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Abstract
Vaccination against infectious bursal disease failed to provide complete protection from the disease in different field researches.The present study investigates the effect of levamisole, bursal extract, and thymus extract on the immune response of chicks to vaccination with D78 strain of IBDV.First experiment : In this investigation the use of levamisole in a dose of 10 mg/kg and bursal extract and thymus extract in a dose of 2 mg chick in 0.5 ml subcutaneously administered during vaccination of chicks by D78 strain of IBDV. Measurement of the immune response carried out by assaying the cell-mediated immune response by lymphocyte blastogenesis using MTT assay, measuring the humoral response by using ELISA technique for detection of antibody and by protein analysis, challenging birds by using vvIBDV field strain for detection of the percent of protection, also the histopathological lesions in immune organs (bursa of Fabricius, thymus gland, and spleen) were recorded. The experimental results revealed that : High lymphocyte cell mediated response by using immune stimulants specially thymus extract, bursal extract and levamisole respectively.High antibody titer was reported in immune stimulants administered groups with vaccination; group 7 (bursal extract treated), group 8 (thymus extract treated), and group 6 (levamisole treated) respectively.Protein analysis showed non significant differences between all treated and non treated groups in total serum protein, globulin levels and albumin globulin ratio.Challenge with vvIBDV field strain produce 100% protection in vaccinated and treated chicks (G6, G7 and G8), while 87% protection was obtained in vaccinated group without treatment (G5). Signs of non vaccinated birds and challenged were depression, Anorexia, ruffled feather, white watery diarrhea, high body temperature, and finally death, and the macroscopic lesions were congested pectoral and thigh muscles, hemorrhages in pectoral muscle, enlarged discolored bursa of Fabricius, petechial hemorrhages in the mucosal surface of bursa of Fabricius, congested spleen and thymus gland, petechial hemorrhage in thymus gland, and urates in ureters.Histopathological lesions were more severe in non vaccinated groups (G1, G2, G3, and G4) as there were severe hemorrhages, depletion and necrosis of lymphoid follicles of bursa of Fabricius, spleen and thymus gland.While in group (G5) (vaccinated non treated) showed severe lesions but less than non vaccinated groups as there were lymphoid depletion and little hemorrhages in bursa of Fabricius, depletion of lymphoid tissues and congestion of thymus gland and spleen. Levamisole treated group (G6) showed very little lesions as slight lymphoid depletion in bursa of Fabricius, thymus gland and spleen. While vaccinated groups treated with bursal extract (G7), or thymus extract treated group (G8) had no lesions as non challenged chicks with normal histological structure of bursa of Fabricius, thymus gland, and spleen. Second experiment : In this experiment comparison between orally and subcutaneously administered levamisole by using ELISA technique for detection of the antibody response to IBDV vaccine D87 were : Non significant elevated antibody titers to IBDV vaccine D87 in the group orally administered levamisole in the first three weeks after vaccination than in the subcutaneously administered one, while in the fourth week non significant elevated antibody titers to IBDV vaccine D87 in the group subcutaneously administered levamisole than in the orally administered one 8. REFERENCES Abdel-Alim, G. A. and Y. M. Saif.(2001).Immunogenicity and antigenicity of very virulent strains of infectious bursal disease viruses. Avian Dis. 45 : 92-101.