Pathomorphological changes in laying hens organs in case of infection by a field strain of the Mareks disease virus
In small private farms, Marek’s disease is one of the causes of laying hens’ death, especially in case of a spontaneous infection by a field strain of the virus. For several decades, the disease has been successfully prevented using vaccination. However, the vaccines’ effectiveness decreases over time due to the emergence of more virulent strains. Economic losses from the disease are caused by the high mortality rate, reduced poultry productivity, and the additional financial burden on implementing veterinary measures. Marek’s disease is still being registered in all countries worldwide that have the developed poultry farming industry.
The article highlights the results of the autopsy and histopathological studies of the organs of laying hens of the Leghorn breed in various age groups (120 to 350 days) affected by the field strain of Marek’s disease virus. During the disease period, sick fowl lost its productivity sharply, and the mortality rate accounted for 35% (150 hens). The main clinical signs were exhaustion, paresis of the wings, atypical gait, and neck curvature (in some cases). The fowl with the feet oriented in different directions was not detected. The autopsy results revealed tumors on the liver, heart, kidneys, spleen, and ovaries in most hens. Macroscopically, affected organs are enlarged, with miliary proliferates, especially the spleen. Histologically, diffuse massive infiltration and proliferation of pleomorphic lymphoid cells into the liver’s parenchyma, heart muscle, lungs, spleen, pancreas, kidney, and glandular stomach were detected. Morphological changes in the spleen were characterized by lymphocyte pleomorphism and necrosis of the reactive centers of lymphoid nodules. Massive diffuse foci of lymphoblast proliferation were found in the glandular stomach. Areas of lymphoblast proliferation with significant damage to the parenchyma, hemorrhage, and stasis were found in the liver and kidneys. Characteristic lymphoid infiltrations were also discovered in the peripheral nerves of some laying hens.