Pathology and Molecular Diagnosis of Marek's Disease Virus in Chickens in Nigeria

Marek's disease caused by Marek's disease virus (MDV) serotype 1 is an economically important neoplastic disease of poultry. Diagnosis of this disease is usually based on clinical signs, postmortem lesions, and diagnostic tests like cytology, histopathology, and molecular-based methods. However, there might be the problem of inaccurate diagnosis in Nigeria. Employment of gross pathology, histopathology, immunohistochemistry, and polymerase chain reaction (PCR) coupled with sequence analysis provides a reliable approach to arrive at precise confirmatory diagnosis of the disease. Therefore, visceral organs including liver, proventriculus intestine, spleen, and heart samples were collected at postmortem examinations from two pullets suspected of having Marek's disease. Histopathology and immunohistochemistry, PCR amplification of a 576 bp fragment of the MDV glycoprotein L (gL) gene, and sequence analysis were employed in this diagnostic approach. Histopathological examinations of the liver, heart and proventriculus showed neoplastic pleomorphic cellular infiltration comprising lymphoblasts, lymphocytes, macrophages, and heterophils which correspond with the pathology of Marek's disease. Liver samples were positive for the virus using PCR. Sequence analysis based on phylogenetic tree reconstruction revealed the positive MDV. MDV sequences from this study clustered with MDV serotype 1 sequences retrieved from the GenBank. This approach provides a reliable and precise diagnosis of Marek's disease in chickens which is applicable to other avian diseases.