Development of a recombinant N-Gp5c fusion protein-based ELISA for detection of antibodies to porcine reproductive and respiratory syndrome virus

Research progress on the N protein of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease caused by the porcine reproductive and respiratory syndrome virus (PRRSV). PRRSV exhibits genetic diversity and complexity in terms of immune responses, posing challenges for eradication. The nucleocapsid (N) protein of PRRSV, an alkaline phosphoprotein, is important for various biological functions. This review summarizes the structural characteristics, genetic evolution, impact on PRRSV replication and virulence, interactions between viral and host proteins, modulation of host immunity, detection techniques targeting the N protein, and progress in vaccine development. The discussion provides a theoretical foundation for understanding the pathogenic mechanisms underlying PRRSV virulence, developing diagnostic techniques, and designing effective vaccines.

Development of CD163 receptor-based enzyme-linked immunosorbent assay for diagnosis of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) is an important economical disease in the global swine industry. The accurate detection of the PRRS virus (PRRSV) antigen is essential for the disease control and prevention programme. In this study, an indirect enzyme-linked immunosorbent test (PRRSVCD163-iELISA) was developed for the detection of the PRRSV antigen in samples of post-mortem swine tissue using the recombinant pig CD163 receptor protein as the capture ligand. The test was found to be specific for PRRSV, with no cross-reactions with other prevalent pig viral pathogens. The assay was validated by testing 217 post-mortem porcine tissue samples and the results were found to be satisfactory with a relative accuracy of 88.88%. Our assay is also quite precise, with intra- and inter-assay CVs of 6% and 10%, respectively. These findings imply that the PRRSVCD163-iELISA developed is capable of detecting the PRRSV antigen in swine post-mortem tissue samples. This research showed that porcine CD163, the PRRSV cellular receptor, can be exploited to build a diagnostic technique for the detection of PRRSV antigen.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03376-z.

Isolation and molecular characterization of GP5 glycoprotein gene of Betaarterivirus suid 2 from Mizoram, India

Porcine reproductive and respiratory syndrome (PRRS) is a serious swine disease causing great economic impact worldwide. The emergence of highly pathogenic strains in Asian countries is associated with large scale mortality in all age groups of pigs besides the classical presentation of severe respiratory distress, pneumonia, and a series of reproductive disorders in sows, like late-term abortion, premature farrowing, and an increased number of stillborn piglets. The present study was designed with the aim of isolation and characterization of the Betaarterivirus suid 2 from outbreaks in Mizoram in primary porcine alveolar macrophage and subsequently characterized the GP5 gene sequence of the isolate in terms of phylogenetic analysis and deduce amino acid sequence comparison. Virus propagation was performed in the porcine alveolar macrophage (PAM) primary cell culture and confirmed by immunoperoxidase test, FAT, and nested RT-PCR. The full-length GP5 gene (603nt) was amplified from the isolate and subsequently cloned and sequenced (MN928985). Phylogenetic analysis and sequence comparison of the present isolate was found to have similarity 98.7-98.8% with Myanmar HP-PRRS strains, 98-98.5% with Vietnam strains, 98.2-98.3% with China strains, indicating a close lineage with highly pathogenic PRRS strains. In deduced amino acid sequence analysis, one mutation was found in the primary neutralizing epitope (PNE) at position ³⁹L → I³⁹ and one more mutation was also found in the decoy epitope (DCE) at position ³⁰ N → D³⁰. The amino acid at this position is an N-linked glycosylation site, and mutation of the N-linked glycosylation is an immune escaped strategy adopted by this virus causing a persistent infection in the natural host.

Development of recombinant nucleocapsid protein-based indirect enzyme-linked immunosorbent assay for sero-survey of porcine reproductive and respiratory syndrome

Background and Aim:

Porcine reproductive and respiratory syndrome (PRRS) is a disease endemic in many countries and is of economic importance. India was free from PRRS until the first outbreak was reported from a North-East Indian state in 2013. Since then, disease outbreaks have been reported from North-East India and the pilot study conducted earlier showed that it is gradually spreading to the rest of India. Considering there are no locally developed population screening tests available for PRRS and imported diagnostic/screening tests are expensive, the present study was aimed at developing recombinant nucleocapsid (rN) protein-based indirect enzyme-linked immunosorbent assay (iELISA).

Materials and Methods:

The rN protein of PRRS virus (PRRSV) was produced following standard cloning, expression, and purification procedures. Using this antigen, iELISA was optimized for the detection of serum antibodies to PRRSV. The sensitivity and specificity of the test were assessed by comparing it with a commercial PRRSV antibody detection kit.

Result:

A total of 745 serum samples from ten different states of India were screened using the developed iELISA. The iELISA had a relative specificity of 76.18% and sensitivity of 82.61% compared to the commercial ELISA (Priocheck PRRSV ELISA kit, Thermo Fisher Scientific, USA).

Conclusion:

The iELISA, which deployed rN protein from Indian PRRSV, was found to be suitable in the serological survey and may be a useful tool in future disease surveillance programs.

A rapid and quantitative fluorescent microsphere immunochromatographic strip test for detection of antibodies to porcine reproductive and respiratory syndrome virus

A fluorescent microsphere-based immunochromatographic strip test (FICT) was developed for the rapid, sensitive, and quantitative detection of porcine reproductive and respiratory syndrome virus (PRRSV) antibodies at the pen-side. The assay was based on the formation of a sandwich immune-complex (anti-pig IgG-PRRSV antibodies-NSP7/N), which was validated by a comparison with IDEXX-ELISA using 3325 clinical specimens. The diagnostic specificity, sensitivity, and accuracy of FICT were 97.28, 93.41, and 94.95%, respectively. FICT showed a good correlation with the virus neutralization assay. Overall, a promising pen-side diagnostic tool was developed for the rapid and quantitative detection of PRRSV antibodies within 15 min.

Recent Trends in the Analysis of Chemical Contaminants in Beverages

Chemical contaminants should not be present in beverages for human consumption, but could eventually be ingested by consumers as they may appear naturally from the environment or be produced by anthropogenic sources. These contaminants could belong to many different chemical sources, including heavy metals, amines, bisphenols, phthalates, pesticides, perfluorinated compounds, inks, ethyl carbamate, and others. It is well known that these hazardous chemicals in beverages can represent a severe threat by the potential risk of generating diseases to humans if no strict quality control is applied during beverages processing. This review compiles the most updated knowledge of the presence of potential contaminants in various types of beverages (both alcoholic and non-alcoholic), as well as in their containers, to prevent undesired migration. Special attention is given to the extraction and pre-concentration techniques applied to these samples, as well as to the analytical techniques necessary for the determination of chemicals with a potential contaminant effect. Finally, an overview of the current legislation is carried out, as well as future trends of research in this field.

Novel biotechnological platform based on baculovirus occlusion bodies carrying Babesia bovis small antigenic peptides for the design of a diagnostic enzyme-linked immunosorbent assay (ELISA)

Baculoviruses are large DNA virus of insects principally employed in recombinant protein expression. Its ability to form occlusion bodies (OBs), which are composed mainly of polyhedrin protein (POLH), makes them biotechnologically attractive, as these crystals (polyhedra) can incorporate foreign peptides and can be easily isolated. On the other hand, peptide microarrays allow rapid and inexpensive high-throughput serological screening of new candidates to be incorporated to OBs. To integrate these 2 biotechnological approaches, we worked on Babesia bovis, one of the causative agents of bovine babesiosis. Current molecular diagnosis of infection with B. bovis includes enzyme-linked immunosorbent assay (ELISA) techniques, which use merozoite lysate obtained from infected bovine erythrocytes. However, it is important to produce recombinant antigens that replace the use of crude antigens. Here, we describe a new biotechnological platform for the design of indirect ELISAs based on 5 antigenic peptides of 15 amino acid residues of B. bovis (ApBb), selected from a peptide microarray and expressed as a fusion to POLH. An Sf9POLH_E44G packaging cell line infected with recombinant baculoviruses carrying POLH-ApBb fusions yielded higher levels of chimeric polyhedra, highlighting the advantage of a trans-contribution of a mutant copy of polyhedrin. Finally, the use of dissolved recombinant polyhedra as antigens was successful in an ELISA assay, as B. bovis-positive sera recognized the fusion POLH-ApBb. Thus, the use of this platform resulted in a promising alternative for molecular diagnosis of relevant infectious diseases.

Ability of ELISAs to detect antibodies against porcine respiratory and reproductive syndrome virus in serum of pigs after inactivated vaccination and subsequent challenge

BACKGROUND

In this study, six enzyme-linked immunosorbent assays (ELISA), intended for routine porcine reproductive and respiratory syndrome virus (PRRSV) herd monitoring, are tested for their ability to detect PRRSV specific antibodies in the serum of pigs after vaccination with an inactivated PRRSV type 1 vaccine and subsequent infection with a highly pathogenic (HP) PRRSV field strain. For this reason, ten piglets (group V) from a PRRSV negative herd were vaccinated twice at the age of 2 and 4 weeks with an inactivated PRRSV vaccine. Ten additional piglets (group N) from the same herd remained unvaccinated. Three weeks after second vaccination, each of the piglets received an intradermal application of an HP PRRSV field strain. Serum samples were taken before first vaccination as well as before and 3, 7, 10 and 14 days after HP PRRSV application. All serum samples were tested for PRRSV RNA by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) as well as for PRRSV antibodies with all six study ELISAs.

RESULTS

At the beginning of the study (before vaccination), all of the piglets were PRRSV antibody negative with all study ELISAs. They also tested negative for PRRSV RNA measured by RT-qPCR. From day 3 after HP PRRSV application until the end of the study, a viremia was detected by RT-qPCR in all of the piglets. On day 0 (day of HP PRRSV application), nine out of ten piglets of the pre-vaccinated group tested PRRSV antibody positive with one of the tested ELISAs, although with lower S/P values than after infection. On day 10 after HP PRRSV application, all study ELISAs except one had significantly higher S/P or OD values, respectively more positive samples, in group V than in group N.

CONCLUSIONS

Only one of the tested ELISAs was able to detect reliably PRRSV antibodies in pigs vaccinated with an inactivated PRRSV vaccine. With most of the tested ELISAs, higher S/P values respectively more positive samples after PRRSV infection were seen in the pre-vaccinated group than in the non-vaccinated.

Performance of ELISAs for detection of antibodies against porcine respiratory and reproductive syndrome virus in serum of pigs after PRRSV type 2 live vaccination and challenge

Background

The aim of the study was to evaluate the performance of different newly developed and/or commercially available ELISAs for detection of PRRSV specific antibodies. Consequently, ten PRRSV negative piglets (group V) were vaccinated with a PRRSV type 2 vaccine. Blood samples were taken before as well as seven, 21 and 42 days after vaccination. At day 42 after vaccination (day 0 of the study) all of the piglets from group V and 10 non-prevaccinated PRRSV negative piglets (group N) were challenged with an HP PRRSV type 2 field strain. Blood samples were taken before and at days 3, 7, 10, 14, 21 and 28 after challenge. The success of vaccination and challenge was measured with RT qPCR. All serum samples were tested with six ELISAs for detection of PRRSV antibodies. Three of them are nucleocapsid-based, two use a glycoprotein extract and one uses inactivated whole virus as antigen. The specificity of the ELISAs was evaluated using 301 serum samples of piglets from PRRSV negative herds.

Results

The piglets from group V tested positive by RT qPCR at day 7 after vaccination and all piglets tested positive at day 3 after challenge. PRRSV specific antibodies were seen with all nucleocapsid-based ELISAs from day 21 after vaccination onwards in group V and from day 10 after challenge in group N. The glycoprotein-based ELISAs detected antibodies from day 42 after vaccination (group V) and day 21 after challenge (group N). The agreement according to kappa-coefficient was almost perfect. The glycoprotein-based ELISAs were able to distinguish PRRSV type 2, although with some cross reactions. Regarding specificity, the ELISAs performed differently (specificity between 97.4 % and 100 %), whereas most of the ELISAs with higher sensitivity had a slightly lower specificity.

Conclusions

All tested ELISA were able to detect PRRSV antibodies in the serum of pigs vaccinated with a PRRSV type 2 vaccine and after challenge with an HP PRRSV type 2 field strain. The onset on antibody detection differed, depending on the type of antigen used in the ELISAs. Most of the ELISAs with a higher sensitivity had a lower specificity.

Evaluation of two commercial PRRSV antibody ELISA kits with samples of known status and singleton reactors

Two commercial PRRSV ELISA kits (IDEXX and Bionote) were evaluated for their sensitivity and specificity using 476 PRRS-positive serum samples collected from 7 animal challenge experiments and 1,000 PRRS-negative sera. Both ELISA kits exhibited 100% sensitivity with sera collected 14 to 42 days post-infection, and the results from the kits were highly correlated (R²=0.9207). The specificity of IDEXX or Bionote kit was 99.9% or 99.7%, respectively. In addition, the Bionote ELISA kit was used to examine 100 sera that were determined to be falsely positive either by IDEXX 2XR or 3XR ELISA, and only 7 of these samples were found to be positive. These results indicate that both ELISA kits exhibited similar levels of sensitivity and specificity and would complement one another for the verification of false-positive samples.

Comparison of different commercial ELISAs for detection of antibodies against porcine respiratory and reproductive syndrome virus in serum

BACKGROUND

In recent years, several new ELISAs for the detection of antibodies against the porcine reproductive and respiratory disease virus (PRRSV) in pig serum have been developed. To interpret the results, specificity and sensitivity data as well as agreement to a reference ELISA must be available. In this study, three commercial ELISAs (INgezim PRRS 2.0 - ELISA II, Priocheck® PRRSV Ab porcine - ELISA III and CIVTEST suis PRRS E/S PLUS - ELISA IV, detecting PRRSV type 1 antibodies) were compared to a standard ELISA (IDEXX PRRS X3 Ab Test - ELISA I). The serum of three pigs vaccinated with an attenuated PRRSV live vaccine (genotype 2) was tested prior to and several times after the vaccination. Furthermore, serum samples of 245 pigs of PRRSV positive herds, 309 pigs of monitored PRRSV negative herds, 256 fatteners of assumed PRRSV negative herds with unknown herd history and 92 wild boars were tested with all four ELISAs.

RESULTS

ELISAs II and III were able to detect seroconversion of vaccinated pigs with a similar reliability. According to kappa coefficient, the results showed an almost perfect agreement between ELISA I as reference and ELISA II and III (kappa > 0.8), and substantial agreement between ELISA I and ELISA IV (kappa = 0.71). Sensitivity of ELISA II, III and IV was 96.0%, 100% and 91.5%, respectively. The specificity of the ELISAs determined in samples of monitored PRRSV negative herds was 99.0%, 95.1% and 96.4%, respectively. In assumed negative farms that were not continually monitored, more positive samples were found with ELISA II to IV. The reference ELISA I had a specificity of 100% in this study.

CONCLUSIONS

All tested ELISAs were able to detect a PRRSV positive herd. The specificity and sensitivity of the tested commercial ELISAs, however, differed. ELISA II had the highest specificity and ELISA III had the highest sensitivity in comparison to the reference ELISA. ELISA IV had a lower sensitivity and specificity than the other ELISAs.

Development and application of a blocking enzyme-linked immunosorbent assay (ELISA) to differentiate antibodies against live and inactivated porcine reproductive and respiratory syndrome virus

The aim of this study was to establish a method that could differentiate antibodies against live and inactivated vaccines of porcine reproductive and respiratory syndrome virus (PRRSV). A blocking ELISA (b-ELISA) was established using the PRRSV non-structural protein, Nsp9, as the antigen and a monoclonal antibody, 2D6, against the Nsp9 protein as the capture antibody. The test was validated by using 415 clinical sera in the b-ELISA compared to a commercial kit based on the indirect ELISA using the nucleocapsid (N) protein as antigen. Significant differences were observed for the data obtained by the two detection methods. This may be due to the commercial kit detecting antibodies elicited by live and inactivated virus, whereas the b-ELISA only detects antibodies produced by any active viral replication, such as natural infection or live vaccination. Therefore, the b-ELISA in this study is able to distinguish between antibodies against live and inactivated viruses in pigs.