الفهرس 
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Abstract
The study was performed to declare the pathogenesis and pathogenicity of BVDV NADL strain in both New Zealand white and balady rabbits both male and female ones. The experiment was carried on 54 New Zealand white rabbits and 54 balady rabbits. 30 New Zealand white and 30 balady doe rabbits were divided into 4 groups, 15 doe for each. The 1st and 2nd groups subdivided into 10 groups according to the number of the injected dose and time of scarification, 3 doe for each. The 3rd and 4th groups were used as control negative and subdivided as the injected groups. 24 New Zealand white and 24 balady male rabbits were divided into 4 groups, 12 buck rabbits for each. The 1st and 2nd groups subdivided into 8 groups according to the number of the injected dose and time of scarification. The 3rd and 4th groups were used as control negative and subdivided as the injected groups. The injection dose and the rout of administration used were I/V injection of 0.5 ml 107.2TCID50. The experiment extended for 33 to 35 days from the infection day. Serum was collected from all rabbits at 4th , 7th , 14th, 21th, 28th,35th days PI for ELISA. Samples were collected from different organs and fixed in 10% neutral buffer formalin for histopathology and Immunoflurescence. Parts of the same tissue specimens were put in freeze at -20 C for immunohistochemistry. The main post mortem lesion observed was pneumonia. The histopathological lesions were severe in New Zealand rabbits. BVDV causing multisystemic affection in rabbits and the main histopathological lesions recorded were non suppurative myocarditis, acute meningioencephalitis, marked depletion of lymphoid follicles in spleen, acute tracheitis, interstitial pneumonia, acute orchitis and necrotic placentitis. The histopathological lesions were confirmed by the presence of viral antigen by Immunoflurescence technique. The antibodies titer by ELISA recorded high values at early stages of infection then decline in the late stages indicating the immunosuppressive effect of BVDV.