qPCR Detection of Infectious Laryingotracheitis Virus in Tissues, Faeces, Dust and Litter Post Infection

Abstract

Infectious laryngotracheitis (ILT) is caused by ILT virus (ILTV), a herpesvirus that is prevalent worldwide including Australia where two local partially attenuated ILT live vaccines, A-20 and SA-2 are used to control it. To determine the tissue distribution and shedding rate of these strains 10 specific pathogen free chicks in each of two isolators were orally infected with 105.1 (A-20) or 105.4 (SA-2) pfu at day old and maintained to 28 days post infection (dpi). The treatments induced acute clinical signs with some mortality. Faecal samples were collected at frequent intervals from 6 individuals for each vires with exhaust dust and litter sampled less frequently. Tissue samples were collected from 3-4 sacrificed or dead birds at approximately weekly intervals. ILTV was detected in the Harderian gland, trachea, lungs and kidneys at the first sampling (6 dpi), declining until 28 dpi. ILTV load tended to be higher for SA-2 than A-20 and highest in the Harderian gland, followed by trachea, lung and kidney. Fecal excretion was detected at 2 dpi, peaking at 5 dpi (>105.5 genome copies/mg) before gradually declining to 28 dpi. In dust there was a high load of ILTV at 7 dpi (-109.5 copies/mg) declining to approximately 108 copies/mg by 28 dpi. Litter sampled at 28 dpi contained significant ILTV (>105.5 copies/mg). Detection of very high levels of ILTV in dust samples raises the possibility of monitoring for ILTV using dust samples as these are easy to collect, store and transport and have proved useful for monitoring Marek's disease virus, another poultry herpesvirus.