Assessment of a rapid immunochromatographic assay for the detection of avian influenza viruses

Rapid spreading of the low pathogenic avian influenza virus (AIV) caused by the H9N2 subtype and the highly pathogenic AIV caused by H5N1 have caused serious economic losses in the poultry industries of Asia. Therefore, the early detection of AIVs is crucial for the control of the disease. In the present study, the applicability of a rapid immunochromatographic (RIC) assay, which specifically detected type A antigens of AIVs, was evaluated. This assay detected H9N2 viruses at 103.2 ELD50/ml and H5, H7 and H9 antigens at 128 HA titers, but did not react with other respiratory viruses. The assessment of cloacal swab samples prepared from 1 to 10 d post-inoculation (PI) revealed that the first positive samples were detectable on day 2 and 3 PI, and the last positive samples were detectable on day 10 and 9 PI, by the virus isolation (VI) and RIC assays, respectively. Collectively, the relative specificity, sensitivity, positive predictive value, negative predictive value, accuracy and correlation rate of the RIC and VI assays, were 100%, 71.5%, 100%, 78.5%, 0.86, and 0.98, respectively. There was also a good correlation (? > 0.81) between the results of the haemagglutination (HI), VI and RIC assays of cloacal/tracheal swab samples that were obtained from broiler flocks involved with viral respiratory diseases. Overall, RIC showed a low sensitivity and high specificity for the rapid diagnosis of H9N2 isolates in both experimental and clinical infections.