The role of porcine teschovirus in causing diseases in endemically infected pigs

doi:10.1016/j.vetmic.2012.07.031

Veterinary Microbiology

Volume 161, Issues 1–2, 28 December 2012, Pages 88-95

https://doi.org/10.1016/j.vetmic.2012.07.031 Get rights and content

Abstract

Porcine teschoviruses (PTVs) belong to the genus Teschovirus within the family Picornaviridae. Hitherto, PTVs have had 13 serotypes associated with a variety of clinical diseases. The virulent PTV-1 strains were associated with highly fatal, nonsuppurative encephalomyelitis of pigs (Teschen disease) in the 1930–1950s. Today, less virulent Talfan strains of PTV-1 are more widespread, and PTVs have contaminated swine herds worldwide (endemic or enzootic) together with a variety of common swine pathogens (multi-infection status). The aim of this study was to investigate the extent to which PTVs play a role in causing diseases in the field, under the endemic and multi-infection situation, when most pigs in the herds are infected and immune. Based on the fecal-oral model of pathogenesis, a set of 15 organs were collected from 30 culled post-weanling piglets of 4–8 weeks old. For nested RT-PCR targeted on the 5′-NTR, the PTV detection rate was 96.7% (by heads), confirming the endemic status, and infection was most commonly detected in the intestines (averaged 61%) and lymphoid organs (averaged 59%), followed by visceral organs (averaged 37%) and the CNS (different parts varied from 17 to 47%). The correlation of PTVs detected by nested RT-PCR and a histological lesion were analyzed by Chi-square test showing that in the field situation only non-suppurative encephalitis in the caudal part of the brain (P = 0.054) may be marginal significantly attributed to infection by PTVs. By genotyping based on partial VP1 sequences, 5 serotypes, namely PTV-1, -4, -6, -7, and -11, were identified, with some animals having two serotypes co-existed in different organs.

Introduction

Porcine teschoviruses (PTVs) belong to the genus Teschovirus within the family Picornaviridae. The virions are spherical, nonenveloped, 25–30 nm in diameter, and contain a linear plus sense single-stranded ribonucleic acid (ssRNA) genome surrounded by an icosahedral capsid (Knowles, 2006). The original genus Enterovirus was reclassified based on (i) cytopathic effect (CPE), (ii) replication properties in various host cell lines, (iii) serological assays, and (iv) sequence data into three groups: Teschovirus (CPE group I, PEV types 1–7 and 11–13), Sapelovirus (Porcine Enterovirus A, CPE group II, PEV-8), and Porcine Enterovirus B (CPE group III, PEV-9 and PEV-10) (Kaku et al., 2001, Zell et al., 2001). Hitherto, PTVs have been reclassified into 13 serotypes associated with a variety of clinical conditions, including polioencephalomyelitis, female reproductive disorders, enteric disease, and pneumonia (Knowles, 2006, Cano-Gomez et al., 2011, Boros et al., 2012). Recently a PTV-12 was identified in domestic pigs (Cano-Gomez et al., 2011) and a PTV-13 in wild boars (Boros et al., 2012).

The virulent PTV-1 strains, associated with highly fatal, nonsuppurative encephalomyelitis of pigs (Teschen disease), caused considerable economic loss in the 1930–1950s. Subsequently, the severity of polioencephalomyelitis decreased and the highly virulent Teschen strains were replaced by less virulent Talfan strains (Knowles, 2006, La Rosa et al., 2006, Yamada et al., 2007).

In the recent past, Taiwan has had two waves of PTV-1 epidemics, one in 2000 and a second in 2004 (Table 1). During these episodes, the diseased pigs exhibited prominent neurological signs and diarrhea, mimicking Talfan disease. In addition, common swine pathogens such as PCV2 and PRRSV have been frequently co-isolated, reflecting the multi-infection status in the field (Table 1). Furthermore, although clinical symptoms in several outbreaks implicated the involvement of classical swine fever virus (CSFV), CSFV was only rarely isolated (Table 1). Since 2004, PTVs have been increasingly isolated, ranging from 20.59% to 33% (by herd), and ranking as the first or second most commonly isolated virus from culled pigs in Taiwan (Huang et al., 2009), suggesting an endemicity status. The question is thus the extent to which PTVs play a role in causing diseases in the field under the current endemic and multi-infection status, where most pigs are infected and immune. The aims of this study were to investigate the current status of PTVs in the endemic situation, to determine the role PTVs play under the multiple infection status in causing diseases, and to determine which samples or methods would be appropriate choices for diagnostics.

Section snippets

Sampling

Culled post-weanling piglets (n = 30), aged from 4 to 8 weeks, were collected from 2 out of 3 farrow-to-finish herds belong to the same corporation in central Taiwan. Each herd operated at approximately 10,000 heads level, and maintained in the past 3 years a weaned-to-finish livability of >88%. In these herds sows were routinely vaccinated for classical swine fever, pseudorabies, Japanese encephalitis, and parvovirus. Piglets were injected with vaccines of Mycoplasma at 1 and 3 weeks old, of

Pathological findings in the culled pigs

Grossly, the most common lesions found were the polyserositis, bronchopneumonias, and interstitial pneumonia, with increased pleural effusions. Other common lesions included swollen or peripheral hemorrhagic LN, intestines distended with fluid or mucus, and yellow fragile liver. These gross lesions were non-specific, mostly bacteria-induced, and largely unrelated to PTV infection.

The histopathology confirmed the gross findings. Those in the respiratory system were lymphoplasmacytic interstitial

Discussion

The pathogenesis of PTVs in pigs is similar to poliovirus in humans. PTVs are thought to be transmitted mainly via the fecal-oral route, followed by a primary replication in the tonsils and alimentary tract, and later a viremia. Virus enters the CNS either via a hematogenous or a vascular route, breaching the blood–brain barrier (BBB) and/or via retrograde axonal transport along cranial nerves (Knowles, 2006, Racaniello, 2006). Based on this model, the presence of PTVs detected by PCR (Table 4,

Conclusion

PTVs were commonly detected in the intestines, confirming the endemic or enzootic status in the swine herd. The decreasing order of presence of PTVs in the intestines, lymphoid, and visceral organs is consistent with a viremia based on the known fecal-oral pathogenesis model. The higher detection rates in the cranial parts of the brain suggest the importance of the intranasal route of infection, in addition to viremia, in invasion into the CNS. However, under the endemic and multi-infections

Acknowledgements

This study was supported by grants from the BAPHIQ of the Council of Agriculture, Taiwan (NTU grant number 97A2028, 98A2071, 99A2086).

References (25)

C. Cano-Gomez et al.
Analyzing the genetic diversity of teschovirus in Spanish pig populations using complete VP1 sequences
Infect. Genet. Evol.
(2011)
V.R. Racaniello
One hundred years of poliovirus pathogenesis
Virology
(2006)
A. Tichopad et al.
Inhibition of real-time RT-PCR quantification due to tissue-specific contaminants
Mol. Cell. Probes
(2004)
R. Zell et al.
Detection of porcine enteroviruses by nRT-PCR: differentiation of CPE groups I-III with specific primer sets
J. Virol. Methods
(2000)
Anon.
Teschovirus encephalomyelitis (previously enterovirus encephalomyelitis or Teschen/Talfan disease)
Manual of Diagnostic Tests and Vaccines for Terrestrial Animals
(2008)
A. Boros et al.
Porcine teschovirus in wild boars in Hungary
Arch. Virol.
(2012)
D. Buitrago et al.
A survey of porcine picornaviruses and adenoviruses in fecal samples in Spain
J. Vet. Diagn. Invest.
(2010)
W.A. Chittick et al.
Comparison of RNA extraction and real-time reverse transcription polymerase chain reaction methods for the detection of porcine reproductive and respiratory syndrome virus in porcine oral fluid specimens
J. Vet. Diagn. Invest.
(2011)
A. Das et al.
Removal of real-time reverse transcription polymerase chain reaction (RT-PCR) inhibitors associated with cloacal swab samples and tissues for improved diagnosis of avian influenza virus by RT-PCR
J. Vet. Diagn. Invest.
(2009)
D.M. Horstmann et al.
Experiments with Teschen disease (virus encephalomyelitis of swine)
J. Immunol.
(1952)

T.S. Huang et al.

The results of virus isolation in swine tissue samples submitted by LDCC and tested by viral isolation and PCR and/or RT-PCR in 2008

Exp. Rep. AHRI (Animal Health Research Institute)

(2009)

Y. Kaku et al.

Genetic reclassification of porcine enteroviruses

J. Gen. Virol.

(2001)

Cited by (31)

Seneca Valley virus induces immunodepressionin suckling piglets by selective apoptosis of B lymphocytes
2021, Microbial Pathogenesis
Seneca Valley virus (SVV) is the causative agent of an emerging infectious vesicular disease in swine that is clinically indistinguishable from other vesicular diseases of swine. This study utilized healthy suckling piglets (control) and SVV-naturally infected suckling piglets to determine the effects of SVV on lymphoid tissues and determined the SVV RNA load by quantitative RT-PCR (qRT-PCR). Furthermore, immunohistochemistry (IHC) analyses were performed to quantify the expression of T and B cell lymphocytes, natural killer cells, cleaved caspase 3, and ki-67. The main histopathologic finding in the infected group was severe lymphoid depletion. The highest average of SVV RNA load by qRT-PCR (Log¹⁰ genomic copies/g of tissue) occurred at the spleen (8.54 ± 0.8), followed by the tonsils (8.04 ± 1.42), and mesenteric lymph nodes (6.90 ± 1.42). The IHC analyses revealed that there was an increased in cellular apoptosis with concomitant reduction in the proliferation of B cells. The results from this study have demonstrated that SVV-infected piglets exhibited decreased lymphocyte density probably due to lymphoid apoptosis, affecting particularly B-cells lymphocytes.
Metagenomic identification and sequence analysis of a Teschovirus A-related virus in porcine feces in Japan, 2014–2016
2018, Infection, Genetics and Evolution
Porcine Teschoviruses (PTVs) are associated with polioencephalomyelitis and various diseases, including reproductive and gastrointestinal disorders, of pigs and wild boars, and are also detected in the feces of healthy pigs. The genus Teschovirus contains a single species Teschovirus A that currently includes 13 serotypes. In the present study, we identified novel PTVs that are distantly related to Teschovirus A and were found in fecal samples of pigs with or without diarrhea in Japan. Phylogenetic analysis of amino acid (aa) sequences of the complete coding region revealed that these newly identified viruses did not cluster with any strains of PTVs or other strains within the picornavirus supergroup 1, suggesting that the viruses may not belong to Teschovirus A or any genus of the family Picornaviridae. These novel PTVs share a type IV internal ribosomal entry site and conserved characteristic motifs in the coding region, yet exhibit 62.2–79.0%, 86.6–92.8%, 77.1–81.0%, and 84.3–86.7% aa identities to PTV strains in P1, 2C, 3C, and 3D regions, respectively. In contrast, PTV 1–13 strains of the Teschovirus A share 76.5–92.1%, 88.1–99.7%, 93.2–100%, and 95.8–100% aa identities in the P1, 2C, 3C, and 3D, respectively, within the species. These data imply that the newly identified viruses belong to teschoviruses, and may represent a novel species in the genus Teschovirus.
The urinary shedding of porcine teschovirus in endemic field situations
2016, Veterinary Microbiology
Citation Excerpt :
However, because of the recognized bias and the limited detection capacity of the primer pairs (Table 2, section 2.5), the existence of a wider variety of serotypes is highly likely (Cano-Gómez et al., 2011b). For molecular serotyping, two published primers (La Rosa et al., 2006) were initially used and had a success rate of 19.3% (Chiu et al., 2012), as compared to that by pan-PTV nested PCR (Zell et al., 2000 in Chiu et al., 2012). Multiple bands were also observed, with one band of expected size (data not shown).
Porcine teschoviruses (PTVs) belong to the genus Teschovirus within the family Picornaviridae. PTVs are universal contaminants in pig herds in endemic and multi-infection statuses. Previous research has demonstrated PTV antigens and nucleic acid in renal glomeruli and tubular epithelia, suggesting the possibility that PTVs might be shed and transmitted via urine. The study aimed to demonstrate, in the context of pathogenesis, the presence of PTVs in the urine of naturally infected pigs. Viral loads of fluid and tissue samples quantified by an established qRT-PCR showed detection rates of 100% by head and in urine, feces, plasma and nasal swabs, and 38% in kidney. As predicted, PTVs were present in urine at 10^{4.02 ± 1.45} copies/100 μl volume, equivalent to 17% of that in plasma. No significant differences were observed between healthy and culled pigs or among the 7 sampled herds. The presence of PTVs in urine was further substantiated by molecular serotyping. In particular, PTV-10 was identified in the urine of 3 piglets from 3 separate herds, consistent with the most prevalent serotype found in this study, and in plasma. The urine mixes with feces to form slurry making it easier for PTV to spread and contaminate the environment.
Single virus detection by means of atomic force microscopy in combination with advanced image analysis
2014, Journal of Structural Biology
In the present contribution virions of five different virus species, namely Varicella-zoster virus, Porcine teschovirus, Tobacco mosaic virus, Coliphage M13 and Enterobacteria phage PsP3, are investigated using atomic force microscopy (AFM). From the resulting height images quantitative features like maximal height, area and volume of the viruses could be extracted and compared to reference values. Subsequently, these features were accompanied by image moments, which quantify the morphology of the virions. Both types of features could be utilized for an automatic discrimination of the five virus species. The accuracy of this classification model was 96.8%. Thus, a virus detection on a single-particle level using AFM images is possible. Due to the application of advanced image analysis the morphology could be quantified and used for further analysis. Here, an automatic recognition by means of a classification model could be achieved in a reliable and objective manner.
Multiple models of porcine teschovirus pathogenesis in endemically infected pigs
2014, Veterinary Microbiology
Citation Excerpt :
Hence the results did not conflict with the fecal-oral pathogenesis in general. Inguinal LN seems to be an ideal all-purpose specimen due to its reasonable viral load (Tables 3–5), reasonable viral detection rate by nested RT-PCR (Chiu et al., 2012), and easier sampling, for few veterinarians will mistake it. This was further supported by ISH, wherein signals primarily presented in the dark zone of the germinal center and adjacent paracortex (Fig. 4B; Table 6).
Porcine teschoviruses (PTVs) belong to the genus Teschovirus within the family Picornaviridae. PTVs are universal contaminants in pig herds in endemic and multi-infection status. To further the understanding of PTV pathogenesis in endemically infected pigs, a set of samples was studied by real time reverse transcription PCR (qRT-PCR) to quantitate viral loads in tissues and by in situ hybridization (ISH) to locate PTV signals in target cells, both targeting the 5′-NTR. cRNA of PTV-1 and PTV-7, in vitro transcribed from cloned fragments of 5′-NTR of 2 viruses, was used to construct standard curves and to run parallel in qRT-PCR, which had detection limits of 10¹ copies/per reaction, with a linearity in between 10¹ and 10⁷ copies/per reaction and correlation coefficients of 0.997–0.9988. The qRT-PCR specifically amplified RNA from PTV-1 to -11, while excluding those of Sapelovirus, PEV-9 and PEV-10. Inguinal lymph node (LN) had the highest viral load of all (assuming 100%), followed by ileac LN (89–91%), tonsil (66–68%), ileum (59–60%), spleen (38–40%), and kidney (30–31%), with the least in brain (22.9%) of the inguinal LN. The 22.9% load in brain was higher than that anticipated from a simple fecal-oral-viremia operative model. The results suggested in addition that intranasal infection and retrograding axonal infection from the tonsils were equally operative and significant. ISH revealed PTV signals in a wider variety of tissue cell types than before. PTV signals were noted most impressively in neurons of the cerebral cortex and hippocampus and in the dark zone of the germinal center and adjacent paracortex of regional LN. Multiple operative models indicated that PTVs seemed to have no difficulty invading the brain. The key to whether encephalitis would ensue resided in the animal's immune status and topographic differences of neurons’ susceptibilities to PTVs. When common co-infected agents are present, as is typical in the field, PTVs may synergize in causing diseases.
The prevalence of porcine teschovirus in the pig population in northeast of China
2013, Journal of Virological Methods
The prevalence of porcine teschovirus (PTV) in swine herds in northeast China was investigated. In 2008–2009, 1384 samples of pig sera were collected from 42 farms in Shandong, Hebei, Heilongjiang, and Jilin provinces and in Tianjin City and were tested for specific antibody against PTV-8 by immunofluorescence assay. All 42 pig herds were positive for antibodies against PTV-8, and 61.3% of the serum samples were PTV-8 positive. During the survey, one PTV strain was isolated and named Fuyu/2009; phylogenetic analysis showed that the PTV Fuyu/2009 belongs to the PTV-8 serotype. The serological results indicate that most if not all pig herds in northeast of China have been exposed to PTV. RT-PCR performed on 114 clinical samples indicated a possible association between PTV and disease. According to genotyping based on partial VP1 sequences, four serotypes (PTV-2, -4, -6, and -8) were identified in northeast of China; sequence data also provided evidence of natural recombination between PTV serotypes and indicated that homologous recombination may be a driving force in PTV evolution. The role of PTV in disease remains inconclusive. The current results together with published results indicate that the prevalence of PTV is increasing among swine herds in northeast of China.

View all citing articles on Scopus

View full text

The role of porcine teschovirus in causing diseases in endemically infected pigs

Abstract

Introduction

Section snippets

Sampling

Pathological findings in the culled pigs

Discussion

Conclusion

Acknowledgements

Infect. Genet. Evol.

Virology

Mol. Cell. Probes

J. Virol. Methods

Teschovirus encephalomyelitis (previously enterovirus encephalomyelitis or Teschen/Talfan disease)

Manual of Diagnostic Tests and Vaccines for Terrestrial Animals

Porcine teschovirus in wild boars in Hungary

Arch. Virol.

A survey of porcine picornaviruses and adenoviruses in fecal samples in Spain

J. Vet. Diagn. Invest.

Comparison of RNA extraction and real-time reverse transcription polymerase chain reaction methods for the detection of porcine reproductive and respiratory syndrome virus in porcine oral fluid specimens

J. Vet. Diagn. Invest.

Removal of real-time reverse transcription polymerase chain reaction (RT-PCR) inhibitors associated with cloacal swab samples and tissues for improved diagnosis of avian influenza virus by RT-PCR

J. Vet. Diagn. Invest.

Experiments with Teschen disease (virus encephalomyelitis of swine)

J. Immunol.

The results of virus isolation in swine tissue samples submitted by LDCC and tested by viral isolation and PCR and/or RT-PCR in 2008

Exp. Rep. AHRI (Animal Health Research Institute)

Genetic reclassification of porcine enteroviruses

J. Gen. Virol.