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, post-mortem lesions, and diagnostic tests like cytology, histopathology, and molecular-based methods. However, there might be a problem of inaccurate diagnosis in Nigeria. Employment of gross pathology, histopathology, immunohistochemistry, Polymerase Chain Reaction (PCR), coupled with sequence analysis, provides a reliable approach to arrive at a precise confirmatory diagnosis of the disease. Therefore, visceral organs, including liver, proventriculus, intestine, spleen, and heart samples, were collected at post-mortem examinations from two pullets suspected of having Marek’s disease. Histopathology and immunohistochemistry, as well as 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 that the positive Marek’s disease virus sequences from this study clustered with Marek’s disease virus 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.