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

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.

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.