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

A Review on the Methods Used for the Detection and Diagnosis of Rabbit Hemorrhagic Disease Virus (RHDV)

Since the early 1980s, the European rabbit (Oryctolagus cuniculus) has been threatened by the rabbit hemorrhagic disease (RHD). The disease is caused by a lagovirus of the family Caliciviridae, the rabbit hemorrhagic disease virus (RHDV). The need for detection, identification and further characterization of RHDV led to the development of several diagnostic tests. Owing to the lack of an appropriate cell culture system for in vitro propagation of the virus, much of the methods involved in these tests contributed to our current knowledge on RHD and RHDV and to the development of vaccines to contain the disease. Here, we provide a comprehensive review of the RHDV diagnostic tests used since the first RHD outbreak and that include molecular, histological and serological techniques, ranging from simpler tests initially used, such as the hemagglutination test, to the more recent and sophisticated high-throughput sequencing, along with an overview of their potential and their limitations.

Diagnostic clinical microbiology

Technological advancements have changed the way clinical microbiology laboratories are detecting and identifying bacterial, viral, parasitic, and yeast/fungal pathogens. Such advancements have improved sensitivity and specificity and reduce turnaround time to reporting of clinically important results. This article discusses and reviews some traditional methodologies along with some of the technological innovations introduced into diagnostic microbiology laboratories. Some insight to what might be available in the coming years is also discussed.

Veterinary Diagnostic Practice and the Use of Rapid Tests in Antimicrobial Stewardship on UK Livestock Farms

In this paper we consider the shifting role, practice and context of veterinary diagnosis in addressing concerns over what is, in the context of the growing threat of antimicrobial resistance, considered unnecessary or excessive antimicrobial medicine use in UK livestock farms. With increasing policy and regulatory interest in diagnostic practices and technologies, coupled with an expanding focus on the development and deployment of new rapid and point-of-care on-farm diagnostic testing, this paper investigates current diagnostic practices amongst veterinarians working on dairy, pig and poultry farms in Great Britain (England, Wales, and Scotland) and, more specifically, veterinarians' use and perceptions of new and emerging rapid and point-of-care diagnostic tests. Drawing on a series of 30 semi-structured interviews with farm animal veterinary professionals across the three sectors, this paper examines the manner in which such tests are both used and anticipated in clinical farm animal veterinary practice and the possible impact rapid test technologies might have on broader farm animal health management and disease control. Analysis of the transcribed interviews reveals a number of complexities around the use of rapid and point-of-care diagnostic tests. The relative rapidity and simplification of such tests, facilitating immediate treatment responses, is held in balance against both the accuracy and the more detailed and documented procedures of established laboratory testing routes. In situations of multifaceted on-farm etiologies, respondents maintained that rapid tests may offer restricted diagnostic capabilities, though in other situations they were found to offer ready confirmation of disease presence. A third complexity arising from the growth of rapid and point-of-care testing and revealed in this study relates to the shifting distribution of responsibilities in animal health care within contemporary food chains. The growing availability of rapid and point-of-care tests effectively diversifies the range of diagnostic actors with consequences for the flow of diagnostic and disease information. The veterinarians in this study identified areas where new rapid and point-of-care tests would be of particular value to them in their clinical practice particularly in addressing concerns over inappropriate antimicrobial use in animal treatment. However, despite the considerable policy advocacy on rapid and point-of-care tests as key tools in shifting diagnostic practice and reducing unnecessary antimicrobial use, veterinarians in this study, while recognizing the potential future role of such tools and technologies, nonetheless viewed diagnostic practice as a far more complex process for which rapid tests might constitute only a part.

Rapid detection of BoHV-1 genomic DNA by loop-mediated isothermal amplification assay

Bovine herpes virus-1 (BoHV-1) is a serious viral pathogen of domestic and wild cattle. Herein, we report development of a new molecular diagnostic assay for rapid and sensitive detection of BoHV-1 utilizing the loop-mediated isothermal amplification (LAMP) technique. BoHV-1-LAMP assay was optimized to amplify the target DNA by incubation the Bst-DNA polymerase enzyme with a set of specially constructed six primers, based on the gE-gene of BoHV-1 virus, at 65°C for 60min. BoHV-1-LAMP products were detected by visual inspection using SYBR Green-I stain and had a ladder-like appearance by gel electrophoresis analysis. Negative results obtained with DNA from other tested fish viruses confirmed the specificity of the assay. The analytical sensitivity of the BoHV-1-LAMP assay was 1fg of BoHV-1 DNA (dilution of 10(6)). The developed assay could successfully detect BoVH-1 DNA from clinical samples. Results of this study indicate that the developed BoHV-1-LAMP is rapid and highly sensitive assay not only for detection of BoHV-1 in clinical samples, but also for differentiation between wild-type (gE-positive) and gE-negative BoHV-1 viruses, which will improve the control programs of BoHV-1 in Egypt.

Heminested reverse-transcriptase polymerase chain reaction (hnRT-PCR) as a tool for rabies virus detection in stored and decomposed samples

Background

The use of methods, both sensitive and specific, for rabies diagnosis are important tools for the control and prophylaxis of the disease. Reverse-Transcriptase Polymerase Chain Reaction (RT-PCR) has been used in rabies diagnosis with good results, even in decomposed materials. Additionally, molecular techniques have been used for epidemiological studies and to gain a better knowledge of viral epidemiology.

Findings

The aim of this work was to evaluate the RT-PCR and hnRT-PCR for rabies virus detection in original tissues stored at -20°C for different periods considering their use for rabies virus detection in stored and decomposed samples. RT-PCR and hnRT-PCR were evaluated in 151 brain samples from different animal species, thawed and left at room temperature for 72 hours for decomposition.

The RT-PCR and hnRT-PCR results were compared with previous results from Direct Fluorescent Antibody Test and Mouse Inoculation Test. From the 50 positive fresh samples, 26 (52%) were positive for RT-PCR and 45 (90%) for hnRT-PCR. From the 48 positive decomposed samples, 17 (34, 3%) were positive for RT-PCR and 36 (75%) for hnRT-PCR. No false-positives results were found in the negatives samples evaluated to the molecular techniques.

Conclusion

These results show that the hnRT-PCR was more sensitive than RT-PCR, and both techniques presented lower sensibility in decomposed samples. The hnRT-PCR demonstrated efficacy in rabies virus detection in stored and decomposed materials suggesting it's application for rabies virus retrospective epidemiological studies.

Simultaneous detection of three porcine viruses by multiplex PCR

Specific oligonucleotide primers were selected and combined in a multiplex arrangement, in order to detect simultaneously three economically important porcine viruses by polymerase chain reaction (PCR). The pathogen panel was comprised of viruses that cause reproductive failure in infected herds: Aujeszky's disease virus (ADV), porcine parvovirus (PPV) and porcine respiratory and reproductive syndrome virus (PRRSV). In order to reduce the time required for the detection of the pathogens, the assay was optimised to a RapidCycler PCR instrument. The multiplex PCR assay was shown to be specific, sensitive and rapid, because the results were read in less than 60 min after sample preparation. Due to its speed, efficiency and sensitivity, the described rapid multiplex PCR assay serves as a useful novel tool in the veterinary diagnostic laboratories for the quick and complex detection of these important porcine pathogens.

Ultrastructural findings in feline corneal sequestra

OBJECTIVES

(1) To describe the ultrastructural features of corneal sequestra in cats; and (2) to enhance our understanding regarding the pathogenesis of feline corneal sequestration.

METHODS

Nine corneal sequestra were harvested via keratectomy from globes of nine cats. The sequestra were routinely fixed then postfixed for high resolution light and transmission electron microscopy (HR-LM and TEM, respectively). The tissues were embedded in Epon/Araldite. Sections of 0.5-microm thickness were cut and stained with 1% toluidine blue in 1% sodium tetraborate solution for HR-LM. Ultrathin sections were collected on copper grids and stained with uranyl acetate and Sato's lead stain for TEM. Ultrathin sections were examined and the images were captured on an Advantage HR CCD camera using a Hitachi 7500 electron microscope operated at 80 kV. Two healthy corneas from two cats were harvested immediately following euthanasia. These corneal tissues (control samples) were processed in the same manner as the corneal sequestra for HR-LM and TEM. A portion of each sequestrum was also submitted for polymerase chain reaction (PCR) testing for infectious agents including feline herpesvirus-1 (FHV-1), Toxoplasma gondii, Chlamydophila felis and Mycoplasma spp.

RESULTS

Ultrastructure of healthy corneal tissues revealed basal corneal epithelial cells aligned adjacent to a thin acellular layer similar to Bowman's layer with underlying tightly packed, regularly arranged, collagen fibrils oriented in different planes. Keratocytes were elongated and had long and irregularly shaped nuclei, and cytoplasm contained rough endoplasmic reticulum and abundant membrane-bound vesicles. In contrast, corneal sequestra contained varying amounts of an amorphous, electron-dense substance, continuous with intact basal epithelial basement membranes peripherally, and overlying corneal ulceration and loosely packed collagen fibrils. Remnants of necrotic keratocytes were seen in spaces between disarranged collagen layers. In all samples, occasional keratocytes exhibited morphology indicative of apoptosis including clumping and margination of chromatin, and shrunken cytoplasm. Varying degrees of inflammation were noted on HR-LM and TEM of affected corneas including peri- and intralesional neutrophils, lymphocytes, plasma cells, and macrophages. Corneal sequestra were FHV-1-positive (n = 3), FHV-1- and T. gondii-positive (n = 1), T. gondii-positive (n = 3), or negative for DNA of these infectious agents (n = 2) using PCR. All corneal sequestra were negative for DNA of Chlamydophila felis and Mycoplasma spp. using PCR.

CONCLUSIONS

Apoptosis may play a role in the pathogenesis of feline corneal sequestration independent of the presence of DNA of these infectious organisms. Prospective clinical studies are warranted to further understand the significance of T. gondii in relation to feline corneal sequestration.

The molecular diagnosis of porcine viral diseases: a review

The worldwide occurrence and re-occurrence of transboundary diseases like foot-and-mouth disease or classical swine fever indicates that there is a high need for the development of powerful, robust and high-capacity new diagnostic methods, which are able to detect the causative agents before they could spread to large populations and cause tremendous losses. This article reports the experiences of a research group on the development of molecular methods for the improved diagnosis of a range of porcine viral diseases, including diseases on List A of the Office International des Epizooties (OIE). Nucleic acid hybridisation and various polymerase chain reaction (PCR) assays have been applied for routine diagnosis of a large range of viral diseases. During the last one-and-a-half decade more than 40 nested PCR assays have been developed to detect a variety of DNA and RNA viruses. False positive and negative results are avoided by the use of special tools, practices and internal controls of amplification (mimics). Recently, real-time PCR methods (TaqMan, molecular beacons, Primer-Probe Energy Transfer system) have been developed for the diagnosis of a wide range of diseases, such as foot-and-mouth disease, swine vesicular disease and vesicular stomatitis. Multiplex PCR packages have been developed for the simultaneous detection of eight important viruses of swine. By introducing nucleic acid extraction and pipetting robotics, together with the multi-channel real-time PCR machines, the diagnostic procedures have become rapid, robust and automated. In order to standardise the real-time PCR assays, the rules of OIE are considered. By following the five steps of OIE standardisation and validation, the new diagnostic procedures are nationally and internationally standardised and harmonised. The rapid, powerful and internationally standardised molecular diagnosis contributes to the reduction of losses caused by the transboundary viral diseases in swine populations.

A survey for BVDV antibodies in cattle farms in Slovakia and genetic typing of BVDV isolates from imported animals

A serological survey for bovine viral diarrhoea virus (BVDV) antibodies on a collection of 1295 serum samples obtained from 6-12 months old cattle originating from 45 farms in Slovakia was carried out. On 13 farms more than 90% of the examined animals were seropositive, on 14 farms 71-90% seroprevalence was observed, on 13 farms only 50-70% animals were found to be positive for BVDV antibodies, while the remaining 5 farms showed fewer than 50% seropositive animals. The average incidence of BVDV antibodies (around 70%) was similar as determined 30 years ago. Of 84 serum samples from seronegative animals originating from 14 farms in which 70-98% seropositivity was observed, six were positive in Ag-BVDV ELISA indicating persistently infected (PI) cattle. On a farm to which animals were imported from abroad, a BVD outbreak was observed. Of 110 animals tested, four were positive in Ag-ELISA indicating the presence of PI cattle on this farm. Genetic typing of two isolates from imported animals performed by RT-PCR (324/326 primers from 5'-UTR), sequencing of PCR products and computer-assisted phylogenetic analysis revealed that they belong to BVDV-1 h group.

Bluetongue virus diagnosis of clinical cases by a duplex reverse transcription-PCR: a comparison with conventional methods

A duplex reverse transcription polymerase chain reaction (RT-PCR) assay for the detection of bluetongue virus (BTV) in clinical samples was developed. This assay, which detects the highly conserved S10 region of BTV, was assessed for sensitivity and application as a rapid and dependable diagnostic tool by comparison with standard assays of virus detection, such as virus isolation in embryonated chicken eggs and cell culture. Simultaneous detection of BTV and host beta-actin RNAs minimizes the possibility of false negative results. The sensitivity of the assay was found to be equal to five cell culture infectious dose (CCID(50)) units and its specificity was confirmed as no RT-PCR product was detected with RNAs from two closely related orbiviruses, i.e. epizootic haemorrhagic disease virus (serotypes 1, 2 and 318) and African horse sickness virus, serotype 9, or RNAs from uninfected BHK-21 cells and blood samples from uninfected sheep or goats. In this study, 36 blood samples from naturally infected mixed flocks of sheep and goats were examined. Seventeen animals were identified as BTV-positive by RT-PCR, whereas only 13 were found positive by virus isolation in embryonated chicken eggs and nine by cell culture assays. These results indicate that the duplex RT-PCR could be a useful technique for monitoring BTV infection in the field.

Development of a multiplex polymerase chain reaction for the differentiation of bovine herpesvirus-1 and -5

Bovine herpesvirus-1 (BHV-1) and bovine herpesvirus-5 (BHV-5) are closely related viruses which exhibit some important differences at the genetic and immunogenic levels which may explain the differences in their pathogenicity and epidemiological characteristics. A multiplex polymerase chain reaction (M-PCR) was developed to detect and differentiate between BHV-1 and BHV-5. In this M-PCR two pairs of primers (TK1, TK2 and GD1, GD2) were used in the same reaction mix to amplify a thymidine kinase genomic region (183 bp) of BHV-1 and one genomic region of the gLycoprotein D (564 bp) of BHV-5. The specificity of the M-PCR was demonstrated when using both primers pairs simultaneously with BHV-1 and BHV-5 templates. The two expected bands were amplified without the apparition of non-specific products. However, when other herpesvirus strains were used, there was no amplification. To evaluate the sensitivity of the assay, dilutions of purified viral DNA were made for M-PCR amplification. The detection limit was 7 pg for BHV-1 and 22 pg for BHV-5. It was also determined by comparing the M-PCR with viral isolation. M-PCR was able to detect one log10 more than viral isolation for BHV-1 and for BHV-5 was two logarithms lower. The applicability of M-PCR was demonstrated on different specimens. Twenty isolates from field samples (11 BHV-1 and nine BHV-5) were positive by M-PCR, and the results were completely coincident with previous characterization using the immunoperoxidase assay. M-PCR could detect viral DNA in organ samples from natural infections, such as semen and brain. In addition, M-PCR detected more positive samples than observation of the citophatic effect in cell culture of nasal swabs from experimentally infected animals in two different assays. Owing to the difference in size of the M-PCR products which allows easy identification in an electrophoretic run, it is not necessary to use extra blotting and hybridization steps or a second round of amplification to differentiate clearly between BHV-1 and BHV-5.

Characterization of an Indian bluetongue virus isolate by RT-PCR and restriction enzyme analysis of the VP-7 gene sequence

The reverse transcription-polymerase chain reaction (RT-PCR) was standardized to amplify the VP-7 gene sequences of an Indian isolate of bluetongue virus serotype 23. Using two different sets of primers, a sequence of 1156 bp comprising the complete coding sequence of the VP-7 gene and its 770 bp internal sequence were amplified. The sensitivity of RT-PCR, using these two sets of primers individually was 40 pg and 4 pg, with the external and internal primers, respectively, whereas the nested PCR was 100-fold more sensitive than the single PCR with the external primers. Further, by restriction enzyme digestion of the 1156 bp amplicon, using CfoI, PstI and TaqI enzymes, the Indian isolate was found to be genetically different from isolates from the United States and Australia. RT-PCR and restriction enzyme digestion were applied to detect virus directly in blood samples taken from sheep suspected of bluetongue virus infection.

Bovine respiratory syncytial virus (BRSV): a review

Bovine respiratory syncytial virus (BRSV) infection is the major cause of respiratory disease in calves during the first year of life. The study of the virus has been difficult because of its lability and very poor growth in cell culture. However, during the last decade, the introduction of new immunological and biotechnological techniques has facilitated a more extensive study of BRSV as illustrated by the increasing number of papers published. Despite this growing focus, many aspects of the pathogenesis, epidemiology, immunology etc. remain obscure. The course and outcome of the infection is very complex and unpredictable which makes the diagnosis and subsequent therapy very difficult. BRSV is closely related to human respiratory syncytial virus (HRSV) which is an important cause of respiratory disease in young children. In contrast to BRSV, the recent knowledge of HRSV is regularly extensively reviewed in several books and journals. The present paper contains an updated review on BRSV covering most aspects of the structure, molecular biology, pathogenesis, pathology, clinical features, epidemiology, diagnosis and immunology based on approximately 140 references from international research journals.

Partial characterization of a Brazilian strain of Aujeszky’s disease virus recovered from a pig with subclinical infection

One Brazilian strain of Aujeszky’s disease virus isolated from a piglet in which the disease had not been observed was studied as for its virulence in pigs. The genome of the virus was molecularly analysed as for their restriction endonuclease cleavage pattern. Fifty-day-old non-immune weanlings exposed to this strain showed no disease although the virus was present in their oropharyngeal area for at least three days. All animals developed moderate titers of neutralizing antibody. Based on number of bands and migration rate of restriction fragments the isolate was classified into Herrmann’s type I group. Latent infection was detected in all pigs by PCR. Some variations were detected in the cleavage pattern of the strain ASB Piau when compared to LA031 virulent Brazilian strain, that could be related to differences in the virulence.

A rapid and sensitive PCR-based diagnostic assay to detect bovine herpesvirus 1 in routine diagnostic submissions

We describe a rapid, sensitive and specific polymerase chain reaction (PCR) assay for the detection of BHV1 DNA in a range of routine diagnostic submissions without the need for prior virus isolation. The assay, which is based on the selected amplification of a portion of the viral tk gene, detected both BHV1.1 and BHV1.2 subtypes in a panel of 15 characterised field isolates, and its sensitivity was estimated to be <0.125 TCID(50). BHV2, alcephaline herpesvirus, BHV4, equine herpesvirus 1 (EHV1), EHV4 and pseudorabies virus were not detected confirming the specificity of the assay. One hundred and five diagnostic submissions, including tissues, nasal secretions and nasal swabs were taken from cattle with respiratory disease and tested using the routine methods of virus isolation (VI) and the fluorescent antibody test (FAT), and the results were compared with those obtained by PCR. The PCR assay detected BHV1 DNA in all samples that were positive by VI. BHV1 DNA was also detectable by PCR in raw and extended semen samples at a sensitivity of 1 TCID(50) per 50microl. The assay also detected BHV5, permitting differentiation between it and BHV1 by virtue of the size of the amplified PCR product. The PCR assay is more sensitive and independent of sample quality than either virus isolation or FAT, and it is faster than virus isolation. The sample preparation method is simple with few steps involved. There are no extra post-amplification blotting/hybridisation steps and the assay is not based on a nested PCR strategy that might otherwise exacerbate the problem of oversensitivity/contamination in the routine use of such a test in a diagnostic laboratory. This assay would permit discrimination between those animals naturally infected with wild type BHV1 and those vaccinated with tk-BHV1 strains.

Bovine respiratory syncytial virus (BRSV): a review

Bovine respiratory syncytial virus (BRSV) infection is the major cause of respiratory disease in calves during the first year of life. The study of the virus has been difficult because of its lability and very poor growth in cell culture. However, during the last decade, the introduction of new immunological and biotechnological techniques has facilitated a more extensive study of BRSV as illustrated by the increasing number of papers published. Despite this growing focus, many aspects of the pathogenesis, epidemiology, immunology etc. remain obscure. The course and outcome of the infection is very complex and unpredictable which makes the diagnosis and subsequent therapy very difficult. BRSV is closely related to human respiratory syncytial virus (HRSV) which is an important cause of respiratory disease in young children. In contrast to BRSV, the recent knowledge of HRSV is regularly extensively reviewed in several books and journals. The present paper contains an updated review on BRSV covering most aspects of the structure, molecular biology, pathogenesis, pathology, clinical features, epidemiology, diagnosis and immunology based on approximately 140 references from international research journals.

Diagnosis of enzootic pneumonia in Danish cattle: reverse transcription-polymerase chain reaction assay for detection of bovine respiratory syncytial virus in naturally and experimentally infected cattle

A reverse transcription-polymerase chain reaction (RT-PCR) assay was developed for detection of bovine respiratory syncytial virus (BRSV) in lung tissue of naturally and experimentally infected cattle. Primers were selected from the gene coding the F fusion protein, which is relatively conserved among BRSV isolates. The RT-PCR assay was highly specific, it yielded positive reactions only when performed on BRSV-infected cell cultures or tissues. The detection limit of the RT-PCR assay was assessed as 5 TCID50. BRSV was detected in tissues of the respiratory tract and in the tracheobroncheal lymph node of calves euthanized 2-8 days after experimental infection with BRSV, whereas samples of other tissues and samples from mock-infected animals were negative at all time points. Examination of lung samples from 8 different regions of the lungs revealed that although the virus was most often found in the cranioventral lobules, it was frequently present in all lung lobules. Microbiologic examinations of all acute fatal cases of pneumonia (135 animals) in cattle submitted for diagnostic purposes during 1 year revealed that Actinomyces pyogenes (11%), Haemophilus somnus (10%), Pasteurella sp. (7%), and Pasteurella haemolytica (7%) were the most common bacterial agents found in the lungs. BRSV was identified using a conventional antigen enzyme-linked immunosorbent assay (ELISA) in 23 (17%) animals. The established BRSV-specific RT-PCR assay yielded positive results for the same 23 animals. In addition, 10 animals that were negative with the ELISA were positive with the RT-PCR assay. These results indicates that the RT-PCR assay can be a sensitive, reliable alternative to conventional diagnostic procedures.

Studies on the pathogenicity of bovine herpesvirus type 5 in sheep

Four Merino lambs were intranasally inoculated with bovine herpesvirus type 5 (BHV-5) reference strain N569. Two lambs were mock-inoculated as negative controls. The virus-inoculated animals developed apathy, inappetence, rhinitis, nasal, ocular and genital discharge, slight diarrhea and neurological disorders, like tremor and salivation. BHV-5 was isolated from the nasal discharge in two of the animals, while the polymerase chain reaction (PCR) detected the virus in all the infected lambs. Two lambs died on post infection day (PID) 13, while the other two infected animals were euthanized on PID 15 and 30. Gross pathological changes were not observed, however, histopathological examinations revealed diffuse nonsuppurative meningo-encephalitis in all infected animals. Viral antigen was detected by immunohistochemistry and viral nucleic acid was revealed by in situ hybridization in the brain of the two lambs, which died on PID 13. The virus was demonstrated by virus isolation and by PCR from different organs of all the infected animals. Slight rise of antibodies was observed in the infected animals from PID 15. The results show that BHV-5 is able to cross the species barrier and may establish infection in sheep.

Detection of canine herpesvirus DNA in the ganglionic neurons and the lymph node lymphocytes of latently infected dogs

To determine the site of latent infection of canine herpesvirus (CHV), tissues from dogs convalescent from acute infection with CHV were examined for the presence of viral genome DNA by the nested polymerase chain reaction. CHV DNA was detected in the trigeminal ganglia and the retropharyngeal lymph nodes. In situ hybridization study of the tissues revealed that CHV genome persisted in the nuclei of ganglionic neurons and lymphocytes.

Detection of BHV-1 in a naturally infected bovine fetus by a nested PCR assay

Bovine herpesvirus 1 (BHV-1) is frequently associated with abortion in naturally and experimentally infected cattle. Most of the virus isolation and immunofluorescent antibody protocols described in the literature for detecting BHV-1 in bovine foetuses are rather laborious, costly and time-consuming. The detection is described of BHV-1 in the tissues of a naturally aborted bovine foetus by a nested PCR assay with no further hybridization procedures. Optimal results were achieved by filtering the foetal tissues on a chromatography column before DNA extraction, by using two pairs of primers in a nested PCR and by evaluating the amplification products on silver-stained polyacrylamide gels. This nested PCR was faster and easier to perform than the virus isolation test. To our knowledge, this is the first time that BHV-1 has been detected in the tissues of a naturally infected bovine foetus by means of a nested PCR. The test seems to be a practical alternative for rapid detection of BHV-1 in bovine foetus.

Laboratory diagnostic investigations for bovine viral diarrhoea virus infections in cattle

There are no pathognomonic clinical signs of infection with bovine viral diarrhoea virus (BVDV) in cattle. Diagnostic investigations therefore rely on laboratory-based detection of the virus, or of virus-induced antigens or antibodies in submitted samples. In unvaccinated dairy herds, serological testing of bulk milk is a convenient method for BVDV prevalence screening. Alternatively, serological testing of young stock may indicate if BVDV is present in a herd. In BVDV positive herds, animals persistently infected (PI) with BVDV can be identified by combined use of serological and virological tests for examination of blood samples. ELISAs have been used for rapid detection of both BVDV antibodies and antigens in blood, but should preferably be backed up by other methods such as virus neutralization, virus isolation in cell cultures or amplification of viral nucleic acid. Detailed knowledge of the performance of the diagnostic tests in use, as well as of the epidemiology of bovine virus diarrhoea is essential for identification of viremic animals in affected herds.

A high sensitivity-nested PCR assay for BHV-1 detection in semen of naturally infected bulls

Several different PCR protocols for the detection of Bovine herpesvirus-1 (BHV-1) in bovine semen, are available in the literature. Most of them are rather laborious and the majority were performed on laboratory samples, artificially contaminated semen or semen provided from experimentally inoculated animals. Furthermore, to obtain higher levels of sensitivity, additional dot-blot procedures are frequently necessary. We describe the detection of BHV-1 in bovine semen and the supernatant of cell cultures with titres of 0.001 TCID50/50 microliter by a nested PCR assay, with no further hybridization procedures. The high sensitivity was achieved by filtering the semen samples on chromatography columns before DNA extraction, by using two pairs of primers in a nested PCR and by evaluating the amplification products on silver-stained polyacrylamide gels. Specificity of the amplified fragments was confirmed by RFLP and sequence analysis of the PCR products. This nested PCR procedure was performed in parallel with viral isolation (VI) on 101 semen samples provided from naturally infected bulls housed at an artificial insemination centre. The nested PCR was shown to be more sensitive, faster and easier to perform than the standard VI test. To our knowledge, it is the most sensitive PCR test for BHV-1 detection in bovine semen and could be easily used for routine diagnosis.

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.

Nested polymerase chain reaction and in situ hybridization for diagnosis of canine herpesvirus infection in puppies

The usefulness of two nucleic acid detection systems in suspected cases of spontaneous canine herpesvirus (CHV) infection in puppies was evaluated. Formalin-fixed, paraffin-embedded tissues from seven 1-3-week-old naturally infected puppies with lesions characteristic of CHV infection were investigated in a retrospective study. Nested polymerase chain reaction (PCR) and nonradioactive in situ hybridization (ISH) were used to detect nucleotide sequences of the CHV thymidine kinase (TK) gene. According to the original necropsy reports, CHV was isolated in four of the seven puppies using primary canine lung and/or kidney cells. In all seven puppies, gross and histologic lesions consisted of disseminated focal necroses and hemorrhages predominantly in kidneys, lung, liver, and spleen. In addition, few small amphophilic intranuclear inclusion bodies were detected by light microscopy mainly in epithelial cells of kidney, lung, and liver. ISH was performed with a 111-base-pair (bp) digoxigenin-labeled double-stranded DNA probe. Viral DNA was detected in the nuclei of cells near and within lesions. Various cell types, including bronchiolar and alveolar epithelial cells, hepatocytes, renal tubular epithelial cells, neurons, fibrocytes, cardiac myocytes, and endothelial cells, were positive for viral DNA. PCR amplification products of the expected length of 168 bp containing the expected cleavage site for the restriction enzyme EcoRI, derived from paraffin blocks containing lung, kidney, and liver tissues, were detected in all seven puppies. The specificity of the obtained amplicon was further confirmed by Southern blot analysis. ISH and PCR are both useful methods for diagnosing CHV infection in formalin-fixed, paraffin-embedded tissues and are highly specific and sensitive methods for further investigations of the pathogenesis of CHV-induced lesions.

PCR studies on the potential sites for latency of BHV-4 in calves

The aim of the study was to examine various tissues of experimentally infected calves for the BHV-4 genome so as to detect in which cells the virus persists during the latent phase of the infection. The presence of the bovine herpesvirus type 4 genome was detected by a nested PCR in a variety of tissues collected from two susceptible calves experimentally infected 62 days earlier. Mild clinical signs of bronchitis, an elevated body temperature for 2-3 days, and a slightly increased number of blood leukocytes were observed in both inoculated calves. BHV-4 was demonstrated in seven samples from the 12 different parts of the nervous system tested from each calf (29.1%), from the cornea, from lymph nodes near to the inoculation site, from the gallbladder and from the bone marrow. Thus a member of the predominantly lymphotropic Gammaherpesvirinae subfamily was detected in neural tissue and other organs that have never been associated with persistence.

Detection of challenge virus in fetal tissues by nested PCR as a test of the potency of a porcine parvovirus vaccine

To estimate the potency of a porcine parvovirus (PPV) vaccine, three vaccinated and three non-vaccinated pregnant gilts were infected with PPV and the distribution of the virus was studied in the tissues of their 51 fetuses. Virus detection was attempted using haemagglutination (HA) and immunofluorescence (IF) assays, as well as by standard (single) and nested polymerase chain reactions (PCR). None of the detection methods yielded positive results when used to test for the presence of virus in suspensions of organs from the fetuses from the vaccinated gilts. However, the virus was detected in the fetuses from non-vaccinated gilts as follows: HA was positive in 14 cases out of 23 (60.8%), IF in 16/23 (69.5%), standard PCR in 12/20 (60%), and the nested PCR in 19/23 (82.6%). Although the correlation among the results of various methods of virus detection was rather close (r < 0.83), the sensitivity of the nested PCR was the highest, both when testing dilutions of PPV and when analysing the fetal organs. The nested PCR therefore provides a reliable approach for studies of virus distribution in fetal organs, with special reference to potency tests on vaccines.

Sequence analysis of equine adenovirus 2 hexon and 23K proteinase genes indicates a phylogenetic origin distinct from equine adenovirus 1

We report the first nucleotide sequence data on equine adenovirus 2 (EAdV2) which corroborate on the molecular level that EAdV2 is distinct from equine adenovirus 1 (EAdV1). Based on sequence homology with Eadv1 the hexon gene of Eadv2 was identified. HindIII restriction fragments containing the hexon and eight other viral genes were cloned into the plasmid pUC19 and the nucleotide sequence of the hexon and the 23K proteinase genes completely determined. Amino acid (aa) comparison of sequence fragments with published adenovirus (AdV) proteins identified the genes for the E1B/19K, IVa2, DNA polymerase, terminal protein, pVI, DNA binding and 100K proteins, usually with highest similarities to human AdV. The nine EAdV2 genes appeared to be in the same relative order as homologous genes of other AdV. The EAdV2 hexon was encoded between the minor capsid precursor protein pVI upstream and the 23K proteinase gene downstream and comprised 2712 nucleotides which translated into 903 aa residues. It was more closely related to the human AdV48 hexon with 71.6% identical and 82.7% functionally similar aa than to the EAdV1 hexon gene with 69.3% aa identity and 80.7% functional similarity. The deduced aa sequence of the EAdV2 23K proteinase gene was 201 residues; it shared 59.7% identical and 75% similar aa residues with the bovine AdV3 23K proteinase as the closest relative. Phylogenetic analysis of the hexon and 23K proteinase genes indicated that EAdV2 does not share an immediate common ancestor with EAdV1 and other AdV.

Rapid diagnosis of encephalomyocarditis virus infections in pigs using a reverse transcription-polymerase chain reaction

Encephalomyocarditis virus (EMCV) is widespread and the economic losses caused by an EMCV outbreak in pig holdings and the similarity between a foot-and-mouth disease virus (FMDV) and an EMCV infection in young piglets stress the need for a rapid, specific and broad diagnostic assay. An alternative to the time-consuming seroneutralisation assay, currently used for the characterisation of EMCV, is described. An EMCV specific reverse transcription-polymerase chain reaction (RT-PCR), using primers located in a conserved region of the 3D gene of the viral genome, was developed and tested on 114 different EMCV isolates. The identity of the respective amplicons was confirmed by sequencing. The potential of this assay for future diagnostic purposes was demonstrated by applying the RT-PCR on tissue samples collected from an experimentally infected piglet.

Use of reverse transcriptase polymerase chain reaction for detection of vaccine contamination by avian leukosis virus

A reverse transcriptase polymerase chain reaction (RT-PCR) for avian leukosis virus (ALV) was developed for the detection of contamination of vaccines produced in embryonated eggs and cell cultures derived from chicken. ALV is highly pathogenic and induces a wide spectrum of disease in infected animals. ALV can be divided into five subgroups (A-E). The envelope glycoprotein (env gp85) is the main antigen determinant and responsible for subgroup classification. Viral RNA of all subgroups (A-E) was isolated and amplified using three sets of primers. Subsequently, restriction endonuclease analysis confirmed the product identity and discriminated between subgroups. In specific pathogen free (SPF) eggs experimentally inoculated with ALV, viral RNA was found in allantoic fluids, as well as in vaccines spiked with different subgroups of ALV. No adventitious virus was detected in commercially available preparations. This system provides a rapid and specific in vitro method for the detection of ALV RNA as an extraneous agent and may be applied for quality control of avian vaccines.

Bluetongue virus detection: a safer reverse-transcriptase polymerase chain reaction for prediction of viremia in sheep

A reversible target capture viral RNA extraction procedure was combined with a reverse-transcriptase nested polymerase chain reaction (PCR) to develop a capture PCR assay providing a rapid and safe prediction method for circulating bluetongue virus in infected ruminants. This new assay was compared with virus isolation and a recently developed antigen-capture enzyme-linked immunosorbent assay (ELISA) for the detection of bluetongue virus. Eight Warhill crossbred sheep were inoculated subcutaneously with bluetongue virus serotype 10, and blood samples were taken sequentially over a period of 28 days. The capture PCR detected the peak of viremia, as determined by virus isolation and antigen-capture ELISA, from day 5 to day 14 after challenge. The results indicate that the rapid-capture bluetongue virus PCR provides a rapid indicator of samples in which virus can be isolated. In addition, this capture bluetongue virus PCR procedure does not require a lengthy phenol extraction or the use of the highly toxic methyl mercury hydroxide denaturant.

Rapid diagnosis of avian infectious bronchitis virus by the polymerase chain reaction

A simple, sensitive and specific polymerase chain reaction (PCR) procedure was developed in order to detect infectious bronchitis virus (IBV) directly in tissue samples. Viral RNA was extracted from allantoic fluids and cell cultures infected experimentally with different strains of IBV and from tissues of naturally infected birds. Viral RNA was then amplified and identified by a nested RT-PCR assay using two sets of primers flanking a well-conserved region of the nucleocapsid gene. The selected IBV nucleocapsid sequence was detected successfully by simple direct electrophoresis of amplified material.

Detection and identification of ruminant and porcine pestiviruses by nested amplification of 5' untranslated cDNA regions

Based on published gene sequences of bovine viral diarrhoea virus (BVDV) type I and classical swine fever virus (CSFV), genus- and species-specific primers were designed to detect and identify pestivirus cDNA sequences in a nested polymerase chain reaction (PCR). The PCR primers were validated using cDNA synthesized from 146 pestivirus isolates, comprising representatives of all four so far described genotypes (BVDV type I, BVDV type II, CSFV and border disease virus), as well as others of uncertain classification. PCR products of the predicted size were amplified from all viruses with the genus-specific primers. All 53 cattle isolates, including 5 typed antigenically as BVDV type II were amplified by the internal BVDV-specific primers, but not the CSFV-specific primers. The same result was found for other BVDV type I and II viruses isolated from sheep and pigs. Seventy-seven CSF viruses were amplified by their respective internal primers. Available information strongly indicate that 4 CSF viruses also amplified by the BVDV-specific primers had been contaminated with BVDV in cell cultures. Border disease viruses were mostly not detected by the BVDV-specific primers, but were detected weakly by the CSFV-specific primer pair. Using carrier RNA for extraction of viral RNA, the sensitivity of detection of the single and nested PCR was, respectively, 5 and 50 times higher than obtained with a cell culture assay. The RT-PCR also detected BVDV in all of 15 commercial batches of fetal calf serum examined, and verified three earlier diagnoses of CSFV by detecting specific gene sequences in 30 year old frozen archival organ samples.

Detection of canine herpesvirus 1 in a wide range of tissues using the polymerase chain reaction

Canine herpesvirus 1 (CHV-1), a member of the alphaherpesvirus sub-family, is known to cause fatal infections in litters of puppies and may also be involved in infertility, abortion, and stillbirths in adult dogs. The purpose of this study was to determine the presence of CHV-1 DNA using the polymerase chain reaction (PCR) in twelve key sites that have been associated with latency for the other herpesviruses. A 605 base pair portion of the viral glycoprotein B (gB) gene was amplified using degenerate primers, cloned, and sequenced. Conventional 20 mer primers were designed using this sequence information to amplify a 120 bp fragment of gB situated between the original degenerate primers. The specificity of amplification was confirmed by Southern Blot hybridisation using an internal oligonucleotide probe. DNA was extracted from tissue samples taken from twelve dogs at post mortem and from twenty-four blood samples. Nine out of twelve dogs showed evidence of infection with CHV-1; the tissues most commonly affected were lumbo-sacral ganglia (5/12 dogs), tonsil (5/12), parotid salivary gland (4/9), and liver (4/9). No positive results were detected within the twenty-four blood samples. These results indicate that exposure to CHV-1 may be much more common than previously suggested.

Rapid and efficient method to eliminate substances inhibitory to the polymerase chain reaction from animal fecal samples

To detect pathogenic viruses in animal fecal specimens by polymerase chain reaction (PCR) assays, it is important to remove or inactivate PCR-inhibitory substances. Recently, it was reported that such inhibitory substances in human feces could be efficiently eliminated by a cationic surfactant, Catrimox-14 (Iowa Biotechnology, Iowa) during extraction of viral RNA. In the present report, Catrimox-14 was successfully applied to detect pathogenic viruses in fecal specimens from a variety of animals. By extraction of viral DNA in the presence of this cationic surfactant, the PCR assay could detect canine parvovirus (CPV) in all fecal specimens prepared from 13 kinds of animals, i.e., cat, chicken, cow, dog, gerbil, goat, golden hamster, horse, mouse, pig, rat, rabbit, or sheep. Pretreatment by gel-filtration or boiling failed to remove or inactivate the PCR-inhibitory substances in fecal specimens from mouse, goat, rat, and sheep.

Genetic variability of classical swine fever virus

The genetic variability of classical swine fever virus was studied by comparative nucleotide sequence analysis of 76 virus isolates, collected during a half century from three continents. Parts of the E2 (gp55) and the polymerase gene coding regions of the viral genome were amplified by RT-PCR and DNA fragments of 254 and 207 bp, respectively, were sequenced. The comparative sequence analysis of the E2 region revealed two main phylogenetic groups of CSFV, indicating that the virus apparently evolved from two ancestor nodes. Group I (represented by Brescia strain) consisted of old and recent American and Asian viruses, as well as old English isolates from the 1950s. This group was subdivided into three subgroups, termed I.A-I.C. Group II (represented by Alfort strain) consisted of relatively recent isolates from Europe, together with strain Osaka, which was isolated in Japan from a pig of European origin. Based on genetic distances the group was divided into subgroups II.A and II.B. Malaysian isolates were branched into both groups, indicating multiple origins for contemporaneous outbreaks in that country. All ten vaccine strains tested were branched in group I, implying a common ancestor. The Japanese Kanagawa strain, isolated in 1974, and the British Congenital Tremor strain from 1964 were the most distinct variants of CSFV in our collection. The comparison of the nucleotide sequences of the polymerase coding region of 32 European strains distinguished subgroups II.A and II.B which were similar to the corresponding subgroups of the E2 phylogenetic tree. Thus, the results revealed that the E2 region and the polymerase coding regions seem to be appropriate for the grouping of CSFV isolates from all over the world, distinguishing two major groups of the virus. The reliability of these regions for phylogenetic analysis is indicated by the similarity of the results obtained from the two separate parts of the CSFV genome.

Studies of in vivo distribution of bovine herpesvirus type 4 in the natural host

The in vivo distribution of bovine herpesvirus type 4 (BHV-4) was examined by testing nasal and conjunctival exudates, peripheral blood leukocytes, and various organs of experimentally infected calves. For virus detection, a nested PCR assay, virus isolation, and immunohistochemistry were applied. The nervous system and the muscles were free of viral DNA. Liver and intestinal lymph nodes contained low amounts of virus (less than two copies per 1 microgram of cellular DNA). Intestinal, tonsil, thymus, and kidney tissues contained more viral DNA copies (5 to 50 copies per 1 microgram of cellular DNA). The highest amounts of BHV-4 DNA (50 to 500 copies per 1 microgram of cellular DNA) were found in the spleen, lungs, trachea, and nasal epithelium. Amplification of DNA from blood lymphocytes through postinoculation (p.i.) day 48 proved that the virus started to replicate in these cells immediately after inoculation of the calves and that intensive virus growth took place during the 7 to 8 weeks of the infection. The number of virus-infected lymphocytes reached the maximum on p.i. days 22 to 26 and slowly declined thereafter. Virus-infected cells were found only in the spleen on p.i. day 48 by immunohistochemistry. Western blotting (immunoblotting) detected signs of an immune response against 9 of the 29 BHV-4 proteins.

A simple touch-down polymerase chain reaction for the detection of canine parvovirus and feline panleukopenia virus in feces

A polymerase chain reaction (PCR) assay is described for the detection of parvovirus in feces of dogs and cats. A touch-down protocol was used which enabled the specific amplification of virion DNA from feces after a fast and simple boiling pretreatment. The sensitivity of PCR was as high as ten infectious particles per reaction which corresponds to a titer of about 10(3) infectious particles per gram of unprocessed feces. This renders the PCR about 10- to 100-fold more sensitive than electron microscopy, the standard method for parvovirus diagnosis. The very rapid and simple sample preparation recommends this PCR assay as an alternative technique for routine parvovirus diagnosis.

Diagnosis of equine gammaherpesvirus 2 and 5 infections by polymerase chain reaction

Nested polymerase chain reaction (PCR) assays were developed for the detection of equine herpesvirus 2 (EHV2) and equine herpesvirus 5 (EHV5) using the nucleotide sequences from the glycoprotein B (gB) gene of EHV2 and the thymidine kinase (TK) gene of EHV5. The simultaneous use of EHV2 specific and EHV5 specific primers in one nested amplification assay (multiplex PCR) enabled a rapid, specific and sensitive diagnosis for each virus. PCR was found to be 10(3) times more sensitive than virus isolation by cell culture for EHV2 and 10(6) for EHV5. In separate PCR assays, the routine detection limit after ethidium bromide staining was 0.6 fg for EHV2 plasmid DNA and 2.3 fg for EHV5 plasmid DNA, equivalent for both viruses to approximately 100 genome copies. The detection limits in multiplex PCR were 6 pg for EHV2 and 2.3 fg for EHV5, respectively. PCR assays were applied to studies of the epidemiology of EHV2 and EHV5 infections of racehorses and breeding mares in Victoria and New South Wales, Australia. Peripheral blood leukocytes from 31% of horses were positive for EHV2, 16% positive for EHV5, 8% positive for both viruses and 63% negative for both viruses. EHV2 PCR was also successfully used to detect EHV2 DNA in nasal secretions from horses. The multiplex PCR assay proved to be a rapid and reliable method for the simultaneous detection and differentiation of 2 related equine gammaherpesviruses.

Establishment of conditions for the detection of bovine herpesvirus-1 by polymerase chain reaction using primers in the thymidine kinase region

Polymerase chain reaction (PCR) for detection of bovine herpesvirus-1 (BHV-1) was developed and optimized using 22 bp sense and 20 bp antisense primers in the thymidine kinase (TK) coding region. The amplification product is 183 bp long. The PCR optimization was done using BHV-1 tissue culture supernate (BHV-1TCS), concentrated BHV-1 tissue culture supernate (cBHV-1TCS) and sucrose gradient purified BHV-1 (pBHV-1). The sensitivity of four methods of sample preparation which are standard DNA extraction, modified proteinase K (PK) digestion, GeneReleaserTM + 34 cycles or + 44 cycles, and boiling were compared with virus isolation (VI) using BHV-1TCS. The incorporation of 10% glycerol in the reaction mixture, the incubation in PK for 18 hours and predenaturation of samples and cooling in ice prior to PCR were essential for the amplification of BHV-1 DNA for samples prepared by standard DNA extraction and modified PK digestion. The preparation of samples by Gene-ReleaserTM, a proprietary nucleic acid releasing cocktail, showed 10 to 1,000-fold increase in sensitivity compared to standard DNA extraction and modified PK digestion. No amplification was observed in samples prepared by boiling. The sample preparation of BHV-1 LA strain by GeneReleaserTM showed sensitivity equivalent to virus isolation. The BHV-1 TK PCR using GeneReleaserTM has a detection limit of 1 picogram and 10 fentograms of purified BHV-1 DNA using ethidium bromide stained gel and Southern blot hybridization, respectively. It could detect viral DNA in 1,000 infected cells in a total suspension of 10,000 cells using either ethidium bromide stained gel or Southern blot hybridization.

Rapid method utilizing the polymerase chain reaction for detection of canine parvovirus in feces of diarrheic dogs

By using primers based on the sequence of the VP2 gene of canine parovirus (CPV), we established a rapid and specific assay for identification of the virus from fecal specimens based on the polymerase chain reaction (PCR). By use of a pair of primers, a specific 226-bp sequence was amplified by the PCR. All strains of CPV tested gave a specific amplification product by the PCR, while neither porcine parovirus nor host cell did so. The PCR assay can detect fewer particles of CPV than the conventional methods, being able to detect CPV from fecal specimens in a rapid manner, provided that gel filtration of the samples through a spun column was done to remove inhibitory substances from the fecal specimens. These results suggest that the PCR assay can detect the presence of CPV in dogs early enough to prevent secondary infection by CPV in veterinary hospitals.

Current state and future trends in the diagnosis of babesiosis

An overview is given of the currently available methods to diagnose babesiosis in livestock. Microscopic techniques are still the only appropriate techniques to diagnose acute disease. Thin or thick blood films stained with Giemsa's stain are sufficient. The sensitivity ranges from 10(-5) to 10(-6), i.e. one parasite per 10(5)-10(6) erythrocytes can be detected. Thick films stained with acridine orange (sensitivity approximately 10(-7)) and the Quantitative Buffy Coat (QBC) analysis tube system (sensitivity approximately 10(-7)-10(-8)) are applicable for diagnosis in the laboratory. DNA probes are very specific tools to identify haemoparasites in organs post mortem and in ticks. For the identification of carrier animals the sensitivity (approximately 10(-5)-10(-6)) is generally not sufficient. For the latter the polymerase chain reaction (PCR) technique is a very powerful tool (sensitivity approximately 10(-9)). Many different serodiagnostic tests have been described; however, the immunofluorescence antibody test is the most widely used, while the enzyme-linked immunosorbent assay (ELISA) is the test system which holds the greatest promise for the future. Thus far, improvements to the ELISA have been limited as the quality of antigen preparations made from infected blood is generally poor with a few exceptions (Babesia bovis, Babesia caballi). Potentially, most of the problems associated with crude antigens can be overcome by the production of recombinant antigens. Several ELISAs based on highly defined recombinant antigens have been described and show promise. None of these tests has been validated to the extent that it could be applied globally. Future research requirements as well as the need for coordination of the research effort and collaboration between institutions involved in the diagnosis of babesiosis are discussed.

Applications of DNA amplification techniques in veterinary diagnostics

An overview of the principles of the polymerase chain reaction, ligase chain reaction, self-sustained sequence replication and Q beta replicase is given. The application of these methods for the diagnosis of veterinary infectious and hereditary diseases as well as for other diagnostic purposes is discussed and comprehensive tables of reported assays are provided. Specific areas where these DNA-based amplification methods provide substantial advantages over traditional approaches are also highlighted. With regard to PCR-based assays for the detection of viral pathogens, this article is an update of a previous review by Belák and Ballagi-Pordány (1993).

Evaluation of a 'one tube' reverse transcription-polymerase chain reaction for the detection of ruminant pestiviruses

A 'one tube' reverse transcription-polymerase chain reaction ('one tube' RT-PCR) using rTth DNA polymerase was compared with an existing RT-PCR using Taq DNA polymerase (Taq RT-PCR) to detect ruminant pestiviruses in infected cell cultures. The technically simpler and more convenient 'one tube' method was relatively insensitive detecting only 11 of the 34 samples tested, all of which were positive by Taq RT-PCR.

Bovine leukaemia virus: rapid detection of proviral DNA by nested PCR in blood and organs of experimentally infected calves

The early stage of bovine leukaemia virus (BLV) infection was studied in experimentally infected calves in order to assess the diagnostic applicability of a double polymerase chain reaction (PCR). In addition, the kinetics of infection and virus distribution were evaluated. To simulate the natural route of virus transmission, the calves were infected by transferring two different infectious doses of whole blood from a BLV infected cow. The establishment of infection was determined by the double PCR and syncytia formation assay and by indirect serological methods including indirect ELISA, gp51/p24 ELISA, agar gel immunodiffusion (AGID) and Western blotting. BLV antibodies were first detected in ELISA on post infection (p.i.) day 26. Close agreement was found between the results of the various indirect methods. BLV infection was first detected in peripheral blood lymphocytes (PBL) by the PCR on p.i. day 7. No animal became seropositive to BLV prior to direct detection of BLV infection by the PCR. At slaughter, urine and saliva specimens as well as various organs were collected from the calves and tested by the double PCR. Several of the organs yielded positive results: e.g. spleen, uterus, liver, kidney, abomasum, and lymph nodes. Nine out of eleven spleen suspensions were positive by the PCR, including the spleen from one calf, which otherwise remained negative in all tests throughout the experiment. This phenomenon indicates that an animal may be infected without detectable levels of BLV proviral DNA in PBLs and without circulating antibodies, further emphasizing the diagnostic importance of the PCR. The findings indicate that the PCR is the most rapid method for the early detection of BLV infection in cattle and a valuable tool for studying the tropism of the virus.

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.