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

A multiplex nanoparticle-assisted polymerase chain reaction assay for detecting three canine epidemic viruses using a dual priming oligonucleotide system

A rapid and accurate diagnosis of mixed viral infections is important for providing timely therapeutic interventions. The aim of this study was to develop a highly sensitive and specific method for the simultaneous detection of canine distemper virus (CDV), canine parvovirus (CPV) and canine coronavirus (CCV) in mixed infections by combining the high specificity of a dual priming oligonucleotide (DPO) primer system with the high sensitivity of a nanoparticle-assisted PCR (nanoPCR) assay. Under the optimised assay conditions, the multiplex DPO-nanoPCR assay developed using DPO primers was 100-fold more sensitive than the multiplex PCR assay using conventional primers. The detection limits of the multiplex DPO-nanoPCR assay for the recombinant plasmids containing the cloned CDV, CPV and CCV target sequences were 5.4 × 10², 6.5 × 10² and 1.6 × 10² copies in a 25 μL assay, respectively. No cross-reaction with other canine viruses was observed. This is the first reported use of a multiplex nanoPCR assay with the DPO primer system for the simultaneous detection of CDV, CPV and CCV in mixed infections. The high sensitivity and specificity of the assay indicated its potential for use in clinical diagnosis and field surveillance of animal epidemics.

Risk and Environmental Factors Associated with the Presence of Canine Parvovirus Type 2 in Diarrheic Dogs from Thessaly, Central Greece

Canine parvovirus type 2 (CPV-2) primarily infects dogs, which are the main host reservoir, causing severe gastrointestinal disease associated with immunosuppression. The present study was conducted in Thessaly, Greece and aimed to identify risk and environmental factors associated with CPV-2 infection in diarrheic dogs. Fecal samples were collected from 116 dogs presenting diarrhea and were tested by polymerase chain reaction (PCR) for the presence of CPV-2 DNA. Supplementary data regarding clinical symptoms, individual features, management factors and medical history were also gathered for each animal during clinical evaluation. Sixty-eight diarrheic dogs were found to be positive for the virus DNA in their feces. Statistical analysis revealed that CPV-2 DNA was less likely to be detected in senior dogs, while working dogs, namely hounds and shepherds, had higher odds to be positive for the virus. Livestock density and land uses, specifically the categories of discontinuous urban fabric and of human population density, were identified as significant environmental parameters associated with CPV-2 infection by using Geographical Information System (GIS) together with the Ecological Niche Model (ENM). This is the first description of the environmental variables associated with the presence of CPV-2 DNA in dogs’ feces in Greece.

CRISPR-Cas13a mediated nanosystem for attomolar detection of canine parvovirus type 2

Canine parvovirus type 2 (CPV-2) infection is the most lethal disease of dogs with higher mortality in puppies worldwide. In today’s world, dogs are an integral part of our communities as well as dogs breeding and rearing has become a lucrative business. Therefore, a fast, accurate, portable, and cost-effective CPV-2 detection method with the ability for on-site detection is highly desired. In this study, we for the first time proposed a nanosystem for CPV-2 DNA detection with RNA-guided RNA endonuclease Cas13a, which upon activation results in collateral RNA degradation. We expressed LwCas13a in prokaryotic expression system and purified it through nickel column. Activity of Cas13a was verified by RNA-bound fluorescent group while using a quenched fluorescent probe as signals. Further Cas13a was combined with Recombinase polymerase amplification (RPA) and T7 transcription to establish molecular detection system termed specific high-sensitivity enzymatic reporter un-locking (SHERLOCK) for sensitive detection of CPV-2 DNA. This nanosystem can detect 100 amol/L CPV-2 DNA within 30 min. The proposed nanosystem exhibited high specificity when tested for CPV-2 and other dog viruses. This CRISPR-Cas13a mediated sensitive detection approach can be of formidable advantage during CPV-2 outbreaks because it is time-efficient, less laborious and does not involve the use of sophisticated instruments.

Diagnostics and genotyping of Canine parvovirus type 2 (CPV-2) from disease cases in south-eastern Poland

Canine parvovirus type 2 is one of the most common causes of death among puppies. Despite preventive vaccination, the disease continues to be diagnosed. The aim of the study was to provide a molecular characterization of CPV-2 isolates found in southeastern Poland. Genetic CPV-2 material was isolated from the blood (n=10) and feces (n=50) of infected dogs. The presence of CPV-2 was confirmed by amplification of sequences coding both VP1 and VP2 protein. The products of the PCR reaction with primers amplifying VP2 protein were sequenced and used for genotyping. Bioinformatics analysis of the sequenced PCR product was performed to determine the phylogenetic relationships with variants recorded in the public databases. Based on the analysis of polymorphism in the nucleotide sequence 7 nucleotide variants were detected and assigned into four amino acid groups. Representatives of three groups contained asparagine at amino acid position 426 of the VP2 protein, which is characteristic of CPV-2a. The variant from the fourth group belonged to type CPV-2b. CPV-2a is the dominant antigenic type of CPV-2 in Poland. The pathogen’s high degree of polymorphism is manifested not only by the presence of numerous variants within the type, but also by the presence of representatives of type CPV-2b. Further studies of the molecular epidemiology of CPV-2 are necessary to optimize the effectiveness of preventive measures.

Polymerase chain reaction combined with fluorescent lateral flow immunoassay based on magnetic purification for rapid detection of canine parvovirus 2

BACKGROUND

Canine parvovirus 2 (CPV-2) is one of the most common etiological agents that cause severe gastroenteritis in puppies. Early accurate diagnosis is important for infected dogs. In recent years, magnetic separation has become an efficient and useful tool for bioassays. In this study, polymerase chain reaction (PCR) combined with fluorescent lateral flow immunoassay (LFIA) based on magnetic purification assay was developed for the quantitative detection of CPV-2.

RESULTS

The optimum working reaction volume and reaction time for LFIA was 100 μL and 2 min, respectively. The PCR-LFIA assay only detected CPV-2, and did not show cross-detection of non-CPV strains. Experiments showed analytical sensitivity of 3 × 10¹ copies/μL and demonstrated the PCR-LFIA has a diagnostic agreement of 100% with conventional PCR on detection of clinical samples (22.6% positive, 14/62). Cutoff value is 146. The results were further verified by sequencing and BLAST software. The entire process from PCR step only takes ~ 80 min.

CONCLUSIONS

This approach provides an attractive platform for rapid and quantitative detection of CPV-2, indicating great promise as a convenient molecular detection tool to facilitate disease outbreak investigations and response timely.

Equipment-free recombinase polymerase amplification assay using body heat for visual and rapid point-of-need detection of canine parvovirus 2

A visible and equipment-free recombinase polymerase amplification assay combined with a lateral flow strip (LFS RPA) was developed to detect canine parvovirus type 2 (CPV-2), which is the etiological agent of canine parvovirus disease. The CPV-2 LFS RPA assay was developed based on the VP2 gene and is performed in a closed fist using body heat for 15 min; the products are visible to the naked eye on the LFS within 5 min. The assay could detect CPV-2a, CPV-2b and CPV-2c, and there was no cross-reaction with the other viruses tested. Using the standard CPV-2 DNA as a template, the analytical sensitivity was 1.0 × 10² copies per reaction, which was the same result as that of a real-time PCR. The assay performance was further evaluated by testing 60 canine fecal samples, and CPV-2 DNA was detected in 46 samples (76.7%, 46/60) by LFS RPA, which was the same result as that of the real-time PCR assay and higher than that of the SNAP method (48.3%, 29/60). The novel CPV-2 LFS RPA assay is an attractive and promising tool for rapid and convenient diagnosis of CPV disease, especially cage side and in underequipped laboratories.

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Visual and rapid molecular assay for detection of CPV-2 was developed.

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Assay was based on recombinase polymerase amplification and use of lateral flow strip to visualize product.

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Assay was incubated successfully in a closed fist using body heat.

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Assay showed high sensitivity and specificity for detection of CPV-2.

A multiplex TaqMan real-time PCR for detection and differentiation of four antigenic types of canine parvovirus in China

Canine parvovirus (CPV) is an important pathogen in domestic dogs, and the original antigenic types CPV-2 and its variants, CPV-2a, 2b and 2c, are prevalent worldwide. A multiplex TaqMan real-time PCR method was developed for the detection and differentiation of four antigenic types of CPV. A set of primers and probes, CPV-305F/CPV-305R and CPV-2-305P (for CPV-2)/CPV-2a-305P (for CPV-2a, 2b and 2c), was able to differentiate CPV-2 and its variants (CPV-2a, 2b and 2c). Another set of primers and probes, CPV-426F/CPV-426R and CPV-2-426P (for CPV-2 and 2a)/CPV-2b-426P (for CPV-2b)/CPV-2c-426P (for CPV-2c), was able to differentiate CPV-2a (2), CPV-2b, and CPV-2c. With these primers and probes, the multiplex TaqMan real-time PCR assay detected effectively and differentiated CPV-2, 2a, 2b and 2c by two separate real-time PCRs. No cross reactivity was observed with canine distemper virus, canine adenovirus, and canine coronavirus. The detection limit of the assay is 10¹ genome copies/μL for CPV-2, CPV-2a, CPV-2b, and 10² copies/μL for CPV-2c. The multiplex real-time PCR has 100% agreement with DNA sequencing. We provide a sensitive assay that simultaneously detects and differentiate four antigenic types of CPV and the method was also used for quantification of CPVs viral genome.

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The Multiplex TaqMan real-time PCR can simultaneously detect and differentiate four antigenic types of CPV.

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The method is suit for using in detection of CPVs in China.

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The method showed a high specificity and sensitivity.

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The method was also used for quantification of CPVs viral genome.

Immunocapture loop-mediated isothermal amplification assays for the detection of canine parvovirus

A loop-mediated isothermal amplification (LAMP) assay was used for rapid canine parvovirus (CPV) diagnosis. To reduce the time required and increase the sensitivity of the assay, an immunocapture (IC) technique was developed in this study to exclude the DNA extraction step in molecular diagnostic procedures for CPV. A polyclonal rabbit anti-CPV serum was produced against VP2-EpC that was cloned via DNA recombination. The polyclonal anti-VP2-EpC serum was used for virus capture to prepare microtubes. IC-LAMP was performed to amplify a specific CPV target gene sequence from the CPV viral particles that were captured on the microtubes, and the amplicons were analyzed using agarose electrophoresis or enzyme-linked immunosorbent assay (IC-LAMP-ELISA) and lateral-flow dipstick (IC-LAMP-LFD). The detection sensitivities of IC-LAMP, IC-LAMP-ELISA, and IC-LAMP-LFD were 10^-1, 10^-1, and 10^-1 TCID₅₀/mL, respectively. Using the IC-LAMP-ELISA and IC-LAMP-LFD assays, the complete CPV diagnostic process can be achieved within 1.5h. Both of the developed IC-LAMP-based assays are simple, direct visual and efficient techniques that are applicable to the detection of CPV.

Genetic characterization of canine parvovirus type 2 subtypes in Maputo, Mozambique

Canine parvovirus type 2 (CPV-2) comprises three antigenic subtypes (2a, 2b and 2c) that have been reported in many countries. These subtypes cause serious disease in dogs with characteristic gastroenteritis signs. Little information has been documented in Africa about the genetic characterization of CPV-2. The aim of this study was to detect and to characterize the CPV-2 subtypes circulating in dogs admitted to Veterinary Clinics from two cities of Mozambique, Maputo and Matola, in 2010. A total of 40 field fecal samples were collected and tested for CPV-2 by polymerase chain reaction assay. The partial length VP2 gene of the positive samples were sequenced and genetically analyzed. Twenty-six (65%) fecal samples were positive for CPV-2. The restriction fragment length polymorphism analysis was also performed from positive samples and did not reveal the presence of CPV-2c subtype. The results of the sequencing revealed the presence of CPV-2a (n = 9) and CPV-2b (n = 17). No CPV-2 and CPV-2c were detected. Sequence analysis comparison showed nucleotide identities of 99.6-100% among our CPV-2 isolates. Amino acid analysis showed predicted amino acid changes. Phylogenetically, all of the CPV-2a strains isolated formed a cluster together with South African and Nigerian isolates. Most of Mozambican CPV-2b isolates also tended to cluster together with South African isolates; however, four were more closely related to French strain and one isolates to the American strain. The present study was the first to characterize the CPV-2 circulating in the Mozambican dog population.

Reliability of clinical diagnosis and laboratory testing techniques currently used for identification of canine parvovirus enteritis in clinical settings

Canine parvovirus type 2 (CPV-2) is the main etiological agent of viral enteritis in dogs. Actually in literature, CPV-2 has been reported with clinical signs that vary from the classical disease, and immunochromatography test and PCR technique have been introduced to veterinary hospitals to confirm CPV-2 diagnosis and other infections. However, the reliability of these techniques has been poorly analyzed. In this study, we evaluated the sensitivity and specificity of veterinary clinical diagnosis, immunochromatography test and PCR technique. Our data indicate that variations in the clinical signs of CPV-2 complicate the gathering of an appropriate diagnosis; and immunochromatography test and PCR technique do not have adequate sensitivity to diagnose positive cases.

Rapid and sensitive detection of canine parvovirus type 2 by recombinase polymerase amplification

A novel recombinase polymerase amplification (RPA)-based method for detection of canine parvovirus type 2 (CPV-2) was developed. Sensitivity analysis showed that the detection limit of RPA was 10 copies of CPV-2 genomic DNA. RPA amplified both CPV-2a and -2b DNA but did not amplify the template of other important dog viruses (CCoV, PRV or CDV), demonstrating high specificity. The method was further validated with 57 canine fecal samples. An outstanding advantage of RPA is that it is an isothermal reaction and can be performed in a water bath, making RPA a potential alternative method for CPV-2 detection in resource-limited settings.

Diagnostic performance of a rapid in-clinic test for the detection of Canine Parvovirus under different storage conditions and vaccination status

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Quick laboratory confirmation of parvoenteritis is important to start treatment.

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In-clinic tests are quick and simple in use.

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A positive rapid test result almost certainly indicates the presence of the virus.

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Vaccination status and storage condition affects the results of the in-clinic test.

Canine parvovirus (CPV) is one of the most common causes of acute haemorrhagic enteritis in young dogs, while clinical diagnosis is often indecisive. The aim of our study was to evaluate the diagnostic accuracy of an in-clinic rapid test in the detection of CPV infection in dogs. To this end, we compared the Rapid Diagnostic Kit of Canine Parvovirus, Coronavirus and Rotavirus antigen (Quicking^®) to PCR, which is considered as the most reliable diagnostic method. A total of 78 duplicated faecal samples were collected from diarrhoeic dogs. Vaccination history within a month prior to the onset of diarrhoea was reported for 12 of the sampled dogs. The rapid diagnostic test was performed in 23 of the faecal samples directly, while the rest were placed into a sterile cotton tipped swab suitable for collection and transportation of viruses (Sigma Σ-VCM^®) and stored at −20 °C. The sensitivity of the Quicking rapid diagnostic test compared to PCR in the total number of samples, in samples from non-vaccinated dogs and in samples tested directly after collection were 22.22% (95% CI: 13.27–33.57%), 26.67% (95% CI: 16.08–39.66%) and 76.47% (95% CI: 50.10–93.04%) respectively, while the specificity of the test was 100% in any case. In conclusion, negative results do not exclude parvoenteritis from the differential diagnosis, especially in dogs with early vaccination history, but a positive result almost certainly indicates CPV infection. An improved sensitivity may be expected when the test is performed immediately.

Characterization of a new epidemic necrotic pyoderma in fur animals and its association with Arcanobacterium phocae infection

A new type of pyoderma was detected in Finnish fur animals in 2007. The disease continues to spread within and between farms, with severe and potentially fatal symptoms. It compromises animal welfare and causes considerable economic losses to farmers. A case-control study was performed in 2010–2011 to describe the entity and to identify the causative agent. Altogether 99 fur animals were necropsied followed by pathological and microbiological examination. The data indicated that the disease clinically manifests in mink (Neovison vison) by necrotic dermatitis of the feet and facial skin. In finnraccoons (Nyctereutes procyonoides), it causes painful abscesses in the paws. Foxes (Vulpes lagopus) are affected by severe conjunctivitis and the infection rapidly spreads to the eyelids and facial skin. A common finding at necropsy was necrotic pyoderma. Microbiological analysis revealed the presence of a number of potential causative agents, including a novel Streptococcus sp. The common finding from all diseased animals of all species was Arcanobacterium phocae. This bacterium has previously been isolated from marine mammals with skin lesions but this is the first report of A. phocae isolated in fur animals with pyoderma. The results obtained from this study implicate A. phocae as a potential causative pathogen of fur animal epidemic necrotic pyoderma (FENP) and support observations that the epidemic may have originated in a species -shift of the causative agent from marine mammals. The variable disease pattern and the presence of other infectious agents (in particular the novel Streptococcus sp.) suggest a multifactorial etiology for FENP, and further studies are needed to determine the environmental, immunological and infectious factors contributing to the disease.

Visual detection of canine parvovirus based on loop-mediated isothermal amplification combined with enzyme-linked immunosorbent assay and with lateral flow dipstick

Loop-mediated isothermal amplification (LAMP) combined with enzyme-linked immunosorbent assay (LAMP–ELISA) and with lateral flow dipstick (LAMP–LFD) are rapid, sensitive and specific methods for the visual detection of clinical pathogens. In this study, LAMP–ELISA and LAMP–LFD were developed for the visual detection of canine parvovirus (CPV). For LAMP, a set of four primers (biotin-labeled forward inner primers) was designed to specifically amplify a region of the VP2 gene of CPV. The optimum time and temperature for LAMP were 60 min and 65°C, respectively. The specific capture oligonucleotide probes, biotin-labeled CPV probe for LAMP–ELISA and fluorescein isothiocyanate-labeled CPV probe for LAMP–LFD were also designed for hybridization with LAMP amplicons on streptavidin-coated wells and LFD strips, respectively. For the comparison of detection sensitivity, conventional PCR and LAMP for CPV detection were also performed. The CPV detection limits by PCR, PCR–ELISA, LAMP, LAMP–ELISA and LAMP–LFD were 10², 10², 10⁻¹, 10⁻¹ and 10⁻¹ TCID₅₀/ml, respectively. In tests using artificially contaminated dog fecal samples, the samples with CPV inoculation levels of ≥1 TCID₅₀/ml gave positive results by both LAMP–ELISA and LAMP–LFD. Our data indicated that both LAMP–ELISA and LAMP–LFD are promising as rapid, sensitive and specific methods for an efficient diagnosis of CPV infection.

An updated TaqMan real-time PCR for canine and feline parvoviruses

Canine parvovirus type 2 (CPV-2) emerged in late 1970s from the feline panleukopenia virus (FPLV) and developed, since then, into novel genetic and antigenic variants (CPV-2a, -2b and -2c). Canine and feline parvoviruses cause an acute enteric disease in their hosts, with high level of viral shedding. In this study, a quantitative TaqMan PCR for detection and quantitation of canine and feline parvoviruses in serum and fecal samples was developed. The primers were designed based upon the entire GenBank content for CPV and FPLV. A standard curve was generated, and validation tests were performed using 10-fold serial dilutions of CPV-2 virus in CPV/FPLV-negative feces and CPV/FPLV-negative serum samples. As a result, the 100% detection limit of the PCR was 18 copies of the viral genome per μl of serum and fecal sample. All canine parvovirus types as well as FPLV were detected. In conclusion, the real-time PCR represents an upgraded and useful tool to identify and quantify canine and feline parvoviruses in different sample matrices.

Comparison of Three Rapid Commercial Canine Parvovirus Antigen Detection Tests with Electron Microscopy and Polymerase Chain Reaction

Different antibody-based tests for rapid detection of Canine parvovirus antigens in feces are commercially available, allowing quick diagnosis in a clinical setting. However, the diagnostic accuracy of these tests compared with standard methods has not been evaluated so far. In the current study, 3 commercial tests were compared with immune-electron microscopy (IEM) and polymerase chain reaction (PCR). Dogs were divided into 3 groups: group A, samples from dogs with acute hemorrhagic diarrhea ( n = 50); group B, dogs with chronic diarrhea ( n = 10); and group C, dogs with no evidence of gastrointestinal disease ( n = 40). Specificity of all 3 commercial tests versus PCR and IEM was good to excellent (92.2–100%). Sensitivity, in contrast, was poor: 15.8–26.3% versus PCR and 50–60% versus IEM. In group A, 10 dogs were positive by IEM and 24 dogs were positive by PCR. Positive PCR results were also obtained from animals in control groups (group B, 1 dog; group C, 5 dogs). No dog in group B or C was positive by IEM. In conclusion, the rapid tests are useful to diagnose canine parvoviral enteritis, but they do not rule out parvovirus infection in an animal with typical clinical signs. In addition, a small percentage of healthy dogs and dogs with chronic diarrhea showed positive PCR results; this may be due to asymptomatic/persistent infection or intestinal passage of virus. The significance of this finding remains unclear.

Detection of canine adenoviral infections in urine and faeces by the polymerase chain reaction

The present study was aimed at developing the polymerase chain reaction (PCR) assay for detection of canine adenoviruses from faecal or urine samples. Urine or faecal samples were treated with chloroform or activated charcoal to eliminate the PCR inhibitory substances and the total DNA was extracted. The PCR was optimized using common set of primers to amplify 508 bp or 1,030 bp DNA sequence within E3 gene of canine adenovirus-1 (CAV-1) and canine adenovirus-2 (CAV-2), respectively. The PCR assay could detect up to 0.016 TCID(50) viruses from CAV-1 infected MDCK cell culture fluid, 1.6 TCID(50) viruses from faeces and 16 TCID(50) viruses from urine. In addition, the PCR assay was validated using clinical samples. Based on the results, it is concluded that, the present PCR assay can be used for rapid detection of canine adenoviral infections.

Detection of infectious canine parvovirus type 2 by mRNA real-time RT-PCR

A TaqMan real-time RT-PCR assay was developed for detection of RNA transcripts produced by replicating CPV-2. A pair of primers and a TaqMan probe targeting the spliced NS2 mRNA were designed. A synthetic DNA fragment was constructed to mimic the spliced NS2 mRNA by PCR-based gene assembly and was used for generation of standard RNAs. The detection limit of the assay was 1 × 10² RNA copies and standard curve displayed a linear range from 1 × 10² to 1 × 10⁹ copies and a good reproducibility. The assay was then applied to determine the mRNA loads in the tissues of dogs naturally infected by CPV-2. mRNA was detected in a variety of tissues, including the central nervous system.

Diagnostic tools based on minor groove binder probe technology for rapid identification of vaccinal and field strains of canine parvovirus type 2b

TaqMan-based diagnostic tests have been developed for the identification of canine parvovirus type 2 (CPV-2) strains in the faeces of dogs with diarrhoea, including a minor groove binder (MGB) probe assay for identification of type 2-based vaccines and field strains (types 2a, 2b and 2c). Since type 2b vaccines have been licensed recently in Europe, two novel MGB assays were developed for discrimination between type 2b vaccines and field strains of CPV. Such assays have been found to be highly sensitive, specific and reproducible, allowing for simultaneous detection of type 2b vaccinal and field strains present in the same specimens. These new assays will help resolution of the diagnostic problems related to the detection of a type 2b strain in the faeces of dogs shortly after the administration of a type 2b vaccine.

First detection of canine parvovirus type 2c in pups with haemorrhagic enteritis in Spain

Canine parvovirus type 2 (CPV-2), the aetiological agent of haemorrhagic enteritis in dogs, includes three antigenic variants, types 2a, 2b and 2c. CPV-2c has been detected initially in Italy and subsequently in Vietnam. We report the first identification of this novel antigenic variant in Spain, where it caused an outbreak of fatal enteritis in basset hound pups in association with canine coronavirus type I and type II. We suggest that this new antigenic variant of CPV-2 could spread throughout Europe and that there is a subsequent need to update current CPV vaccines.

Tissue distribution of the antigenic variants of canine parvovirus type 2 in dogs

Twelve dogs dead as consequence of natural infection caused by canine parvovirus (CPV) type 2a (n=4), type 2b (n=4) or type 2c (n=4) were investigated for determining the viral DNA loads in different tissue samples. By means of a real-time PCR assay, CPV DNA was detected in all tissues examined, with the highest titres observed in the lymphoid tissue and the lowest loads in the urinary tract. Surprisingly, the nervous tissue was found to contain considerable amounts of CPV nucleic acid. Similar patterns of tissue distribution were observed in all the examined dogs irrespective of the antigenic variant causing the disease.

A minor groove binder probe real-time PCR assay for discrimination between type 2-based vaccines and field strains of canine parvovirus

A minor groove binder (MGB) probe assay was developed to discriminate between type 2-based vaccines and field strains of canine parvovirus (CPV). Considering that most of the CPV vaccines contain the old type 2, no longer circulating in canine population, two MGB probes specific for CPV-2 and the antigenic variants (types 2a, 2b and 2c), respectively, were labeled with different fluorophores. The MGB probe assay was able to discriminate correctly between the old type and the variants, with a detection limit of 10(1) DNA copies and a good reproducibility. Quantitation of the viral DNA loads was accurate, as demonstrated by comparing the CPV DNA titres to those calculated by means of the TaqMan assay recognising all CPV types. This assay will ensure resolution of most diagnostic problems in dogs showing CPV disease shortly after CPV vaccination, although it does not discriminate between field strains and type 2b-based vaccines, recently licensed to market in some countries.

New approaches for the molecular characterization of canine parvovirus type 2 strains

Characterization of the canine parvovirus type 2 (CPV-2) is sometimes ambiguous, frequently requiring more than one technique for definitive prediction of the viral type. Taking into account the single-nucleotide polymorphisms encountered in the VP2-protein gene between types 2a and 2b and between type 2b and Glu-426 mutant (type 2c), two different minor groove binder (MGB) probe assays were developed for rapid identification of the CPV-2 variants. A total of 315 samples collected from dogs with diarrhoea were screened for CPV-2 by a real-time polymerase chain reaction (PCR) assay capable of detecting all CPV-2 types. In order to compare the type-specific assays with the traditional techniques [haemagglutination inhibition with monoclonal antibodies, PCR-restriction fragment-length polymorphism (RFLP), sequence analysis] for prediction of CPV-2 antigen specificity, the 203 samples tested CPV-2 positive were analysed using the different methods. The results showed a 100% concordance between the MGB probe assays and the combined conventional methods, with 116 samples characterized as type 2a, 32 as type 2b and 55 as type 2c. Therefore, the MGB probe assays represent a quick, reliable tool for prediction of CPV-2 antigen specificity, with regard to the more time-consuming assays currently used.

Characterisation of the canine parvovirus type 2 variants using minor groove binder probe technology

Two minor groove binder (MGB) probe assays were developed for rapid identification and quantitation of the canine parvovirus type 2 (CPV-2) variants in the faecal samples of dogs. The MGB probe assays using type-specific probes labeled with different fluorophores (FAM and VIC) were able to detect the single nucleotide polymorphisms existing between types 2a/2b and 2b/2c. Both the MGB probe assays were found to be highly specific, sensitive and reproducible, ensuring a precise quantitation of the CPV-2 DNA, as confirmed by comparing the obtained viral DNA loads to those calculated using a real-time TaqMan-based PCR assay established previously. A total of 414 faecal specimens collected from diarrhoeic dogs and tested positive to CPV-2 were analysed by the MGB probe assays and by conventional methods (haemagglutination inhibition with MAbs, PCR-RFLP and sequence analysis) for prediction of the CPV-2 antigen specificity, with an overall agreement of 100%. These results make the established MGB probe assays an attractive tool for direct and rapid characterisation of type 2a, 2b and 2c CPVs.

Canine parvovirus infection: Which diagnostic test for virus?

Five laboratory tests for diagnosis of canine parvovirus type 2 (CPV-2) infection were employed to test 89 faecal samples collected from dogs with diarrhoea. The tests analysed were immunochromatography (IC), haemagglutination (HA), virus isolation (VI), conventional and real-time PCR. IC, HA, VI and conventional or real-time PCR were able, respectively, to detect CPV-2 antigen or nucleic acid in 41, 50, 54, 68 and 73 of the samples. The best correlation was found between conventional and real-time PCR, with an overall agreement of 94.38%. Sixty-eight samples that tested positive by HA, VI or conventional PCR were subjected to antigenic and/or genetic analyses of the CPV-2 strains by monoclonal antibody (MAb), restriction fragment-length polymorphism (RFLP) and/or sequence analyses. In sum, out of the 68 strains analysed, 26 were characterised as CPV-2a, 18 as CPV-2b and 24 as a CPV-2 Glu-426 mutant recently identified in Italy.

A real-time PCR assay for rapid detection and quantitation of canine parvovirus type 2 in the feces of dogs

We describe a rapid, sensitive and reproducible real-time PCR assay for detecting and quantifying canine parvovirus type 2 (CPV-2) DNA in the feces of dogs with diarrhea. An exogenous internal control was added to control the assay performance from extraction to amplification. The method was demonstrated to be highly specific and sensitive, allowing a precise CPV-2 DNA quantitation over a range of eight orders of magnitude (from 10(2) to 10(9) copies of standard DNA). The reproducibility of the CPV-2 real-time PCR assay was assessed by calculating the coefficients of variation (CV) intra-assay and inter-assay for samples containing amounts of CPV-2 DNA spanning the whole range of the real-time PCR standard curve. Then, fecal specimens from diarrheic dogs were analyzed by hemagglutination (HA), conventional PCR and real-time amplification. Comparison between these different techniques revealed that real-time PCR is more sensitive than HA and conventional gel-based PCR, allowing to detect low viral titers of CPV-2 in infected dogs.

Diagnosis of canine parvovirus by rapid immunomigration on a membrane

Rapid immunomigration on a membrane was applied to the diagnosis of canine parvovirus (CPV) in 128 samples of faeces containing four strains of parvovirus (two CPV-2a strains, including one vaccine strain, and two CPV-2b strains). The results were compared with the results of haemagglutination and ELISA sandwich techniques. The new test was quick and easy to use, and made it possible to identify both the CPV-2a and CPV-2b strains. Its detection thresholds per gram of faeces corresponded to specific haemagglutination titres of between 320 and 640 and a virus titre of between 10(4) and 10(5) CCID50 (dose required to infect 50 per cent of cell cultures).

Identification of canine coronavirus strains from feces by S gene nested PCR and molecular characterization of a new Australian isolate

A nested PCR (nPCR) assay for the detection of canine coronavirus (CCV) in fecal samples is described. The target sequence for the assay was a 514-bp fragment within the spike (S) glycoprotein gene. The sensitivity of the assay is extremely high, detecting as little as 25 50% tissue culture infective doses per g of unprocessed feces. A clinical trial using dogs challenged orally with CCV SA4 and CCV NVSL was used to compare viral isolation and the nPCR assay as detection techniques over a 2-week period of infection. Virus isolation detected CCV shedding from day 4 to 9 postchallenge, while the nPCR assay detected CCV shedding from day 4 to 13 postchallenge. Cloning and sequencing of the nPCR assay product enabled investigation of the evolutionary relationships between strains within the S gene. The simple and rapid procedure described here makes this assay an ideal alternative technique to electron microscopy and viral isolation in cell culture for detection of CCV shedding in feces. The described assay also provides a method of identifying new strains of CCV without the complicated and time-consuming practice of raising antibodies to individual strains. This is illustrated by the identification, for the first time, of an Australian isolate of CCV (UWSMN-1).

Detection of canine parvovirus in naturally infected dogs with enteritis and myocarditis by in situ hybridization

An improved method for the diagnosis of canine parvovirus using in situ hybridization in standard formalin-fixed, paraffin-embedded tissue sections was developed. A digoxigenin-labeled probe complementary to DNA sequences that code for the entire sequence of the capsid protein VP-1 and the middle part of the sequence of the capsid protein VP-2 was designed. Specific histologic localization of canine parvovirus-infected cells was demonstrated in small intestine, tonsil, lymph node, thymus, spleen, heart, liver, and kidney from dogs diagnosed at necropsy with canine parvovirus infection. The in situ hybridization accurately pinpointed the specific sites of viral infection. The detection of canine parvovirus in liver, kidney, and heart tissues together in the same pups could represent an enhanced virulence of this strain of canine parvovirus and suggests a broadened tissue tropism not seen before in Korean strains of canine parvovirus.

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.

Detection and genomic analysis of canine parvovirus by the polymerase chain reaction

Prevalence of canine parvovirus type 2 (CPV-2) in Japanese dogs and genomic variations among the virus strains were examined. Two-step polymerase chain reaction with double-nested primer pairs designed in the NS and VP1/VP2 genes of CPV-2 was developed for the detection of the viral genome in faecal samples. A total of 74 samples obtained from diarrhoeal house dogs between 1993 and 1995 were tested by the PCR. The virus-positive rate was 54.1%, showing that CPV-2 is still involved in many cases of acute infectious diarrhoea in Japanese dogs. The VP1/VP2 gene of the positive samples was subjected to restriction fragment length polymorphism (RFLP) analysis and nucleotide sequencing. RFLP patterns of the samples were almost identical to those of one CPV-2 strain (TDKet-91-42) isolated in 1991, but different from those of the CPV-2 in the late 1970s and 1980s. The results suggest that a new genotype of CPV-2 appeared and spread among Japanese dogs in the early 1990s.

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.

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.