Infectious Bursal Disease: Transmission, Pathogenesis, Pathology and Control - An Overview

Molecular characterisation of IBDV isolates in Turkey revealed reassortant strains

1. Infectious bursal disease (IBD) is an acute, highly contagious viral disease of chickens caused by a virus (IBDV) which has a bi-segmented, double-stranded RNA genome. It has five viral proteins in its structure; the VP1 gene is encoded in segment B and the other four are in segment A.2. In this study, bursae of Fabricius and spleen samples taken from chickens suspected of having clinical or subclinical IBD from a total of 50 chicken flocks located in different geographical regions of Turkey were examined.3. The RT-PCR analysis of the VP2 gene showed that 30 of the 50 samples (60%) tested positive. Eight positive isolates were chosen and RT-PCR was performed to amplify the VP1 gene.4. The study showed that reassortant field strains that cause clinical or subclinical disease are currently circulating in broiler flocks across Turkey.

Phytochemicals: a promising approach to control infectious bursal disease

Infectious bursal disease (IBD) is one of the dangerous diseases of poultry that affects the bursa of Fabricius, which is an important organ of the bird's immune system. IBD virus is resistant to many drugs, making its control difficult. Vaccination of IBD is in practice for a long time worldwide to control IBD, but secondary issues like vaccine failure and lower efficacy lead to their reduced use in the field. Multiple medicines are currently used, but the phytochemicals have emerged as promising agents for controlling IBD. The drugs to be developed should possess direct antiviral properties by targeting viral entry mechanisms, enhancing the host immune response, and inhibiting viral protein synthesis. Phytochemicals have potential to contribute to food security by minimizing the possibility of disease outbreaks and ensuring that consumers worldwide obtain healthy poultry products. It has been now claimed that direct and indirect activities of phytochemicals can be effective in the control of IBDV. Although available evidence suggest that the phytochemicals can contribute in controlling occurrence IBDV, there is a definite need of focused studies to gain more insight and develop rational strategies for their practical use. This review highlights the disease caused by IBDV, inhibition of viral replication, boosting the immune system, disruption of viral membrane, and important phytochemicals showing antiviral activities against IBDV.

Exploring Variability: Inflammation Mediator Levels across Tissues and Time in Poultry Experimentally Infected by the G1a and G6 Genogroups of Infectious Bursal Disease Virus (IBDV)

Infectious bursal disease virus (IBDV) is a significant burden for poultry production and market due to both direct disease and induced immunosuppression. In the present study, the expression of different cytokines in the bursa of Fabricius and thymus was evaluated during a 28-day-long experimental infection with two strains classified in the G1a (Classical) and G6 (ITA) genogroups. Although both strains significantly affected and modulated the expression of different molecules, the G6 strain seemed to induce a delayed immune response or suppress it more promptly. A recovery in the expression of several mediators was observed in the G1a-infected group at the end of the study, but not in the G6 one, further supporting a more persistent immunosuppression. This evidence fits with the higher replication level previously reported for the G6 and with the clinical outcome, as this genotype, although subclinical, has often been considered more immunosuppressive. However, unlike other studies focused on shorter time periods after infection, the patterns observed in this paper were highly variable and complex, depending on the strain, tissue, and time point, and characterized by a non-negligible within-group variability. Besides confirming the strain/genogroup effect on immune system modulation, the present study suggests the usefulness of longer monitoring activities after experimental infection to better understand the complex patterns and interactions with the host response.

The effect of micronutrient supplementation on bioavailability, antioxidants activity, and weight gain in response to Infectious Bursal Disease vaccination in commercial broilers

The effect of supplementing organic selenium and zinc on bioavailability, oxidative stress, weight gain in commercial broilers was studied. A total of 180-day-old chicks were divided into six groups: NSUV (Not supplemented, unvaccinated), NSV (Not supplemented, vaccinated), VS (vaccinated, supplemented selenium), VZ (vaccinated supplemented zinc), VSZ (vaccinated supplemented selenium and zinc), UVSZ (unvaccinated supplemented selenium and zinc). 1 mg/kg selenium and 60 mg/kg zinc were added to the feed of supplemented groups. The concentration of selenium (0.05 ± 0.00 mg/L) in VS and zinc (0.66 ± 0.13 mg/L) in VZ were lower on day 27 post-vaccination compared to day 10 (VS= 0.07 ± 0.01 mg/L; VZ= 1.46 ± 0.30 mg/L). Glutathione peroxidase and catalase concentrations were highest in the supplemented groups compared to unsupplemented groups on day 27 post vaccination, expressing a similar trend with the micronutrients. There was no difference (P ≥ 0.05) in the glutathione concentration between all groups except on day 27 post vaccination where SZV group was significantly higher (P=0.02) compared to the NSV group. Catalase concentration was significantly decreased in the NSV group compared to SZV (P=0.04) on day 27 post vaccination. The NSV group (1.64 ± 0.13 kg) weighed significantly lower (P=0.02) than the VSZ (2.00 ± 0.12 kg) in the fifth week, while on the sixth week, the SZV group gained the highest weight (2.04 ± 0.18 kg). The supplementation of organic selenium and zinc in broilers increased the serum micronutrients bioavailability, decreased oxidative stress, increased weight gain, thus, enhancing immunity in the broilers.

Examination of macroscopic and microscopic lesions in IBDV-infected organs and molecular characterization of IBDV VP1 gene fragments obtained from commercial broiler farms in Indonesia

Background and Aim

Infectious bursal disease (IBD) is an infectious immunosuppressive disease that affects young chickens. Instead of strict biosecurity practices, vaccination is used to control IBD. However, the disease has not been effectively managed. Variations in the observed clinical symptoms lead to confounding diagnoses. The study aimed to obtain pathological lesion data from chickens suspected of IBD virus (IBDV) infection by gross pathology, confirm IBDV infection through molecular diagnostics, and genotype the VP1 gene fragments of circulating IBDV in the field.

Materials and Methods

The bursa of Fabricius, thymus, spleen, proventricular-ventricular junction, thigh muscles, and kidneys samples were collected from chickens suspected of IBDV infection from four commercial broiler farms in Central Java and The Yogyakarta Special Region Province between 2021 and 2022. The collected samples were examined histopathologically. Infectious bursal disease virus RNA was extracted from the bursa of Fabricius and VP1 gene was identified by reverse-transcriptase polimerase chain reaction (RT-PCR). The RT-PCR positive sample were sequenced and analyzed in Mega X for homology search and phylogenetic tree analysis.

Results

Macroscopic pathological lesions in the bursa of Fabricius were demonstrated by enlarged edema and thickened plica, presence of gelatinous exudate, hemorrhage, atrophy, and caseous exudate in the lumen. Moreover, the thymus had atrophy and small gray foci were observed in the spleen. Petechiae or hemorrhage was detected on the thigh muscle, and the kidney was dull and pale. Hemorrhage in the proventricular-ventricular junction was distinct. The histopathological examination of the bursa of Fabricius showed follicular vacuolization, edema, heterophilic infiltration, follicular atrophy, congestion, and hemorrhage. The thymus and spleen showed the presence of multifocal necrosis. Hemorrhage was observed in thigh muscle and mucosal part of proventricular-ventricular junction. Vacuolization was seen in renal tubules (nephrosis). Reverse transcriptase-PCR of 26 bursa of Fabricius samples from chickens suspected of IBDV infection showed four negative and 22 positive samples. Phylogenetic analysis of the VP1 gene fragment has indicated very virulent IBD (vvIBD) and belonged to B2 genotype.

Conclusion

Infectious bursal diseases virus infection in broiler chicken generated macroscopic and microscopic primary lesions in the bursa of Fabricius and thigh muscle. Other organs such as the spleen, thymus, proventricular-ventricular junction, and kidney, were also involved. Molecular analysis of the VP1 gene confirmed the causative agent and grouped the virus into vvIBD and B2 genotype. All samples were collected from vaccinated birds therefore, the efficacy of available vaccine is required for urgent evaluation. Since most studies only focused on VP1, further exploration on VP2 gene is suggested notably for new-generation vaccines. Monitoring clinical signs' transformation over time could assist field diagnostics.

Molasses, Antox® and EN-FLORAX® decreased antibody decay rate and enhanced response to a very virulent infectious bursal disease virus and Newcastle disease vaccine La Sota in ISA Brown chicks

This study evaluated the effects of molasses, Antox® and EN-FLORAX® on antibody (Ab) decay and response to a very virulent IBD virus (vvIBDV) and ND vaccine La Sota (NDVLS) in ISA Brown chicks. Five groups, (A, B, C, D and E) of 50 chicks each were used for the study. Groups A, B and C were supplemented with molasses, Antox® and EN-FLORAX®, respectively, orally from 1 to 49 days, and inoculated with a vvIBDV at 28 days of age. Groups D, and E were positive, and negative controls, respectively. At 35 days of age, all groups were vaccinated with NDVLS. Antibody (Ab) titers to vvIBDV, and NDV, were determined by indirect enzyme linked immunosorbent assay (I-ELISA), and hemagglutination-inhibition (HI) tests, respectively. Results revealed significantly (P < .05) decreased Ab decay rates in supplemented groups (A, B, and C) compared to controls (D and E) up to day 28. There were significantly (P < .05) higher mean IBDV and ND HI Ab titers in supplemented groups compared to D with the highest in A up to day 49. Molasses, Antox®, and EN-FLORAX® decreased rate of Ab decay, elicited stronger Ab response against vvIBDV and production of protective NDVLS HI Ab titers.

Seroepidemiology of Infectious Bursal Disease in Poultry Reared Under Backyard Production System in Wolaita Zone, Southern Ethiopia

Background

Infectious bursal disease (IBD) has been known to cause high morbidity and mortality in chickens resulting in considerable financial losses to poultry producers. This study was performed with the objectives of estimating the seroprevalence and associated risk factors of IBD in backyard chickens in Wolaita zone, southern Ethiopia.

Methods

A total of 482 serum samples were collected from chickens reared under backyard systems using a multi-stage cross-sectional study design. The serum samples were tested for the presence of anti-IBDV antibodies using an indirect enzyme-linked immunosorbent assay (ELISA). A questionnaire survey was also performed to identify risk factors affecting chicken production in the study area.

Results

From the total of 482 serum samples tested, 236 (48.96%; 95% CI: 44.32–53.42) were positive for anti-IBDV antibodies. Higher seroprevalence was recorded in Humbo district (55.75%; 95% CI: 46.11–65.09) followed by Sodo Zuria (51.54%; 95% CI: 42.62–60.39), Damotgale (46.22%; 95% CI: 36.49–56.18), and Kindokoysha district (42.86%; 95% CI: 34.32–51.72) although the difference was not statistically significant. Significantly lower prevalence was recorded in indigenous chickens (43.36%; 95% CI: 37.53–49.32) compared to exotic chickens (57.14%; 95% CI: 49.89–64.17). The odds of occurrence of IBD in the local chicken breed was 0.67 times lower than that of the exotic chicken breed. The odds of occurrence of IBD in chickens from flock size ≥5 chickens was 4.33 times higher than chickens from flock size <5 chickens. A statistically significant association (P < 0.05) was observed between treatment history and isolation of sick chickens with mortality in the flock.

Conclusion

This study revealed that IBD is one of the major infectious diseases that affect the traditionally managed chickens in the study area with the flock size and breed of chickens are identified as important risk factors for IBD occurrence. Besides, chicken producers did not have enough knowledge about the nature and epidemiology of IBD. Thus, proper management practices together with appropriate vaccination programs are necessary to reduce IBD incidence in the study areas.

Very virulent infectious bursal disease virus infection caused changes in cloacal temperature and clinical manifestations in pigeons (Columba livia domestica) and is transmitted to sentinel chickens

In this study, changes in cloacal temperature and clinical manifestations due to very virulent infectious bursal disease virus (vvIBDV) infection in pigeons (Columba livia domestica) and transmission to chickens were demonstrated. Thirty pigeons (3-6 weeks old) and thirty chickens (3 weeks old) divided into 4 groups (I-IV) were used for this study. Group I comprised of 10 uninoculated pigeons only; II comprised of 10 inoculated pigeons and 10 sentinel chickens; III comprised of 10 sentinel pigeons and 10 inoculated chickens, while IV comprised of 10 uninoculated chickens only. Pigeons in group II and chickens in group III were each inoculated with 0.20 mL (titre of 10^9.76CID₅₀/mL) of vvIBDV (Nigerian strain). Cloacal temperature was monitored and clinical manifestations scored post-inoculation (pi). Results indicated significant (P < 0.05) pyrexia at 2 days pi (dpi), mild clinical signs and no mortality in inoculated pigeons. Significant (P < 0.05) pyrexia at 2-4 dpi, severe clinical signs and mortality (50%; 60%) were observed in inoculated and sentinel chickens. IBDV antigen and antibody were detected in pigeons and chickens. Pigeons showed response to vvIBDV infection thus suggesting susceptibility of pigeons to IBD. Sentinel chickens presented clinical manifestations of IBD and this suggests transmission from pigeons to chickens. This study therefore documents pyrexia and clinical manifestations due to vvIBDV infection in pigeons and successful transmission of the virus between pigeons and chickens.

Pigeons (Columba livia domestica) Are Susceptible to Infectious Bursal Disease: A Comparative Study of Their Hematological and Serum Biochemical Alterations

The hematological and serum biochemical alterations following very virulent infectious bursal disease virus (IBDV) infection in pigeons and chickens were evaluated in this study. Sixty IBDV seronegative birds comprising 30 (3–6 weeks old) pigeons and 30 (3 weeks old) chickens were randomly divided as follows: 10 uninoculated pigeons only, 10 inoculated pigeons + 10 sentinel chickens, 10 inoculated chickens + 10 sentinel pigeons, and 10 uninoculated chickens. Inoculated birds were administered 0.20 ml of inoculum containing very virulent IBDV (vvIBDV). Blood was collected postinoculation/exposure (pi/pe) and processed for hematology and biochemistry. The results revealed significantly (P < 0.05) increased packed cell volume, decreased mean corpuscular hemoglobin (MCH), and MCH concentration (MCHC) in inoculated and sentinel chickens. Total leukocyte count (TLC), heterophil, and heterophil/lymphocyte (H/L) ratio were increased from 3 dpi/dpe in inoculated pigeons and from 3 to 14 dpi/dpe in inoculated and sentinel chickens. At 10 and 14 dpi/dpe, there was significantly (P < 0.05) increased serum total protein and globulin concentrations and decreased albumin/globulin ratio in pigeons and chickens. Serum urea concentration showed significant (P < 0.05) increase in inoculated and sentinel chickens at 3 and 4 dpi/dpe. To the authors' knowledge, this is the first report on hematological and serum biochemical alterations due to vvIBDV infection in pigeons.

Comparison of two attenuated infectious bursal disease vaccine strains focused on safety and antibody response in commercial broilers

Background and Aim:

Infectious bursal disease (IBD) or Gumboro disease is one of the most detrimental diseases in the poultry industry worldwide. Previous scientific studies have shown that live IBD vaccination might induce transient immunosuppression, leading to suboptimal vaccine responses, and therefore lack of protection against other infectious diseases; therefore, selecting an IBD vaccine in commercial farms is a concern. This study aims to compare two commercially attenuated IBD vaccines (intermediate and intermediate-plus strains) in terms of safety and antibody response to IBD and Newcastle disease viruses (NDV) in commercial broilers.

Materials and Methods:

Overall, 216 Cobb broiler chickens were divided into three groups based on the IBD vaccine strain administered: V217 strain (Group 1), M.B. strain (Group 2), and an unvaccinated group (Group 3). Groups 1 and 2 were orally vaccinated with Hitchner B1 NDV vaccine strain 7 days after IBD vaccination. Blood samples were collected at IBD vaccination day (15 days of age) and at 7, 14, 21, and 28 days post-IBD vaccination. The immunosuppressive effects of the IBD vaccination were determined by NDV antibody response, the bursa:body weight (B:BW) ratio, and the histopathological lesion scores of the bursa of Fabricius. Phylogenetic analysis was also performed.

Results:

Phylogenetic analysis revealed that the M.B. strain belonged to a very virulent IBD strain, whereas the V217 strain belonged to a classical IBD virus strain. NDV antibody titers of the two vaccinated groups increased after ND vaccination, reaching their maximum at 14 days post-ND vaccination and decreasing thereafter. The V217 group presented the highest NDV humoral response from 7 days post-vaccination (dpv) to the end of the study. The mean NDV antibody titer of the V217 group was significantly (p<0.05) higher than that of the M.B. group at 14 dpv. In addition, the V217 strain-induced lower bursal lesions post-IBD vaccination and a higher B: BW ratio at 7 and 21 dpv compared to the M.B. group. The higher B: BW ratio, lower bursal lesions, and higher ND antibody response present in the V217 group indicate that the V217 strain induces lower immunosuppressive effects compared to the M.B. strain.

Conclusion:

The results of this study indicate that IBD vaccine selection merits consideration, as avoiding the immunosuppressive effects induced by live IBD vaccination and the consequent impact on response to other vaccines is important.