Comparison of the detection performance of two different one-step-combined test strips with fluorescent microspheres or colored microspheres as tracers for influenza A and B viruses

Development of a dual immunochromatographic test strip to detect E2 and Erns antibodies against classical swine fever

Background

It is essential to consider a practical antibody test to successfully implement marker vaccines and validate vaccination efficacy against classical swine fever virus (CSFV). The test should include a serological antibody assay, combined with a tool for differentiating infected from vaccinated animals (DIVA). The immunochromatographic test strip (ICS) has been exclusively designed for detecting CSFV E2 antibodies while lacking in detecting Erns antibodies, which can be employed and satisfy DIVA strategy. This study developed a novel ICS for detecting CSFV E2/Erns dual-antibody. The effectiveness of ICS in evaluating the DIVA capability of two novel chimeric pestivirus vaccine candidates was assessed.

Methods

Recombinant E2 or Erns protein was transiently expressed in the plant benthamiana using Agrobacterium tumefaciens. ICS was subsequently assembled, and goat anti-rabbit IgG and recombinant CSFV E2 or Erns protein were plated onto the nitrocellulose membrane as control and test lines, respectively. The sensitivity and specificity of ICS were evaluated using sera with different neutralizing antibody titers or positive for antibodies against CSFV and other pestiviruses. The coincidence rates for detecting E2 and Erns antibodies between ICS and commercial enzyme-linked immunosorbent assay (ELISA) kits were also computed. ICS performance for DIVA capability was evaluated using sera from pigs vaccinated with conventional vaccine or chimeric vaccine candidates.

Results

E2 and Erns proteins were successfully expressed in N. benthamiana-produced recombinant proteins. ICS demonstrated high sensitivity in identifying CSFV E2 and Erns antibodies, even at the low neutralizing antibody titers. No cross-reactivity with antibodies from other pestiviruses was confirmed using ICS. There were high agreement rates of 93.0 and 96.5% between ICS and two commercial ELISA kits for E2 antibody testing. ICS also achieved strong coincidence rates of 92.9 and 89.3% with two ELISA kits for Erns antibody detection. ICS confirmed the absence of CSFV Erns-specific antibodies in sera from pigs vaccinated with chimeric vaccine candidates.

Conclusion

E2 and Erns proteins derived from the plant showed great potential and can be used to engineer a CSFV E2/Erns dual-antibody ICS. The ICS was also highly sensitive and specific for detecting CSFV E2 and Erns antibodies. Significantly, ICS can fulfill the DIVA concept by incorporating chimeric vaccine candidates.

Development of a multiplex isothermal amplification molecular diagnosis method for on-site diagnosis of influenza

Influenza, which is an acute respiratory disease caused by the influenza virus, represents a worldwide public health and economic problem owing to the significant morbidity and mortality caused by its seasonal epidemics and pandemics. Sensitive and convenient methodologies for the detection of influenza viruses are important for clinical care and infection control as well as epidemiological investigations. Here, we developed a multiplex reverse transcription loop-mediated isothermal amplification (RT-LAMP) with quencher/fluorescence oligonucleotides connected by a 5' backward loop (LF or LB) primer for the detection of two subtypes of influenza viruses: Influenza A (A/H1 and A/H3) and influenza B. The detection limits of the multiplex RT-LAMP assay were 103 copies and 102 copies of RNA for influenza A and influenza B, respectively. The sensitivities of the multiplex influenza A/B/IC RT-LAMP assay were 94.62% and 97.50% for influenza A and influenza B clinical samples, respectively. The specificities of the multiplex influenza A/B/IC RT-LAMP assay were 100% for influenza A, influenza B, and healthy clinical samples. In addition, the multiplex influenza A/B/IC RT-LAMP assay had no cross-reactivity with other respiratory viruses.