Vol. 12, Issue 3 (2023)

A total of 37 samples from the birds brought for post mortem examination to Poultry Disease Diagnosis and Surveillance Laboratory, VC&RI Campus, Namakkal, representing 10 different farms in and around Namakkal were collected. A detailed gross examination was carried out on the birds which had lesions suggestive of ILT and impression/scraping smears were collected for cytology. Tissue samples from trachea, bursa of Fabricius, thymus, spleen and Harderian gland were collected and stored at -20° C for molecular confirmation of ILT by PCR. The DNA was extracted from tissue samples by using DNA extraction kit. Impression smears/ smears from scrapings were taken from trachea, bursa of Fabricius, thymus, spleen and Harderian gland for cytology, fixed in methanol and stained using Giemsa stain. Representative tissue samples from trachea, bursa of Fabricius, thymus, spleen and Harderian gland were fixed in 10% neutral buffered formalin (NBF) for histopathology. The samples were processed by routine paraffin-embedding technique and sections were cut at 4 -5 μm thickness. The sections were stained by routine Haematoxylin and Eosin (H&E) stain for detailed microscopic study. The results revealed the presence of virus in lymphoid organs such as bursa of Fabricius, thymus and spleen by PCR. Positive band for virus could not be detected in Harderian gland. Gross examination of trachea showed congestion and mucoid exudate in the lumen in mild cases, haemorrhages and diphtheritic changes in moderate to severe cases. Bursa and spleen showed moderate enlargement. Thymus showed moderate to severe congestion whereas spleen showed mild enlargement. Cytology of bursa, thymus, spleen and Harderian gland did not show any characteristic changes. Histopathological examination of trachea revealed characteristic syncytium formation with intranuclear inclusion bodies. Areas of lymphoid depletion in bursa, congestion of blood vessels and lymphoid depletion in PELT in spleen and lymphoid depletion in thymus were noticed. Based on the PCR results and microscopical examination it is concluded that ILT virus has greater affinity towards the trachea and lesser affinity towards bursa, thymus and spleen.