Histological effect of infectious bursal disease virus on bursa of fabricia, Thymus gland and bone marrow tissues with monitoring of virus antibodies level during experimental infection on broiler chicken

Infectious bursal disease virus infect wide range of poultry flocks across the word causing variable ranges of economic loses come from direct or indirect mortality through immune suppression by invading of B cell tissues, this study designed to show the effect of oral and ocular inoculated virus collected and processed from infected farms on bursa of fabricia, Thymus gland, bone marrow tissues with monitoring of virus antibody titer before and after age of inoculation (21 day old), the study showed different degrees of damage varies between tissues including degeneration, necrosis, congestion and edema, the study also showed that the maternal antibodies was high at the first day of hatching and the decrement of antibody titer happen directly after virus inoculation then increase in antibodies titer started gradually after two weeks of inoculation. Introduction: Infectious bursal disease (IBD) or Gumboro disease is an acute, highly contagious viral disease of young birds characterized mainly by severe lesions in the bursa of Fabricius followed by immunosuppression. (1) & (2).The disease causing destruction to the lymphoid cells especially in bursa of fabricia (3). Within thymus gland from which the virus was frequently isolated the virus causes severe lesions (4). Bone marrow lesions including lysis, depletion and other different pathologic changes depend on severity of infection were described within many researchers results (5). Materials and Methods: Fifty non-vaccinated chick was used in experimental infection for monitoring antibodies titer and histological effect before and after oral and ocular inoculation (at day 22) of the virus suspension, the inoculum prepared from bursa gland, the gland was collected from infected farms around Tikrit city and stored in deep freezer before thawed and 1 gm of bursa with equal amount of sterile sand with 9 ml of phosphate buffer saline to make a suspension, centrifuged at 700 xg for 15 mint (three time) to take supernatant fluid, penicillin and streptomycin was added (10,000 IU of penicillin and 10 mg of streptomycin) to the suspension then incubated for 30 minutes and the suspension was kept at -20°C until time of use, Bursa of fabricia, thymus gland and bone that suggested being a model for histological diagnosis after experimental infection were collected with aseptic technique and immersed in 10% formaldehyde 24 hour then washed under running water for one hour and kept in 70% ethanol until time of histology except bone samples which treated with 5% hydrochloric acid one week before it kept in 70% ethanol, the stains prepared according to Drury et al. (1988) (6), tissues sections was stained according to procedure of Humason (1979) (7), blood was collected from the right jugular vein without using of coagulant, then samples were centrifuged at 252 xg 15 minutes to isolate the serum that stored at -20°C till use for serological purposes, the procedure was according to Symbiotic Kit protocol with using of (BIO-TEK ELX800) ELISA reader and washer, the optical density used for calculating antibodies titer by using the equation below: Sp = Sample Absorbance − Averag Normal Control Absorbance Corrected Positive Control Absorbance IBD ELISA titer calculated using the following suggested equation using Microsoft Excel software: LOG10 TITER = (1.172 X LOG10 Sp) + 3.614 TITER = ANTILOG OF LOG10 TITER Results:The collagen bundles of the Bursa of fabricia capsule were small and scattered, in between the bundles there were different types of the inflammatory cells the follicles of the bursa showed variable degrees of depletion, congestion and edema (figure 1), the tissue of the Thymus gland show many areas of hyperplasia in germinal center and different areas of congestion (figure 2). bone marrow show cellular depletion especially in the paratrabecular area (figure 3), Chicks maternal antibody titer level was high at one day old which decreased at 21 day after hatching, before antibody titer returned to increase after one week of oral and ocular inoculation (histogram 1 and table 1).