Molecular characterization of the meq oncogene of Marek’s disease virus in vaccinated Brazilian poultry farms reveals selective pressure on prevalent strains

Abstract

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.

Keywords:

• Mardivirus gallidalpha2
• meq oncoprotein
• selective pressure
• phylodynamics
• phylogeography

Acknowledgments

The authors are grateful to the staff of the farms for supplying the biological material and epidemiological information.

Disclosure statement

No potential conflict of interest was reported by the authors.

Ethics statement

This study was approved by the Ethics Commission on Animal Use of the School of Veterinary Medicine, University of São Paulo (FMVZUSP), under CEUAVET protocol no. 1727010620.

Data availability statement

The obtained sequences were submitted to GenBank under the accession numbers ON228225 to ON228254.

Additional 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.