The replication characteristics of infectious laryngotracheitis virus (ILTV) in the respiratory and conjunctival mucosa

Avian infectious laryngotracheitis virus (ILTV) is an alphaherpesvirus of poultry that is spread worldwide. ILTV enters its host via the respiratory tract and the eyes. Although ILTV has been known for a long time, the replication characteristics of the virus in the respiratory and conjunctival mucosa are still poorly studied. To study this, two in vitro explant models were developed. Light microscopy and a fluorescent terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) staining were used to evaluate the viability of mucosal explants, which were found to be viable up to the end of the experiment at 96h of cultivation. The tracheal and conjunctival mucosal explants were inoculated with ILTV and collected at 0, 24, 48 and 72h post inoculation (p.i.). ILTV spread in a plaque wise manner in both mucosae. A reproducible quantitative analysis of this mucosal spread was evaluated by measuring plaque numbers, plaque latitude and invasion depth underneath the basement membrane (BM). No major differences in plaque numbers were observed over time. Plaque latitude progressively increased up to 70.4 ± 12.9μm in the trachea and 97.8 ± 9.5μm in the conjunctiva at 72h p.i. The virus had difficulty in crossing the BM and was first observed only at 48h p.i. It was observed at 72h p.i. in 56% (trachea) and 74% (conjunctiva) of the plaques. Viability analysis of infected explants indicated that ILTV blocks apoptosis in infected cells of both mucosae but activates apoptosis in bystander cells.