In situ hybridization for the detection and localization of porcine epidemic diarrhea virus in the intestinal tissues from naturally infected piglets

Inhibitory effects of quercetin on porcine epidemic diarrhea virus in vitro and in vivo

Porcine epidemic diarrhea (PED) is an acute, severe, highly contagious disease. Porcine epidemic diarrhea virus (PEDV) strains are prone to mutation, and the immune response induced by traditional vaccines may not be strong enough to be effective against the virus. Therefore, there is an urgent need to develop novel anti-PEDV drugs. This study aimed to explore the therapeutic effects of quercetin in PEDV infections in vitro (Vero cells) and in vivo (suckling piglets). Using transmission electron microscopy and laser confocal microscopy, we found that PEDV infection promotes the accumulation of lipid droplets (LDs). In vitro, studies showed that quercetin inhibits LD accumulation by down-regulating NF-κB signaling and IL-1β, IL-8, and IL-6 levels, thereby inhibiting viral replication. In vivo, studies in pigs demonstrated that quercetin can effectively relieve the clinical symptoms and intestinal injury caused by PEDV. Collectively, our findings suggest that quercetin inhibits PEDV replication both in vivo and in vitro, which provides a new direction for the development of PED antiviral drugs.

Hypomethylated interferon regulatory factor 8 recruits activating protein-2α to attenuate porcine epidemic diarrhea virus infection in porcine jejunum

Interferon regulatory factor 8 (IRF8) is a key regulator of innate immune receptor signaling that resists pathogen invasion by regulating cell growth and differentiation. Porcine epidemic diarrhea virus (PEDV) targets the intestine and damages the mucosal barrier. However, whether IRF8 regulates PEDV replication remains unclear. We revealed that PEDV infection activated IRF8 expression. Moreover, IRF8 deletion drastically promoted PEDV replication and invasion, increasing the virus copies and titers. Hypomethylation enrichment of activating protein (AP)-2α was significantly negatively correlated with high IRF8 expression, and AP-2α directly targeted the IRF8 promoter to regulate PEDV replication. Furthermore, IRF8 overexpression decreased the cellular reactive oxygen species levels and mitochondrial membrane potential and increased the antioxidant enzyme activities to alleviate PEDV-induced oxidative damage. IRF8 overexpression suppressed apoptotic gene expression, thereby inhibiting apoptosis in response to PEDV stimulation. Taken together, this study demonstrates that AP-2α is involved in PEDV-induced epigenetic modification of IRF8 to reduce cell apoptosis and oxidative stress and facilitate host resistance to PEDV in the intestinal epithelium.

Impact of porcine circovirus type 2 on porcine epidemic diarrhea virus replication in the IPI-FX cell line depends on the order of infection

Introduction

A study in 2006 showed that the clinical course of PEDV disease was markedly aggravated by transplacental infection of PCV2. Therefore, we investigated whether the small intestine supports PCV2 replication and the effect of PCV2 infection on PEDV replication in epithelial cells in vitro.

Methods

To confirm the intestinal tropism of PCV2, the viral loads in the small-intestinal tissues after PCV2 infection were determined with virus titration, and the viral titers in the infected pig jejunum, ileum, ileocecal valve, and colon were 104.86, 104.09, 102.52, and 102.35 TCID50/g, respectively. We then determined the propagation characteristics of PCV2 in ileal epithelial cells (IPI-FX) and jejunal epithelial cells (IPEC-J2) with an immunoperoxidase monolayer assay, virus titration, and an immunofluorescence assay. Both IPI-FX and IPEC-J2 cells supported the replication of PCV2, with titers of 105.5 and 105.0 TCID50/ml, respectively. We established an infection model of PCV2 and PEDV in IPI-FX cells and found that PEDV and PCV2 infected the cells individually and together. The effects of PCV2 infection on PEDV replication were determined with reverse transcription–quantitative PCR (qPCR), western blotting, and virus titration. When PCV2 infected IPI-FX cells before PEDV, PCV2 significantly inhibited the replication of PEDV in a dose- and time-dependent manner and that the mRNAs of IFN-β, TNF-α, IL1β, and OASL were downregulated (detected with qPCR). Surprisingly, when IPI-FX cells were co-infected with PCV2 and PEDV, PCV2 promoted the replication of PEDV, the expression of the host IFN-β, TNF-α, IL1β, and OASL mRNAs was upregulated.

Discussion

These findings demonstrate that the co-infection of IPI-FX cells with PCV2 and PEDV represents an excellent in vitro model in which to investigate their combined pathogenic mechanisms.

Puerarin enhances intestinal function in piglets infected with porcine epidemic diarrhea virus

Puerarin has been reported to be an excellent antioxidant, anti-inflammatory and antimicrobial agent, but the potential effect of puerarin on porcine epidemic diarrhea virus (PEDV) is unclear. This study aimed to determine whether puerarin could alleviate intestinal injury in piglets infected with PEDV. A PEDV (Yunnan province strain) infection model was applied to 7-day-old piglets at 104.5 TCID50 (50% tissue culture infectious dose). Piglets were orally administered with puerarin at the dosage of 0.5 mg/kg body weight from day 5 to day 9. On day 9 of the trial, piglets were inoculated orally with PEDV. Three days later, jugular vein blood and intestinal samples were collected. Results showed puerarin reduced morbidity of piglets infected with PEDV. In addition, puerarin reduced the activities of aspartate aminotransferase and alkaline phosphatase, the ratio of serum aspartate aminotransferase to serum alanine aminotransferase, the number of white blood cells and neutrophils, and the plasma concentrations of interleukin-6, interleukin-8 and tumor necrosis factor-α, as well as protein abundances of heat shock protein-70 in PEDV-infected piglets. Moreover, puerarin increased D-xylose concentration but decreased intestinal fatty acid-binding protein concentration and diamine oxidase activity in the plasma of piglets infected with PEDV. Puerarin increased the activities of total superoxide dismutase, glutathione peroxidase and catalase, while decreasing the activities of myeloperoxidase and concentration of hydrogen peroxide in both the intestine and plasma of PEDV-infected piglets. Puerarin decreased mRNA levels of glutathione S-transferase omega 2 but increased the levels of nuclear factor erythroid 2-related factor 2. Furthermore, puerarin increased the abundance of total eubacteria (16S rRNA), Enterococcus genus, Lactobacillus genus and Enterobacteriaceae family in the intestine, but reduced the abundance of Clostridium coccoides in the caecum. These data indicate puerarin improved intestinal function in piglets infected by PEDV and may be a promising supplement for the prevention of PEDV infection.

Porcine epidemic diarrhea virus: Molecular mechanisms of attenuation and vaccines

Porcine epidemic diarrhea virus (PEDV) causes an emerging and re-emerging coronavirus disease characterized by vomiting, acute diarrhea, dehydration, and up to 100% mortality in neonatal suckling piglets, leading to huge economic losses in the global swine industry. Vaccination remains the most promising and effective way to prevent and control PEDV. However, effective vaccines for PEDV are still under development. Understanding the genomic structure and function of PEDV and the influence of the viral components on innate immunity is essential for developing effective vaccines. In the current review, we systematically describe the recent developments in vaccine against PEDV and the roles of structural proteins, non-structural proteins and accessory proteins of PEDV in affecting viral virulence and regulating innate immunity, which will provide insight into the rational design of effective and safe vaccines for PEDV or other coronaviruses.

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Advances in vaccines of PEDV, such as inactivated and attenuated live vaccines, subunit vaccines, and nucleic acid vaccines.

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The application of reverse genetics in the development of live attenuated PEDV vaccines.

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The roles of PEDV proteins in affecting viral virulence and regulating innate immunity.

Quantitative Proteomic Analysis Reveals Antiviral and Anti-inflammatory Effects of Puerarin in Piglets Infected With Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV) has caused enormous economic losses to the swine industry worldwide in recent years. Puerarin (PR), a major isoflavonoid isolated from the Chinese herb Gegen, possesses many pharmacological activities, including anti-inflammatory, and anti-viral activities. This study was conducted with both PEDV-infected African green monkey kidney cells (Vero) and neonatal pigs to determine the effect of PR on PEDV infection and to elucidate the underlying mechanisms by using proteomic analyses. Twenty-four piglets fed a milk replacer were randomly allocated into one of three groups (Control, PEDV, and PEDV + PR). After a 5-day period of adaption, piglets (n = 8/group) in the PEDV + PR were orally administered with PR (0.5 mg/kg body weight) between days 5 and 9, whereas piglets in the other two groups received the same volume of liquid milk replacer. On day 9, piglets were orally administered with either sterile saline or PEDV (Yunnan province strain) at 10^4.5 TCID₅₀ (50% tissue culture infectious dose) per pig. On day 12 of the trial, jugular vein blood and intestinal samples were collected. In addition, Vero cells were assigned randomly into three groups (Control, PEDV, PEDV + PR). Cells in the PEDV and PEDV + PR groups were infected with PEDV at a multiplicity of infection of 0.01, while cells in the control group were treated with the same volume of sterile saline. One hour later, cells in the Control and PEDV groups were cultured in serum-free DMEM, while cells in the PEDV + PR group were supplemented with PR. After 36 h of culture, cells were harvested. PR attenuated the reductions in cell proliferation in vitro and growth performance in PEDV-infected piglets, and inhibited PEDV replication and the expression of several cytokines (including IL-8) both in vitro and in vivo. Proteomic analyses identified that the abundances of 29 proteins in the ileum were altered by PEDV infection and restored to the control level by PR. Pathway analyses revealed that PR restored the expression of several interferon-stimulated genes and selectively upregulated the expression of guanylate-binding proteins. Western blot analyses showed that PR supplementation inhibited the PEDV-induced NF-κB activation. Collectively, these results indicate that PR could exert antiviral and anti-inflammatory effects in piglets infected with PEDV and have the potential to be an effective antiviral feed additive.

Dietary 25-Hydroxyvitamin D3 Supplementation Alleviates Porcine Epidemic Diarrhea Virus Infection by Improving Intestinal Structure and Immune Response in Weaned Pigs

Simple Summary

Porcine epidemic diarrhea is one of the major problems in current swine husbandry worldwide, and effective measures for prevention and treatment are scarce. We found that high dose 25-hydroxyvitamin D₃ supplementation could ease intestinal injury and inhibit intestinal immune response induced by porcine epidemic diarrhea virus (PEDV), suggesting that feeding a high dose of 25-hydroxyvitamin D₃ could be used as an approach against PEDV infection.

Abstract

We conducted this experiment to determine if feeding 25-hydroxyvitamin D₃ (25(OH)D₃) to weaned pigs would alleviate porcine epidemic diarrhea virus (PEDV) infection and immune response. Forty-two weaned pigs were allotted to 1 of 6 dietary 25(OH)D₃ treatments (5.5, 5.5, 43.0, 80.5, 118.0, 155.5 μg 25(OH)D₃/kg diet) for 26 days. On day 22 of the trial, all the treatments were orally administrated with PEDV except for one of the 5.5 μg 25(OH)D₃/kg treatments, which was challenged with the same volume of sterile saline and served as control. Another 5.5 μg 25(OH)D₃/kg group for PEDV challenge was named CON-PEDV. Average daily gain (p < 0.05) was reduced by PEDV infection. PEDV administration also induced severe diarrhea (p < 0.05), reduction of villous height and the ratio of villous height to crypt depth, and increase of crypt depth and serum diamine oxidase activity (p < 0.05). Serum IgM and complement component 4 levels were increased by PEDV challenge. However, 155.5 μg 25(OH)D₃/kg supplementation alleviated intestinal damage (p < 0.05) compared with CON-PEDV. Furthermore, 155.5 μg 25(OH)D₃/kg supplementation downregulated the mRNA abundance of inflammatory cytokines and interferon signal pathway-related genes (p < 0.05) compared with CON-PEDV. These results suggested that dietary supplementation of 155.5 μg 25(OH)D₃/kg could alleviate intestinal damage and protect against PEDV-induced inflammatory status.

Global Mapping of H3K4 Trimethylation (H3K4me3) and Transcriptome Analysis Reveal Genes Involved in the Response to Epidemic Diarrhea Virus Infections in Pigs

Porcine epidemic diarrhea virus (PEDV) is currently detected as the main pathogen causing severe diarrhea in pig farms. The phenotypic alterations induced by pathogenic infections are usually tightly linked with marked changes in epigenetic modification and gene expression. We performed global mapping of H3K4 trimethylation (H3K4me3) and transcriptomic analyses in the jejunum of PEDV-infected and healthy piglets using chromatin immunoprecipitation sequencing and RNA-seq techniques. A total of 1885 H3K4me3 peaks that are associated with 1723 genes were characterized. Moreover, 290 differentially expressed genes were identified, including 104 up-regulated and 186 down-regulated genes. Several antiviral genes including 2'-5'-oligoadenylate synthetase 1 (OAS1), 2'-5'-oligoadenylate synthetase 2 (OAS2), ephrin B2 (EFNB2), and CDC28 protein kinase regulatory subunit 1B (CKS1B) with higher H3K4me3 enrichment and expression levels in PEDV-infected samples suggested the potential roles of H3K4me3 deposition in promoting their expressions. Transcription factor annotation analysis highlighted the potential roles of two transcription factors interferon regulatory factor 8 (IRF8) and Kruppel like factor 4 (KLF4) in modulating the differential expression of genes involved in PEDV infection. The results provided novel insights into PEDV infection from the transcriptomic and epigenetic layers and revealed previously unknown and intriguing elements potentially involved in the host responses.

Single-domain antibodies as promising experimental tools in imaging and isolation of porcine epidemic diarrhea virus

Single-domain antibody (sdAb) or nanobody possesses specific features non-accessible for conventional antibodies that make them suitable for research and biotechnological applications. Porcine epidemic diarrhea virus (PEDV) causes lethal diarrhea in piglets, resulting in great economic losses all over the world. To detect and isolate PEDV rapidly and accurately is important for the control and further research of the clinical PEDV strains. In this study, four sdAb fragments (sdAb-Mc19/29/30/37) targeting the membrane (M) protein of PEDV were selected from sdAb library that was constructed through M protein-immunized Camelus bactrianus. The selected sdAb-Mcs were solubly expressed in Escherichia coli. The functional characteristics analysis revealed that the recombinant sdAb-Mcs have excellent binding activity and specificity to M protein but have no neutralizing activity to PEDV. For further application, sdAb-Mc37 was conjugated with quantum dots to synthesize a nanoprobe for imaging PEDV in vero cells. The observed fluorescence in vero cells clearly reflects that PEDV virions can be reliably recognized and labeled by the nanoprobe. Furthermore, the sdAb-Mc29 was conjugated with superparamagnetic nanobeads to construct immunomagnetic nanobeads (IMNBs) used to isolate PEDV. One PEDV strain was successfully isolated from clinical fecal sample, suggesting IMNBs as a novel and efficient tool suitable for PEDV isolation from clinical samples. This study provided a novel application and substantiated the suitability of sdAb as a specific binder for the isolation of viruses.

Development and application of an indirect ELISA for the detection of antibodies to porcine epidemic diarrhea virus based on a recombinant spike protein

Background

As the major causative agent of swine viral diarrhea, porcine epidemic diarrhea virus (PEDV) has caused massive losses to the economies of swine raising countries. Accordingly, the serological detection of corresponding antibodies would be beneficial to diagnose PEDV indirectly to control the disease. In this study, an indirect enzyme-linked immunosorbent assay (ELISA) based on the recombinant truncated spike (S) protein of PEDV was developed and validated.

Results

The reaction conditions of the developed indirect ELISA were optimized. This indirect ELISA was compared to indirect immunoinfluscent assay (IFA), and the overall coincidence rate was 96.74% based on testing 368 clinical serum samples with different PEDV antibody levels. No cross-reactivity with other common swine pathogens was detected for the developed S1 indirect ELISA. Finally, the S1 indirect ELISA was applied to detect serum antibodies of 3304 field samples collected from different pig farms in eastern China, and it presented an overall substantial agreement on the PEDV infection status.

Conclusions

This established S1 indirect ELISA is capable of detecting serum antibodies against PEDV, and due to its high sensitivity and specificity, it could be applied for serological evaluation and indirect diagnosis of PEDV infection.

Viral and bacterial investigations on the aetiology of recurrent pig neonatal diarrhoea cases in Spain

Background

Neonatal diarrhoea represents a major disease problem in the early stages of animal production, increasing significantly pre-weaning mortality and piglets weaned below the target weight. Enteric diseases in newborn piglets are often of endemic presentation, but may also occur as outbreaks with high morbidity and mortality. The objective of this study was to assess the frequency of different pathogens involved in cases of recurrent neonatal diarrhoea in Spain.

Results

A total of 327 litters from 109 sow farms located in Spain with neonatal recurrent diarrhoea were sampled to establish a differential diagnosis against the main enteric pathogens in piglets. In total, 105 out of 109 (96.3%) case submissions were positive to one of the examined enteric organisms considered potentially pathogenic (Escherichia coli, Clostridium perfringens types A and C, Transmissible gastroenteritis virus [TGEV], Porcine epidemic diarrhoea virus [PEDV] or Rotavirus A [RVA]). Fifty-eight out of 109 (53.2%) submissions were positive for only one of these pathogens, 47 out of 109 (43.1%) were positive for more than one pathogen and, finally, 4 out of 109 (3.7%) were negative for all these agents. Escherichia coli strains were isolated from all submissions tested, but only 11 of them were classified into defined pathotypes. Clostridium perfringens type A was detected in 98 submissions (89.9%) and no C. perfringens type C was found. Regarding viruses, 47 (43.1%) submissions were positive for RVA, 4 (3.7%) for PEDV and none of them for TGEV.

Conclusion

In conclusion, C. perfringens type A, E. coli and RVA were the main pathogens found in faeces of neonatal diarrheic piglets in Spain.

Porcine epidemic diarrhea (PED) infection, diagnosis and vaccination: A mini review

Porcine epidemic diarrhea virus (PEDV) is a main etiology causing severe enteric disease in piglets with clinical signs of anorexia, vomiting, diarrhea and dehydration resulting in loss of condition and death within a few days. Historically, PED is one of major causes of loss in swine and remains prevalent in some parts of the world. Even with increase in the available tests for PED diagnosis, which include histological diagnosis; virological diagnosis and serological diagnosis, there is no vaccine or specific treatment for this disease yet. In this mini review, the overview and current situation of PED is described with updated techniques, in an effort to comprehensively discuss and understand the disease characteristics.

Porcine Epidemic Diarrhea

Porcine epidemic diarrhea (PED) first appeared in England and Belgium in the 1970s. The etiological agent of the disease is porcine epidemic diarrhea virus (PEDV), which belongs to Coronaviridae. The disease has spread globally and became an endemic disease in many Asian and European countries causing transient diarrhea in postweaning pigs with low mortalities for several decades. Since late 2010, field outbreaks of PED, which reemerged in China, spread to Asian and some European countries and emerged in North America; all led to enormous economic losses in porcine industry. New variants of PEDV exhibit not only significant genetic variations as compared to historic PEDV strains but also more virulent causing severe vomiting and watery yellowish diarrhea in suckling piglets under 1 week of age. Factors underlying the potential pathogenesis of the recent PEDV outbreaks include the mutation of the virus, the lacking of maternal antibodies for the protection of piglets, and the slower turnover rate of enterocytes (5–7 days) of the neonatal piglets as compared to postweaning pigs (2–3 days). The emerging and reemerging of the new variants of PEDV highlight the importance of reviewing the etiology, pathogenesis, diagnosis, and epidemiology of the disease.

Porcine aminopeptidase N is not a cellular receptor of porcine epidemic diarrhea virus, but promotes its infectivity via aminopeptidase activity

Porcine epidemic diarrhea virus (PEDV), a causative agent of pig diarrhoea, has recently caused significant economic damage worldwide. Porcine aminopeptidase N (pAPN) has been reported to be the receptor for PEDV, although robust evidence is lacking. In the present study, we explored whether pAPN functions as a receptor for PEDV. Human HeLa cells expressing pAPN and pAPN-positive porcine CPK cells failed to support PEDV infection, but were susceptible to infection by transmissible gastroenteritis virus (TGEV), which utilizes pAPN as a functional receptor. In contrast to TGEV, PEDV did not bind soluble porcine aminopeptidases (pAPs) and infection was not inhibited by the soluble form of pAPs. However, overexpression of pAPN in porcine CPK cells (CPK-pAPN cells) slightly increased the production of PEDV, and the increased replication in CPK-pAPN cells was inhibited by bestatin, an inhibitor of the protease activity of aminopeptidase N. These results suggest that pAPN is not a functional receptor for PEDV, but promotes the infection of PEDV through its protease activity.

Porcine epidemic diarrhoea: new insights into an old disease

Porcine epidemic diarrhea (PED) is an enteric disease in swine caused by an alphacoronavirus. It affects swine of all ages causing acute diarrhoea and can lead to severe dehydration and death in suckling piglets. Being recognized for the first time in Europe and Asia during the seventies and the eighties, respectively, it has remained a relevant cause of diarrhea outbreaks in Asia for years and to the present. It has become a major concern in swine production since 2013 when the virus was detected for first time in the USA and in other American countries causing a high number of pig deaths and significant economic losses. The present review aims at approaching the reader to the state of the art of PED giving answer to some of the most recent questions which have arisen related to this disease.

Development of an enzyme-linked immunosorbent assay for the monitoring and surveillance of antibodies to porcine epidemic diarrhea virus based on a recombinant membrane protein

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Expressed membrane protein of porcine epidemic diarrhea virus in Escherichia coli.

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An indirect ELISA was developed using purified recombinant M protein as detection antigen.

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Assessing fit for immunologic surveillance and sero-diagnosis of PEDV.

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The developed iELISA is specific, sensitive and does not require PEDV cultivation.

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This iELISA could be used for large-scale serological testing.

The recent dramatic increase in reported cases of porcine epidemic diarrhea (PED) in pig farms is a potential threat to the global swine industry. Therefore, the accurate diagnosis, serological monitoring, and surveillance of specific antibodies in pigs resulting from porcine epidemic diarrhea virus (PEDV) infection or vaccination would be essential in helping to control the spread of PED. We developed and validated an indirect enzyme-linked immunosorbent assay (ELISA) based on the recombinant membrane (M) protein of PEDV. To detect PEDV antibodies in eight herds, 382 serum samples were collected from sows that had been immunized with a PED vaccine, and screened using the developed ELISA in parallel with a serum neutralization (SN) assay. Of the tested samples, 276 were positive for the presence of PEDV antibodies according to both assays, while 98 were negative. An excellent agreement between the ELISA and the SN assay was observed (kappa = 0.947; 95% confidence interval = 0.910–0.984; McNemar's test, P = 0.727). No cross-reaction was detected for the developed ELISA with other coronaviruses or other common pig pathogens. The developed ELISA could be used for serological evaluation and indirect diagnosis of PED infection.

Comparative pathogenesis of US porcine epidemic diarrhea virus (PEDV) strain PC21A in conventional 9-day-old nursing piglets vs. 26-day-old weaned pigs

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US PEDV was highly enteropathogenic in seronegative 9-day-old nursing piglets.

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Infected weaned pigs were mostly sub-clinical and required a longer incubation period prior to PEDV infection, compared to nursing pigs.

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There was a lack of LGR5⁺ crypt stem cells and low proliferation of crypts in uninfected nursing piglets.

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The numbers of Ki67⁺ (marker for crypt proliferation) or LGR5⁺ crypt cells increased remarkably in nursing piglets after PEDV infection.

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Biologic mediators that promote crypt stem cell regeneration would be therapeutic targets.

Our study demonstrated potential mechanisms by which porcine epidemic diarrhea virus (PEDV) infection induces greater disease severity of nursing vs. weaned conventional pigs. Twenty-six-day-old weaned [PEDV-inoculated (n = 11); mock (n = 9)] and 9-day-old nursing pigs [PEDV-inoculated (n = 9); mock (n = 11)] were inoculated orally [8.9 log₁₀ genomic equivalents (GE)/pig] with PC21A strain or mock (MEM). Pigs were monitored for clinical signs and PEDV RNA titers in feces and serum. For pathology and immunofluorescence staining for Ki67 (marker for crypt proliferation) and LGR5 (marker for crypt stem cell), 3–4 pigs were euthanized at postinoculation days (PIDs) 1, 3 and 5. Severe watery diarrhea and atrophic enteritis with moderate to high PEDV RNA titers in feces (7.5–12.2 log₁₀ GE/ml) and low viral RNA titers in serum (5.6–8.6 log₁₀ GE/ml) were observed in all inoculated nursing piglets at PIDs 1–5. In contrast, weaned pigs did not show evidence of PEDV infection at PID 1. Pigs exhibited high fecal shedding titers at PIDs 2–5 and mild to severe atrophic enteritis at PIDs 3–5, indicating a longer incubation for PEDV infection. While uninoculated or inoculated 27–31-day-old pigs showed large numbers of Ki67- or LGR5-positive cells in the intestinal crypts, there was a lack of LGR5-positive cells and low proliferation of crypts in jejunum of uninoculated 10–14-day-old piglets, possibly causing a slower turnover of enterocytes; however, the number of LGR5-positive cells and proliferation of intestinal crypts increased remarkably at 3–5 days after inoculation. Biologic mediators that promote crypt stem cell regeneration would be targets to improve the intestinal epithelium renewal during PEDV infection.

Development of a nanoparticle-assisted PCR assay for detection of porcine epidemic diarrhea virus

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A nanoPCR method was developed for the detection of PEDV.

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The nanoPCR assay was 100-fold more sensitive than a conventional RT-PCR assay.

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The lower detection limit was 2.7 × 10⁻⁶  ng/μL of PEDV RNA.

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This test could be applied for clinical diagnosis and field surveillance of PEDV.

Porcine epidemic diarrhea virus (PEDV) is an important pig pathogen that can cause vomiting, diarrhea, and dehydration, leading to serious damage to the swine industry worldwide. In this study, a nanoparticle-assisted polymerase chain reaction (nanoPCR) assay targeting the N gene of PEDV was developed and the sensitivity and specificity were investigated. Under the optimized conditions for detection of PEDV RNA, the nanoPCR assay was 100-fold more sensitive than a conventional RT-PCR assay. The lower detection limit of the nanoPCR assay was 2.7 × 10⁻⁶ ng/μL of PEDV RNA and no cross-reaction was observed with other viruses. This is the first report to demonstrate the application of a nanoPCR assay for the detection of PEDV. The sensitive and specific nanoPCR assay developed in this study can be applied widely in clinical diagnosis and field surveillance of PEDV-infection.

Pathology of US porcine epidemic diarrhea virus strain PC21A in gnotobiotic pigs

To understand the progression of porcine epidemic diarrhea virus infection, we inoculated gnotobiotic pigs with a newly emerged US strain, PC21A, of the virus. At 24–48 hours postinoculation, the pigs exhibited severe diarrhea and vomiting, fecal shedding, viremia, and severe atrophic enteritis. These findings confirm that strain PC21A is highly enteropathogenic.

Rapid and sensitive detection of porcine epidemic diarrhea virus by reverse transcription loop-mediated isothermal amplification combined with a vertical flow visualization strip

Porcine epidemic diarrhea virus (PEDV) is an important pathogen that causes vomiting, diarrhea, and dehydration, leading to serious damage to the swine industry worldwide. The establishment of effective diagnostic methods is imperative. However, traditional methods are often unsuitable. In this study, reverse transcription loop-mediated isothermal amplification (RT-LAMP) was combined with a vertical flow (VF) nucleic acid detection strip to detect PEDV. Parameters that affect the RT-LAMP reaction were optimized. The RT-LAMP-VF assay that we established was performed at 62 °C for 40 min, and then directly evaluated on the VF visualization strip cassette. The method demonstrated high specificity for PEDV. The detection limit was 10 pg of ribonucleic acid, consistent with RT-PCR, RT-LAMP detected products on agarose gels and by direct calcein fluorescence. Application of this method to clinical samples yielded a positivity rate that was comparable to that obtained for RT-PCR. This technique saves time and is efficient, and is thus expected to be useful for the diagnosis of PEDV infection in the field.

Scientific Opinion on porcine epidemic diarrhoea and emerging porcine deltacoronavirus

In the last decade, many porcine epidemic diarrhoea (PED) outbreaks have been reported by several countries in Asia whereas only a few Member States of the European Union (EU) have reported PED clinical cases and/or PED virus (PEDV)-seropositive animals. This alphacoronavirus was first reported in the USA in May 2013, followed by rapid spread throughout the country and outbreaks reported by several countries in the Americas. The recent PEDV-EU isolates have high level of sequence identity to PEDV-Am isolates. Based on nucleotide sequencing, multiple variants of PEDV are circulating in Europe, the Americas and Asia but any difference in virulence and antigenicity is currently unknown. Serological cross-reactivity has been reported between PEDV isolated in Europe and in the Americas; however no data regarding cross-protection are available. The impact of different PEDV strains is difficult to compare between one country and another, since impact is dependent not only on pathogenicity but also on factors such as biosecurity, farm management, sanitary status or herd immune status. However, the clinical signs of PEDV infections in naive pigs are similar in different countries with mortalities up to 100% in naive newborn piglets. The impact of recently reported PED outbreaks in Asia and the USA seems to be more severe than what has been described in Europe. Infected animals, faeces, feed and objects contaminated with faeces are matrices that have been reported to transmit PEDV between farms. Infectious PEDV has been detected in spray-dried porcine plasma (SDPP) in one study but the origin of the infectious PEDV in SDPP is not clear. Detection of porcine deltacoronavirus (PDCoV) has been reported in a few countries but only limited testing has been done. Based on the currently available information, it seems that PDCoV would have a lower impact than PEDV.

Porcine epidemic diarrhea virus infects and replicates in porcine alveolar macrophages

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Porcine epidemic diarrhea virus (PEDV) is a causative agent of porcine epidemic diarrhea; consequently, the small intestine was believed to be its only target organ.

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We found that PEDV infected not only the small intestines, but also the respiratory tract.

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Infection and replication of PEDV in the respiratory tract from naturally PEDV-infected piglets were examined by reverse transcription polymerase chain reaction, immunohistochemistry, and virus re-isolation.

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Our observations were confirmed by experimental inoculation, and we found that PEDV infection in the respiratory tract was specifically associated with alveolar macrophages in the lung.

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The discovery that PEDV infects and replicates in alveolar macrophages provides new insights into its pathogenesis.

Porcine epidemic diarrhea virus (PEDV) is a causative agent of porcine epidemic diarrhea; consequently, the small intestine was believed to be its only target organ. In this study, we found that PEDV infected not only the small intestines, but also the respiratory tract. Infection and replication of PEDV in the respiratory tract from naturally PEDV-infected piglets were examined by reverse transcription polymerase chain reaction, immunohistochemistry, and virus re-isolation. Our observations were confirmed by experimental inoculation, and we found that PEDV infection in the respiratory tract was specifically associated with alveolar macrophages in the lung. Vero cell-adapted PEDV was able to replicate in both primary alveolar macrophages and continuous porcine alveolar macrophage cells. Sequencing analysis of the spike (S) glycoprotein revealed that mutations in S might be a potential determinant of auxiliary targets for PEDV. The discovery that PEDV infects and replicates in alveolar macrophages provides new insights into its pathogenesis.

Monoclonal antibody against membrane protein of transmissible gastroenteritis virus

Transmissible gastroenteritis virus (TGEV) is a porcine coronavirus that can cause piglet diarrhea with high mortality rates. TGEV membrane (M) protein not only plays a vital role in the process of virus assembly and budding, but also induces the production of interferon-α during infection. In this study, a monoclonal antibody (MAb) designated 7G7, against the TGEV M protein was generated by inoculating BALB/c mice with TGEV followed by hybridoma technique. Immunofluorescence assays indicated that MAb 7G7 was capable of detecting cell infection by TGEV. Virus-based ELISA demonstrated that MAb 7G7 can be used as a highly specific diagnostic reagent for TGEV.

Complete genome sequence of porcine epidemic diarrhea virus strain AJ1102 isolated from a suckling piglet with acute diarrhea in China

A diarrhea outbreak caused by porcine epidemic diarrhea virus (PEDV) has been observed in China since December 2010. We report here the complete genome sequence of PEDV strain AJ1102 isolated from a suckling piglet with acute diarrhea, which will help toward understanding the molecular and evolutionary characteristics of the epidemic PEDV in China.

Concurrent infections are important for expression of porcine circovirus associated disease

Porcine circovirus type 2 (PCV2) is the essential component of porcine circovirus disease (PCVD) as the disease syndrome is referred to in Europe and porcine circovirus associated disease (PCVAD) as it is referred to in North America. Singular PCV2 infection rarely results in clinical disease; however, PCVAD is often accelerated in onset, enhanced in severity and prolonged in duration by concurrent viral or bacterial infections. Due to its effect on the immune system, PCV2 has also been shown to enhance protozoal, metazoal, and fungal infections. Several retrospective or cross-sectional studies have investigated the presence and prevalence of various infectious agents associated with PCVAD under field conditions. Experimental models confirm that PCV2 replication and associated lesions can be enhanced by concurrent infection with other viruses or bacteria. The exact mechanisms by which concurrent pathogens upregulate PCV2 are unknown. Co-infections may promote PCV2 infection by increasing immune host cell replication and accumulation in tissues thereby enhancing targets for PCV2 replication. It has also been proposed that co-infections interfere with PCV2 clearance by alteration of cytokine production and profiles. The outcome of differences in timing of co-infections in PCV2-infected pigs is also likely very important and is an area where more research is needed. Given the current knowledge base, it is important that veterinarians do a thorough diagnostic investigation on herds where PCVAD is a recurrent problem in order to implement the most appropriate and cost effective intervention strategies.

Development of reverse transcription loop-mediated isothermal amplification for rapid detection of porcine epidemic diarrhea virus

In this study, a reverse transcription loop-mediated isothermal amplification (RT-LAMP) was developed for detection of porcine epidemic diarrhea virus (PEDV). Six primers were designed to amplify the nucleocapsid (N) gene of PEDV. The optimization, sensitivity, and specificity of the RT-LAMP were investigated. The results showed that the optimal reaction condition for RT-LAMP amplifying PEDV N gene was achieved at 63°C for 50 min. The RT-LAMP assay was more sensitive than gel-based RT-PCR and enzyme-linked immunosorbent assay. It was capable of detecting PEDV from clinical samples and differentiating PEDV from Porcine transmissible gastroenteritis virus, Porcine rotavirus, Porcine pseudorabies virus, Porcine reproductive and respiratory syndrome virus, and Avian infectious bronchitis virus.

Development of a porcine epidemic diarrhea virus M protein-based ELISA for virus detection

A membrane (M), protein-based ELISA was developed to detect porcine epidemic diarrhea virus (PEDV). The M gene of PEDV was expressed in Escherichia coli. The purified recombinant M protein was used to immunize rabbits to generate a polyclonal antibody. Immunofluorescence analysis indicated that the anti-PEDV-M antibody reacted with PEDV-infected cells. The antibody was utilized to develop an indirect ELISA to detect PEDV. Other viruses, porcine transmissible gastroenteritis coronavirus, avian infectious bronchitis coronavirus, porcine reproductive and respiratory syndrome virus, classic swine fever virus and porcine pseudorabies virus, were unreactive.

Application of a focus formation assay for detection and titration of porcine epidemic diarrhea virus

A focus formation assay (FFA) for detection and titration of porcine epidemic diarrhea virus (PEDV) in a micro-culture system using Vero cells and PAP staining technique was evaluated. A linear correlation between the virus dilution and virus titer determined by FFA was observed between the range of 10 and 30 foci per well. Comparative analysis between FFA and plaque assay showed no significant difference in estimating the titer of cell adapted PEDV. However, the culture time required for detecting the virus was considerably shorter for FFA. In addition, FFA had higher sensitivity for detecting field isolates of PEDV as well as positive identification of the virus with the antibody specific reaction. A broader range of dilutions and number of replicates may be used for titration. A FFA may be applied as an alternative method for detection and titration of PEDV.

The effects of transplacental porcine circovirus type 2 infection on porcine epidemic diarrhoea virus-induced enteritis in preweaning piglets

The effects of transplacental porcine circovirus type 2 (PCV2) infection on porcine epidemic diarrhoea virus (PEDV)-induced enteritis were examined in neonatal piglets. Six pregnant sows were randomly allocated to an infected (n = 3) or control group (n = 3). Three pregnant sows were inoculated intranasally with 6 mL of tissue culture fluid containing 1.2 × 10⁵ tissue culture infective doses 50% (TCID₅₀)/mL of PCV2 strain SNUVR000470 three weeks before the expected farrowing date. Three control pregnant sows were similarly exposed to uninfected cell culture supernatants. Thirty piglets from PCV2-infected sows were randomly assigned to two groups (A and B) of 15 piglets each. Another 30 piglets from noninfected sows were randomly assigned to two groups (C and D) of 15 piglets each. The piglets in groups A and C were dosed orally at three days of age with 2 mL of virus stock (1 × 10^6.5 TCID₅₀/mL) of the PEDV strain, SNUVR971496, at the third passage.

The mean villous height and crypt depth (VH:CD) ratio in PEDV-infected piglets from PCV2-infected sows (group A) were significantly different from those of the PEDV-infected piglets from PCV2 negative sows (group C) at 36, 48, and 72 h post-inoculation (hpi) (P < 0.05). In PEDV-infected piglets from PCV2-infected sows (group A), significantly more PEDV nucleic acid was detected in the jejunal tissues (P < 0.05) at 24 hpi than in the same tissues of the PEDV-infected piglets from PCV2 negative sows (group C). Thereafter, at 36, 48, 60, and 70 hpi significantly more PEDV nucleic acid (P < 0.05) was detected in the jejunal tissues of the PEDV-infected piglets from PCV2 negative sows (group C) than those of the PEDV-infected piglets from the PCV2-infected sows (group A). It is concluded that the clinical course of PEDV disease was markedly affected by transplacental infection of PCV2.

Decreased activity of brush border membrane-bound digestive enzymes in small intestines from pigs experimentally infected with porcine epidemic diarrhea virus

Brush border membrane-bound digestive enzymes such as disaccharidases (lactase, sucrase, and maltase), leucine aminopeptidase N, and alkaline phosphatase were measured in jejunum from pigs experimentally infected with porcine epidemic diarrhea virus (PEDV). Three piglets from the infected and control groups were euthanized by electrocution and subjected to necropsy at 24, 36, 48, 60, and 72 hours post-inoculation (hpi). The infection of PEDV to jejunum resulted in significant decreases in brush border membrane-bound digestive enzymes such as disaccharidases (lactase, sucrase, and maltase), leucine aminopeptidase N, and alkaline phosphatase. PEDV replication results in massive destruction of villous enterocytes leading to a marked reduction of intestinal epithelial surface and brush border membrane-bound digestive enzyme activity. Reduced enzymatic activity and villous atrophy in the small intestine is thought to result in a maldigestive and malabsorptive diarrhea.

RT-PCR-based dot blot hybridization for the detection and differentiation between porcine epidemic diarrhea virus and transmissible gastroenteritis virus in fecal samples using a non-radioactive digoxigenin cDNA probe

Multiplex reverse transcription-polymerase chain reaction (RT-PCR)-based dot blot hybridization was developed to increase the sensitivity for the detection and differentiation between porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) in fecal samples. Fecal samples found positive by RT-PCR-based agarose gel electrophoresis were always found positive by RT-PCR-based dot blot hybridization. In addition, 5 out of 10 fecal samples which were negative for PEDV by RT-PCR-based agarose gel electrophoresis were positive for PEDV by RT-PCR-based dot blot hybridization. This RT-PCR-based dot blot hybridization increased 1000-fold in sensitivity for PEDV and 100-fold for TGEV; weakly positive bands in the agarose gel electrophoresis gave a clear positive result with dot blot hybridization.

Identification of porcine circovirus type 2 in retrospective cases of pigs naturally infected with porcine epidemic diarrhoea virus

The identification of porcine circovirus type 2 (PCV2) was studied in fresh intestinal tissues by polymerase chain reaction (PCR) and in formalin-fixed, paraffin-wax-embedded intestinal tissues by in situ hybridisation. The tissues came from pigs naturally infected with porcine epidemic diarrhoea virus (PEDV). A total of 35 (32.7%) of 107 small intestinal samples from pigs naturally infected with PEDV were found to be positive using PCR. Positive signals for PCV2 were detected in 32 (29.9%) of 107 small intestinal samples from pigs naturally infected with PEDV by in situ hybridisation. The distribution of positive cells in the jejunum and ileum was multifocal or patchy. Distinct positive labelling was found throughout the lamina propria in the small intestines. The results of this study indicate that PCV2 is highly prevalent in pigs naturally infected with PEDV.

Effect of temperature on the detection of porcine epidemic diarrhea virus and transmissible gastroenteritis virus in fecal samples by reverse transcription-polymerase chain reaction

The effect of storage temperature was determined for the detection of porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) in fecal samples from experimentally and naturally infected pigs by multiplex reverse transcription-polymerase chain reaction (RT-PCR). To examine the effect of storage temperature on the ability to detect PEDV and TGEV RNA by multiplex RT-PCR, fecal samples were stored for different temperatures (4, 21, 36, and 45 C) before extracting viral RNA. The PEDV and TGEV nucleic acids in fecal samples were stable up to 3 days at 4 C. The PEDV and TGEV nucleic acids were consistently detected in fecal samples up to 60 hours at 21 C and 24 hours only at 36 and 45 C. Thereafter, the number of positive signals declined. Positive signals were detected in fecal samples stored at 4 C by 240 hours. The PEDV and TGEV nucleic acids were consistently detected in fecal samples up to 60 hours at 21 C and 24 hours only at 36 and 45 C. The results of this study suggested that storage temperature has significant effect on the detection of PEDV and TGEV nucleic acids from fecal samples by multiplex RT-PCR.

Optimization of in situ hybridization protocols for detection of feline herpesvirus 1

In situ hybridization (ISH) protocol including microwaving pre-treatment regimes was developed and compared with protease digestion as a pre-treatment regime for its effects on detecting feline herpesvirus 1 (FHV-1) in formalin fixed, paraffin embedded tissue. We found that optimum results were obtained using microwave pre-treatment. The results showed that the use of microwave irradiation would be recommended as a means of supplementing ISH methods, especially when using long-term formalin fixed, paraffin-embedded tissue.

Experimental infection of piglets with a korean strain of porcine epidemic diarrhoea virus

Thirty colostrum-deprived piglets aged 1 day were inoculated with a Korean strain of porcine epidemic diarrhoea virus (PEDV). The purpose was to elucidate the pathogenicity and viral distribution in PEDV-infected piglets over a period of 60 h, by morphometric analysis, in-situ hybridization and immunohistochemistry. At 24-60 h post-inoculation (hpi), the villous height/crypt depth (VH/CD) ratio of infected pigs was significantly less than that of control pigs. Positive cells typically exhibited a dark black reaction product (in-situ hybridization) or brown reaction product (immunohistochemistry) in the cytoplasm, without background staining. PEDV nucleic acid and antigen were detected in the duodenum, jejunum and ileum of experimentally infected pigs. The results suggested that the Korean strain was virulent and caused severe villous atrophy in the small intestine.

Optimal enhancement of in situ hybridization for the detection of porcine circovirus 2 in formalin-fixed, paraffin-wax-embedded tissues using a combined pretreatment of thermocycler and proteinase K

Optimal enhancement of the hybridization signal was developed for the detection of porcine circovirus (PCV) 2 in formalin-fixed, paraffin-wax-embedded tissues from pigs with postweaning multisystemic wasting syndrome. The hybridization signal obtained after thermocycler pretreatment was very uniform across the section, whereas the signal obtained after either proteinase K or microwave pretreatment not only was weaker but was of variable intensity across sections. Thermocycler pretreatment combined with brief proteinase K digestion can enhance signal detection for target viral nucleic acid in formalin-fixed, paraffin-wax-embedded tissues. A strong hybridization signal was detected in the cytoplasm of macrophages and multinucleated giant cells in lymph node and spleen without background staining and morphological damage. The technical improvement results, therefore, in an identical background at the same time as an increased signal and, thus, may help detect lower levels of PCV2 DNA in formalin-fixed, paraffin-wax-embedded tissues.

Differentiation between porcine epidemic diarrhea virus and transmissible gastroenteritis virus in formalin-fixed paraffin-embedded tissues by multiplex RT-nested PCR and comparison with in situ hybridization

Porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) were detected and differentiated in formalin-fixed, paraffin-embedded tissues from experimentally and naturally infected pigs by multiplex reverse transcription-nested polymerase chain reaction (RT-nPCR). The results of this new method were compared with in situ hybridization. A method based on xylene deparaffinization followed by proteinase K digestion yielded RNA of a suitable quality for reliable and consistent multiplex RT-nPCR analyses. PEDV and TGEV cDNAs were detected in jejunal tissues from experimentally and naturally infected pigs by multiplex RT-nPCR. Distinct positive signals for PEDV and TGEV were also detected in the same jejunal tissues by in situ hybridization. The rate of conformity between multiplex RT-nPCR and in situ hybridization was 100% for the detection of PEDV and TGEV in formalin-fixed paraffin-embedded jejunal tissues.

Development of in situ nest PCR and comparison of five molecular biological diagnostic methods for the detection of intracellular viral DNAs in paraffin sections

Nest polymerase chain reaction (PCR), in situ hybridization (ISH), in situ PCR, in situ PCR/hybridization (PCR-ISH) and in situ nest PCR were compared for the detection and localization of intracellular viral DNAs in paraffin sections. MDBK cells were infected with alcelapine herpesvirus 1 ranging from 10(1) to 10(5) 50% tissue culture infected doses (TCID(50)), incubated 18 hr, then fixed and processed into paraffin blocks. Sections of the cell preparation were subjected to nest PCR, ISH, in situ PCR, PCR-ISH and in situ nest PCR using specific oligonucleotide primers or probes directed against the viral open reading frame 50. In situ nest PCR and nest PCR were found to be capable of detecting the viral DNA in the cells infected with the lowest virus titer. As compared with other molecular biological methods for the detection of the virus, in situ nest PCR was found to be more sensitive than ISH, in situ PCR and PCR-ISH. In situ nest PCR has wide applications for sensitive localization of low copy viral sequences within cells to investigate the role of viruses in a variety of clinical conditions.

Localization of swine influenza virus in naturally infected pigs

Swine influenza virus (SIV) RNA and antigen were detected in 15 naturally infected pigs by in situ hybridization using a nonradioactive digoxigenin-labeled cDNA probe and by immunohistochemistry using an influenza virus H1N1-specific monoclonal antibody. A 582-base pair cDNA probe for viral RNA encoding the nucleocapsid protein of SIV type A H1N1 strain was generated by the reverse transcription polymerase chain reaction. In situ hybridization and immunohistochemistry gave similar results for serial sections from each of 15 lung samples. Positive cells typically exhibited a dark brown (in situ hybridization) or red (immunohistochemistry) reaction product in the nucleus and cytoplasm without background staining. A strong positive signal for both in situ hybridization and immunohistochemistry was detected mainly in the bronchial and bronchiolar epithelial cells. A less intense signal was detected in the interstitial and alveolar macrophages. Simultaneous detection of hybridization and immunohistochemical signals on serial sections provided evidence that SIV had replicated in positive cells. The in situ hybridization technique developed in this study was useful for the detection of SIV RNA in tissues taken from naturally infected pigs and may be a valuable technique for studying the pathogenesis of SIV infection.

Experimental infection of piglets with transmissible gastroenteritis virus: a comparison of three strains (Korean, Purdue and Miller)

Eighty-four colostrum-deprived piglets aged 1 day were inoculated with either a Korean strain of transmissible gastroenteritis virus (TGEV) or one of two American strains (Purdue and Miller). The purpose was to compare, by morphometric analysis and in-situ hybridization, the Korean strain with the two American strains in respect of pathogenicity and viral distribution over a period of 72 h. The progression of infection in pigs infected with the Korean strain was much slower than that in pigs infected with either of the two American strains. At 6 h post-inoculation (hpi), the mean score of the villous height/crypt depth (VH/CD) ratio of pigs inoculated with the Purdue or Miller strain was significantly less than that of pigs inoculated with the Korean strain or uninfected control pigs. At 12-72 hpi, however, the VH/CD ratio of all infected pigs was significantly less than that of control pigs. In-situ hybridization showed significant differences between the Korean and American strains in terms of the amount of TGEV nucleic acid at 6, 12 and 60 hpi. TGEV nucleic acid was detected in the duodenum, jejunum and ileum of pigs inoculated with the Purdue or Miller strain but only in the jejunum and ileum of those inoculated with the Korean strain. The results suggested that the Korean strain was less virulent than the two American strains.

Differentiation of porcine circovirus 1 and 2 in formalin-fixed, paraffin-wax-embedded tissues from pigs with postweaning multisystemic wasting syndrome by in-situ hybridisation

Non-radioactive digoxigenin (DIG)-labelled probes that can differentiate porcine circovirus (PCV) 1 from PCV2 in formalin-fixed, paraffin-wax-embedded tissues by in-situ hybridisation were developed. A 349 base pair (bp) DNA fragment from open reading frame (ORF) 1 of PCV1 and a 481 bp DNA fragment from ORF2 of PCV2 generated by polymerase chain reaction (PCR) were used as PCV1 and PCV2 probes, respectively. A specific DIG-labelled PCV1 DNA probe did not hybridise with PCV2-infected PK-15 cells and vice versa. From the 40 field cases with postweaning multisystemic wasting syndrome tested by in-situ hybridisation, 30 (75 per cent) cases were PCV2-positive only and 10 (25 per cent) cases were positive for both PCV1 and PCV2. PCV1 and PCV2 DNAS were detected mainly in the macrophages of lymph nodes and spleens. Positive cells typically exhibited a dark brown to black reaction product mainly in the cytoplasm but also occasionally in the nucleus. In-situ hybridisation together with the differential probes developed in the present study represent an additional tool capable of differentiating of both types of PCV in formalin-fixed, paraffin-wax-embedded tissues.

Optimized protocols for the detection of porcine circovirus 2 DNA from formalin-fixed paraffin-embedded tissues using nested polymerase chain reaction and comparison of nested PCR with in situ hybridization

Optimized DNA extraction method and nested polymerase chain reaction (PCR) were developed for the detection of porcine circovirus 2 (PCV2) from formalin-fixed, paraffin-embedded tissues. Conventional PCR, nested PCR, and in situ hybridization methods were also compared for the detection of PCV2 in archival tissues. A method based on xylene deparaffinization followed by proteinase K digestion yielded DNA of sufficient quality for PCR analyses reliably and consistently. Twenty-six (70%) of the 37 tissues examined gave positive results with conventional PCR, whereas all the 37 tissues gave positive results using the nested PCR. A distinct positive signal for PCV2 was detected in spleen and lymph node from all the 37 pigs by in situ hybridization. The nested PCR and in situ hybridization could be applied successfully to archival tissues for the detection of porcine circovirus 2 DNA.