الفهرس 
cover englishOnly 14 pages are availabe for public view
 |  | from | 197 |  |  |
| | | from | 197 | | |
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 three Egyptian governorates. The study include 31 affected layer farms either vaccinated or non vaccinated 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 non vaccinated field strain (434 bp) or vaccine strain ( multiple repeats of 132 bp ) of MDV. results revealed 4 farm representative samples out of 31 were positive (two field and two vaccinal strains of MDV) .the two field isolates of MDV were from flocks Qalioubia at 15 weeks old and from Sharkia at 21 weeks old whereas the other two positive vaccinal strains were from Qalioupia at 22 weeks old and Gharbia at 16 weeks old . Sequencing of the amplified 434bp fragments of MDV genome were carried out and the obtained sequences were submitted to GenBank with accession numbers (OK040950 MDV1/AHRI-1/Egypt and OK040951 MDV1/AHRI-2/Egypt) .Sequence analysis of the 2 field viruses showed that both viruses are identical. Trial for detection in sixty SPF chicks was divided into 2 groups (20 challenged and 10 control) per each group for +ve field virus. challenged group was Injected by spleen homogenate from positive tumor samples 0.5 ml Intraabdominal route (witter et al,1980) and then follow up on daily basis for clinical signs and weekly samples sent for histopathology and PCR up to 80 days. These samples reported typical pictures of very virulent plus MDV by clinical signs, gross examination, histopathology and PCR. Indeed, the study reports the circulation of VV+ MDV in commercial layer farms.whether the existence of such field strains due to a vaccination failure or emerging of new strains of MDV need further investigation.