A flu optical immunoassay (ThermoBioStar's FLU OIA): a diagnostic tool for improved influenza management

Commercial Immunoassay Kits for the Detection of Influenza Virus Type A: Evaluation of Their Use with Poultry

Five antigen capture immunoassay test kits, Directigen Flu A (Becton Dickinson), QuickVue Influenza test kit (Quidel), FLU OIA (ThermoBiostar), Zstat Flu (ZymeTx, Inc.) and NOW FLU A Test (Binax) were used to detect avian influenza virus (AIV) in clinical specimens as per manufacturers' protocols. Each kit was shown to be specific for AIV propagated in embryonating chicken eggs (ECE); other respiratory viruses of poultry tested gave negative results. The Directigen Flu A kit proved to be 10-fold more sensitive than the other kits, capable of detecting 10(4.7) mean embryo lethal dose (ELD50)/ml in allantoic fluid; this is more sensitive than the hemagglutination test using chicken erythrocytes. None of the kits proved to be sufficiently sensitive to reliably detect AIV in oropharyngeal and cloacal swabs collected from chickens experimentally infected with AIV subtype H6N2. In two different experiments, individual swabs and pools of five or six swabs were tested. By virus isolation, 39 individual oropharyngeal swabs tested positive for AIV, but Directigen and Flu OIA only detected 2/39 and NOW FLU A 1/39. Zstat and QuickVue did not detect any. Five individual cloacal swabs positive by virus isolation were negative with all five kits. In a second experiment using pools of five swabs, 26 swab pools were positive by virus isolation and 5/26 were positive by Directigen, the only kit to provide any positive results. Five cloacal swab pools were also positive by virus isolation and 1/5 was positive by Directigen; all other test kits were negative. All of these experiments were performed using the H6N2 subtype of AIV. The results are disappointing, as the kits have proven to be insensitive for detecting AIV when compared with the gold standard, virus isolation. This limits their use in diagnostic field investigations. Individual or groups of chickens could be assumed to be positive for AIV if positive by any of the kits, but a negative result with any of the kits would not prove that birds were AIV free.

ZstatFlu-II test: a chemiluminescent neuraminidase assay for influenza viral diagnostics

The ZstatFlu-II test is a highly sensitive, specific, rapid, point-of-care chemiluminescent diagnostic test for influenza infection. Influenza viral neuraminidase-specific substrate, spiroadamantyl-1,2-dioxetane-4,7-dimethoxy-N-acetyl-neuraminic acid, is at the core of the ZstatFlu-II Test. The enzymatic reaction was carried out at 25 degrees C and neutral pH, representing the optimum assay conditions for influenza types A and B viral neuraminidases. The results were outputted on a Polaroid trade mark High Speed Detector Film. Positive results appeared as a '+'-shaped white film image; negative results produced no image. The 'glow' kinetics, facilitated by a unique combination of light enhancers, also 'tuned' the wavelength of emission to match the spectral properties of the film. The substrate hydrolysed non-enzymatically at acid pH or at temperatures above 25 degrees C. In order to minimize false positives, the ZstatFlu-II Test was formatted with 0.3-0.4 K(m) substrate and freezing the test kit until use. The pH optimization of the ZstatFlu-II test is discussed with reference to model compounds of sialyl-glycosides. A nucleophilic attack or an electrostatic stabilization of a developing carbonium ion under the influence of the adjacent carboxyl group was probably responsible for non-enzymatic hydrolysis of the substrate. Intramolecular general acid catalysis is proposed as a mechanism for the lability of the O-glycosidic linkage of the substrate.