EVALUATION OF ELISA TITERS TO INFECTIOUS LARYNGOTRACHEITIS

Infectious laryngotracheitis (ILT), a highly infectious upper respirat ory disease of chickens, can cause serious economic loss in areas wher e the poultry industry is concentrated. To determine the antibody leve ls associated with vaccine administration, field challenge, and protec tion, six groups of 20 specific-pathogen-free leghorn chickens were ho used in biosecured isolation units. Individual groups served as either negative controls, vaccinated (one full dose per bird of chicken embr yo origin [CEO] administered by the eyedrop method) and challenged (in tratracheal administration with USDA strain ILT virus at 10(4.1) 50% e mbryo infective dose [EID50]), or unvaccinated and challenged with USD A strain ILT virus at various dose levels (10(2.1), 10(3.1), or 10(4.1 ) EID50). Chickens in each group were bled weekly, and their sera were tested for antibody using a commercially available enzyme-linked immu nosorbent assay test kit. The antibody response using CEO vaccine resu lted in a 400-600 geometric mean titer that appeared to be protective against severe field challenge. Negative controls had no titers, where as vaccinated and/or challenged chickens had detectable titers within 2 wk of exposure, and these titers remained high for the next 4-7 wk M ortality in nonvaccinated controls began at 3 days post-challenge and continued for up to 10 days.