Two test kits for the identification of spring viraemia of carp virus (SVCV), one an enzyme-linked immunosorbent assay (ELISA) using a rabbit polyclonal antiserum, and the other an indirect fluorescent antibody test (IFAT) using a mouse monoclonal antibody, were assessed for specificity using a range of virus isolates. The test viruses were selected from 4 recently described genogroups of piscine rhabdoviruses: Genogroup I (SVCV), Genogroup II (grass carp rhabdovirus), Genogroup III (pike fry rhabdovirus) and Genogroup IV ('tench rhabdovirus'). The test viruses included SVCV isolates from all 4 subgroups of Genogroup I. The ELISA was non-specific for these viruses and did not distinguish between SVCV and isolates from the other 3 Genogroups. However, the IFAT was too specific and detected SVCV isolates from only 1 of the 4 SVCV subgroups. Reliance on these test kits alone could result in misidentification of this OIE notifiable disease.
KEY WORDS: SVCV · IFAT · ELISA · Serological comparison · Identification
Resale or republication not permitted without written consent of the publisherDis Aquat Org 67: [25][26][27][28][29] 2005
MATERIALS AND METHODSViruses and propagation. Viruses were selected from distinct branches of the neighbour-joining distance tree (Table 1) within a Genogroup or subgroup (Stone et al. 2003, Dikkeboom et al. 2004 and grown at 20°C in Epithelioma papulosum cyprini cells (Fijan et al. 1983) or fathead minnow cells (ATCC CCL 42) (isolate WI02-131 only) as described previously (Hill et al. 1975, Way 1991, and harvested when complete cytopathic effect (CPE) was observed. The viruses were titrated in 96-well cell cultivation plates and TCID 50 values were calculated according to Kärber (1931). For the IFAT, virusinfected cell culture harvests were diluted to 1:100 and 1:1000 in cell culture medium and used to inoculate the appropriate cell cultures on 24-well IWAKI plates (Scientific Laboratory Supplies). Following incubation for 16 to 20 h at 20°C, the medium was removed, and the cells were fixed with the solution provided with the test kit, or with 80% acetone for the in-house IFAT (see below). For the ELISA, virus-infected cell culture harvests were diluted in diluent supplied with the kit. The remaining steps of the ELISA and IFAT were conducted according to the procedures supplied with the kits; cells inoculated with both the 1:100 and 1:1000 dilutions of virus were tested in the IFAT. An in-house rabbit polyclonal antiserum (produced against SVCV isolate S30) was used as a positive control for the IFAT.Test kits. Kit SVC048, which is an ELISA using a rabbit polyclonal antiserum was obtained from TestLine, (Brno, Czech Republic) and Kit BIO K12, which is an IFAT using a mouse monoclonal antibody (MAb) came from Bio-X Diagnostics SPRL (Jemelle, Belgium). Tests were conducted according to the procedures specified by the manufacturers with the following exceptions. TestLine specified the use of doubling dilutions of sample from 1:2 to 1:256, but doubling dilutions from 1:20 to 1...