Histopathological changes and sequence analysis of field strains of MDV associated with tumors in commercial layer farms in 2015 to 2019

Meligy, Mohamed A.; El Deeb, Ayman H.; Tantawy, Laila A.; Hussein, Hussein Ali

doi:10.21608/vmjg.2023.191881.1022

Histopathological changes and sequence analysis of field strains of MDV associated with tumors in commercial layer farms in 2015 to 2019

Document Type : Original Article

Authors

¹ Department of Diagnosis and Research of Poultry Diseases, Animal Health Research Institute, Agriculture Research Center, Giza, Egypt.

² Department of Virology, Faculty of Veterinary Medicine, Cairo University, Giza 12211, Egypt

10.21608/vmjg.2023.191881.1022

Abstract

Marek’s disease is considered one of the major economic problems in all poultry sectors especially commercial layers despite of intensive vaccination. This study reports the existence of MDV serotype1 very virulent plus (VV+) in commercial layer farms aged 16-40 weeks during 2015 to 2019 in eight Egyptian governorates. The study includes 31 affected layer farms demonstrating characteristic tumors with clear typical picture of Marek’s disease (high mortality and paralysis). Tumor samples (Liver and spleen) were collected for detection of MDV viral genome by (PCR) using oligonucleotide primers to amplify 132 bp tandem repeat of specific DNA sequence to differentiate between the field strain (434 bp) or vaccine strain (multiple repeats of 132 bp) of MDV. Results revealed that 4 samples out of 31 were positive (two field and two vaccinal strains of MDV). The two field isolates of MDV were from Qalioubia flocks at 15 weeks old, and from Sharkia at 21weeks old, whereas the other two positive vaccinal strains were from Qalioubia at 22 weeks old and Gharbia at 16 weeks old. Sequencing of the amplified fragments of MDV genome was carried out and the obtained sequences were submitted to gene bank with accession numbers (OK040950 MDV1/AHRI-1/Egypt and OK040951 MDV1/AHRI-2/Egypt). Sequence analysis of the 2 isolates showed that both viruses are identical. Indeed, the study reports the circulation of VV+ MDV in commercial layer farms. Whether the existence of field strains due to a vaccination failure or emerging of new strains of MDV need further investigation

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