Sero-marker and Detection of Avian Leukosis and Marek s Disease Viruses in Commercial Chicken Flocks in Egypt During 2019 to 2022

In the poultry industry, oncogenic disease viruses result in significant financial losses. This study aimed to update incidence data in Egyptian chicken flocks from 2019 to 2022. The prevalence of Marek’s disease virus (MDV) and Avian leukosis virus (ALV) was monitored during the passive surveillance program in commercial poultry flocks, including (43) breeders, (45) layers, and (7) broiler flocks during 2019-2022 in Egypt. This passive surveillance was adopted depending on molecular detection of MDV and ALV viruses using PCR tests and serological detection of ALV using ELISA test kits. The histological and post-mortem results for clinically diseased birds have been recorded in different organs, including the Liver, spleen, kidney, ovary, intestine, and brain. Ninety-five flocks were reported and tested using PCR for monitoring ALV viruses (subtypes A, B, C, D, and J) and vvMDV. Samples used for PCR were prepared from liver and spleen tissues (5 chickens/pool). The tested flocks were negative for ALV subtypes A, B, C, and D, while only two cases were positive for ALV-J (2/95, 2.1%), including one breeder flock in 2021 and one-layer flock in 2022, both from Sharqia governorate. Although the overall detection rate of vvMDV was 18.9% (18/95), breeder flocks showed the highest detection rate (25.6%), compared to layer flocks (15.6%). Furthermore, the vvMDV virus detection rate varied from one year to another, including 4/13 (30.8%), 7/43 (16.3%), 4/24 (16.7%), and 3/15 (20 %) in 2019, 2020, 2021, and 2022, respectively. The vvMDV-positive cases were reported in eight governorates, including Sharqia, Menofia, Daqahlia, Gharbia, Qualiobia, Al Beheira, Giza, and Damietta. Moreover, the study indicated that vvMDV was detected in chickens aged 5 to 61 weeks. The ELISA test was used to detect ALV antibodies serologically. The seroprevalence of ALV was 4.7% in the study area. In conclusion, among the tested samples, only two cases of ALV-J were reported in Egyptian commercial chicken flocks during 2019-2022. During the same period, vvMDV showed an 18.9% prevalence rate. Further studies are recommended to evaluate the MDV vaccination program, including vaccine quality and efficacy.