Rapid detection of hog cholera virus in tissues by the polymerase chain reaction

Rapid pre-clinical detection of classical swine fever by reverse transcription loop-mediated isothermal amplification

The usefulness of reverse transcription loop-mediated isothermal amplification (RT-LAMP) for rapid pre-clinical detection of classical swine fever virus (CSFV) infection was evaluated. The RT-LAMP reaction could be finished in 60 min under isothermal condition at 65 °C by employing a set of four primers targeting the 5′ untranslated region of CSFV. The RT-LAMP assay of CSFV showed higher sensitivities than that of RT-PCR, with a detection limit of 5 copies per reaction. No cross-reactivity was observed from the samples of other related viruses including porcine circovirus type 2, porcine parvovirus, porcine pseudorabies virus, Japanese encephalitis virus, and porcine reproductive and respiratory syndrome virus. The detection rates of CSFV RT-LAMP, RT-PCR and virus isolation for samples including blood, tonsil, nasal and rectal swabs from uninoculated pigs without any clear clinical symptom were 89%, 78% and 71%, respectively. Furthermore, all of the assays showed higher sensitivity for blood and tonsil swabs samples than nasal and rectal swabs. These results indicate that the CSFV RT-LAMP assay is a valuable tool for its rapid, cost-effective detection and has potential usefulness for rapid pre-clinical detection and surveillance of classical swine fever in developing countries.

Diagnostic methods for detection of Classical swine fever virus—Status quo and new developments

Classical swine fever (CSF) is a highly contagious disease causing major losses in pig populations almost worldwide. The disease occurs in many regions of Asia, Central and South America and parts of Europe and Africa. Some countries have eradicated the disease (Australia, USA, Canada, within the EU), yet it keeps recurring sporadically (South Africa, Germany, Netherlands, England). The causative virus is a member of the genus Pestivirus, family Flaviviridae. The first diagnosis of CSF is based on the recognition of clinical signs by the veterinarian in the field and by post mortem findings. Many signs are not exclusively associated with CSF and they may vary with the strain of virus, age and health status of the pigs. Since clinical signs may be confused with other pig diseases, laboratory diagnosis of CSF is indispensable. Both the Office International des Epizooties (OIE) and the European Union, have approved diagnostic manuals establishing sampling methods and diagnostic procedures for the confirmation of the disease. In this review, experiences with current tests will be analyzed and complemented with new developments, with emphasis on the polymerase chain reaction after reverse transcription of the RNA genome (RT-PCR).

A multiplex nested RT-PCR for the detection and differentiation of wild-type viruses from C-strain vaccine of classical swine fever virus

A multiplex nested RT-PCR (RT-nPCR) was developed for the detection and differentiation of classical swine fever virus (CSFV). A fragment of 447 or 343 bp was amplified from the genomic RNA of C-strain or virulent Shimen strain, respectively, and two fragments of 447 and 343 bp were simultaneously amplified from the mixed samples of C-strain and Shimen. When detecting several wild-type isolates representative of different subgroups (1.1, 2.1, 2.2, and 2.3) circulating in Mainland China and samples from pigs experimentally infected with Shimen strain, the RT-nPCR resulted in an amplification pattern similar to Shimen. No amplification was achieved for uninfected cells, or cells infected with bovine viral diarrhea virus (BVDV), and other viruses of porcine origin. The RT-nPCR was able to detect as little as 0.04 pg of CSFV RNA. The restrictive fragment length polymorphism (RFLP) demonstrated unique patterns of wild-type viruses and C-strain. Among the 133 field samples, 42 were tested to contain wild-type viruses and 18 showing presence of C-strain. The RT-nPCR can be used to detect and differentiate pigs infected with wild-type CSFV from those vaccinated with C-strain vaccine, thus minimizing the risk of culling vaccinates during outbreaks.

Detection and quantitative pathogenesis study of classical swine fever virus using a real time RT-PCR assay

A real time reverse transcription (RT) TaqMan PCR assay for the detection of classical swine fever virus (CSFV) previously described for use on a SmartCycler was validated on the Applied Biosystems AB 7700 Sequence Detection System using the Roche MagNA pure instrument for nucleic acid extraction and reaction set up. The primers and probe were specific for the CSFV strains (NSW, Baker and Weybridge) and did not react with other pestiviruses (BDV Tobias, BDV #327, BVDV non-CPE and BVDV C24V). Analysis of blood samples collected from pigs 1-6 and 8 days post-oronasal infection showed that over >10(6) range there was a linear relationship between log10TCID50ml-1 blood and the log10 normalised genetic load measured by quantitative TaqMan assay. The assay was used to assess CSFV shedding from infected pigs by quantitative TaqMan assay of virus genetic loads in tonsil, nasal and rectal swabs. Infection of tonsils was detected as early as 1 day post-inoculation. Shedding of virus detected by nasal and rectal swabs commenced on the third day post-inoculation. Quantitative TaqMan was used to analyse virus genetic load in tissues collected from pigs killed on days 1-3, 5 and 8 post-infection. Virus infection appeared first in tonsil (day 1), then submandibular lymph node, spleen, ileum and mesenteric lymph node (by day 3). Thereafter, virus spread to the visceral organs and finally to the pancreas and brain. Tonsil, nasal and rectal swabs as well as whole blood were found to be suitable samples for the rapid detection of CSFV using the TaqMan assay and automated nucleic acid extraction and reaction set up.

Classical swine fever (CSF) in wild boar: the role of the transplacental infection in the perpetuation of CSF

Thirty-four pregnant wild sows and their unborn progeny derived from an endemically infected population in the district of Nordvorpommern (Mecklenburg-Western Pomerania) were investigated for classical swine fever virus (CSFV) and antibodies. During the last 2.5 years of the epidemic, 20 out of 34 pregnant wild sows investigated were serologically positive. No CSFV or viral RNA was detected in organs derived from these animals and their progeny. This indicates that young wild boars persistently infected by transplacental virus transmission do not play a crucial role in the perpetuation of CSFV in wild boar. Other factors seem to be more important for the establishment of CSF as well as for virus perpetuation in the population.

Diagnostic evaluation of a real-time reverse transcriptase PCR assay for detection of classical swine fever virus

A fluorogenic-probe hydrolysis (TaqMan)-reverse transcriptase (RT) PCR for classical swine fever virus (CSFV) was evaluated for diagnostic sensitivity and specificity by using clinical samples obtained from the Dominican Republic, where the disease is enzootic. The sensitivity of this test, using nasal swab samples taken from both symptomatic and asymptomatic animals, exceeded the diagnostic sensitivity of virus isolation (100% versus 72.4%, respectively) with little loss of specificity (98.9% versus 100%, respectively). At the herd level, three of four infected farms were identified by virus isolation, while the CSFV real-time RT-PCR assay identified all four infected premises. This simple and accurate test permits rapid detection of CSFV in affected herds.

Studies on the Virulence of Two Field Isolates of the Classical Swine Fever Virus Genotype 2.3 Rostock in Wild Boars of Different Age Groups

The virulence of two isolates of the classical swine fever virus (CSFV) was studied in experimentally infected wild boars of different ages. The isolates, originating from wild boars shot in Mecklenburg-Western Pomerania (isolate '1829-NVP') and in Rhineland-Palatinate (isolate '11722-WIL'), belong to the genetic subgroup 2.3 Rostock. Clinical picture, transient viraemia, virus excretion and gross lesions at necropsy as well as a failure of virus detection at the end of the experiment revealed that this virus subtype was only moderately virulent. Whereas one subadult wild boar and both 7-week-old wild boar piglets infected intranasally became sick and died, only one of three 8-week-old animals which survived after contact infection remained CSFV positive until the end of the experiment [34 days post infection (dpi)], although neutralizing antibodies were present. This underlines the role of young boars in CSF epidemics. The isolate '11722-WIL' was shed by an infected adult wild boar and was transmitted to susceptible piglets. Interestingly, all animals which became sick and died also were found to be infected with a secondary pathogen. Therefore, we assume that after infection with moderately virulent CSFV simultaneous infections with other pathogens may be important for the clinical course and the outcome of the disease as well as for a spread of the virus in field.

Localization of classical swine fever virus from chronically infected pigs by in situ hybridization and immunohistochemistry

Classical swine fever (CSF) virus (CSFV) nucleic acid and antigen were detected in 15 pigs with naturally occurring chronic CSF by in situ hybridization and immunohistochemistry. The most consistent and prominent microscopic lesions were perivascular mononuclear cell infiltration and gliosis in the central nervous system of pigs with chronic CSF. Positive cells typically exhibited a dark brown (in situ hybridization) or red (immunohistochemistry) reaction product in the cytoplasm without background staining. A positive signal for both in situ hybridization and immunohistochemistry was detected in mononuclear cells and lymphocytes of lymphoid tissues. Viral nucleic acid was detected in some tissue sections in the absence of viral antigen. The in situ hybridization technique developed in this study was useful for the detection of CSFV RNA in tissues taken from chronically infected pigs and may be a valuable technique for studying the pathogenesis of chronic CSFV infection.

Detection of classical swine fever virus in boar semen by reverse transcription-polymerase chain reaction

A seminested reverse transcription-polymerase chain reaction (RT-PCR) was developed for the detection of classical swine fever virus (CSFV) in semen. Five boars were inoculated intranasally with CSFV isolate propagated in PK15 cells. Two boars inoculated with the supernatant of noninfected PK15 cells were kept as controls. Semen and serum samples were collected twice weekly for 63 days postinoculation (dpi). Samples were tested for the presence of antibodies to CSFV by an enzyme-linked immunosorbent assay and for the presence of CSFV nucleic acid by seminested RT-PCR. Antibodies to CSFV could be detected as early as 7 dpi in 1 boar, and all 5 infected boars were found positive by 14 dpi. CSFV from boar semen was infrequently identified by virus isolation compared with seminested RT-PCR. CSFV nucleic acid was detected in semen by seminested RT-PCR as early as 7 dpi in 3 infected boars and persistently thereafter in all 5 infected boars until 63 dpi. When separated fractions of CSFV-contaminated semen were analyzed by the seminested RT-PCR, the CSFV nucleic acid was detected mainly in seminal fluid and occasionally in nonsperm cells. CSFV antigen was also detected in nonsperm cells from semen smear by immunohistochemistry. Thus, infection via semen, specially through CSFV-infected seminal fluid, seems to be a major route of transmission of CSFV.

Rapid detection of classical swine fever virus by a portable real-time reverse transcriptase PCR assay

A fluorogenic-probe hydrolysis (TaqMan)-reverse transcriptase PCR assay for classical swine fever virus (CSFV) was developed and evaluated in experimentally infected swine. The assay detected CSFV, representing different phylogenetic groupings, but did not amplify viral RNA from related pestiviruses. The assay met or exceeded the sensitivity (1 to 100 50% tissue culture infective doses per ml) of viral cultures of samples from experimentally infected animals. Viral RNA was detected in nasal and tonsil scraping samples 2 to 4 days prior to the onset of clinical disease. The assay can be performed in 2 h or less, thus providing a rapid method for the diagnosis of classical swine fever.

Detection of classical swine fever virus in the ovaries of experimentally infected sows

Six sows were infected intranasally with a Korean isolate of classical swine fever virus (CSFV). The distribution of virus in ovarian tissues was then assessed for 21 days by in-situ hybridization and immunohistochemistry. CSFV was detected in the ovaries between 7 and 21 days post-inoculation (dpi) by both methods, but the labelling was particularly intense and widespread at 7 dpi. CSFV nucleic acid and antigen were located almost exclusively within the cytoplasm of cells shown by haematoxylin and eosin staining to be macrophages, which were numerous in atretic follicles. Small numbers of CSFV nucleic acid-positive cells with distinctly round morphology and oval nuclei, resembling monocytes, were also observed in the blood vessels of sows at 7 and 14 dpi. CSFV nucleic acid and antigen were not observed in primordial, primary or secondary follicles from infected sows at 7, 14 or 21 dpi. The results suggest that CSFV replicates in circulating peripheral monocytes and gains access to ovarian tissues from the bloodstream, and that this contributes to the distribution of CSFV in macrophages throughout the atretic follicles.

Localization of classical swine fever virus in male gonads during subclinical infection

In an experiment using ten boars, the distribution of classical swine fever virus (CSFV) was determined in the male reproductive tract by in situ hybridization over a period of 120 days after intranasal inoculation. CSFV was detected in the testicular tissue of infected boars. Viral nucleic acid was localized to spermatogonia, spermatocytes and spermatids but was not detected in the epithelia of the prostate, epididymis or bulbourethral gland. Sections from control, CSFV-negative, pigs showed no hybridization signals for CSFV. The demonstration that CSFV infects the spermatogonia (and their progeny) suggests that this may serve as a primary reservoir for the venereal spread of CSFV.

Detection of porcine enteroviruses by nRT-PCR: differentiation of CPE groups I-III with specific primer sets

Porcine enteroviruses (PEV) comprising at least 13 serotypes grouped into three species are described as causative agents of neurological disorders, fertility disorders, and dermal lesions of swine. Despite their well-documented acid stability, enteric infection route, and similarity of clinical symptoms, most of the porcine enterovirus (PEV) serotypes are set apart from the genus Enterovirus of the Picornaviridae. Hence, PCR procedures used commonly to detect enteroviruses are not applicable to epizootic relevant PEV serotypes. A nested RT-PCR protocol is described now suited to detect all known porcine enterovirus serotypes using three sets of primer pairs. These primer pairs were designed to amplify either highly conserved sequences of the 5'-nontranslated region (5'-NTR) or the polymerase gene region of the relevant virus species. All 13 acknowledged serotypes of three PEV species and several field isolates of clinical specimens were detectable. The specificity of the PCR procedure is supported by the observation that RT-PCR-positive field isolates coincide with serological PEV classification. PEV PCR is more rapid and less laborious than the time-consuming virus isolation by tissue culture techniques over several passages and serotyping. Because other viruses such as classical swine fever virus, pseudorabies virus, porcine parvovirus, swine vesicular disease virus, and foot-and-mouth disease virus may cause diseases with similar clinical symptoms, PCR detection of all PEVs closes a diagnostic gap and offers the opportunity to use comprehensive PCR procedures for the diagnosis of all relevant viruses causing such symptoms.

Classical swine fever virus: a ring test to evaluate RT-PCR detection methods

Six laboratories participated in an exercise to compare the sensitivity and specificity of RT-PCR tests for the detection of classical swine fever virus (CSFV). Two sets of coded samples were prepared by serial dilution of positive samples and then distributed to each of the laboratories. One set comprised 34 samples of random primed cDNA. These had been synthesised from viral RNA representative of seven different genetic subtypes of CSFV. The other set comprised 40 clinical samples containing tonsil, spleen, whole blood or serum from a pig that had been experimentally infected with CSFV. Each laboratory tested the samples using one or more PCR/RT-PCR tests that they were accustomed to using. The methods and results of the laboratories were compared with one another. The RT-PCR results obtained from testing the clinical samples were also compared with those obtained by virus isolation and antigen ELISA.ELISA. Both RT-PCR and RT-nested PCR appeared to give some false positive results. Several of the PCR tests appear suitable in terms of specificity and sensitivity. Further trials are necessary to compare results when the same test is performed by different laboratories, and to show that improved control procedures can eliminate problems due to false positive reactions.A limited comparison of extraction and reverse transcription procedures showed similar results in each of three participating laboratories, even though the methods were not standardised.

Oral immunisation of wild boar against classical swine fever: evaluation of the first field study in Germany

The effectiveness of oral immunisation of wild boar against classical swine fever (CSF) was studied in a field trial in Lower Saxony for two years, from 1993 to 1995. This field study was performed in an area of ca. 270 km(2)50% of young boars did not feed on vaccine baits nor become immunised. Therefore, an intensive hunting of this age group is a necessary adjunct to the use of oral vaccination. After the third immunisation period, no virus was detected in the areas where oral immunisation took place.

Detection of animal pathogens by using the polymerase chain reaction (PCR)

The polymerase chain reaction (PCR) is a nucleic acid-based technique that enables the rapid and sensitive detection of specific micro-organisms. Although this technique is widely used in veterinary research, it has not yet found applications in routine microbiological analysis of veterinary clinical samples. However, advances in sample preparation together with the increasing availability of specific gene sequences will probably lead to the more widespread diagnostic use of PCR in the future. PCR is likely to have a strong impact in the epidemiology, treatment and prevention of animal infectious diseases.

Evaluation of nucleic acid amplification methods for the detection of hog cholera virus

A blind panel was tested in a diagnostic evaluation of a reverse transcription (RT) polymerase chain reaction (PCR) method for detecting hog cholera virus (HCV) from pig tissues. The capability of the RT-PCR test to discriminate between HCV and related pestiviruses, bovine viral diarrhea virus (BVDV), and those viruses causing similar diseases in swine, including African swine fever virus (ASFV) and pseudorabies virus (PRV), was also considered. Nucleic acid extraction involved either kit-based or conventional phenol:chloroform:isoamyl alcohol methods. A single-round PCR assay, using primers that hybridize to the conserved p120 nonstructural gene region, was 82.5% sensitive (n = 17) and 100% specific (n = 18) in the detection of the presence of HCV RNA. However, the sensitivity was increased to 100% following a second PCR test. In all, 4 HCV, 7 BVDV, 2 ASFV, and 1 PRV isolates were studied. Novel nucleic acid sequences were generated for 9 HCV strains. Analysis of a portion of the p120 region using these methods was suitable for HCV isolate characterization.

Genetic identification of pestivirus strain Frijters as a border disease virus from pigs

A pig pestivirus isolate, the Frijters strain, was characterized by using reverse transcription-PCR (RT-PCR), followed by RFLP and direct sequencing of the amplicons. Restriction endonuclease enzyme AvaI and Bg/I digestion of 5' NC genomic region PCR products suggested that Frijters strain belongs to the border disease viruses (BDV). This finding was confirmed by nucleotide sequencing of the amplified part of the 5-NC genomic region, which revealed 94% and 95% nucleotide similarity between the Frijters strain and the BDV prototype strains Moredun cp and Moredun ncp, respectively. On the other hand, 55-77% nucleotide identity was observed between the Frijters strain and prototypes of BVDV and CSFV. The amino acid similarity in the Npro (p20) region was 89% between Frijters and the Moredun strains and 70-77% between Frijters and the BVDV of CSFV strains. It was concluded that the Frijters virus is a member of the BDV group of the Pestivirus genus. Considering that this virus circulates in the large swine populations of Europe, the spread of certain pestiviruses to more than one animal species should not be considered sporadic. Since the presence of BDV in swine herds might be a confusing factor during classical swine fever eradication programmes, highly specific methods are required for reliable identification of these isolates. RT-PCR, followed by RFLP and sequencing of the amplicons proved to be a reliable approach for the rapid detection and identification of pestiviruses.

Molecular cloning and nucleotide sequence determination of three envelope genes of classical swine fever virus Taiwan isolate p97

A strain of classical swine fever virus (CSFV) has been isolated in Taiwan. The cDNA coding for three envelope glycoproteins E1, E2 and E3 were molecularly cloned from purified viral particles using the reverse transcription-polymerase chain reaction (RT-PCR) method and sequence-specific primers. The resulting PCR products (1113 bp for E1. 699 bp for E2 and 567 bp for E3) were cloned into the SmaI site of pUC19 and then subjected to DNA sequence analysis. Data showed that nucleotide sequence of the three envelope genes shared a 82-83% homology with the corresponding genes of three other strains (Alfort, Brescia and Weybridge). However, the homology of the deduced amino acid sequence was greater than 90% among the four strains. The potential asparagine-linked glycosylation sites for E1 (5 sites), E2 (7 sites) and E3 (2 sites) were conserved. This suggests that the Taiwan p97 strain is distinct from other three strains described. The variations may have implications for future vaccine development. The sequence has been submitted to GenBank. The accession numbers are U43924 and U03290.

Differentiation of classical swine fever virus from ruminant pestiviruses by reverse transcription and polymerase chain reaction (RT-PCR)

A reverse transcriptase-polymerase chain reaction (RT-PCR) assay was designed to allow the differentiation of pestiviruses by the expected size of the amplified fragments. One oligonucleotide primer, conserved amongst pestiviruses, and two others specific for either classical swine fever virus (CSFV) or bovine viral diarrhea virus (BVDV), were designed from the 5' non-coding region of the genome. CSFV infected cultures (10 strains) amplified a fragment of an expected size of 200 bp; BVDV cultures (23 strains) or border disease virus (BDV) (2 strains) amplified a fragment of an expected size of 260 bp. The specificity of the amplified fragments was confirmed by restriction enzyme analysis. The threshold of sensitivity was 100 TCID50 for CSFV and 1 TCID50 for BVDV. The RT-PCR described here provides a rapid and sensitive diagnostic tool for the detection and differentiation of CSFV from ruminant pestiviruses.

A nested polymerase chain reaction assay to differentiate pestiviruses

Viruses that comprise the Pestivirus genus cause significant losses to the livestock industry. Based on sequence analysis, currently 4 distinct genotypes are identified of which 3 infect cattle and sheep. Distinguishing between bovine and ovine isolates by serological tests has often been difficult because of a high degree of cross reactivity. In this study, a nested polymerase chain reaction (PCR) assay was developed to identify and distinguish between bovine viral diarrhea virus (BVDV) type I, BVDV type II, as well as border disease virus (BDV) genotypes. Consensus oligonucleotide primers were designed to amplify a 826-bp product from any of the 3 pestivirus types in a reverse transcription-PCR (RT-PCR). This product was subjected to a second round of nested PCR with type-specific primers which yielded DNA products of unique size characteristic for each pestivirus genotype. Using this assay, we were able to rapidly characterize several viral isolates and determine that all 3 genotypes can be found among ovine isolates.

Transcriptional activation of flanking sequences by Tn1000 insertion

The carotenoid biosynthesis operon of Erwinia herbicola Eho13 consists of five genes, which are organized in the order crtE-crtX-crtY-crtI-crtB. These genes, with the exception of crtX, encode functions of beta-carotene biosynthesis and give an orange-coloured phenotype in Escherichia coli. Since crtX is not involved in the biosynthesis of beta-carotene, deletion of this gene does not alter the phenotype of pigmented cells. On the other hand, insertion of Tn1000 into crtX or into the upstream untranslated region of the operon resulted in a light-yellow, rather than an unpigmented phenotype, indicating that Tn1000 does not exert a strong polar effect when inserted in this operon. RNA analysis revealed that the sequence downstream from the insertion site was transcribed at a low level. Primer extension showed that the "-35"-like sequence in the terminal inverted repeats was not responsible for the transcription of the downstream sequence. Furthermore, primer extension and polymerase chain reaction (PCR) studies revealed that RNA transcribed from the promoters inside of Tn1000 was extended through the terminal inverted repeats into the adjacent sequences. In addition Tn1000, in either orientation, was able to generate fusion transcripts when placed upstream of a promoter-less tetracycline-resistance gene and resulted in cells resistant to the drug. These results showed that Tn1000 insertion transcriptionally activates the DNA sequences adjacent to the transposon.

Reverse transcriptase-PCR assay for detection of hog cholera virus

A reverse transcriptase-PCR strategy was developed for the detection of hog cholera virus. Hog cholera virus template was amplified from tissue culture fluids and from tissues and blood of infected pigs, but not from samples containing other pestiviruses. Restriction endonuclease analysis identified samples as historic or recent isolates.

Pestiviruses isolated from pigs, cattle and sheep can be allocated into at least three genogroups using polymerase chain reaction and restriction endonuclease analysis

A polymerase chain reaction-based assay capable of detecting a broad range of pestiviruses from pigs, cattle, or sheep was developed. Of six sets of primers selected from different parts of the pestivirus genome, the best results were provided by a pair from the highly conserved 5' non-coding region which gave amplification with all 129 isolates tested. This panel consisted of 33 isolates from pigs, 79 from cattle, and 17 from sheep. Differentiation between the viruses was achieved by cutting the PCR-amplified products with the restriction endonucleases AvaI and Bg1I. Using this procedure it was possible to distinguish at least 3 genogroups; group 1 (HCV) contained 32 of the pig isolates, group II (BVDV) contained all the cattle isolates tested plus 6 sheep isolates and group III (BDV) contained 11 sheep isolates and 1 pig isolate.

Rapid characterization of new pestivirus strains by direct sequencing of PCR-amplified cDNA from the 5' noncoding region

Reverse transcription coupled with the polymerase chain reaction (RT-PCR) was used for the rapid laboratory diagnosis of pestivirus infections. A direct DNA sequencing method was developed for the analysis of the amplified cDNA from the 5' noncoding region of the viral genome. 70 pestivirus strains were compared in this study. Sequence analysis allowed the characterization of each isolate as either classical swine fever virus (CSFV), bovine viral diarrhea virus, or border disease virus, respectively. The 48 CSFV strains could be further classified into several subgroups, which correlated either with the geographical origin or the date of the first isolation of the respective isolate.

Detection and identification of equine herpesvirus-1 and -4 by polymerase chain reaction

A rapid method for detection and identification of equine herpesvirus-1 and -4 (EHV-1 and EHV-4) was developed using polymerase chain reaction (PCR). Primers for PCR were designed from aligned nucleotide sequences of glycoprotein B genes of EHV-1 and EHV-4 to amplify specific regions for EHV-1 or EHV-4 or a common region of both viruses. By using type specific primer mixture, amplified fragments were identified as EHV-1 or EHV-4 in a one-step reaction. We have applied this technique on specimens from aborted fetuses. The samples contained only EHV-1 and there was complete accordance between the results of PCR and virus isolation. Our PCR system could differentiate the two virus types rapidly in a one-step reaction.

Detection of hog cholera virus and differentiation from other pestiviruses by polymerase chain reaction

Reverse transcription coupled with the polymerase chain reaction (RT-PCR) was used for the detection and differentiation of pestiviruses. For this purpose, one primer pair was selected from a highly conserved region of the genome of pestiviruses. Using these primers (PEST 1-PEST 2), DNA fragments of between 72 and 74 bp could be amplified from all pestivirus isolates tested. In order to differentiate hog cholera virus (HCV) from bovine viral diarrhea virus (BVDV) and border disease virus (BDV), we selected a primer pair from a conserved region in the genome of HCV strains that differed from that sequenced in the genome of BVDV strains. By using these primers (HCV 1-HCV 2), a DNA fragment of 478 bp could be specifically amplified from HCV isolates. By these means, viral RNA was detected in extracts of lymph node, spleen, tonsil, and lung. Such extracts were used directly for RT-PCR without prior RNA isolation. We also performed multiplex PCR by using both the PEST 1-PEST 2 and HCV 1-HCV 2 primer pairs in a single reaction. This allowed the differentiation of HCV from BVDV and BDV in one step. To assess the sensitivity of the method, RT-PCR was compared with virus propagation in tissue culture and subsequent detection by immunofluorescence staining. The results show that RT-PCR is useful for the rapid detection and differentiation of pestiviruses.

Presumptive diagnostic differentiation of hog cholera virus from bovine viral diarrhea and border disease viruses by using a cDNA nested-amplification approach

Hog cholera virus (HCV), bovine viral diarrhea virus (BVDV), and border disease virus (BDV) are closely related pestiviruses. BVDV and BDV are found worldwide but seldom cause disease in swine. In contrast, HCV has been successfully eradicated from swine in several nations but poses a potentially devastating threat to them because of its great virulence. Rapid differential diagnosis of HCV from BVDV and BDV infections in swine is vital for detection of the possible reintroduction of HCV into national herds from which it has been eradicated. Nested polymerase chain reactions (PCRs) for each of two pestiviral genomic segments are described. Amplification of the relatively conserved 5' genomic terminus identified 59 of 61 HCV, BVDV, and BDV isolates generically as pestiviruses. Nested amplification of the second region was designed to differentiate HCV from BVDV and BDV by exploiting relatively conserved differences in the nucleotide sequences that encode the major envelope glycoprotein. This second PCR correctly identified 36 of 36 diverse HCV isolates while failing to recognize any of 25 BVDV and BDV isolates. Multiple restriction fragment length analyses confirmed the identities of both external and nested PCR products. The two sets of PCRs may help confirm the generic identity of most pestiviruses and may permit presumptive differential diagnosis of HCV from BVDV and BDV.

Application of the polymerase chain reaction (PCR) in veterinary diagnostic virology

The polymerase chain reaction has become an important diagnostic tool for the veterinary virologist. Conventional methods for detecting viral diseases can be laborious or ineffective. In many cases PCR can provide a rapid and accurate test. In this article we explain the basic principles of PCR and supply a reference list of its uses in diagnostic veterinary virology.