Development and evaluation of an enzyme-linked immunosorbent assay based on recombinant VP2 capsids for the detection of antibodies to Aleutian mink disease virus

Abstract

Aleutian disease (AD), a common infectious disease in farmed minks worldwide, is caused by Aleutian mink disease virus (AMDV). Serodiagnosis of AD in minks has been based on detection of AMDV antibodies by counterimmunoelectrophoresis (CIE) since the 1980s. The aim of this study was to develop and evaluate an enzyme-linked immunosorbent assay (ELISA) based on recombinant virus-like particles (VLPs) for identifying AMDV antibodies from mink sera. AMDV capsid protein (VP2) of a Finnish wild-type strain was expressed by the baculovirus system in Spodoptera frugiperda 9 insect cells and was shown to self-assemble to VLPs (with an ultrastructure similar to that of the actual virion). A direct immunoglobulin G ELISA was established using purified recombinant AMDV VP2 VLPs as an antigen. Sera from farmed minks were collected to evaluate the AMDV VP2 ELISA (n = 316) and CIE (n = 209) based on AMDV VP2 recombinant antigen in parallel with CIE performed using a commercially available traditional antigen. CIE performed with the recombinant antigen had a sensitivity and specificity of 100% and ELISA a sensitivity of 99% and a specificity of 97%, with reference to CIE performed with the commercial antigen. The results show that the recombinant AMDV VP2 VLPs are antigenic and that AMDV VP2 ELISA is sensitive and specific and encourage further development of the method for high-throughput diagnostics, involving hundreds of thousands of samples in Finland annually.

FIG. 1.

SDS-PAGE gel (A) and Western blot (B) of recombinant AMDV VP2 protein with sera from ADMV antibody-positive mink. Lanes: 1 and 5, molecular-mass marker; 2, S. frugiperda 9 cells; 3, recombinant baculovirus-infected Sf9 cells; 4, purified recombinant antigen; 6, Western blot of the purified recombinant antigen.

FIG. 2.

Negative-stain electron micrograph of recombinant AMDV VP2 VLPs. The white bar at the bottom indicates 200 nm.

FIG. 3.

Graph of the ELISA samples. The x axis shows the number of samples and the y axis the OD of the samples as obtained by ELISA.