Oxidative Stress in Liver Tissues of Marek ’ s Disease Affected Layer Chicken KV

Introduction Marek‘s Disease is one of the economically important poultry diseases all over the world. Due to potentially high mortality rate and reduced performance MD infection is recognized as a significant health risk to poultry farming [1]. In chicken, MD occurs at 3–4 weeks of age or older and is most common between 12 and 40 weeks of age in layers. Increased generation of ROS is a feature of many viral infections and can be caused by both direct effect of virus on cells and inflammatory responses of the host [2]. In many viral infections, oxidative stress is primarily due to increased generation of reactive oxygen species (ROS) which modulate the permissiveness of cells to viral replication, regulate host inflammatory and immune responses, and cause oxidative damage to both host tissue and progeny virus [3]. To protect themselves, body maintains antioxidant enzymes such as Superoxide Dismutase (SOD), Catalase (CAT) [4]. Superoxide dismutase catalyzes the breakdown of the superoxide anion into oxygen and hydrogen peroxide [5] and this enzyme forms the first line of defense against superoxide radicals. Catalase catalyzes the decomposition of hydrogen peroxide to water and oxygen [6]. Glutathione is important particularly in the regulation of redox state and prevention of the cell damage induced by oxidative stress. Glutathione is the most important freely available antioxidant, which acts directly as an antioxidant and also participates in catalytic cycles of several antioxidant enzymes such as GPx, GR and GST [7]. Glutathione Peroxidase plays an important role in the detoxification of hydrogen peroxides with the conversion of reduced glutathione (GSH) to Glutathione Disulfide (GSSG). GlutathioneS-transferase is believed to detoxify endogenous substances that are formed as a consequence of oxidative stress. Most of the electrophilic molecules, such as endogenous oxidative stress products, carcinogens, drugs, pesticides and herbicides, pass through the liver before they reach and accumulate in target tissues. Hence, it is essential to study the antioxidant enzyme activities and oxidative stress in liver tissues of birds. Therefore, the present experiment was carried out to study the activities of SOD, Catalase, GPx, GST, levels of GSH and malondialdehyde in liver tissues of Marek‘s disease (MD) affected layer chicken liver as compared to control. Abstract Marek's disease is a lymphoproliferative and neuropathic disease of domestic chickens which was found to be caused by a highly contagious, cell-associated, oncogenic herpes virus. Increased generation of ROS is a feature of many viral infections. Hence an experiment was conducted to study the activities of antioxidant enzymes such as Superoxide dismutase (SOD), Catalase (CAT), glutathione-S-transferase, Glutathione peroxidase and reduced glutathione in liver tissues of Marek‘s disease (MD) affected chicken in layers of 35 to 40 weeks age. A total of ten control and ten MD affected layer chicken were collected from poultry farms in Chittoor district. The histopathological examination revealed severe infiltration of pleomorphic lymphoid cells and PCR analysis showed positivity of MDV-1 serotype at 314 bp region in MD affected liver. The SOD, CAT, GST, GPx activities and GSH levels significantly reduced in MD affected chicken liver when compared to control. Lipid peroxidation (malondialdehyde) levels were measured to know the intensity of oxidative stress. Malondialdehyde levels were significantly elevated in MD affected chicken liver compared to control. These results indicate that MD virus causes oxidative stress in layers which may be due to reduced activity of antioxidant enzymes in liver tissue.