An enzyme-linked immunosorbent assay for the detection of antibody against avian influenza virus.

An enzyme-linked immunosorbent assay (ELISA) was developed for detecting antibody to type A avian influenza (AI) virus. The sensitivity and group specificity of the AI-ELISA were compared with those of the agar-gel-precipitin test (AGPT) and the hemagglutination-inhibition (HI) test under conditions of both controlled and field exposure. During the course of temporal experimental infection (0-76 days) of specific-pathogen-free (SPF) chickens with AI subtype Hav9N2, the AI-ELISA was able to detect specific AI antibody as early as 8 days postinoculation (PI), and it measured rising levels of antibody through 35 days PI, at which time the chickens were re-exposed to AI virus. Conversely, AGP tests were negative through 35 days PI, and HI tests began to detect low levels of AI antibody only at 21 days PI. Following a secondary infection at 35 days PI with the same AI subtype, all tests measured rising levels of AI-specific antibody (35-76 days PI). However, the AGP test was positive at only the 7- and 14-day samplings postsecondary immunization. Under field conditions, the AI-ELISA was able to detect serum AI antibody in flocks from which highly pathogenic AI was isolated, but the AGP tests of these sera were negative.