INFECTIOUS LARYNGOTRACHEITIS VIRUS IN COMMERCIAL HENS - A SEROLOGICALSTUDY BASED ON ENZYME-LINKED-IMMUNOSORBENT-ASSAY

Serum samples collected from 23 flocks of commercial hens from three d ifferent companies were tested by enzyme-linked immunosorbent assay (E LISA) for antibodies against infectious laryngotracheitis (ILT) virus, and data were analyzed statistically. Geometric mean titers (GMTs) we re compared from hens that were unvaccinated, once-vaccinated, or twic e-vaccinated, from single-age farms or multiple-age farms, from molted or unmolted flocks, and from different companies. There were signific ant differences among the groups compared by vaccination, between the single-age and multiple-age groups, and between the molted and unmolte d groups. The GMT of unvaccinated flocks and the GMT of molted flocks that had been vaccinated once as pullets with a chick-tissue-culture-o rigin (CTCO) live vaccine could not be differentiated. The ELISA is us eful to detect and quantitate ILT vaccine-induced antibody, but it doe s not reliably identify older flocks that were vaccinated at a young a ge with CTCO vaccine.