Detection and localization of naturally transmitted avian leukosis subgroup J virus in egg-type chickens by in situ PCR hybridization

Establishment and Application of a Real-Time Recombinase Polymerase Amplification Assay for the Detection of Avian Leukosis Virus Subgroup J

Avian leukosis caused by avian leukosis virus (ALV), belonging to the genus Alpharetrovirus of the family Retroviridae, is associated with benign and malignant tumors in hemopoietic cells in poultry. Although several methods have been developed for ALV detection, most of them are not suitable for rapid on-site testing due to instrument limitations, professional operators, or the low sensitivity of the method. Herein, we described the real-time recombinase polymerase amplification (RPA) assay for rapid detection of ALV subgroup J (ALV-J). The major viral structural glycoprotein gp85, highly specific for the subgroup, was used as the molecular target for the real-time RPA assay. The results were obtained at 38°C within 20 min, with the detection sensitivity of 10 copies/μl of standard plasmid pMD18-T-gp85 as the template per reaction. Real-time RPA was capable of ALV-J-specific detection without cross-reaction with other non-targeted avian pathogens. Of the 62 clinical samples tested, the ALV-positive rates of real-time RPA, PCR, and real-time PCR were 66.13% (41/62), 59.68% (37/62), and 67.74% (42/62), respectively. The diagnostic agreement between real-time RPA and real-time PCR was 98.39% (61/62), and the kappa value was 0.9636. The developed real-time ALV-J assay seems promising for rapid and sensitive detection of ALV-J in diagnostic laboratories. It is suitable for on-site detection, especially in a poor resource environment, thus facilitating the prevention and control of ALV-J.

Rapid detection of avian leukosis virus subgroup J by cross-priming amplification

Avian leukosis virus subgroup J (ALV-J) causes oncogenic disease in chickens in China, resulting in great harm to poultry production, and remains widespread in China. Herein, we employed a cross-priming amplification (CPA) approach and a nucleic acid detection device to establish a visual rapid detection method for ALV-J. The sensitivity of CPA, polymerase chain reaction (PCR) and real-time PCR (RT-PCR) was compared, and the three methods were used to detect ALV-J in the cell cultures which inoculated with clinical plasma. The result showed when the amplification reaction was carried out at 60 °C for just 60 min, the sensitivity of CPA was 10 times higher than conventional PCR, with high specificity, which was comparable with RT-PCR, based on detection of 123 cell cultures which inoculated with clinical plasma, the coincidence rate with real-time PCR was 97.3% (71/73). CPA detection of ALV-J does not require an expensive PCR instrument; a simple water bath or incubator is sufficient for complete DNA amplification, and the closed nucleic acid detection device avoids aerosol pollution, making judgment of results more intuitive and objective. The CPA assay would be a promising simple, rapid and sensitive method for identification of ALV-J.

Oral Immunization of Chickens With Recombinant Lactobacillus plantarum Vaccine Against Early ALV-J Infection

In this study, a novel oral vaccine of recombinant Lactobacillus plantarum (L. plantarum) containing the gp85 protein was explored, and the effects of this vaccine on the prevention of subgroup J Avian Leukosis Virus (ALV-J) infection were assessed. In the current study, the gp85 protein of ALV-J was expressed on the surface of L. plantarum with the surface-display motif, pgsA, by constructing a shuttle vector pMG36e:pgsA:gp85. Surface localization of the fusion protein was verified by western blotting and flow cytometry. Subsequently, Specific Pathogen Free Hy-Line Brown layer chickens were orally vaccinated with the recombinant L. plantarum and presented with high levels of serum immunoglobulin G (IgG) and secretory immunoglobulin A (sIgA) titers in bile and duodenal-mucosal fluid. After challenged with ALV-J of a 3 × 10³ 50% tissue culture infective dose (TCID50), serum samples of the chickens were collected and viremia was analyzed. Results showed that, compared to the L. plantarum and PBS control group, the recombinant L. plantarum group showed a significant rise in antibody levels after inoculation, and provide improved protection against ALV-J according to viremia detection. These results indicate that oral immunization with the recombinant L. plantarum provided an effective means for eliciting protective immune response against early ALV-J infection.