Development of real-time polymerase chain reaction assays for rapid detection and differentiation of wild-type pseudorabies and gene-deleted vaccine viruses

Molecular Detection of Porcine Cytomegalovirus, Porcine Parvovirus, Aujeszky Disease Virus and Porcine Reproductive and Respiratory Syndrome Virus in Wild Boars Hunted in Serbia during 2023

Porcine cytomegalovirus (PCMV) infection is widespread worldwide and has a high prevalence in swine herds, especially in countries with intensive swine production. PCMV is zoonotic and can impact xenotransplants. It is the third swine virus known to be zoonotic, following swine influenza virus (influenza A) and hepatitis E virus genotype 3 (HEVgt3 or HEV-3). Wild boars, serving as reservoirs for various pathogens, including PCMV, pose a risk to both the pig industry and public health. This study aimed to investigate PCMV infection in Serbian wild boars using real-time PCR and assess other viral infections. We also tested samples for the presence of other viral infections: Aujeszky disease virus (ADV), Porcine parvovirus (PPV) and Porcine reproductive respiratory syndrome (PRRSV). Samples from 50 wild boars across 3 districts were tested. Results showed 8% positivity for PCMV DNA, with females showing higher infection rates. Porcine parvovirus (PPV) was detected in 56% of samples, while Porcine reproductive respiratory syndrome virus (PRRSV) was absent. ADV was found in 18% of samples, primarily in younger animals. This research contributes to understanding PCMV prevalence in Serbian wild boars and emphasizes the importance of monitoring viral infections in wild populations, considering the potential zoonotic and economic implications.

Pathogenicity and immunogenicity of a quadruple gene-deleted pseudorabies virus variant as a vaccine candidate

Since late 2011, the PRV variants have emerged in China, characterized by the increased virulence. The traditional attenuated vaccines have proven insufficient in providing complete protection, resulting in substantial economic losses to swine industry. In this study, a vaccine candidate strain, ZJ01-ΔgI/gE/TK/UL21, carrying the quadruple gene deletion was derived from the previously generated three gene-deleted virus ZJ01-ΔgI/gE/TK. As anticipated, piglets inoculated with ZJ01-ΔgI/gE/TK/UL21 exhibited normal body temperatures and showed no viral shedding, consistent with the observations from piglets treated with ZJ01-ΔgI/gE/TK. Importantly, a significant higher level of interferon induction was observed among piglets in the ZJ01-ΔgI/gE/TK/UL21 group compared to those in the ZJ01-ΔgI/gE/TK group. Upon challenge with the PRV variant ZJ01, piglets immunized with ZJ01-ΔgI/gE/TK/UL21 exhibited reduced viral shedding compared to the ZJ01-ΔgI/gE/TK group. Furthermore, piglets vaccinated with ZJ01-ΔgI/gE/TK/UL21 exhibited minimal pathological lesions in brain tissues, similar to those in the ZJ01-ΔgI/gE/TK group. These results underscore the potential of ZJ01-ΔgI/gE/TK/UL21 as a promising vaccine for controlling PRV infection.

Natto extract inhibits infection caused by the Aujeszky's disease virus in mice

Aujeszky's disease virus (ADV), also known as Suid alphaherpesvirus 1, which mainly infects swine, causes life-threatening neurological disorders. This disease is a serious global risk factor for economic losses in the swine industry. The development of new anti-ADV drugs is highly anticipated and required. Natto, a traditional Japanese fermented food made from soybeans, is a well-known health food. In our previous study, we confirmed that natto has the potential to inhibit viral infections by severe acute respiratory syndrome coronavirus 2 and bovine alphaherpesvirus 1 through their putative serine protease(s). In this study, we found that an agent(s) in natto functionally impaired ADV infection in cell culture assays. In addition, ADV treated with natto extract lost viral infectivity in the mice. We conducted an HPLC gel-filtration analysis of natto extract and molecular weight markers and confirmed that Fraction No. 10 had ADV-inactivating ability. Furthermore, the antiviral activity of Fraction No. 10 was inhibited by the serine protease inhibitor 4-(2-Aminoethyl) benzene sulfonyl fluoride hydrochloride (AEBSF). These results also suggest that Fraction No. 10, adjacent to the 12.5 kDa peak of the marker in natto extract, may inactivate ADV by proteolysis. Our findings provide new avenues of research for the prevention of Aujeszky's disease.

Development of a quadruplex real-time quantitative RT-PCR for detection and differentiation of PHEV, PRV, CSFV, and JEV

Porcine hemagglutinating encephalomyelitis virus (PHEV), porcine pseudorabies virus (PRV), classical swine fever virus (CSFV), and Japanese encephalitis virus (JEV) cause similar neurological symptoms in the infected pigs, and their differential diagnosis depends on laboratory testing. Four pairs of specific primers and probes were designed targeting the PHEV N gene, PRV gB gene, CSFV 5' untranslated region (5'UTR), and JEV NS1 gene, respectively, and a quadruplex real-time quantitative RT-PCR (qRT-PCR) was developed to detect and differentiate PHEV, PRV, CSFV, and JEV. The assay showed high sensitivity, with the limit of detection (LOD) of 1.5 × 101 copies/μL for each pathogen. The assay specifically detected only PHEV, PRV, CSFV, and JEV, without cross-reaction with other swine viruses. The coefficients of variation (CVs) of the intra-assay and the inter-assay were less than 1.84%, with great repeatability. A total of 1,977 clinical samples, including tissue samples, and whole blood samples collected from Guangxi province in China, were tested by the developed quadruplex qRT-PCR, and the positivity rates of PHEV, PRV, CSFV, and JEV were 1.57% (31/1,977), 0.35% (7/1,977), 1.06% (21/1,977), and 0.10% (2/1,977), respectively. These 1,977 samples were also tested by the previously reported qRT-PCR assays, and the coincidence rates of these methods were more than 99.90%. The developed assay is demonstrated to be rapid, sensitive, and accurate for detection and differentiation of PHEV, PRV, CSFV, and JEV.

Epidemiology of Aujeszky disease in wild boars (Sus scrofa L.) in Croatia

Aujeszky disease (AD) or pseudorabies is a viral disease of domestic and wild animals caused by the Suid alphaherpesvirus 1. In wild boar infection usually undergo latent phase but under certain conditions reactivation of the virus can result in a disease. Seroprevalence in wild boars ranges from 0.8 to 100%, and is among other influenced by region, type of management, age and sex of the studied animals. In this study we analyzed blood, lungs, olfactory bulbs and spleen from 222 free-living wild boars from different localities in Croatia and compared results obtained by ELISA with PCR, sex, age and locality. Total seroprevalence was 33.78%, ranging from 25.26% in males to 40.15% in females (p = 0.0346; χ2 = 4.47). According to the age categories prevalence was 10% in offspring, 27.53% in subadults, and 66.75% in adults. Seroprevalence in adult males (66.66%) and females (65.30%) was almost identical. In males, significantly lower seroprevalence was detected in offspring compared to subadults (χ2 = 4.07, p < 0.05) and adults (χ2 = 31.04; p < 0.05), and in subadults compared to adults (χ2 = 15.13; p < 0.0001). Among females, adults had a significantly higher prevalence compared to offspring (χ2 = 19.27; p < 0.0001) and subadults (χ2 = 8.62; p < 0.01). Analysis between counties revealed Sisačko-moslavačka county as a hot-spot for AD. None of the samples was positive for ADV antigens. The observed trend in prevalence points to the fact that the main transmission occurs during one part of the year (most probably the mating season). Also, triggers for virus reactivation might be more complex than previously thought, since none of our samples, collected during the mating and hunting season, was PCR positive. Finally, we can conclude that adult males represent the main transmission link between different wild boar groups.

First Report of Swinepox in a Wild Boar in Italy: Pathologic and Molecular Findings

Swinepox virus (SWPV) is responsible for sporadic acute poxvirus infections in swine worldwide, causing a pathognomonic eruptive proliferative dermatitis. Beside direct and congenital transmission, the pig louse Haematopinus suis acts as a mechanical vector and favors virus infection through skin lesions. Infections are generally described in domestic pigs, while only a few cases have been reported in wild boars, in Austria and Germany. In September 2022, SWPV infection was suspected at post-mortem examination of a wild boar piglet with characteristic lesions in Liguria, Northwest Italy. The piglet was heavily parasitized by swine lice (H. suis). SWPV was then confirmed by histological and molecular analyses. Possible viral co-infections were also investigated (African swine fever virus, classical swine fever virus, parvovirus, circovirus, Aujeszky’s disease virus and hepatitis E virus). This article describes gross and histopathologic features of SWPV infection, differential diagnosis, and potential vector-borne transmission to domestic pigs, presenting a brief review of the literature on the topic. SWPV infection is reported in wild boars in Italy for the first time. The finding of SWPV in a wild boar in an area with a very limited pig population may suggest the existence of a “wildlife cycle” in the area. Further investigations are needed to understand the real risk of transmission of SWPV to domestic pigs as well as the role of other arthropod vectors.

Napyradiomycin A4 and Its Relate Compounds, a New Anti-PRV Agent and Their Antibacterial Activities, from Streptomyces kebangsaanensis WS-68302

Two new napyradiomycins derivatives, napyradiomycin A4 (1) and A80915 H (2), along with five known ones, were isolated from the ethyl acetate extract of fermentation culture of Streptomyces kebangsaanensis WS-68302. Their structures were elucidated by extensive spectroscopic analysis, including HR-MS, 1D and 2D NMR, CD spectrum, as well as comparison with literature data. Compound 1 exhibited significant antiviral activity against PRV (Pseudorabies virus) with an IC₅₀ value of 2.056 μM and therapeutic ratio at 14.98, suggesting that it might have potential for development of an antiviral agent. Moreover, compound 1 displayed the strongest inhibition against PRV protein among the tested napyradiomycins in the indirect immunofuorescence assay. Compounds 3 and 4 showed higher activities against swine pathogenic Streptococcus suis than the positive control penicillin G sodium salt, with MIC values of 3.125 and 6.25 μg/mL, respectively. Compounds 1 and 3-6 exhibited moderate antibacterial activity against the swine pathogenic Erysipelothrix rhusiopathiae, with MIC values ranging from 25 to 50 μg/mL.

Detection of pseudorabies virus antibody in swine serum and oral fluid specimens using a recombinant gE glycoprotein dual-matrix indirect ELISA

Pseudorabies (Aujeszky disease) virus (PRV) was eliminated from domestic swine in many countries using glycoprotein E (gE)-deleted vaccines and serum antibody gE ELISAs, but PRV continues to circulate in some regions and in most feral swine populations in the world. We created a dual-matrix (serum and oral fluid) indirect IgG gE ELISA (iELISA) and evaluated its performance using samples from 4 groups of 10 pigs each: negative control (NC), vaccination (MLV), PRV inoculation (PRV), and vaccination followed by challenge (MLV-PRV). All serum and oral fluid samples collected before PRV challenge and all NC samples throughout the study were negative for gE antibodies by commercial blocking ELISA (bELISA) and our iELISA. Nasal swab samples from 9 of 10 animals in the PRV group were gB quantitative PRC (qPCR) positive at 2 days post-inoculation (dpi). The oral fluid iELISA detected a significant S/P response in the PRV (p = 0.03) and MLV-PRV (p = 0.01) groups by 6 dpi. ROC analyses of serum bELISA (n = 428), serum iELISA (n = 426), and oral fluid iELISA (n = 247) showed no significant differences in performance (p > 0.05). Our data support the concept of PRV surveillance based on oral fluid samples tested by an indirect gE ELISA.

Diagnosis and gI antibody dynamics of pseudorabies virus in an intensive pig farm in Hei Longjiang Province

Background

Pseudorabies (PR), caused by the pseudorabies virus (PRV), is an endemic disease in some regions of China. Although there are many reports on epidemiological investigations into pseudorabies, information on PRV gI antibody dynamics in one pig farm is sparse.

Objectives

To diagnose PR and analyze the course of PR eradication in one pig farm.

Methods

Ten brains and 1,513 serum samples from different groups of pigs in a pig farm were collected to detect PRV gE gene and PRV gI antibody presence using real-time polymerase chain reaction and enzyme-linked immunosorbent assay, respectively.

Results

The July 2015 results indicated that almost all brain samples were PRV gE gene positive, but PRV gI antibody results in the serum samples of the same piglets were all negative. In the boar herd, from October 2015 to July 2018 three positive individuals were culled in October 2015, and the negative status of the remaining boars was maintained in the following tests. In the sow herd, the PRV gI antibody positive rate was always more than 70% from October 2015 to October 2017; however, it decreased to 27% in January 2018 but increased to 40% and 52% in April and July 2018, respectively. The PRV gI antibody positive rate in 100-day pigs markedly decreased in October 2016 and was maintained at less than 30% in the following tests. For 150-day pigs, the PRV gI antibody positive rate decreased notably to 10% in April 2017 and maintained a negative status from July 2017. The positive trend of PRV gI antibody with an increase in pig age remarkably decreased in three tests in 2018.

Conclusions

The results indicate that serological testing is not sensitive in the early stage of a PRV infection and that gilt introduction is a risk factor for a PRV-negative pig farm. The data on PRV gI antibody dynamics can provide reference information for pig farms wanting to eradicate PR.

Detection of pseudorabies virus with a real-time recombinase-aided amplification assay

Pseudorabies (PR) is an acute infectious disease of pigs caused by pseudorabies virus (PRV), which has caused great economic losses to the pig industry worldwide. Reliable and timely diagnose is crucial for the surveillance, control and eradication of PR. Here, a real-time fluorescent recombinase-aided amplification (real-time RAA) assay was established to detect PRV. Primers and probes were designed based on the conserved regions of the PRV gE gene. The assay was specific for the detection of wild-type PRV, showing no cross-reactivity with other important porcine viruses (including PRV gE-deleted vaccine strains). Analytical sensitivity of the assay was three 50% tissue culture infectious doses (TCID₅₀ ) of PRV DNA per reaction with 95% reliability, which is comparable to that of a PRV-specific real-time PCR (qPCR) assay. In diagnosis of 206 clinical tissue samples, the diagnose accordance rate between the real-time RAA assay and qPCR assay was 97.57% (201/206). Interestingly, the amplified products of real-time RAA could be visualized under a portable blue light instrument, making it possible for the rapid detection of PRV in resource-limited settings and on-site screening. Therefore, our developed real-time RAA assay is a diagnostic method for the rapid detection of PRV in the field.

Detection and genetic analysis of a novel atypical porcine pestivirus from piglets with congenital tremor in Japan

Atypical porcine pestivirus (APPV), which has been confirmed to be associated with congenital tremor (CT) in pigs, is a newly discovered porcine virus that has been found in the Americas, Europe and Asia; however, no report of APPV in Japan has been published. We identified an APPV in the central nervous system of Japanese piglets with CT and firstly determined and analysed the complete genome sequence. Phylogenetic analysis using the complete genome nucleotide sequence of the Japanese APPV, named Anna/2020, and those of APPVs from the NCBI database showed that APPVs were divided into three genotypes (genotypes 1 to 3), and that Anna/2020 clustered with the genotype 3 APPV strains, but distantly branched from these strains. Pairwise complete coding region nucleotide sequence comparisons revealed that there was 94.0%- 99.7% sequence identity among the genotype 3 strains, while Anna/2020 showed 87.0%-89.3% identity to those genotype 3 strains, suggesting that Anna/2020 represents a novel APPV lineage within genotype 3. Retrospective examinations using RT-PCR revealed one genotype 1 and two novel genotype 3 APPVs from pigs without CT, and that novel genotype 3 APPVs have been prevalent in Japan since at least 2007.

Pseudorabies (Aujeszky's disease) virus DNA detection in swine nasal swab and oral fluid specimens using a gB-based real-time quantitative PCR

In this study, the detection of PRV DNA in nasal swab (n = 440) and oral fluid (n = 1,545) samples collected over time from experimentally PRV vaccinated and/or PRV inoculated pigs (n = 40) was comparatively evaluated by real-time PCR. Serum samples (n = 440) were tested by PRV gB/gE blocking ELISAs (Pseudorabies Virus gB Antibody Test Kit and Pseudorabies Virus gpI Antibody Test Kit, IDEXX Laboratories, Inc., Westbrook, ME) to monitor PRV status over time. Following exposure to a gE-deleted modified live vaccine (Ingelvac® Aujeszky MLV, Boehringer Ingelheim, Ridgefield, CT) and/or a wild-type virus (3 CR Ossabaw), PRV gB DNA was detected in oral fluid specimens in a pattern similar to that of nasal swabs. For quantitative analyses, PRV PCR quantification cycle (Cq) results were re-expressed as "efficiency standardized Cqs (ECqs)" as a function of PCR efficiency using plate-specific positive amplification controls. ROC analyses of the PRV gB PCR ECqs results showed a similar performance of the PRV gB PCR for nasal swab and oral fluid specimens (area under the ROC curve = 85 % vs 83 %) and, based on an ECq cutoff of 0.01 a diagnostic specificity of 100 % and diagnostic sensitivities for oral fluid and nasal swab specimens of 53 % (95 % CI: 43 %, 62 %) and 70 % (95 % CI: 55 %, 83 %), respectively. Thus, the results described herein demonstrated the detection of PRV gB DNA in swine oral fluid and supported the use of this specimen in PRV diagnosis and surveillance.

Simultaneous identification of 6 pathogens causing porcine reproductive failure by using multiplex ligation-dependent probe amplification

We developed a multiplex ligation-dependent probe amplification (MLPA) assay for the simultaneous detection of 6 clinically relevant viral pathogens causing porcine reproductive failure, that is porcine reproductive and respiratory syndrome virus (PRRSV), Japanese encephalitis virus (JEV), classical swine fever virus (CSFV), porcine circovirus type 2 (PCV2), pseudorabies virus (PRV) and porcine parvovirus (PPV). The limits of detection for the assay varied among the 6 target organisms from 1 to 8 copies per MLPA assay. The MLPA assay was evaluated with 346 heparinized porcine umbilical cord blood specimens, and the results of the assay were compared to those of real-time PCR. The MLPA assay showed specificities and sensitivities of 99.2% and 100%, respectively, for PRRSV; 100% and 100%, respectively, for CSFV, PCV2, PRV and PPV. No sample was found to be positive for JEV by either the MLPA assay or the real-time PCR. In conclusion, the MLPA assay has comparable clinical sensitivity to that of real-time PCR assay and provides a useful tool for fast screening porcine reproductive failure-associated viruses.

Canine parvovirus and pseudorabies virus coinfection as a cause of death in a wolf (Canis lupus) from southern Italy

Pseudorabies virus (PRV) or suid herpesvirus 1 (SHV‐1) is the causative agent of Aujeszky's disease, a highly contagious viral infection which causes neurological fatal illness in mammals other than suids. Here we report a case of a young wolf (Canis lupus) of around 2 years found dead by a hunter in the province of Avellino, Campania Region. Necropsy showed pathological findings consistent with encephalitis and gastroenteritis. Organs were analysed by microbiological and molecular investigations following standard procedures to ascertain the possible cause of death. Real‐time PCR revealed the presence of PRV in the brain and of canine parvovirus 2b in organs like intestine, liver, brain, kidney and pancreas. Death probably occurred very shortly after SHV‐1 infection in an animal already weakened by parvovirosis.

Detection of a gE-deleted Pseudorabies virus strain in an Italian red fox

This study describes an Aujeszky's disease case in an adult male red fox found in an urban area in Central Italy, that exhibited a fatal infection with neurological lesions, but neither itching nor skin lesions. Diagnostic examinations included histology, and parasitological, bacteriological and virological analyses. Detection of parasitic enteric pathogens, bacteria, E. coli, Leptospira spp., rabies, canine distemper virus, parvovirus, hepatitis E virus and pseudorabies virus (PrV) was performed. Results showed the presence of a gE-deleted PrVthat was closely related to the NIA-3 strain but differed from the PrV strains currently circulating in wild boars and domestic pigs in Italy. All the results led to the conclusion that the fox suffered from Aujeszky's disease caused by a gE-deleted PrV strain closely related to a vaccine strain. The epidemiological link between the PrV vaccine strain and fox infection remains unclear. It could involve vaccinated pigs as a primary source of infection by direct or indirect contact with the red fox or less likely it could be related to improper use of the vaccine in the fox.

Current Swine Respiratory Diseases Morphology in Intensive Swine Production in Serbia

Swine respiratory diseases represent one of the most frequent health issues in pig production worldwide. Despite the great progress that has been made in the field of diagnostics, control and prophylaxis, respiratory diseases still remain the most challenging health problem in modern commercial pig production. The list of infectious agents that cause respiratory diseases in swine is extensive and includes both, bacterial and viral pathogens. In Serbia, more than fifteen years after the introduction of modern vaccines, the list of bacterial pathogens related to swine respiratory infections still include Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Haemophilus parasuis and Pasteurella multocida. On the other hand, most commonly involved viral pathogens are Porcine Reproductive and Respiratory Syndrome Virus, Swine influenza virus, Porcine circovirus type 2 and Pseudorabies virus. The morphological features of pneumonia where several agents are involved, depend on the predominant etiological agent. Expanding knowledge of the main pathogens associated with swine respiratory diseases and the effects of their interactions on the disease outcome is important for further investigations of lung diseases and implementation of control strategies in commercial pig populations in Serbia. This review discusses the latest findings on swine respiratory disease and current trends in Serbian pig production.

Development of a one-run real-time PCR detection system for pathogens associated with porcine respiratory diseases

The etiology of Porcine respiratory disease complex is complicated by infections with multiple pathogens, and multiple infections increase the difficulty in identifying the causal pathogen. In this present study, we developed a detection system of microbes from porcine respiratory by using TaqMan real-time PCR (referred to as Dempo-PCR) to screen a broad range of pathogens associated with porcine respiratory diseases in a single run. We selected 17 porcine respiratory pathogens (Actinobacillus pleuropneumoniae, Boldetella bronchiseptica, Haemophilus parasuis, Pasteurella multocida, Pasteurella multocida toxin, Streptococcus suis, Mycoplasma hyopneumoniae, Mycoplasma hyorhinis, Mycoplasma hyosynovie, porcine circovirus 2, pseudorabies virus, porcine cytomegalovirus, swine influenza A virus, porcine reproductive and respiratory virus US strain, EU strain, porcine respiratory coronavirus and porcine hemagglutinating encephalomyelitis virus) as detection targets and designed novel specific primer-probe sets for seven of them. In sensitivity test by using standard curves from synthesized DNA, all primer-probe sets showed high sensitivity. However, porcine reproductive and respiratory virus is known to have a high frequency of genetic mutations, and the primer and probe sequences will need to be checked at a considerable frequency when performing Dempo-PCR from field samples. A total of 30 lung samples from swine showing respiratory symptoms on six farms were tested by the Dempo-PCR to validate the assay’s clinical performance. As the results, 12 pathogens (5 virus and 7 bacteria) were detected and porcine reproductive and respiratory virus US strain, Mycoplasma hyorhinis, Haemophilus parasuis, and porcine cytomegalovirus were detected at high frequency. These results suggest that Dempo-PCR assay can be applied as a screening system with wide detection targets.

Isolation and molecular characterization of a variant of Chinese gC-genotype II pseudorabies virus from a hunting dog infected by biting a wild boar in Japan and its pathogenicity in a mouse model

We isolated a variant of Chinese pseudorabies virus from a hunting dog with symptoms similar to Aujeszky's disease and designated the isolate MY-1 strain. The dog developed symptoms 6 days after hunting and biting a wild boar and died the day after onset. The Bam HI restriction profile of MY-1 DNA was different from those of the Japanese reference strain Yamagata-S81 and two vaccine strains, Bartha and Begonia, and resembled Bam HI-RFLP (restriction fragment length polymorphism) type IV. Complete nucleotide sequences were determined, and phylogenetic analyses revealed that MY-1 belonged to the same cluster of old Chinese strains and variant strains isolated recently in China, but most of the open reading frames of MY-1 were located on a different branch from those of these Chinese strains. Based on a gC phylogenetic analysis, MY-1 belonged to gC-genotype II composed of those Chinese strains. In mice, the 50% lethal dose (LD₅₀) of MY-1 (10^3.0 TCID₅₀) was almost the same as those of Yamagata-S81 and Bartha. The LD₅₀ value of Begonia was 10^≥4.5 TCID₅₀. The mean survival periods of mice after infection with 10⁴ TCID₅₀ of MY-1, Yamagata-S81 and Bartha were 3.9 days, 2.3 days, and 8.0 days, respectively. The results suggested that the variant of Chinese PRV with slightly weaker pathogenicity than that of wild virulent viruses might be maintained in wild boars in Japan. Furthermore, we would like to propose that old Chinese strains, recent Chinese variant strains, and MY-1 should be grouped as an Asian type PRV.

Pseudorabies detected in hunting dogs in Alabama and Arkansas after close contact with feral swine (Sus scrofa)

Background

Pigs (Sus scrofa) are the natural hosts of pseudorabies virus (PRV), also known as Aujeszky’s disease. Infection in mammals, with the exception of humans, typically causes extreme itching, facial swelling, and excessive salivation, followed by death in non-suid species. The risk to susceptible mammals was assumed to decrease when PRV was eliminated from U.S. commercial swine in 2004, though the virus remains endemic in feral swine. Infected feral swine pose a threat to the disease-free status of the commercial swine industry, and to other animals, including dogs, that come in direct or indirect contact with them. Since dogs are commonly used for hunting feral swine, they are at high risk of exposure.

Case presentation

The following report describes the progression of pseudorabies infection in dogs in two states after exposure to feral swine. The first case occurred in a dog in Alabama after participation in a competitive wild hog rodeo. The second case occurred in multiple dogs in Arkansas after hunting feral swine, and subsequent consumption of the offal. The antibody prevalence of feral swine in the two states where the dogs were exposed is also examined.

Conclusions

Dogs that are used for hunting feral swine are at high risk of exposure to pseudorabies because the disease is considered endemic in feral swine in the U.S.

Antiviral Effect of Resveratrol in Piglets Infected with Virulent Pseudorabies Virus

Pseudorabies virus (PRV) is one of the most important pathogens of swine, resulting in devastating disease and economic losses worldwide. Nevertheless, there are currently no antiviral drugs available for PRV infection. Resveratrol (Res) was identified to exert its antiviral activity by inhibiting the PRV replication in preliminary investigations. In our previous study, we found that Res has anti-PRV activity in vitro. Here, we show that Res can effectively reduce the mortality and increase the growth performance of PRV-infected piglets. After Res treatment, the viral loads significantly (p < 0.001) decreased. Pathological symptoms, particularly inflammation in the brain caused by PRV infection, were significantly (p < 0.001) relieved by the effects of Res. In Res-treated groups, higher levels of cytokines in serum, including interferon gama, interleukin 12, tumor necrosis factor-alpha and interferon alpha were observed at 7 days post infection. These results indicated that Res possesses potent inhibitory activity against PRV-infection through inhibiting viral reproduction, alleviating PRV-induced inflammation and enhancing animal immunity, suggesting that Res is expected to be a new alternative control measure for PRV infection.

Detection of Aujeszky's disease virus DNA and antibody in swine oral fluid specimens

Aujeszky's disease virus (ADV) continues to circulate in commercial swine populations in many regions and in feral swine populations in most parts of the world, that is, ADV continues to present a risk to pork producers everywhere. Current DIVA vaccines and assays are highly effective in the control and/or eradication of ADV, but detection of wild-type ADV infection relies on testing individual pig specimens, for example, serum or muscle exudate ("meat juice"). Oral fluid specimens have been shown to be highly effective for the surveillance of a variety of swine pathogens and could offer the means to improve the efficiency of ADV surveillance in the field. In this study, the temporal patterns of ADV DNA and antibody detection in oral fluid and serum specimens were established in ADV-inoculated pigs (n = 14) using gB and gE PCRs, virus neutralization (VN) and three commercial serum antibody ELISAs (gB bELISA, gI bELISA and ADV iELISA). ADV DNA was detected in oral fluid samples (20% to 100%) from 3 to 21 days postinoculation (DPI), but not in serum. ADV antibody was detected in oral fluid specimens at DPI ≥ 10 with the gB bELISA (36% to 79%) and ADV iELISA (29% to 100%), but not the gI bELISA. These results suggest that oral fluid could be used as an alternative to individual pig sampling for ADV surveillance using PCR- and/or antibody-based assays.

Human Endophthalmitis Caused By Pseudorabies Virus Infection, China, 2017

We report human endophthalmitis caused by pseudorabies virus infection after exposure to sewage on a hog farm in China. High-throughput sequencing and real-time PCR of vitreous humor showed pseudorabies virus sequences. This case showed that pseudorabies virus might infect humans after direct contact with contaminants.

Polymorphisms affecting the gE and gI proteins partly contribute to the virulence of a newly-emergent highly virulent Chinese pseudorabies virus

An outbreak of a highly virulent pseudorabies virus strain, ZJ01, occurred in PRV-vaccinated pigs in China in 2011. In this study, ZJ01 caused fatal diseases, while the Chinese prototypic PRV strain LA caused mild respiratory disorders. Full-genome sequencing results indicate the two viruses can be classified into two sub-clusters that distinct from traditional European and US strains. To examine the potential role of the gE and gI proteins in ZJ01 virulence, we generated several recombinant viruses. In two chimeric viruses (rZJ01-LA/gEI and rLA-ZJ01/gEI), the gE and gI genes were swapped using corresponding genes from ZJ01 and LA. rZJ01-LA/gEI and the parental virus rZJ01 retained high virulence in piglets, although the survival time for rZJ01-LA/gEI infected piglets was obviously prolonged. In contrast, rLA-ZJ01/gEI exhibited higher virulence than its parental virus rLA. We conclude that changes in gE and gI proteins partly contribute to the enhanced virulence of ZJ01 strain.

Detection of pseudorabies virus by duplex droplet digital PCR assay

Aujeszky's disease, caused by pseudorabies virus (PRV), has damaged the economy of the Chinese swine industry. A large number of PRV gene-deleted vaccines have been constructed based on deletion of the glycoprotein E ( gE) gene combined with other virulence-related gene deletions, such as thymidine kinase ( TK), whereas PRV wild-type strains contain an intact gE gene. We developed a sensitive duplex droplet digital PCR (ddPCR) assay to rapidly detect PRV wild-type isolates and gE gene-deleted viral vaccines. We compared this assay with a TaqMan real-time PCR (qPCR) using the same primers and probes. Both assays exhibited good linearity and repeatability; however, ddPCR maintained linearity at extremely low concentrations, whereas qPCR did not. Based on positive results for both gE and gB, the detection limit of ddPCR was found to be 4.75 copies/µL in contrast of 76 copies/µL for qPCR, showing that ddPCR provided a 16-fold improvement in sensitivity. In addition, no nonspecific amplification was shown in specificity testing, and the PRV wild-type was distinguished from a gE-deleted strain. The ddPCR was more sensitive when analyzing clinical serum samples. Thus, ddPCR may become an appropriate detection platform for PRV.

Genetic and pathogenic characterization of a Russian subtype 2 PRRSV-1 isolate

Porcine reproductive and respiratory syndrome virus (PRRSV) causes reproductive failure and respiratory problems. Data about the virulence and pathogenicity of subtype 2 PRRSV-1 strains are limited. The main purposes of this investigation were to characterize the full genome sequence of the subtype 2 PRRSV-1 WestSib13 strain and to compare the pathogenicity with that of the subtype 1 PRRSV-1 Lelystad strain. Comparison of the whole genome sequence of the WestSib13 strain with that of PRRSV-1 prototype strains revealed a 76.2% (subtype 1 Lelystad virus) and 79.0% (subtype 3 Lena virus) identity, respectively The virulence and pathogenicity of the European subtype 2 PRRSV strain WestSib13 and the European subtype 1 PRRSV strain Lelystad were compared in 3-week-old piglets upon inoculation of 10^5.4 TCID₅₀ of virus. Non-infected animals (control group) as well as animals infected with the Lelystad strain were clinically healthy until 14days post challenge. In contrast, animals infected with the WestSib13 strain demonstrated dyspnea starting at 3days post-inoculation (dpi). All piglets in this group died between 5 and 8 dpi. During that period, fever was not observed in WestSib13-infected animals. Viremia was detected in animals from both infected groups starting from 2 dpi. Viral loads in serum and lungs upon euthanasia were significantly higher (3 log₁₀) in the WestSib13-infected than in the LV-infected animals. Taken together, this study provides the full genome sequence and the unusual virological and clinical outcome (high level viremia without fever) of the novel WestSib13 strain.

Antiviral properties of resveratrol against pseudorabies virus are associated with the inhibition of IκB kinase activation

Pseudorabies virus (PRV) is a pathogen of swine resulting in devastating disease and economic losses worldwide. Resveratrol (Res) exhibits inhibitory activity against a wide range of viruses. Despite these important advances, the molecular mechanism(s) by which Res exerts its broad biological effects have not yet been elucidated. In this paper, the antiviral activity of Res against PRV and its mechanism of action were investigated. The results showed that Res potently inhibited PRV replication in a dose-dependent manner, with a 50% inhibition concentration of 17.17 μM. The inhibition of virus multiplication in the presence of Res was not attributed to direct inactivation or inhibition of viral entry into the host cells but to the inhibition of viral multiplication in host cells. Further studies demonstrated that Res is a potent inhibitor of both NF-κB activation and NF-κB-dependent gene expression through its ability to inhibit IκB kinase activity, which is the key regulator in NF-κB activation. Thus, the inhibitory effect of Res on PRV-induced cell death and gene expression may be due to its ability to inhibit the degradation of IκB kinase. These results provided a new alternative control measure for PRV infection and new insights into the antiviral mechanism of Res.

Development of a rapid, simple, and specific real-time PCR assay for detection of pseudorabies viral DNA in domestic swine herds

Despite successful eradication of pseudorabies virus (PRV) from the commercial pig industry in the United States in 2004, large populations of feral swine in certain regions act as wildlife reservoirs for the virus. Given the threat of reintroduction of the virus into domestic herds, a rapid, reliable, easily implemented assay is needed for detection of PRV. Although a real-time PCR (rtPCR) assay exists, improvements in rtPCR technology and a greater understanding of the diversity of PRV strains worldwide require an assay that would be easier to implement, more cost effective, and more specific. We developed a single-tube, rapid rtPCR that is capable of detecting 10 copies of PRV glycoprotein B ( gB) DNA per 20-µL total volume reaction. The assay did not produce a false-positive in samples known to be negative for the virus. The assay was negative for genetically similar herpesviruses and other porcine viruses. Our assay is a highly specific and sensitive assay that is also highly repeatable and reproducible. The assay should be a useful tool for early detection of PRV in pigs in the case of a suspected introduction or outbreak situation.

Detection of a novel sapelovirus in central nervous tissue of pigs with polioencephalomyelitis in the USA

An approximately 3,000 finishing swine operation in the United States experienced an outbreak of an atypical neurologic disease in 11-weeks-old pigs with an overall morbidity of 20% and case fatality rate of 30%. The clinical onset and progression of signs in affected pigs varied but included inappetence, compromised ambulation, ataxia, incoordination, mental dullness, paresis, paralysis and decreased response to environmental stimuli. Tissues from affected pigs were submitted for diagnostic investigation. Histopathologic examination of the cerebrum, cerebellum and spinal cord revealed severe lymphoplasmacytic and necrotizing polioencephalomyelitis with multifocal areas of gliosis and neuron satellitosis, suggestive of a neurotropic viral infection. Bacterial pathogens were not isolated by culture of neurologic tissue from affected pigs. Samples tested by polymerase chain reaction (PCR) were negative for pseudorabies virus and atypical porcine pestivirus. Immunohistochemistry for porcine reproductive and respiratory syndrome virus, porcine circovirus and Listeria was negative. Porcine sapelovirus (PSV) was identified in spinal cord by a nested PCR used to detect porcine enterovirus, porcine teschovirus and PSV. Next-generation sequencing of brainstem and spinal cord samples identified PSV and the absence of other or novel pathogens. In addition, Sapelovirus A mRNA was detected in neurons and nerve roots of the spinal cord by in situ hybridization. The PSV is genetically novel with an overall 94% amino acid identity and 86% nucleotide identity to a recently reported sapelovirus from Korea. This is the first case report in the United States associating sapelovirus with severe polioencephalomyelitis in pigs.

Bartha-k61 vaccine protects growing pigs against challenge with an emerging variant pseudorabies virus

Since late 2011, pseudorabies (PR) has resurfaced in many large pig farms, causing great economic loss for the swine industry in China. The PRV variant strain with high virulence and antigenic variation has been considered to be the main cause, and much attention has been focused on how to prevent and control the reoccurrence of this disease in China. In this study, two kinds of vaccination strategy were employed to evaluate the protective effects of Bartha-k61vaccine against both variant PRV (XJ5) and classical PRV (Ra) strain challenge. Humoral immunity response, clinical signs, survival rate, body weight, virus shedding and pathology were assessed in commercial pigs. The results showed that Bartha-k61vaccine, administered either once or twice, was effective against the PRV variant (XJ5) challenge, while no significant differences were observed between single and prime-boost vaccinated pigs. However, pigs vaccinated twice had better body weight gains than those vaccinated once, following challenge with the classical PRV strain (Ra) (p<0.01). Therefore, the Bartha-k61 vaccine appears to be an effective vaccine to control the spread of PRV variants in China in the absence of new powerful candidate vaccines specific to these PRV strains.

Comparative pathogenicity and immunogenicity of triple and double gene-deletion pseudorabies virus vaccine candidates

Pseudorabies (PR) outbreaks have re-emerged in many pig farms with vaccination coverage in China, which suggests that current vaccine strains provide poor protection against novel, epidemic strains. In this study, based on the highly virulent PRV ZJ01 variant, a PR virus (PRV) thymidine kinase (TK)/gE/gI deleted strain-rZJ01ΔTK/gE/gI-was generated, which showed similar growth features in vitro compared to the parent strain PRV ZJ01 and its gE/gI deleted strain rZJ01ΔgE/gI. The results of a piglet experiment (with 10 piglets each group) showed that the rZJ01ΔTK/gE/gI vaccine generated similar levels of neutralizing antibodies against ZJ01 compared to the rZJ01ΔgE/gI vaccine (p>0.05). However, rZJ01ΔgE/gI inoculation resulted in slight inflammatory cell infiltrations, hemorrhages, and congestion in the brain and lungs. After a ZJ01 challenge, all animals in the rZJ01ΔTK/gE/gI- and rZJ01ΔgE/gI-vaccinated groups survived without exhibiting any clinical symptoms, whereas all non-vaccinated control animals died within 7days post-challenge. Furthermore, microscopic lesions and virus loads in the brains and lungs in the two vaccinated groups were significantly lower than those in the control group. Meanwhile, the virus levels in the brains of piglets in the rZJ01ΔTK/gE/gI group were significantly lower than those in the rZJ01ΔgE/gI group. These results indicate that the triple gene-deleted PRV rZJ01ΔTK/gE/gI strain has lower pathogenicity and higher protective efficacy against variant PRV challenge compared with the double gene-deleted PRV rZJ01ΔgE/gI strain. Together, all these data indicate that the PRV rZJ01ΔTK/gE/gI strain should be an ideal vaccine candidate for the prevention of PR in China.

Pseudorabies virus infection (Aujeszky's disease) in an Iberian lynx (Lynx pardinus) in Spain: a case report

Background

The only natural hosts of Pseudorabies virus (PRV) are members of the family Suidae (Sus scrofa scrofa). In species other than suids infection is normally fatal. In these mammals, including carnivores, PRV typically causes serious neurologic disease. The endangered Iberian lynx (Lynx pardinus) is a wild feline endemic to south-western Europe (Iberian Peninsula). The Iberian lynx was found to be the world’s most endangered felid species in 2002. In wild felines, PRV infection has only been previously reported once in a Florida panther in 1994. No seropositive lynxes have ever been found, nor has PRV been detected in dead Iberian lynxes to date.

Case presentation

We describe the first reported case of pseudorabies in an Iberian lynx (Lynx pardinus). Pseudorabies was diagnosed in a young wild Iberian lynx from Extremadura (SW Spain) by histopathological examination, immunohistochemistry, polymerase chain reaction (PCR) and sequence analysis. Gross lesions included alopecia of the ventral neck, bloody gastro-intestinal contents and congestion of the brain. Histopathological analysis showed a moderate nonsuppurative meningoencephalitis with diffuse areas of demyelination, necrotizing gastritis and enteritis of the small intestine. Pseudorabies virus (PRV) antigen was found in neuronal and non-neuronal cells of the brain, tonsils, and gastric glandular epithelial cells by immunohistochemical analysis. The presence of the virus in the brain was confirmed by nested PCR. The sequence analysis of the 146 bp fragment (from the viral glycoprotein B gene) showed that the amplified sequence matched (with 100% identity) the PRV genome. Furthermore, specific DNA from glycoprotein D and E encoding-genes was detected by conventional and real-time PCR, respectively, confirming the latter that this infection was produced by a wild-type PRV strain.

Conclusions

This study supports the suspicion that PRV could infect the Iberian lynx. The detection of PRV in a dead Iberian lynx suggests that the virus may have a negative impact on the survival of endangered lynxes in the wild. However, because this is the first verified instance of lynx mortality resulting from pseudorabies, its true impact on the population is unknown.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0938-7) contains supplementary material, which is available to authorized users.

A multiplex real-time PCR panel assay for simultaneous detection and differentiation of 12 common swine viruses

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A multiplex real-time PCR panel assay was developed for the detection of 12 major swine pathogens including VSV-IN, VSV-NJ, SVDV, CSFV, ASFV, FMDV, PCV2, PPV, PRV, PRRSV-NA, PRRSV-EU;.

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The panel assay was 100% specific against common swine pathogens;.

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Limits of detection of the assay were ranged 1–16 copies per reaction;.

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Detection sensitivity was not reduced by multiplexing three targets into one PCR reaction.

Mixed infection with different pathogens is common in swine production systems especially under intensive production conditions. Quick and accurate detection and differentiation of different pathogens are necessary for epidemiological surveillance, disease management and import and export controls. In this study, we developed and validated a panel of multiplex real-time PCR/RT-PCR assays composed of four subpanels, each detects three common swine pathogens. The panel detects 12 viruses or viral serotypes, namely, VSV-IN, VSV-NJ, SVDV, CSFV, ASFV, FMDV, PCV2, PPV, PRV, PRRSV-NA, PRRSV-EU and SIV. Correlation coefficients (R²) and PCR amplification efficiencies of all singular and triplex real-time PCR reactions are within the acceptable range. Comparison between singular and triplex real-time PCR assays of each subpanel indicates that there is no significant interference on assay sensitivities caused by multiplexing. Specificity tests on 226 target clinical samples or 4 viral strains and 91 non-target clinical samples revealed that the real-time PCR panel is 100% specific, and there is no cross amplification observed. The limit of detection of each triplex real-time PCR is less than 10 copies per reaction for DNA, and less than 16 copies per reaction for RNA viruses. The newly developed multiplex real-time PCR panel also detected different combinations of co-infections as confirmed by other means of detections.

Antiviral activities of 2,6-diaminopurine-based acyclic nucleoside phosphonates against herpesviruses: In vitro study results with pseudorabies virus (PrV, SuHV-1)

Pseudorabies virus (PrV), a causative agent of Aujeszky's disease, is deadly to most mammals with the exception of higher primates and men. This disease causes serious economic loses among farm animals, especially pigs, yet many European countries are today claimed to be Aujeszky's disease free because of the discovery of an efficient vaccination for pigs. In reality, the virus is still present in wild boar. Current vaccines are neither suitable for dogs nor are there anti-PrV drugs approved for veterinary use. Therefore, the disease still represents a high threat, particularly for expensive hunting dogs that can come into close contact with infected boars. Here we report on the anti-PrV activities of a series of synthetic diaminopurine-based acyclic nucleoside phosphonate (DAP-ANP) analogues. Initially, all synthetic DAP-ANPs under investigation are shown to exhibit minimal cytotoxicity by MTT and XTT tests (1-100μM range). Thereafter in vitro infection models are established using PrV virus SuHV-1, optimized on PK-15 and RK-13 cell lines. Out of the six DAP-ANP analogues tested, analogue VI functionalized with a cyclopropyl group on the 6-amino position of the purine ring proves the most effective antiviral DAP-ANP analogue against PrV infection, aided by sufficient hydrophobic character to enhance bioavailability to its cellular target viral DNA-polymerase. Four other DAP-ANP analogues with functional groups introduced to the C2'position are shown ineffective against PrV infection, even with favourable hydrophobic properties. Cidofovir(®), a drug approved against various herpesvirus infections, is found to exert only low activity against PrV in these same in vitro models.

Long-Term Surveillance of Aujeszky's Disease in the Alpine Wild Boar (Sus scrofa)

Although wild boar can act as a persistent Aujeszky's disease (AD) reservoir, limited data are available on long-term epidemiology in free-ranging wild boar living in areas where industrial swine herds are limited. Hence, this study provides crucial information, which fills this knowledge gap, on the natural dynamics of AD infection. From 3260 sera sampled during eight hunting seasons, 162 (4.97%) were tested positive. Factors, including the animal's age class, and the sampling year, had significant effects on the probability of the wild boar being seropositive, while wild boar mean abundance per area, yearly abundance and the total number of pig farms, as well as interactions among age, year and sex, were not significant. In particular, a positive trend of seroprevalence was observed over the years, with values ranging from 2.1 to 10.8%. This long-term surveillance showed an increase in seroprevalence with a higher probability of being seropositive in older individuals and the independence of wild boar seropositivity from the likelihood of contact with pigs in the area.

Pseudorabies virus US3 leads to filamentous actin disassembly and contributes to viral genome delivery to the nucleus

The conserved alphaherpesvirus US3 tegument protein induces rearrangements of the actin cytoskeleton, consisting of protrusion formation and stress fiber breakdown. Although US3 does not affect levels of total actin protein, it remains unclear whether US3 modulates the total levels of filamentous (F) actin. In this report, we show that the pseudorabies virus (PRV) US3 protein, via its kinase activity, leads to disassembly of F-actin in porcine ST cells. F-actin disassembly has been reported before to contribute to host cell entry of HIV. In line with this, in the current study, we report that US3 has a previously uncharacterized role in viral genome delivery to the nucleus, since quantitative polymerase chain reaction (qPCR) assays on nuclear fractions demonstrated a reduced nuclear delivery of US3null PRV compared to wild type PRV genomes. Treatment of cells with the actin depolymerizing drug cytochalasin D enhanced virus genome delivery to the nucleus, particularly of US3null PRV, supporting a role for F-actin disassembly during certain aspects of viral entry. In conclusion, the US3 kinase of PRV leads to F-actin depolymerization, and US3 and F-actin disassembly contribute to viral genome delivery to the nucleus.

A novel inactivated gE/gI deleted pseudorabies virus (PRV) vaccine completely protects pigs from an emerged variant PRV challenge

A highly virulent and antigenic variant of pseudorabies virus (PRV) broke out in China at the end of 2011 and caused great economic loss in the pig industry. In this study, an infectious bacterial artificial chromosome (BAC) clone containing the full-length genome of the emerged variant PRV ZJ01 strain was generated. The BAC-derived viruses, vZJ01-GFPΔgE/gI (gE/gI deleted strain, and exhibiting green autofluorescence), vZJ01ΔgE/gI (gE/gI deleted strain), and vZJ01gE/gI-R (gE/gI revertant strain), showed similar in vitro growth to their parent strain. In pigs, inactivated vZJ01ΔgE/gI vaccine generated significantly high levels of neutralizing antibodies against ZJ01 compared with Bartha-K61 live vaccine (p<0.05). After fatal ZJ01 challenge, all five animals in the inactivated vZJ01ΔgE/gI vaccine group survived without exhibiting any clinical sings, but two of five animals exhibited central nervous signs in the Bartha-K61 group. Meanwhile, all the non-vaccinated control animals died at 7 days post-challenge. This indicates that the inactivated vZJ01ΔgE/gI vaccine is a promising vaccine candidate for controlling the variant strains of PRV now circulating in China.

Molecular double-check strategy for the identification and characterization of Suid herpesvirus 1

Large scale vaccination with glycoprotein E (gE)-deleted marker vaccines and the rapid and reliable differentiation of wild-type and marker vaccine strains are important aspects in eradication programs for Suid herpesvirus 1 [SuHV-1, syn. Aujeszky's disease virus (ADV) or pseudorabies virus (PrV)]. Therefore, two multiplex real-time PCR (qPCR) assays for the genetic differentiation of wild-type and gE-deleted vaccine SuHV-1 strains have been developed. In the first multiplex qPCR SuHV-1 gB-gene specific detection was combined with a gE-gene specific assay and an internal control based on heterologous DNA. In the second system, a SuHV-1 UL19 (major capsid protein gene) assay, a different gE-gene specific assay and an internal control based on the beta-actin gene were combined. The gB-gene, UL19 as well as both gE-gene specific assays had an analytical sensitivity of less than 10 genome copies per reaction in the respective multiplex approaches. A series of reference strains including field isolates obtained from domestic and wild animals, and gE-deleted SuHV-1 were reliably detected, while genetically related non-SuHV-1 herpesviruses tested negative. Both newly developed triplex SuHV-1-specific qPCR assays are specific and sensitive methods for the rapid genetic differentiation of wild-type viruses and gE-deleted vaccine strains in a single reaction.

A nanoparticle-assisted PCR assay to improve the sensitivity for rapid detection and differentiation of wild-type pseudorabies virus and gene-deleted vaccine strains

Nanoparticle-assisted polymerase chain reaction (nanoPCR) is a novel method for the rapid amplification of DNA and has been adopted for the detection of virus because of its simplicity, rapidity, and specificity. A nanoPCR assay was developed to detect and differentiate wild-type and gene-deleted pseudorabies virus (PRV). Three pairs of primers for nanoPCR developed in this study were selected from conserved regions of PRV, producing specific amplicons of 431 bp (gB), 316 bp (gE), and 202 bp (gG). The sensitivity of this assay using purified plasmid constructs containing the specific gene fragments was 100-1000 fold higher than conventional PCR. The PRV nanoPCR assay did not amplify porcine parvovirus, porcine circovirus type 2, porcine reproductive and respiratory syndrome virus, porcine teschovirus, or African swine fever virus but produced three bands of expected size with PRV and two bands of expected size with the gene-deleted PRV-Bartha-K61. Of 110 clinical samples collected from seven provinces in China, 53% and 48% were positive for wild-type PRV according to the nanoPCR assay and virus isolation, respectively.

Snapshot of viral infections in wild carnivores reveals ubiquity of parvovirus and susceptibility of Egyptian mongoose to feline panleukopenia virus

The exposure of wild carnivores to viral pathogens, with emphasis on parvovirus (CPV/FPLV), was assessed based on the molecular screening of tissue samples from 128 hunted or accidentally road-killed animals collected in Portugal from 2008 to 2011, including Egyptian mongoose (Herpestes ichneumon, n = 99), red fox (Vulpes vulpes, n = 19), stone marten (Martes foina, n = 3), common genet (Genetta genetta, n = 3) and Eurasian badger (Meles meles, n = 4). A high prevalence of parvovirus DNA (63%) was detected among all surveyed species, particularly in mongooses (58%) and red foxes (79%), along with the presence of CPV/FPLV circulating antibodies that were identified in 90% of a subset of parvovirus-DNA positive samples. Most specimens were extensively autolysed, restricting macro and microscopic investigations for lesion evaluation. Whenever possible to examine, signs of active disease were not present, supporting the hypothesis that the parvovirus vp2 gene fragments detected by real-time PCR possibly correspond to viral DNA reminiscent from previous infections. The molecular characterization of viruses, based on the analysis of the complete or partial sequence of the vp2 gene, allowed typifying three viral strains of mongoose and four red fox's as feline panleukopenia virus (FPLV) and one stone marten's as newCPV-2b type. The genetic similarity found between the FPLV viruses from free-ranging and captive wild species originated in Portugal and publicly available comparable sequences, suggests a closer genetic relatedness among FPLV circulating in Portugal. Although the clinical and epidemiological significance of infection could not be established, this study evidences that exposure of sympatric wild carnivores to parvovirus is common and geographically widespread, potentially carrying a risk to susceptible populations at the wildlife-domestic interface and to threatened species, such as the wildcat (Felis silvestris) and the critically endangered Iberian lynx (Lynx pardinus).

Validation of a commercial real-time PCR kit for specific and sensitive detection of Pseudorabies

Pseudorabies virus is the causative agent of Aujeszky's disease, one of the OIE listed diseases that mainly affects swine, but also can affect other animal species, and which can lead to heavy economic losses in pig industry. This study was designed to evaluate the performance of the ADIAVET(®) PRV REALTIME kit, a new commercial real time PCR kit for Pseudorabies virus genome detection developed by the French manufacturer Adiagène. It can be used on pig biological samples such as nasal swab supernatant, tonsil, brain or lung samples, or on samples from other susceptible animals, such as domestic carnivores. This ready-to-use duplex PCR assay contains an external positive control, appropriate for assessing DNA extraction efficiency and the presence of PCR inhibitors. The analytical specificity and sensitivity, intra- and inter-assay repeatability and diagnostic characteristics of the kit were determined and compared with virus isolation, which is the gold standard. Based on these results, the ADIAVET(®) PRV REALTIME kit received full validation for diagnostic purposes.

Cytokine protein expression levels in tracheobronchial lymph node homogenates of pigs infected with pseudorabies virus

Pseudorabies virus (PRV) is a neurotropic alphaherpesvirus that produces fatal encephalitis in newborn pigs, respiratory disorders in fattening pigs, and reproductive failure in sows. Following primary infection of the respiratory tract, PRV can develop into a systemic infection with dispersion of the virus via the lymphatic system that involves mononuclear cells in tracheobronchial lymph nodes (TBLNs). The objectives of the present study were to evaluate the pathogenesis and to determine the early immune cytokine profiles in TBLNs following experimental infection with a feral swine PRV isolate at 1, 3, 6, and 14 days postinfection (dpi). Forty healthy pigs were purchased from a PRV-negative herd. Twenty pigs received the Florida strain isolate (FS268) of feral swine PRV intranasally, and 20 uninfected controls received a sham inoculum. Compared to the levels in the controls, the levels of alpha interferon (IFN-alpha), interleukin-1beta (IL-1beta), IL-12, and IFN-gamma were increased in TBLN homogenates from PRV-infected pigs at 1 dpi, whereas the IL-18 levels were decreased from 3 to 6 dpi. The protein levels of IL-4 and IL-10 did not differ between the controls and the PRV-infected pigs at any time point. Flow cytometric analysis of TBLN homogenates of PRV-infected pigs and the controls revealed increases in the percentages of B cells at 6 dpi, CD4(+) cells at 14 dpi, and CD25 expression in TBLN homogenates (in the total mononuclear fraction and on B cells) in the PRV-infected pigs. Collectively, these findings demonstrate that a feral PRV in commercial swine can modulate the host's early immune response to allow the virus to establish an infection.

Variation of Aujeszky's disease viruses in wild swine in USA

In the United States of America, Aujeszky's disease (pseudorabies) has been eradicated from all domestic swine. Some re-emergence of infection occurred as vaccine use diminished. Sporadic outbreaks have also occurred because of the reservoir of infection in feral swine that have spread across the southern two-thirds of the country and Hawaii. In order to be able to understand the origins of re-emerging virus, sequence analysis of variable genes in pseudorabies virus (PRV) has been used to differentiate strains. Most PRV from feral swine can be distinguished from virus circulating in domestic pigs during the national epizootic. However, several feral swine isolates of PRV from south central states are closely related or identical in sequence to strains from domestic pigs. Extensive study by PCR for the presence of virus in the oral cavity of feral pigs disclosed that the viral DNA is distributed widely in tonsils salivary glands, taste buds and even mucosa in the vicinity of tusks. Clearly the virus in feral swine has multiple mechanisms of transmission to insure persistent infection and the threat of re-emergence in domestic swine continues.