Influence Of The Structural Development Of Bursa On The Susceptibility Of Chickens To Infectious Bursal Disease Virus And Oral Administration Of Allium Sativum Extract Protects Against Infectious Bursal Disease Virus In Chickens

Infectious bursal disease (IBD), caused by infectious bursal disease virus (IBDV), is an acute, highly contagious infectious disease in young chickens, mainly of 3 to 12 weeks of age. IBDV-infected chickens show the characteristic lesions of bursal swelling, edema, hyperemia, hemorrhage, depletion of B lymphocytes, bursal dysplasia as well as severe humoral and cellular immunosuppression, which causes subsequent immune failure of a variety of vaccines, and further increases the body’s susceptibility to other pathogens. IBDV infection may cause high mortality in chickens, and the remaining ones are underdeveloped, emaciated, anemic, slow-growing, which leads to significant economic loss in the poultry industry. Antiviral therapy with only inhibiting of viral function but not affecting host cells is very difficult to achieve. Thus, searching for new antiviral agents that can be used to directly kill virus, mobilize the immune defense system, stimulate the body’s immune mechanisms active, enhance immunity, fight viruses indirectly through active defense and not harm the body’s tissues, is significant and desired. Garlic has been used as both food and medicine for many years, and long-term moderate consumption of garlic can not cause harm to the body. So in this study, we firstly developed in vivo experimental model of IBDV infection, then performed curative effect studies of garlic mixture in mice, and therapeutic effect studies of garlic mixture and sac shenduqing against IBD by using the technology of H.E. staining, immunohistochemistry, electron microscopy, ELISA, Western blot analysis and flow cytometry, as well as necropsy observation and organ index determination. Finally, we evaluated whether garlic mixture could prevent and relieve IBDV-induced immunosuppression in order to provide reliable basis for the rational use of feed additives and preventive agent. The results showed as follows:(1) Susceptibility of chickens to IBDV was related to the bursal development status. More IgM+B lymphocytes and less IgA+ B lymphocytes in medulla, richer capillary in cortex, integrity collapse of the interfollicular epithelium between the cortex and medulla, incomplete of subepithelial basement membrane were favorable factors for IBDV susceptibility. New hatching chickens have litter cortex, integral basement membrane, so it was hard for IBDV to infect the bursal medulla. With age, the chicks were susceptible to IBDV because of increased cortical area, incomplete basement membrane between cortex and medulla, gaps between interfollicular epithelium. The chickens were not susceptible to IBDV again because of decreased IgM+B lymphocytes and increased IgA+B lymphocytes in medulla after 6 weeks of age. So we concluded that 3-week-old White Leghorn chickens were more susceptible to IBDV than those of the rest of weeks of age, indicating that they were suitable for in vivo experimental model to study the medicine against infectious bursal disease.(2) Oral garlic mixture less than 20 mg/kg could increase monocyte activation ratio and decrease phagocytic capacity of macrophages of mice, as compared to control mice. However, immunosuppressed mice had decreased monocyte activation ratio and increased phagocytic capacity of macrophages, and oral garlic mixture could increase monocyte activation ratio and decrease phagocytic capacity of macrophages of immunosuppressed mice.(3) The garlic mixture was dissolved in distilled water and administered freely by oral route (p.o.). The results show that the treatment of chicks with garlic mixture (10 mg/kg) could reduce the viral load in the bursa to some extent, preserve original bursal lymphoid follicles, increase the resettled cells ratio of damaged bursa, promote the repair of bursa and thymus, promote the body to produce high level of antibodies for specific immune responses, adjust bursal IL-2 content for nonspecific immune responses, as compared to control group. Moreover, administration of 5 mg/kg of garlic mixture could also adjust bursal IFN-γ content for nonspecific immune responses, induce apoptosis of bursal lymphocytes, reduce the IBDV target cells, inhibit the cellular viral replication and proliferation. Therefore, considering the effects of garlic mixture herein shown, it is feasible to suggest that garlic mixture have certain prevention and treatment effects to the injury by IBDV BC6/85 strain.