Detection of infectious laryngotracheitis virus (ILTV) in tissues and blood fractions from experimentally infected chickens using PCR and immunostaining analyses

The ability of infectious laryngotracheitis virus (ILTV) to replicate in organs outside of the upper respiratory tract and conjunctiva associated-lymphoid tissues is still not well understood. This study investigated the tissue distribution of an Australian field strain of ILTV (class 9) on birds experimentally inoculated via eye-drop at 7 days of age by using quantitative PCR (qPCR) and immunohistochemistry. Tissues including conjunctiva, caecal tonsil, kidney, liver, lung, spleen, thymus, trachea and blood were collected from sham-inoculated (control group; n = 2) and ILTV-inoculated (n = 8) birds at 7 days post-inoculation (dpi). Blood was collected from 13 infected birds at 14 dpi and fractionated using ficoll-paque. At 7 dpi, the highest detection rate and genomic copies (GC) were in conjunctiva (8/8; 8.08 ± 0.48 log₁₀ GC/mg) followed by trachea (8/8; 4.64 ± 0.48) and thymus (8/8; 4.52 ± 0.48), kidney (8/8; 3.97 ± 0.48), lung (8/8; 3.65 ± 0.48), spleen (8/8; 3.55 ± 0.48), liver (8/8; 3.51 ± 0.48), caecal tonsil (7/8; 3.76 ± 0.48) and plasma (4/8; 2.40 ± 0.48 log₁₀ GC/ml). ILTV antigen was only detected in conjunctiva (7/8), trachea (6/8) and lung (4/8) samples. At 14 dpi, ILTV detection rate and genomic copies in buffy coat cells were 12/13 and 2.86 ± 0.39 log₁₀ GC/mg, respectively while those of plasma were 11/13 and 4.29 ± 0.39 log₁₀ GC/ml and red blood cell were 3/13 and 0.36 ± 0.39 log₁₀ GC/mg. In conclusion, ILTV DNA was detected in a wide range of tissues and blood fractions but ILTV antigen was only detected in respiratory organs and conjunctiva.