Pathological and molecular investigation of porcine sapelovirus infection in naturally affected Indian pigs

Rapid detection of porcine sapelovirus by reverse transcription recombinase polymerase amplification assay

BACKGROUND

Porcine Sapelovirus (PSV) infection has been confirmed in pigs worldwide, mostly asymptomatic, but in some cases, it can lead to significant issues in the gastrointestinal, respiratory, neurological, or reproductive systems. PSV is considered an emerging pathogen of porcine species. Recombinase polymerase amplification (RPA) is a simple and fast isothermal technique that uses three enzymes for amplification without the use of any sophisticated equipment.

METHODS AND RESULTS

The reverse transcription recombinase polymerase amplification (RT-RPA) assay was developed and optimized for field based detection of PSV. The assay was developed by targeting 5´UTR region of PSV genome and optimized for reaction time, temperature, primer and MgOAc concentration. The analytical sensitivity and specificity of assay was determined. The assay was evaluated on 85 porcine faecal samples collected from field. In addition to conventional format, this assay was also optimized for visual dye-based detection format and lateral flow strips based detection (in combination with probe). The developed assay works at constant temperature of 35 °C for 20 min with forward primer concentration 20pm, reverse primer concentration 10pm and MgOAc concentration of 14mM. This assay is highly sensitive and detects up to 28 copies of viral nucleic acid both in the conventional as well as in fluorescent dye based detection format. Using the newly developed assay 21 samples out of 85 samples were found positive, showing positivity rate of 24.7%. The positivity rate of RT-RPA assay corroborated with the gold standard RT-PCR test.

CONCLUSIONS

This study presented the development of an RT-RPA isothermal assay for rapid and accurate detection of PSV. The assay is highly sensitive, specific, works at a low and constant temperature, does not require any high-end instrument and can be a potential diagnostics tool for pen-side testing of PSV in the field conditions. The newly developed RT-RPA assay could successfully detect PSV circulating in swine population of Haryana, India. This is a first report of this kind from the region.

Detection of porcine enteric picornaviruses from faecal samples of Indian pigs

Porcine enteric picornaviruses often consequence diarrhoea and nervous complications in pig and pose enormous loss to pig farming. The present study expands the limited Indian data of porcine enteric picornaviruses which is needed for the early implementation of control measures and to check further outbreaks. A total of 398 porcine faecal samples from Uttar Pradesh, Madhya Pradesh, Chhattisgarh and Jharkhand state of India were screened for porcine teschovirus (PTV), porcine sapelovirus (PSV) and enterovirus G (EV-G) by reverse transcriptase-polymerase chain reaction (RT-PCR) using 5'UTR-specific primers. The prevalence of PTV, PSV and EV-G was found to be 12.81% (51/398), 5.77% (23/398) and 24.37% (97/398), respectively. EV-G was relatively higher in circulation in Indian pigs among all the included enteric picornaviruses. Conversely, the concurrent infection of more than one enteric picornavirus was also frequent.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-022-00756-0.

Isolation, Characterization, and Molecular Detection of Porcine Sapelovirus

Porcine sapelovirus (PSV) is an important emerging pathogen associated with a wide variety of diseases in swine, including acute diarrhoea, respiratory distress, skin lesions, severe neurological disorders, and reproductive failure. Although PSV is widespread, serological assays for field-based epidemiological studies are not yet available. Here, four PSV strains were recovered from diarrheic piglets, and electron microscopy revealed virus particles with a diameter of ~32 nm. Analysis of the entire genome sequence revealed that the genomes of PSV isolates ranged 7569–7572 nucleotides in length. Phylogenetic analysis showed that the isolated viruses were classified together with strains from China. Additionally, monoclonal antibodies for the recombinant PSV-VP1 protein were developed to specifically detect PSV infection in cells, and we demonstrated that isolated PSVs could only replicate in cells of porcine origin. Using recombinant PSV-VP1 protein as the coating antigen, we developed an indirect ELISA for the first time for the detection of PSV antibodies in serum. A total of 516 swine serum samples were tested, and PSV positive rate was 79.3%. The virus isolates, monoclonal antibodies and indirect ELISA developed would be useful for further understanding the pathophysiology of PSV, developing new diagnostic assays, and investigating the epidemiology of the PSV.

Porcine teschovirus, sapelovirus, and enterovirus in Swiss pigs: multiplex RT-PCR investigation of viral frequencies and disease association

Porcine teschovirus (PTV), sapelovirus (PSV-A), and enterovirus (EV-G) are enteric viruses that can infect pigs and wild boars worldwide. The viruses have been associated with several diseases, primarily gastrointestinal, neurologic, reproductive, and respiratory disorders, but also with subclinical infections. However, for most serotypes, proof of a causal relationship between viral infection and clinical signs is still lacking. In Switzerland, there has been limited investigation of the occurrence of the 3 viruses. We used a modified multiplex reverse-transcription PCR protocol to study the distribution of the viruses in Swiss pigs by testing 363 fecal, brain, and placental or abortion samples from 282 healthy and diseased animals. We did not detect the 3 viruses in 94 placental or abortion samples or in 31 brain samples from healthy pigs. In brain tissue of 81 diseased pigs, we detected 5 PSV-A and 4 EV-G positive samples. In contrast, all 3 viruses were detected at high frequencies in fecal samples of both healthy and diseased pigs. In healthy animals, PTV was detected in 47%, PSV-A in 51%, and EV-G in 70% of the 76 samples; in diseased animals, frequencies in the 81 samples were 54%, 64%, and 68%, respectively. The viruses were detected more frequently in fecal samples from weaned and fattening pigs compared to suckling piglets and sows. Co-detections of all 3 viruses were the most common finding. Based on clinical and pathology data, statistical analysis yielded no evidence for an association of virus detection and disease. Further research is required to determine if pathogenicity is linked to specific serotypes of these viruses.

High prevalence, genetic diversity and a potentially novel genotype of Sapelovirus A (Picornaviridae) in enteric and respiratory samples in Hungarian swine farms

All of the known porcine sapeloviruses (PSVs) currently belong to a single genotype in the genus Sapelovirus (family Picornaviridae). Here, the complete genome of a second, possibly recombinant, genotype of PSV strain SZ1M-F/PSV/HUN2013 (MN807752) from a faecal sample of a paraplegic pig in Hungary was characterized using viral metagenomics and RT-PCR. This sapelovirus strain showed only 64 % nucleotide identity in the VP1 region to its closest PSV-1 relative. Complete VP1 sequence-based epidemiological investigations of PSVs circulating in Hungary showed the presence of diverse strains found in high prevalence in enteric and respiratory samples collected from both asymptomatic and paraplegic pigs from 12 swine farms. Virus isolation attempts using PK-15 cell cultures were successful in 3/8 cases for the classic but not the novel PSV genotype. Sequence comparisons of faeces and isolate strains derived VP1 showed that cultured PSV strains not always represent the dominant PSVs found in vivo.

Two novel porcine teschovirus strains as the causative agents of encephalomyelitis in the Netherlands

Background

Porcine teschovirus (PTV) circulates among wild and domesticated pig populations without causing clinical disease, however neuroinvasive strains have caused high morbidity and mortality in the past. In recent years, several reports appeared with viral agents as a cause for neurologic signs in weanling and growing pigs among which PTV and new strains of PTV were described.

Case presentation

On two unrelated pig farms in the Netherlands the weanling pig population showed a staggering gate, which developed progressively to paresis or paralysis of the hind legs with a morbidity up to 5%. After necropsy we diagnosed a non-suppurative encephalomyelitis on both farms, which was most consistent with a viral infection. PTV was detected within the central nervous system by qPCR. From both farms PTV full-length genomes were sequenced, which clustered closely with PTV-3 (98%) or PTV-11 (85%). Other common swine viruses were excluded by qPCR and sequencing of the virus.

Conclusion

Our results show that new neuroinvasive PTV strains still emerge in pigs in the Netherlands. Further research is needed to investigate the impact of PTV and other viral agents causing encephalomyelitis within wild and domestic pig populations supported by the awareness of veterinarians.

Sapelovirus

Sapelovirus (SPV), an emerging virus in the family Picornaviridae, is detected in several animal and bird species irrespective of their age. Amid all SPVs, porcine sapeloviruses (PSVs) are more ubiquitously present all over the world in porcine population. These viruses are highly stable in different environmental conditions and spread easily within the susceptible animals mainly through faeco-oral route. Usually, PSVs cause asymptomatic infections but are also clinically associated with encephalomyelitis, respiratory distress, fertility disorders and skin lesions. PSV-associated outbreaks have been reported where death occurs due to polioencephalitis and respiratory paralysis. Till date, PSVs have been detected from several European and Asian countries with moderate-to-high prevalence and clinical course. Viral capsid proteins are immunogenic and mutations in these proteins are responsible for the diverse nature of the viruses. Further, genomic analysis shows the varied evolutionary patterns and the presence of recombination within PSV strains. These viruses also exist as concurrent infections with several enteric bacterial, viral and parasitic pathogens. Classical to modern biotechnological assays are in use to detect PSV involving virus isolation in cell culture, immunohistochemistry, conventional nucleic acid amplification techniques, quantitative real-time amplification assays and isothermal amplification molecular techniques. Till date, there is no vaccine available against PSVs.

Immunohistochemical detection of naturally occurring porcine Sapelovirus infection in Indian pigs

We investigated immunohistochemical detection of porcine Sapelovirus (PSV) in naturally infected pigs of different ages. Forty-nine fecal samples, intestinal contents and other tissue samples from dead pigs were screened in previous study using reverse transcription polymerase chain reaction (RT-PCR) for PSV infection. Eight animals were positive for PSV based on RT-PCR examination. Gross lesions were recorded mainly in the large and small intestines. Microscopic examination of intestines showed severe enteritis. Tissue sections of all organs from PSV positive animals were immunostained using hyperimmune serum raised in rats against PSV that had been grown in a BHK-21 cell line. Staining of PSV was found only in the large and small intestines.

Nearly Complete Genome Sequence of a Sapelovirus A Strain Identified in Swine in Italy

We report the first nearly complete genome sequence of a porcine sapelovirus (PSV) A strain that was identified from feces of piglets suffering from diarrhea in Italy in 2015. Phylogenetic investigations revealed a separate clustering for the Italian PSV, indicating unique molecular features.

We report the first nearly complete genome sequence of a porcine sapelovirus (PSV) A strain that was identified from feces of piglets suffering from diarrhea in Italy in 2015. Phylogenetic investigations revealed a separate clustering for the Italian PSV, indicating unique molecular features.

Immunocytochemistry assay in BHK-21 cell line infected with Porcine Sapelovirus

The present study describes an immunocytochemistry (ICC) assay with self-raised hyperimmune sera and a Baby Hamster Kidney-21 (BHK-21) cell line infected with Porcine Sapelovirus (PSV). Sapelovivus/IVRI/SPF-c-6/2015 strain Indian PSV was isolated from the porcine IBRS-2 cell line and investigated for growth on non-porcine cell lines. After two passages, PSV was successfully grown in BHK-21 and produced the same cytopathic effects as in IBRS-2 such as shrinking of cytoplasm, rounding of cells and detachment of cells from the surface of flask within 24 h. For raising of hyperimmune sera, PSV was grown in IBRS-2 cell line up to the required volume and purified by ultracentrifugation. With self-raised hyperimmune sera in laboratory rats, ICC was performed in BHK-21 cells infected with PSV. Positive signals consisted of large granular aggregates of virus in the cytoplasm near the nucleus, suggesting that PSV can infect cell lines other than those of porcine origin.