Chacón, Ruy D.Sánchez-Llatas, Christian J.L. Pajuelo, SarahDiaz Forero, Andrea J.Jimenez-Vasquez, VictorMédico, Jack A.Soto-Ugaldi, Luis F.Astolfi-Ferreira, Claudete S.Piantino Ferreira, Antonio J.2025-04-242025-04-242024-03-11Chacón, R. D., Sánchez-Llatas, C. J., Pajuelo, S. L., Díaz Forero, A. J., Jimenez-Vasquez, V., Médico, J. A., Soto-Ugaldi, L. F., Astolfi-Ferreira, C. S., & Ferreira, A. J. P. (2024). Molecular characterization of the meq oncogene of Marek’s disease virus in vaccinated Brazilian poultry farms reveals selective pressure on prevalent strains. Veterinary Quarterly, 44(1), 1–13. https://doi.org/10.1080/01652176.2024.2318198.0165-217610.1080/01652176.2024.2318198https://hdl.handle.net/20.500.14352/119690Acknowledgments The authors are grateful to the staff of the farms for supplying the biological material and epidemiological information. Funding This work was supported in part by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) under Grant [2017/05296-6]. A.J.P.F. was supported by the Conselho Nacional de Pesquisa e Desenvolvimento Tecnológico (CNPq) under Grant 301084/2019-0.Marek’s disease virus (MDV) has become an increasingly virulent pathogen in the poultry industry despite vaccination efforts to control it. Brazil has experienced a significant rise of Marek’s disease (MD) outbreaks in recent years. Our study aimed to analyze the complete meq gene sequences to understand the molecular epidemiological basis of MD outbreaks in Brazilian vaccinated layer farms. We detected a high incidence rate of visceral MD (67.74%) and multiple circulating MDV strains. The most prevalent and geographically widespread genotype presented several clinical and molecular characteristics of a highly virulent strain and evolving under positive selective pressure. Phylogenetic and phylogeographic analysis revealed a closer relationship with strains from the USA and Japan. This study sheds light on the circulation of MDV strains capable of infecting vaccinated birds. We emphasize the urgency of adopting preventive measures to manage MDV outbreaks threatening the poultry farming industry.engAttribution-NonCommercial 4.0 Internationalhttp://creativecommons.org/licenses/by-nc/4.0/journal article1875-5941https://doi.org/10.1080/01652176.2024.2318198open access576.858619:636.5Mardivirus Gallidalpha2Meq OncoproteinSelective PressurePhylodynamicsPhylogeographyGenéticaInmunología veterinariaMicrobiología (Veterinaria)Patología veterinariaAviculturaSanidad animalBiología molecular (Biología)2401 Biología Animal (Zoología)2401.11 Patología Animal2401.12 Parasitología Animal2401.13 Fisiología Animal3109.11 Virología