Infectious laryngotracheitis (ILT) is a WOAH-listed respiratory disease in poultry caused by Gallid alphaherpesvirus 1, known as ILT virus (ILTV). We monitored two unvaccinated commercial layer flocks of 46- and 64-weeks old birds, more than 3 months after the onset of ILT. For this purpose, tracheal swabs, cloacal swabs, and blood samples were collected. Molecular and serology results were compared with the mortality data. The increased mortality in flocks 1 and 2 lasted 9 and 15 days, reaching 13.0% and 11.3%, respectively. We isolated the virus by inoculation on chicken embryo’s chorioallantoic membrane. Tracheal swabs were positive at each sampling point, but cloacal swabs were negative. Based on the molecular and phylogenetic analysis of the ICP4 gene, the ILTV closely matched vaccine strains. In flock 1, seroconversion was evident at the second sampling (day 15). Thereafter, an increase in antibody titer was observed, eventually achieving levels that were nearly identical to those on day 15 and on 109. During the acute period of the outbreak, seroconversion was already visible in flock 2, and a similar pattern was then seen as in flock 1. Three months after the outbreak, the virus DNA was still persistently detected in tracheal swabs.
