Molecular detection of virulent Marek's Disease virus strains in poultry birds from two selected states in Southern Nigeria

Marek’s Disease (MD) is a highly contagious and economically significant viral disease of poultry caused by Gallid alphaherpesvirus 2. Despite vaccination efforts, MD remains a major challenge to poultry production in Nigeria. This study investigated the occurrence of Marek’s disease virus (MDV) in selected poultry farms across Oyo and Akwa Ibom States, Nigeria. Using a cross-sectional study design, eighty-four (n=84) samples were purposively collected from clinically affected birds (layers, broilers, and turkeys). These were: blood (40), liver (21), spleen (8), kidney (5), ovaries (6), and Bursa of Fabricius (4). Molecular detection using Polymerase Chain Reaction (PCR) targeted a 491bp segment of the glycoprotein B (glyB) gene, followed by sequencing analysis. The overall MDV prevalence was 14.3%, with turkeys (20.0%), layers (15.0%), and broilers (10.5%), though not statistically significant (χ²=0.38, p=0.82). Birds aged 25-36 weeks showed the highest MDV prevalence (17.3%), and a higher rate was observed in birds with history of single vaccination (18.5%) compared to repeated vaccination and prevalence was higher in Oyo (15.9%) than in Akwa Ibom (6.7%). The PCR analysis confirmed MDV with amplification of the 491bp segment of the glyB gene. Phylogenetic analysis of positive MDV-isolates showed clustering with virulent strains from the USA, Australia, and Israel. This study highlights the persistence of MD in Nigeria despite vaccination efforts, suggesting potential vaccine failures or viral evolution. Enhanced surveillance, vaccination strategies, and biosecurity measures are recommended to mitigate its negative impacts on food security in Nigeria and the West African region.