Comparison of commercial ELISA test kits from Australia and the USA with the serum neutralization test in cell cultures for the detection of antibodies to the infectious laryngotracheitis virus of chickens

The objective of this work was the evaluation under our conditions of two c ommercial ELISA kits for the detection of antibodies to avian infectious la ryngotracheitis (ILT) virus, one from Australia (Trop-ELISA, TropBio) and o ne from the USA (ProFLOK-ELISA, KPL), and to compare their performance with the conventional serum neutralization test (SNT) in chick embryo liver cel ls. Repeatability varied considerably, particularly when using the Trop-ELI SA. Therefore, if individual results are important, at least two parallel m easurements per serum sample are recommended. In 89.3% of the sera tested b y SNT, results of two parallel measurements did not vary by more than one 2 -fold dilution step. There was good linear correlation between both ELISAs and the SNT, the correlation coefficient for the Trop-ELISA being r = 0.758 and for the ProFLOK-ELISA r = 0.867. The negative/positive cut-off was red efined to suit our conditions. Sera with a SN titre of greater than or equa l to 1:4 were considered positive. Sera with less than or equal to 15% abso rption in the ProFLOK-ELISA were considered clearly negative. For the Trop- ELISA, extinctions of greater than or equal to 0.477 were considered positi ve, less than or equal to 0.168 clearly negative. Values in between were re garded as doubtful for young chickens and as possibly due to non-specific r eactions in older chickens. The sensitivity and specificity of the ELISAs r elative to the SNT were 87 and 77% for the Trop-ELISA, and 95 and 60%, resp ectively, for the ProFLOK-ELISA. However, the results indicate that the sen sitivity of the ELISA is higher than that of the SNT, because most sera sho wed similar deviations from SNT results with both ELISAs. Generally, both E LISAs were a suitable alternative to the SNT under our conditions, as long as only negative/positive results are required.