Immunohistochemical Detection of Porcine Teschovirus Antigen in the Formalin-fixed Paraffin-embedded Specimens from Pigs Experimentally Infected with Porcine Teschovirus

Analysis on the genome of a teschovirus type 1 isolates with swine diarrhea

Porcine Teschoviruses (PTVs) are associated with polioencephalomyelitis and various diseases, including reproductive and gastrointestinal disorders of pigs and wild boars, but rarely detected in the feces of pigs. In this study, a sample of swine diarrhea that tested positive for PTVs is subjected to high-throughput sequencing. The viral genome was 7221 nucleotides (nt) in length, which was consisted of twelve genes. Phylogenetic analysis showed and it was closely related to the PTV-HNMY(MG755212.1). The nucleotide homology of VP1 gene of PTVs JS2021 with PTV-1AF 296102.1 reached 82.97%, belonging to a branch of PTV-1 serotype. The nucleotide homology of VP1 protein with other serotypes of PTV is quite different from that of other serotypes of PTV. Bioinformatics analysis showed that PTVs have four capsid proteins, namely VP1, VP2, VP3 and VP4. The VP1 encodes a 29 kDa protein, which is the main protective antigen, a theoretical isoelectric point of 6.73, no transmembrane domain, no signal peptide and potential phosphorylation site. The VP1 protein is an unstable hydrophilic intracellular protein, which contains four secondary structures: irregular curl (c), extended chain (e), α-helix (h) and β-folded (t). The tertiary structure is heart-shaped and has multiple B cell epitopes. By analyzing the tertiary structure, we found that the amino acid at position 129 of VP1 mutated and reduction a larger alpha helix. This may lead to the main cause of piglet diarrhea. These findings enriched our knowledge of the viruses in the role of swine diarrhea, and help to develop an effective strategy for disease prevention and control.

[Hind limb paralysis in fattening pigs due to a new strain of porcine Teschovirus A11]

In a fattening farm in southern Germany, paralysis of the hind limbs was observed in 2 age groups (50 kg as well as 60 kg) during a 4 week period. Despite a low morbidity of 3.3 % the majority of the affected animals needed to be euthanized in consequence to the progression of their hind limb paralysis. During pathomorphological examinations of 2 affected fattening pigs severe lymphohistiocytic meningoencephalomyelitis and vasculitis were detected. Immunhistochemistry revealed the presence of Porcine Teschovirus antigen in all parts of the central nervous system as well as in several cell types (neurons, glia cells, endothelial cells, mononuclear cells). Porcine Teschovirus was detected by PCR in spinal cord samples. The subsequently performed phylogenetic analysis PCR revealed a close relation (88 % full genome sequence) to porcine Teschovirus A11 strain "Dresden". Other swine relevant pathogens were excluded by PCR, bacteriologic examination and sequencing. Following a period of 4 weeks no additional cases of hind limb paralysis were observed in the fattening farm.

Epidemiology and molecular characterization of Porcine teschovirus in Hunan, China

Porcine teschoviruses (PTVs) have been shown to be widely distributed in pig populations. In this study, 261 faecal and 91 intestinal content samples collected from pigs at 29 farms in Hunan, China, were tested for the presence of PTV by reverse transcription-polymerase chain reaction (RT-PCR). An overall PTV-positivity rate of 19.03% was detected by RT-PCR, and a high PTV infection rate was circulating in asymptomatic fattening and nursery pigs. In total, 40 PTV isolates (PTV-HuNs) were obtained. Alignment of their coding sequences with those of other known PTVs revealed that the genomic sequence of the polyprotein contains 6,606-6,621 nucleotides, encoding a 2,202-2,207-amino acid sequence. Phylogenetic analyses based on the VP1 gene and capsid protein gene exhibited 13 main lineages corresponding to PTV serotypes 1-13, and seven PTV serotypes (PTV 2-6, 9, and 11) were identified in the isolates obtained in our study; this is the first report of PTV 5, 9 and 11 in China. Recombination analysis among the PTV-HuNs indicated that nine recombination events have occurred, including both inter- and intraserotype events. In addition, results demonstrated that only limited positive selection is acting on the global population of PTV isolates, and purifying selection is predominant. In conclusion, this study revealed a high infection rate of PTVs circulating in asymptomatic fattening and nursery pigs. The 40 PTV-HuNs showed high genetic diversity, and genetic analysis of all available PTV sequences revealed that strong purifying selection and recombination play important roles in the genetic diversity and evolution of the virus.

Experimental teschovirus encephalomyelitis in gnotobiotic pigs

A central nervous system (CNS) disorder characterized by non-suppurative encephalomyelitis with neurological signs was induced experimentally in gnotobiotic pigs by intravenous and oral or intranasal inoculation of the porcine teschovirus (PTV) Toyama 2002 strain isolated from breeding pigs in Japan. Lesions consisting of perivascular cuffing of mononuclear cells, focal gliosis, neuronal necrosis and neuronophagia were observed in the brainstem, cerebellum and spinal cord. Non-suppurative ganglionitis in the spinal ganglion and neuritis in the spinal root were also observed. Regardless of the route of inoculation, all pigs infected experimentally with PTV showed a similar distribution of CNS lesions. Histological lesions in the CNS caused by oral or intranasal inoculation of the virus were mild compared with those induced by intravenous infection. Immunohistochemically, the distribution of PTV antigens corresponded closely with the distribution of brain lesions. PTV particles were detected via electron microscopy in the cytoplasm of nerve cells and the endothelial cells of blood vessels in the spinal cord of inoculated pigs. Polymerase chain reaction analysis demonstrated the presence of PTV RNA in the CNS, tonsils and large intestines of 21 of the 22 pigs inoculated. Direct CNS invasion via the blood vessels appears to be a major route of infection for PTV. The gnotobiotic pig provides a useful model for further study of PTV pathogenesis.

Multiple models of porcine teschovirus pathogenesis in endemically infected pigs

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 10(1) copies/per reaction, with a linearity in between 10(1) and 10(7) 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.

Development of a reverse transcription loop-mediated isothermal amplification assay for detection of Porcine teschovirus

Loop-mediated isothermal amplification (LAMP) is a sensitive method for DNA amplification. In the present report, the development of a single-tube, one-step, real-time accelerated reverse transcription (RT)-LAMP for the detection of Porcine teschovirus (PTV) is described. Six designed primers amplified target gene sequences successfully at constant temperature (65 °C) within 1 hr, and the amplification results could be visualized directly by the naked eye. The sensitivity of the LAMP was 10 times higher than that of conventional polymerase chain reaction, and no cross-reactivity was found when the genomes of other common swine pathogens were subjected to the RT-LAMP system. When 43 clinical samples were tested by the RT-LAMP method, results indicated that the test is simple, rapid, accurate, and sensitive for the detection of PTV.