Pathological Study of SPF Chickens Experimentally Infected with a Chinese IBDV Strain BC6/85

Differential expression of pro-inflammatory and anti-inflammatory genes of layer chicken bursa after experimental infection with infectious bursal disease virus

Infectious bursal disease (IBD) is one of the most prevalent infectious diseases caused by IBD virus (IBDV), which results in bursal necrosis and immunosuppression that cause severe damage to the immune system in chickens. Cytokines are important mediators and regulators of both types of host responses. In the present study, layer chickens were artificially challenged with IBDV, and the differential expression of inflammatory genes was explored by using quantitative real-time PCR, which offered basic data for further study of IBDV pathogenesis. Data showed that after IBDV infection, the virus load in the bursa of Fabricius (BF) peaked at 96 h and then gradually decreased. Compared with those of the negative-infected group, the mRNA expression levels of pro-inflammatory cytokines (interleukin [IL]-1β, IL-6, IL-7, IL-8, tumor necrosis factor [TNF]-α, transforming growth factor [TGF]-β) and anti-inflammatory cytokine IL-10 in the infected group increased to varying degrees at 12 to 192 h, respectively. Furthermore, the IL-1β mRNA expression peaked at 48 h; the mRNA transcript levels of IL-6, IL-8, and IL-10 were the highest at 96 h; TNF-α mRNA expression peaked at 120 h; the IL-7 mRNA expression peaked at 144 h; and the TGF-β mRNA transcript level was the highest at 192 h. Taken together, these observations indicated that along with the change pattern of IBDV proliferation in BF, the mRNA expression of cytokines (IL-1β, IL-6, IL-7, IL-8, IL-10, TNF-α, TGF-β) obviously increased, and the kinetics of each of these cytokines was different. The kinetics of IL-6/IL-10 mRNA expression ratio was significantly positively correlated with that of the virus load. These results suggest that IBDV infection seriously interferes with the natural immune response mediated by inflammatory cytokines in chickens.

Outbreaks of Virulent Infectious Bursal Disease in Flocks of Battery Cage Brooding System of Commercial Chickens

Clinical and pathological investigations were conducted on outbreaks of infectious bursal disease (IBD) in pullets under brooding using the battery cage system in a commercial poultry farm in Kaduna, Nigeria. Two consecutive outbreaks of IBD on the same farm were studied. The onset of the disease and morbidity and mortality rates were recorded. Postmortem examinations were conducted and gross lesions recorded. Tissues were collected and fixed in 10% buffered formalin and processed for histopathological examinations. In the first outbreak, 80 to 100% of the chicks were affected at the age of 4 to 5 weeks and mortality rate was 95.8% and lasted for 9 days. In the second outbreak, the mortality rate was 43.3% and it also lasted for 9 days. At the onset of the disease, the birds were also 4-week-old like in case 1. The disease was diagnosed based on clinical signs, pathology, and agar gel immunodiffusion test (AGID). Clinical signs, gross lesions, and histopathological findings were characteristic of virulent infectious bursal disease. After the first outbreak (case 1) the house was disinfected using polidine® (iodophor compound), V-ox® (inorganic peroxygen compounds), CID₂₀® (quaternary ammonium chloride, aldehydes, and alcohol), terminator III® (phenols), and glutasan® (aldehyde and quaternary ammonium chloride). But they failed to eliminate the IBD virus from the poultry pen.

Influence of the structural development of bursa on the susceptibility of chickens to infectious bursal disease virus

Infectious bursal disease (IBD), caused by IBD virus (IBDV), is an acute, highly contagious immunosuppressive avian disease. Although age-dependent changes in susceptibility of chickens to IBDV have been established, the relationship between age-dependent structural changes in bursa of Fabricius and susceptibility of chickens to IBDV is still unclear. In the present study, we examined the bursa anatomical structure and pathological changes in specific-pathogen-free (SPF) white leghorn chickens 0 to 8 weeks post hatch (w.p.h.) and IBDV BC6/85-infected SPF chickens 2 to 6 w.p.h. respectively, by histology, histopathology, immunohistochemistry, and transmission electron microscopy. Almost all IBDV-exposed chickens (2 to 6 w.p.h.) were infected, with the severest bursal inflammation and complication in chickens at 3 w.p.h. Furthermore, the bursae of healthy chickens at 3 to 6 w.p.h. had decreased laminin immunoreactivities, lots of splits, and irregular shapes in basement membrane (BM) of cortico-medullary epithelium (CME), irregularly arranged CME, and large numbers of immunoglobulin M-bearing (IgM+) B lymphocytes in the medulla. The decreased barrier function of corticomedullary border and large amount of IgM+ B lymphocytes provide a chance for IBDV to easily contact and infect target cells at 3 to 6 w.p.h. By contrast, regular BM, neatly arranged CME, and few IgM+ B lymphocytes in healthy chickens younger than 2 w.p.h., as well as reduced IgM+ B lymphocytes and high immunoglobulin A (IgA) content in healthy chickens older than 8 w.p.h., were observed, suggesting that the integrity of corticomedullary border barrier, a small amount of target cells and high IgA content of the bursa could be the reasons for these chickens being less susceptible to IBDV. Although studies have shown how IBDV affects bursa, we focus first on the age-dependent changes of CME, BM of CME and IgA content, and our findings are the first to elucidate the structural development of bursa in relation to IBDV susceptibility from a morphological perspective.

Susceptibility of chicken Kupffer cells to Chinese virulent infectious bursal disease virus

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by IBD virus (IBDV). Although the effects of IBDV on bursa of Fabricius in chickens have been well reported, the impacts of IBDV on liver after IBDV infection are still unclear. In the present study, specific pathogen free (SPF) chickens were experimentally inoculated with IBDV Chinese virulent strain BC6/85, and the cells in liver and bursa were examined by immunohistochemistry and transmission electron microscopy (TEM). The congestion of liver tissue and fatty degeneration of hepatocytes were characteristics of microscopical changes in chicken liver at 3 days post infection (d.p.i.), whereas there were follicular lymphoid necrosis, apoptosis, depletion, as well as edema and congestion in bursa. In addition, the number of IBDV-positive cells peaked at 4 d.p.i. in bursa and at 3 d.p.i. in liver, respectively. With respect to ultrastructural pathological changes of hepatocytes, mitochondria swelled and nucleus deformed into an irregular shape or its chromatin peripherally condensed which indicated that the hepatocyte was at the early stage of apoptosis, and the electron-lucent lipid droplets in a variety of sizes were observed within cytoplasm. Kupffer cells became "swollen-like" and the electron-density of their cytoplasm was lower than that of cells in uninfected group. Liver glycogen deposits significantly declined from 2 to 5 d.p.i. and recovered strongly at 6 d.p.i. More importantly, KLU01 (macrophage marker) positive (KUL01(+)) cells were infiltrated in bursa and liver in IBDV-exposed chickens by immunoperoxidase staining. To demonstrate the correlation between IBDV and macrophages in bursa and liver, we further investigated the colocalization of viral antigens and macrophages by double immunofluorescence labeling. At 4 d.p.i., the percentage of double positive cells (IBDV positive and KUL01(+) cells) accounted for 26.5 percent of the total IBDV positive cells or 57 percent of the total KUL01(+) cells in bursa. In comparison, the percentage of double positive cells in liver constituted 97 percent of the total IBDV positive cells or 99 percent of the total KUL01(+) cells. These results suggest that IBDV was susceptible to KUL01(+) cells in liver (mainly Kupffer cells) and replicated in the KUL01(+) cells. By comparison with the influence of IBDV on bursa, our findings were the first to elucidate the pathological changes in liver after IBDV infection on a microscopical and ultrastructural scale, and, especially, to gain the initial insight into the susceptibility of Kupffer cells to IBDV.