Outbreak Investigation of Marek's Disease in Chickens in Central and Western Ethiopia

Marek's Disease (MD) is an economically devastating poultry disease that causes substantial livestock losses and drives up overall health management costs. There was no study conducted on isolation and molecular detection of Marek's disease virus (MDV) in extensively managed local breed chickens in some parts of Central and Western Ethiopia.

The present study was conducted from September 2021 to October 2022 with the aim of isolation and molecular detection of MDV suspected from outbreak cases in chickens in Central and Western Ethiopia. A total of 94 pooled samples were collected from clinically suspected chickens from four areas, namely, Mako, Guto Gida, Holeta, and Sebeta subcity. Samples were collected from chickens in both intensive and extensive production systems, but nonvaccinated birds against MDV were obtained only from the extensive system.

From the clinical samples tested based on quantitative real-time PCR, 75 (79.78%; 75/94) tested positive for meq gene of the virus. Of these, 36.17% (34/94) of the positive samples were obtained from the feather (34/41) and the rest (43.62%; 41/94) were obtained from postmortem tissue (41/53) samples. From the overall prevalence of 79.78% (75/94), the highest score was recorded in Holeta town (95.65%), followed by Mako District (88.89%), Sebeta Subcity (62.5%), and Guto Gida District (57.89%). Though there are confounding factors such as vaccination status, significantly (p = 0.04) higher real-time PCR positive results were obtained in exotic breeds. From 10 pooled liver samples, all samples (100%) tested positive for the virus using real-time PCR. Similarly, all examined organs showed complete positivity: kidney (10/10, 100%) and spleen (10/10, 100%). However, from six pooled samples of proventriculus samples, only one (1/6, 16.67%) sample was positive for the virus, whereas 34 (82.9%) pooled feather follicles from clinically sick chickens were positive for MDV1. From a total of 75 real-time PCR positive samples inoculated into DF-1 cells for virus isolation, 45 (60%) of them were able to show cytopathic effects (CPEs) on the cell line up to the third passage. The seven (40%) feather samples remained negative against the test until the third passage.

This study provides critical insights into the isolation and molecular detection of MDV in chickens from Central and Western Ethiopia, highlighting its significant impact on poultry health and productivity. Detailed genetic characterization of the virus and differentiation of the vaccinal strain from the natural infection in exotic breeds are necessary to have effective prevention and control. Experimental studies are also needed to evaluate differences in susceptibility to MDV among local and exotic poultry breeds.