Replication of infectious laryngotracheitis virus in chickens following vaccination.

The site of replication of infectious laryngotracheitis vaccine virus (ILTV) was studied in chickens vaccinated by drinking water (DW), intraconjunctival (IC) and cloacal (CL) routes. The anatomical sites exposed to vaccine were determined by simulating vaccination with rhodamine red dye. Virus replication was determined by recovering virus from various organs at necropsy. The dye simulation studies clearly demonstrated that DW vaccination did not usually expose susceptible target organs to virus while the CL and IC routes flooded susceptible organs with vaccine. Virus replication was confined to the cloaca in CL vaccination birds while in IC and DW vaccination birds most replication took place in the nasal cavity. Vaccine virus did not always become established in DW vaccinated birds and its establishment did not appear to be related to the amount of vaccine these birds were exposed. It was concluded that DW vaccination depends for its success upon the accidental contamination of the nasal cavity with vaccine virus during the act of drinking.