Early stages of infectious bursal disease virus infection in chickens detected by in situ reverse transcriptase-polymerase chain reaction

Velogenic newcastle disease virus tissue tropism and pathogenesis of infection in chickens by application of in situ PCR, immunoperoxase staining and HE staining

Limited deep studies are available in the field of early stages of pathogenesis of Newcastle disease virus (NDV) infection and tissue tropism of NDV. In this study, 24 specific pathogen free (SPF) chickens of white leghorn breed were infected with Newcastle disease (ND) by intranasal administration of 10⁵ 50% EID50/0.1 mL of velogenic NDV (vNDV). A second group of 15 chickens were kept as a control group. Chickens were monitored every day to record clinical signs. Infected chickens were euthanized by cervical dislocation at successive times, namely at hours (hrs) 2, 4, 6, 12, days 1, 2, 4, and 6 post-inoculation (pi). Whereas, control group chickens were euthanized on days 0, 1, 2, 4, and 6 pi. Tissues of brain, trachea, lung, caecal tonsil, liver, kidney, spleen, heart, proventriculus, intestine, and thymus were collected, fixed in 10% buffered formalin, embedded in paraffin, and sectioned. HS staining, immunoperoxidase staining (IPS) and in situ PCR were applied. It was concluded that at hr 2 pi, virus seemed to be inclined to trachea and respiratory tract. Meanwhile, it attacked caecal tonsils, intestine and bursa of Fabricus. While primary viraemia was ongoing, virus created footing in kidney and thymus. At hr 4 pi, proventriculus, liver, and spleen were attacked. However, at hr 6 pi, brain and heart were involved. Secondary viraemia probably started as early as hr 12 pi since all collected tissues were positive. Tissue tropism was determined in trachea, caecal tonsil, liver, bursa of Fabricius, intestine, proventriculus, lung, spleen, thymus, kidney, heart, and brain.

Infectious bursal disease virus tissue tropism and pathogenesis of the infection in chickens by application of in situ PCR, immunoperoxase and HE staining

Infectious bursal disease is one of an OIE list of notifiable diseases. Chicken is the only host that manifests clinical signs and its pathogenicity is correlated with the distribution of antigens in organs. This study was conducted to determine disease pathogenesis and virus tissue tropism by in situ PCR, immunoperoxidase staining (IPS), and HE staining. Twenty four chickens were infected with very virulent Infectious Bursal Disease Virus (vvIBDV). Fifteen chickens were kept as a control group. Infected chickens were sacrificed at hrs 2, 4, 6, 12, days 1, 2, 4, and 6 post-inoculation (pi). While, control chickens were euthanized on days 0, 1, 2, 4, and 6 pi. Different tissues were collected, fixed in 10% buffered formalin, and processed. At hr 2 pi, virus was detected in intestinal, junction of the proventriculus and gizzard, cecal tonsil, liver, kidney, and bursa of Fabricius. At hr 4 pi, virus reached spleen, and at hr 6 pi, it entered thymus. At hr 12 pi, virus concentration increased in positive tissues. The latest invaded tissue was muscle on day 1 pi. Secondary viraemia occurred during 12-24 h pi. In situ PCR was the most sensitive technique to highlight obscure points of infection in this study.

Changes of CD4+CD25+ cells ratio in immune organs from chickens challenged with infectious bursal disease virus strains with varying virulences

In the current study, we investigate changes in CD4+CD25+ cells in chickens during infectious bursal disease virus (IBDV) infection. The percentage of CD4+CD25+ cells in lymph organs, e.g., the thymus, spleen, bursa of Fabricius and peripheral blood, during the first 1-5 days post infection (dpi) was assessed by flow cytometry. The data revealed a remarkable decrease in the percentage of CD4+CD25+ cells in the thymus from 1 to 5 dpi and in the spleen during early infection. An increase of the percentage of CD4+CD25+ cells among peripheral blood lymphocytes was observed during the first two days of IBDV infection. Additionally, CD4+CD25+ cells infiltrated the bursa along with CD4+ cells after IBDV infection. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to measure the mRNA levels of immune-related cytokines in IBDV-infected thymus and bursa of Fabricius tissues. The data revealed that IBDV caused a significant increase in interleukin (IL)-10 mRNA levels, with the Harbin-1 strain (vvIBDV) inducing higher IL-10 expression than the Ts strain. Taken together, our data suggest that chicken CD4+CD25+ cells may participate in IBDV pathogenicity by migrating from their sites of origin and storage, the thymus and spleen, to the virally targeted bursa of Fabricius during IBDV infection.

Comparison of the expression of cytokine genes in the bursal tissues of the chickens following challenge with infectious bursal disease viruses of varying virulence

BACKGROUND

Cytokines are important mediators and regulators of host responses against foreign antigen, with their main function to orchestrate the functional activities of the cells of the immune system. However little is known about the role of cytokines in pathogenesis and immune responses caused by infectious bursa disease virus (IBDV). The aim of this study was to examine the transcripts of cell-mediated immune response-related cytokine genes in the bursal tissues of chickens infected with IBDVs of varying virulence to gain an understanding of pathological changes and mechanisms of immunosuppression caused by IBDV infection and the immune responses evoked.

RESULTS

Real-time quantitative PCR analysis revealed that the expression levels of both Th1 [interferon (IFN)-γ, interleukins (IL)-2 and IL-12p40] and Th2 (IL-4, IL-5, IL-13 and IL-10) cytokines were significantly up-regulated following challenge with the H strain (vvIBDV) and up to 2- and 30-fold, respectively (P < 0.05). Following infection with the Ts strain (cell-adapted virus) these cytokine transcripts were up-regulated at 5 days post-infection (dpi), 2- and 13-fold respectively (P < 0.05), while the expression levels of IL-2 and IL-4 were not significantly different (P > 0.05). A higher degree of cytokine expression was induced by the H strain compared with the Ts strain.

CONCLUSION

The results indicate that the expression of cell-mediated immune-related cytokine genes is strongly induced by IBDV, especially by the vvIBDV, H strain and reveal that these cytokines could play a crucial role in driving cellular immune responses during the acute phase of IBDV infection, and the cellular immune responses caused by IBDV of varying virulence are through different signaling pathways.

Relative quantification and detection of different types of infectious bursal disease virus in bursa of Fabricius and cloacal swabs using real time RT-PCR SYBR green technology

In present study, different types of infectious bursal disease virus (IBDV), virulent strain DK01, classic strain F52/70 and vaccine strain D78 were quantified and detected in infected bursa of Fabricius (BF) and cloacal swabs using quantitative real time RT-PCR with SYBR green dye. For selection of a suitable internal control gene, real time PCR parameters were evaluated for three candidate genes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), 28S rRNA and beta-actin to IBDVs. Based on this beta-actin was selected as an internal control for quantification of IBDVs in BF. All BF samples with D78, DK01 or F52/70 inoculation were detected as virus positive at day 1 post inoculation (p.i.). The D78 viral load peaked at day 4 and day 8 p.i., while the DK01 and F52/70 viral load showed relatively high levels at day 2 p.i. In cloacal swabs, viruses detectable were at day 2 p.i. for DK01 and F52/70, day 8 p.i. for D78. Importantly, the primers set were specific as the D78 primer set gave no amplification of F52/70 and DK01 and the DK01 primer set gave no amplification of D78, thus DK01 and D78 could be quantified simultaneously in dually infected chickens by use of these two set of primers. The method described here is robust and may sever as a useful tool with high capacity for diagnostics as well as in viral pathogenesis studies.

Economically important non-oncogenic immunosuppressive viral diseases of chicken--current status

Immunosuppressive viral diseases threaten the poultry industry by causing heavy mortality and economic loss of production, often as a result of the chickens' increased susceptibility to secondary infections and sub-optimal response to vaccinations. This paper aimed to present an up-to-date review of three specific economically important non-oncogenic immunosuppressive viral diseases of chickens, viz. chicken infectious anaemia (CIA), infectious bursal disease (IBD) and hydropericardium syndrome (HPS), with emphasis on their immunosuppressive effects. CIA and IBD causes immunosuppression in chickens and the socio-economic significance of these diseases is considerable worldwide. CIA occurs following transovarian transmission of chicken anaemia virus and has potential for inducing immunosuppression alone or in combination with other infectious agents, and is characterized by generalized lymphoid atrophy, increased mortality and severe anemia. The virus replicates in erythroid and lymphoid progenitor cells, causing inapparent, sub-clinical infections that lead to depletion of these cells with consequent immunosuppressive effects. The IBD virus replicates extensively in IgM(+) cells of the bursa and chickens may die during the acute phase of the disease, although IBD virus-induced mortality is highly variable and depends, among other factors, upon the virulence of the virus strain. The sub-clinical form is more common than clinical IBD because of regular vaccination on breeding farms. Infection at an early age significantly compromises the humoral and local immune responses of chickens because of the direct effect of B cells or their precursors. HPS is a recently emerged immunosuppressive disease of 3-6-weeked broilers, characterized by sudden onset, high mortality, typical hydropericardium and enlarged mottled and friable livers, with intranuclear inclusion bodies in the hepatocytes. The agent, fowl adenovirus-4, causes immunosuppression by damaging lymphoid tissues; the presence of IBD and CIA viruses may predispose for HPS or HPS may predispose for other viral infections. Synergism with CIA or other virus infections or prior immunosuppression is necessary to produce IBH-HPS in chickens and the susceptibility of chickens infected with fowl adenovirus varies throughout the course of CIA infection. The mechanism of immunosuppression has been studied in detail for certain chicken viruses at molecular levels, which will provides new opportunities to control these diseases by vaccination.

Development of a One-Step Strip Test for the Diagnosis of Chicken Infectious Bursal Disease

A rapid diagnostic strip for chicken infectious bursal disease (IBD) was developed based on membrane chromatography using high-affinity monoclonal antibodies directed to chicken infectious bursal disease virus (IBDV). The diagnostic strip has high specificity for detection of chicken IBDV antigen and recognizes a variety of the virus isolates, including virulent and attenuated strains, with no cross-reactivity to other viruses, such as Newcastle disease virus, Marek's disease virus, infectious bronchitis virus, infectious laryngotracheitis virus, and egg-drop-syndrome virus. The results showed that its specificity was highly consistent with the agar-gel precipitation test (AGP). The diagnostic strip detected as low as 800 median egg lethal dose (ELD50) viruses in the IBDV BC6/85-infected sample, which was comparable with AC-ELISA (400 ELD50) and 32 times more sensitive than the AGP test (2.56 x 10(4) ELD50). In experimental infection, IBDV was detected in the bursa as early as 36 hr postinfection with the diagnostic strip before the clinical signs and gross lesions appeared. It takes only 1-2 min to do a strip test to detect chicken IBDV antigen after the specimen is grounded in a whirl pack with finger massage.

Research on infectious bursal disease--the past, the present and the future

Infectious bursal disease (IBD) virus (IBDV) is the etiological agent of "Gumboro disease". Although first observed about 40 years ago, this disease continues to pose an important threat to the commercial poultry industry. The emergence of antigenic variant as well as very virulent strains in vaccinated flocks considerably stimulated research efforts on both, IBD and IBDV. In this review, some of the recent advances in the understanding of the structure, morphogenesis and molecular biology of the virus as well as in development of new diagnostic approaches and new strategies for vaccination against IBD are briefly summarized.