The First Record of an Aggressive Form of Ocular Tumour Enhanced by Marek's Disease Virus Infection in Layer Flock in Al-Najaf, Iraq.

Marek's disease (MD) is a highly infectious poultry illness with a tendency to form tumours in peripheral nerves and internal organs of affected birds. Tumours accompany MD, mostly caused by oncogenic Gallid alpha herpesvirus 2 (MD Herpes virus serotype I). Studies on avian tumours associated with MD infection are limited in Iraq. In the presented study, the positive samples of ocular tumour were 168 out of 282 MD positive samples, which accomplished in farm suffered from an unexpectedly high mortality rate. We investigated a rapidly developed tumour mass that was observed in an MD-vaccinated layer flock that showed obvious clinical signs of MD, accompanied by forming a small lump in one eye at age 21 weeks, which developed to a big lump at week 28 of age, leading to death. The diagnosis MD infection was confirmed by a Polymerase Chain Reaction (PCR) amplification of a specific region of the target gene meq of the causative agent, followed by Sanger sequencing and BLASTn search of the sequence against the NCBI nucleic acid database, resulted in Gallid alpha herpes virus 2 strain, and according to the phylogenetic analysis, the sequence from this study was uniquely clustered in its own branch in the tree. Histopathological examination of the ocular tumour core revealed aggregation of neoplastic cells and haemorrhage that replaced the normal eye tissue, as well as early tumour formation in internal organs such as the lung and liver. In addition, abnormal lesions are susceptible to tumours in the gizzard and spleen. To our knowledge, this is the first record of an aggressive MD virus infection-mediated ocular tumour in a layer flock in Al-Najaf province, Iraq.