Further findings on detection of Infectious Laryngotracheitis virus in tissues, faeces and dust in experimental and field infections

Abstract

We have previously reported high levels of Infectious laryngotracheitis virus (ILTV) genome in faeces and isolator dust from specific pathogen free white leghorn type chickens challenged with high doses of vaccine strains of ILTV. In an experiment in commercial Ross broiler chickens challenged at hatch or 16 days of age with SA2 vaccine strain of ILTV at the same high dose, challenge induced significant ILT signs and mortality, particularly in the birds challenged at hatch. Antibody titres revealed an absence of maternally derived antibody and marked humoral response to infection over the 28-day post-infection (dpi) period in both age groups. ILTV was detected in faeces in significant amounts for 16 days post infection (dpi) in the younger group, but for only up to 4 dpi in the older group. A high level of ILTV viral genome copy number (VCN) was detected in dust samples at 7 and 14 dpi (>108/mg/dust) declining by about 1 log at 28 dpi. Field dust and tracheal samples from affected and unaffected flocks from an area with endemic ILT were tested for presence of ILTV by qPCR. A high level of viral genome (107-108 VCN/mg) was detected in trachea of both clinically affected and unaffected birds from an infected flock. Dust samples from affected flocks also contained high levels (107-108 VCN/mg) as did a sample from an unaffected, but vaccinated flock. These results confirm presence of ILTV genome at high levels in faeces and/or dust from infected commercial broilers in pen experiments and the field.