide hybridization) for confirmation of the specificity of ORF 7 RT-PCR reactions. As such, the RT-PCR assay provides a new, powerful diagnostic tool to study the population dynamics between present and emerging PRRSV-types.

Sequence analysis of the nucleocapsid protein gene of the porcine reproductive and respiratory syndrome virus Taiwan MD-001 strain

The 3'-portion of the genome from a Taiwan isolate of porcine reproductive and respiratory syndrome (PRRS) virus, strain MD-001, was cloned and sequenced. The resultant 549 nucleotides contained an open reading frame with a coding capacity of 123 amino acids (predicted Mr 13,600). The predicted protein corresponds to the nucleocapsid protein, the gene product of ORF7. Comparative sequence analysis of several known PRRSV strains indicated that this protein showed the highest degree of amino acid similarity to the US VR2332 and the Canadian IAF-Exp91 strains (92.7%) and the least to the Dutch Lelystad strain (56.5%). The phylogenic trees constructed on the basis of the known PRRSV nucleotide sequences indicated that MD-001 strain belongs to the North American strain cluster and that it is distinct from the European virus.

The reverse transcription polymerase chain reaction for the diagnosis of porcine reproductive and respiratory syndrome: comparison with virus isolation and serology

A single-tube reverse transcription polymerase chain reaction (RT-PCR) assay for the detection of porcine reproductive and respiratory syndrome (PRRS) virus in blood samples from infected pigs was developed. This test was assessed for sensitivity and application as a rapid diagnostic tool by comparison with virus isolation and detection of PRRS virus antibody in blood. The RT-PCR test was slightly more sensitive than virus isolation for detection of virus in serum and markedly more sensitive than virus isolation from plasma from experimentally infected pigs. The RT-PCR test was also applicable when using whole blood-impregnated filter paper discs, with 94% of the specimens taken by this procedure being positive when compared to RT-PCR performed on serum. PRRS viral nucleic acid was detected in blood samples as early as 24 h after infection and persisted for some time, whereas circulating antibody to PRRS virus was not detected in the same animals until 9 days after infection. These results indicate that the RT-PCR may be an useful technique for the early identification of PRRS viral nucleic acid in blood samples of infected pigs.

Transplacental infection following exposure of gilts to porcine reproductive and respiratory syndrome virus at the onset of gestation

Twenty-five gilts without measurable porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) serum antibody titres were used for this experiment. All of them were randomly assigned to one of the treatment groups at the time of artificial insemination. Twelve gilts were exposed to PRRSV, of these, six were slaughtered on day 10 after exposure and constituted group A. The remaining six were slaughtered on day 20 after infection and constituted group C. Thirteen gilts were used as controls, six of these were slaughtered on day 10 after treatment and constituted group B. The remaining seven were slaughtered on day 20 after treatment and constituted group D. The infected gilts were inoculated with PRRSV intranasally and intravenously in the ear vein. They were observed for clinical signs of infection and the effects on conception and fertilization rates were studied, while the gilts and their embryos were tested for PRRSV and homologous antibodies. The infected animals developed signs of PRRS associated with anorexia and slight pyrexia. Infection was verified by reisolation of the virus from serum and other tissue samples and also by seroconversion. Ten out of 12 infected gilts and 10 out of 13 controls were pregnant at the time of slaughter and the ratio of embryos to corpora lutea was the same in both, infected and control groups (0.75). Therefore, infection with PRRSV at the onset of gestation did not appear to interfere with conception and fertilization rates and subsequent pregnancy. The PRRSV was not isolated from any of the embryos collected at day 10 postexposure, but was present in 20-day-old embryos of group C gilts. In this group, 60% of litters were infected prenatally, with 16% of embryos infected. The proportion of dead embryos was three times greater than in a control group D (35.4% and 9.8%, respectively). The results of this report indicate that exposure of susceptible gilts to PRRSV at the onset of gestation has no significant effect on conception and fertilization rates. However, although infection does not appear to have any effect on the embryos before implantation, it can result in transplacental infection and embryo death.

Development of a RT-PCR test coupled with a microplate colorimetric assay for the detection of a swine Arterivirus (PRRSV) in boar semen

Transmission of porcine reproductive and respiratory syndrome virus (PRRSV) through boar semen has been demonstrated, stressing the need for a reliable semen PRRSV detection test. A diagnostic assay was developed based on amplification of the PRRSV RNA by reverse transcription and polymerase chain reaction (RT-PCR) followed by detection of the amplification products by hybridization and colorimetric assay in microwell plates. A highly reproducible and efficient method of viral RNA isolation from semen samples was set up. A combined RT-PCR procedure was performed, incorporating the use of uracil-N-glycosylase (UNG) in combination with dUTP instead of dTTP to prevent false positive results due to carry-over contamination. An RNA internal control was added during the RNA isolation procedure to detect false negative results. The colorimetric detection in microwell plates of amplification products from either PRRSV or IC RNA gave specific and objective results and was automated. A cut-off value of 1000 RNA copies or 10 TCID50 of PRRSV per ml of semen samples could be detected with this assay. Semen samples collected from experimentally-infected boars were tested with this assay and showed PRRSV excretion early after infection and for an extended period.

Diagnosis of PRRS

This paper reviews various diagnostic methods for the detection of porcine reproductive and respiratory syndrome (PRRS) virus or antibodies to PRRS virus reported during the period from 1991 to 1995. In addition, experience from a European Community Concerted Action and especially Danish experiences concerning serological tests are presented. It is concluded that, in general, serological diagnosis with a high specificity and sensitivity is easy to perform on a herd level. However, no serological test has proven to be suitable for individual animal certification.

Insemination of susceptible and preimmunized gilts with boar semen containing porcine reproductive and respiratory syndrome virus

Twenty-one gilts without measurable PRRSV serum antibody titres were identified for this experiment. Seven gilts were used as controls (Group C) and 14 as principals. Of these, 7 gilts were preimmunized to PRRSV and constituted Group B, while 7 gilts remained seronegative and constituted Group A. The principal gilts were inseminated with boar semen containing PRRSV and were killed 20 d later. The control gilts were treated similarly but were not exposed to PRRSV. Gilts were observed for clinical signs of infection. The effects on the conception rates were studied and gilts and embryos were tested for PRRSV and homologous antibodies. Group A and B gilts developed signs of PRRS associated with anorexia and slightly elevated body temperatures. Transmission of the infection was demonstrated by the isolation of PRRSV from serum and other tissue samples of principal gilts and also by seroconversion. The results show that early infection may have an insignificant effect or no effect on the conception and fertilization rates. However, exposure to PRRSV at the time of insemination can result in transplacental infection of embryos. In Group A gilts, 5 of 6 litters were infected prenatally with 7.6% of embryos infected. In Group B gilts, 1 of 5 litters and 1.3% of embryos were infected. Moreover, approximately 2 and 4 times more embryos were dead in litters of gilts from Group A and Group B than in gilts from control Group C. The isolation of PRRSV in 3 dead embryos suggests that the embryos may have died as a result of the direct effect of the virus. It can be concluded that the insemination of either seronegative or preimmunized gilts with boar semen containing PRRS V may have an insignificant effect or no effect on conception and fertilization rates, although it can result in transmission of the virus and embryonic infection and death.

Typing of porcine reproductive and respiratory syndrome viruses by a multiplex PCR assay

A rapid multiplex PCR assay was developed to distinguish between North American and European genotypes of porcine reproductive and respiratory syndrome (PRRS) virus after a portion of the polymerase gene (open reading frame 1b) was sequenced for two North American PRRS virus strains. DNA products with unique sizes characteristic of each genotype were obtained.

Effect of porcine reproductive and respiratory syndrome virus (PRRSV) on development of porcine fertilizedova in vitro

Fertilized pig ova, collected from 14 estrus-synchronized gilts 32 h after presumed ovulation were microinjected or cultured for 72 h in Beltsville Embryo Culture Medium-3 with or without Porcine Reproductive and Respiratory Syndrome Virus (PRRSV). To detect virus in the samples, virus isolation of swine alveolar macrophage, Reverse Transcriptase Polymerase Chain Reaction and Fluorescent Antibody techniques were employed. Microinjection or incubation of embryos with PRRSV did not significantly inhibit development of the porcine embryos in vitro when compared with that of controls (P = 0.75 and P = 0.14, respectively). Although either 10 to 20 TCID50 were microinjected or large concentrations of virus were used for embryo exposure by incubation, PRRSV was not detected in association with the embryos. It is concluded based on the experiments reported here that 4- to 16-cell stage pig embryos are not susceptible to productive infection with PRRSV in vitro.

Phylogenetic relationships of european strains of porcine reproductive and respiratory syndrome virus (PRRSV) inferred from DNA sequences of putative ORF-5 and ORF-7 genes

The complete ORF-5 gene and a fragment of the ORF-7 gene from 14 different European porcine reproductive and respiratory syndrome virus (PRRSV) isolates were amplified by reverse transcriptase polymerase chain reaction (RT-PCR), and their nucleotide sequences were determined. The ORF-7 gene displayed nucleotide and amino acid identities of 94.1-99.6% and 95.3-100% among isolates from different countries. The ORF-5 gene showed higher nucleotide (87.1-99.2% identity) and amino acid (-88% identity) variability. The resulting sequences were aligned with other European and North American PRRSV strains and phylogenetic relationships among these strains were established by the maximum parsimony method. The phylogenetic trees inferred from both genes were in agreement and showed that European and North American PRRSV strains clearly represent two different genotypes. According to both trees, there is a perfect correlation between strains and the countries in which they were isolated. Additionally, the phylogenetic position of European and North American PRRSV strains within the recently proposed family Arteriviridae was also analyzed.

Exposure of gilts in early gestation to porcine reproductive and respiratory syndrome virus

Twenty-five gilts without measurable serum antibody titres to porcine reproductive and respiratory syndrome virus (PRRSV) were identified and 16 were inoculated with PRRSV at seven, 14 or 21 days of gestation and killed 20 to 22 days later to determine the effect of the virus on their embryos. The remaining nine gilts were not exposed to PRRSV, but were killed at the same stages of gestation. The gilts were observed for clinical signs of infection and the gilts and their embryos were tested for PRRSV and homologous antibodies. The infection was demonstrated by the re-isolation of the virus and its detection by the reverse transcriptase polymerase chain reaction in serum and other tissue samples from the inoculated gilts, and also by seroconversion. However, the gilts remained healthy throughout the study, except for one which was depressed and anorexic for two days. Two of the litters from the gilts challenged with PRRSV on day 14 of gestation contained one and three infected live embryos; the other embryos from these two litters did not contain detectable virus, although most of the embryos in one of the litters were dead. The other nine litters from the gilts challenged with PRRSV and the control litters, showed no evidence of infection.